Transcriber’s Note:

The cover image was created by the transcriber and is placed in the public domain.

Eight Cylinder “V” Type Curtiss Aero Motor Having Two Rows of Four Cylinders Per Row. The Carburetor is Shown at the Left Hand Lower Corner Below the Motor. For Front Elevation See Fig. F-3 on Page [23].

PRACTICAL HAND BOOK
of
GAS, OIL AND STEAM ENGINES
STATIONARY, MARINE, TRACTION
GAS BURNERS, OIL BURNERS, ETC.
FARM, TRACTION, AUTOMOBILE, LOCOMOTIVE

A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel.

By

JOHN B. RATHBUN,

Consulting Gas Engineer, Editor “Ignition,” Instructor Chicago Technical College, Author Gas Engine Troubles and Installation.

Published by

CHARLES C. THOMPSON CO.

CHICAGO, U. S. A.

Copyright 1916

CHARLES C. THOMPSON CO.

Copyright MCMXIII

CHARLES C. THOMPSON CO.

Practical Hand Book Gas, Oil & Steam Engines

Table of Contents

Gas, Oil and Steam Engines

CHAPTER I
HEAT AND POWER

(1) The Heat Engine.

Heat engines, of which the steam engine and gas engine are the most prominent examples, are devices by which heat energy is transformed into mechanical power or motion. In all heat engines, this transformation of energy is accomplished by that property of heat known as “expansion,” by which an increase or decrease of temperature causes a corresponding increase or decrease in volume of the material subjected to the varying temperatures. The substance whose expansion and contraction actuates the heat engine is known as the “working medium,” and may be either a solid, liquid, or a gas. The extent to which the working medium is expanded depends not only upon the change of temperature but also on its composition.

In all practical heat engines, the heat energy is developed by the process of combustion, which is a chemical combination of the oxygen of the air with certain substances, such as coal or gasoline, known as “fuels.” The heat producing elements of the fuels are generally compounds of carbon and hydrogen, which when oxydized or burnt by the oxygen form products that are unlike either of the original components. It is due to this chemical change that heat energy is evolved, for the heat represents the energy expended by the sun in building up the fuel in its original form, and as energy can neither be created nor destroyed, heat energy is liberated when the fuel is decomposed. The heat energy thus liberated is applied to the expansion of the working medium to obtain its equivalent in the form of mechanical power.

During the period of expansion, the heat obtained by the combustion is absorbed by the working medium in proportion to its increase in volume, and as this increase is proportional to the mechanical effort exerted by the engine, it will be seen that the output of the engine in work is a measure of the heat applied to the medium. The quantity of heat absorbed by the medium represents the energy required to set the molecules of the medium into their new positions in the greater volume, or to increase their paths of travel. In the conversion of heat, each heat unit applied to the medium results in the production of 778 foot pounds of energy, providing that there are no heat or frictional losses.

In explanation of these terms or units, we wish to say, that the unit of heat quantity, called the BRITISH THERMAL UNIT is the quantity of heat required to raise one pound of water, one degree Fahrenheit, and the FOOT POUND is the work required to raise one pound through the vertical distance of one foot. As the British Thermal Unit = 778 foot pounds it is equivalent to the work required to raise 778 pounds one foot or one pound 778 feet, or any other product of feet and pounds equal to the figure 778.

As liquids expand more than solids with a given temperature, and gases more than either, the mechanical work returned for a given amount of thermal energy (the EFFICIENCY) will be greater with an engine using gas as a working medium than one using a solid or liquid working medium. The steam engine and the gas engine are both examples of heat engines using gaseous working mediums, the medium in the steam engine being water vapor and in the gas engine, air and the gaseous products of combustion. For this reason the working medium will be considered as a gas in the succeeding chapters.

Practically the only way of obtaining mechanical effort from an expanding gas is to enclose it in a cylinder (c) fitted with a freely sliding plunger or piston (p) as shown in Fig. 1. Two positions of the piston are shown, one at M indicated by the dotted lines, and one at N indicated by the full lines. It will be assumed that the space between the cylinder head P and the piston at M represents the volume of the gas before it is heated and expanded, and that the volume between O and N represents the volume after heating and expansion have occurred. The vessel B represents a chamber containing air that is periodically heated by the lamp L, and which is connected to the working cylinder C by the pipe O.

Figs. 1–2–3. Showing Expansion in an External Combustion Engine, the Cycle of Operations in an Internal Combustion Engine, and the Pressure Diagram of the Latter Engine Giving the Pressures at Various Points in the Stroke.

With the piston at M, the lamp L is lighted and placed under the retort B which results in the immediate expansion of the air in B. The expanded air passes through O into the cylinder, and if sufficient heat is supplied, exerts pressure against the piston since it occupies much more than its original volume. Providing that the friction of the device and the load on the shaft S are low enough the pressure on the piston will, move it to the position N in the direction of the arrow, thus accomplishing mechanical work. The motion of the piston revolves the crank to which it is connected by the rod X from D to E. During the trip from M to N the volume of gas has greatly increased being supplied continuously with heat from the lamp. As a considerable amount of heat has been radiated from the cylinder during the piston travel, and a considerable portion of the mechanical work lost through the friction of the piston on the cylinder walls, and by the crank, not all of the heat units are represented at the crank as mechanical effort.

Because of the limiting length of the cylinder, and the temperature limits of the lamp it is not possible to expand the working medium and increase the temperature indefinitely, therefore there must be a point where the application of heat must cease and the temperature be reduced in order to bring the gas back to its original volume and the piston to its original position so that the expansion may be repeated. This condition results in a very considerable loss of heat and power in addition to the losses previously mentioned, as the heat taken from the medium to reduce it to its original volume is thrown away as far as the production of power is concerned. To return the piston to its former position without expending energy on the engine, the volume and pressure may be reduced either by allowing the gas to escape to the atmosphere by means of a valve, or by removing the lamp and cooling the air by the application of water, but in any case the heat of the air is lost and the efficiency of the engine reduced.

To increase the efficiency of the engine and reduce the loss just mentioned, nearly all heat engines, either steam or gas, have the working medium at the highest temperature for only a small portion of the stroke, after which no heat is supplied to the cylinder. As the pressure forces the piston forward the volume increases, and as no more heat is supplied, both the pressure and the temperature continue to decrease until the end of the stroke is reached, thus utilizing the greater part of the heat in the expansion. Since the temperature at the end of the stroke is comparatively low, very little heat is rejected when the valve is opened for the return stroke. This loss would be the least when the temperature of the gas at the end of the stroke was equal to the temperature of the surrounding air. With both the internal and external temperatures equal, there would be no difference between the pressure of the gas in the cylinder and that of the surrounding air.

Fig. 1-a. Fairbanks-Morse Two Cylinder, Type “R E” Stationary Engine Direct Connected to a Dynamo.

It will be seen from the example just given that the heat engine performs mechanical work by dropping the working medium from a high to a low temperature, as it receives the medium at a high temperature from the lamp and rejects it at atmospheric temperature after delivering a small percentage of useful work. This may be compared to a water wheel which receives the working medium (water) at a high pressure and rejects it at a lower pressure. Carrying this comparison still further, it is evident that an increase in the range of the working temperatures (high and low) would increase the output of the heat engine in the same way that an increase in the range of pressures would increase the output of the water wheel. The temperature at which the engine receives the working medium and the temperature at which it is rejected determines the number of heat units that are available for conversion into mechanical energy, and therefore, if the range be increased by either raising the upper limit of temperature or by reducing the lower limit, or by the combined increase and decrease of the limits, the available heat will be increased.

Based on the temperature range, the maximum possible efficiency of the heat engine may be expressed by the ratio—

This maximum defined by Carnot establishes a limit that can be exceeded by no engine, whatever the construction or working medium.

According to the methods adopted in applying the heat of combustion to the working medium, heat engines are divided into two general classes, (1) External combustion engines, (2) Internal combustion engines. The expressions “Internal” or “External” refer to the point at which combustion takes place in regard to the working cylinder, thus an internal combustion engine is one in which the combustion takes place in the working cylinder, and an external combustion engine is one in which the combustion takes place outside of the working cylinder. The steam engine is an example of an external combustion engine, the fuel being burned in the furnace of a boiler which is independent of the engine cylinder proper. As the fuel is burned directly in the cylinder of a gas engine it is commonly known as an internal combustion engine.

An external combustion engine, such as the steam engine is subject to many serious heat losses because of the indirect method by which the heat is supplied to the working cylinder, aside from the losses in the cylinder. Much of the heat goes up the smoke stack and much is radiated from the boiler settings and the steam pipes that lead to the engine. The greatest loss however is due to the fact that the range of temperatures in the working cylinder is very low compared to the temperatures attained in the boiler furnace, for it is practically impossible to have a greater range than 350°F to 100°F with a steam engine, while the furnace temperatures may run up to 2500°F and even beyond.

High temperatures with a steam engine result in the development of enormous pressures, a temperature of 547°F corresponding to an absolute pressure of 1000 pounds per square inch. This pressure would require an extremely heavy and inefficient engine because of the terrific strains set up in the moving parts. The pressures established by air as a working medium are very much lower than those produced by air or any permanent gas at the same temperature, and for this reason it is possible to exceed a working temperature of over 3000°F in the cylinder of a gas engine without meeting with excessive pressures. This high working temperature is one of the reasons of the extremely high efficiency of the gas engine.

In order to compete with the gas engine from the standpoint of efficiency, the steam engine builders have resorted to super-heating the steam after it has left the boiler in order to increase the temperature range in the cylinder. By applying additional heat to the steam after it has passed out of contact with the water it is possible to obtain up to 600°F without material increase in the pressure, but the practical gains have not been great enough to approach the gas engine with its 3000°F. After reaching his maximum temperature at this comparatively low pressure, the steam engineer has still to eliminate a number of other losses that do not obtain with the gas engine.

Since the radiation losses of a burning fuel are proportional to the time required for burning, it is evident that the rate of combustion has much to do with the efficient development of the heat contained in it, and it is true that rapid combustion develops more useful heat from a given fuel than slow. In the gas engine the combustion is practically instantaneous with a low radiation loss, but in the steam engine the rate is slow, and with the excess of air that must necessarily be supplied, a great part of the value of the fuel is lost before reaching the water in the boiler. The temperature of the medium determines the efficiency of the engine and as rapid combustion increases the temperature it is evident that the gas engine again has the best of the problem.

In the case of the gas engine where the fuel (in gaseous form) is drawn directly into the working cylinder in intimate contact with the working medium (air) and in the correct proportions for complete combustion, each particle of fuel, when ignited, applies its heat to the adjacent particle of air instantly and increases its volume with a minimum loss by radiation.

A gas engine is practically a steam engine with the furnace placed directly in the working cylinder with all intervening working mediums removed, the gases of combustion acting as the working medium. It derives its power from the instantaneous combustion of a mixture of fuel and air in the cylinder, the expansion of which causes pressure on the piston. Under the influence of the pressure on the piston, the crank is turned through the connecting rod and delivers power to the belt wheel where it is available for driving machinery. Whether the fuel be of solid, liquid, or gaseous origin it is always introduced into the cylinder in the form of a gas.

Fig. 1-b. The English Adams Automobile Motor (End View), Showing the Magneto Driven by Spiral Gears at Right Angles to the Crank-Shaft.

(3) Combustion In the Cylinder.

As the working medium in an internal combustion engine is in direct contact with the fuel it must not only be uninflammable but it must also be capable of sustaining combustion and must have a great expansion for a given temperature range. Since atmospheric air possesses all of these qualifications in addition to being present in all places in unlimited quantities it is natural that it should be used exclusively as the working medium for gas engines. Unlike the vapor working medium in a steam engine the medium in the gas engine not only acts in an expansive capacity but also as an oxydizing agent for burning the fuel, and therefore must bear a definite relation to the quantity of the fuel in the cylinder to insure complete combustion.

In the gas engine the use of gaseous fuel is imperative since there must be no solid residue existing in the cylinder after combustion and also for the reason that the fuel must be in a very finely subdivided state in order that the combustion shall proceed with the greatest possible rapidity. In addition to the above requirements the introduction of a solid fuel into the cylinder would involve almost unsurmountable mechanical problems in regard to fuel measurement for the varying loads on the engine. This limits the fuel to certain hydrocarbon or compounds of hydrogen and carbon in gaseous form of which the following are the most common examples:

(a) CARBURETED AIR consisting of a mixture of atmospheric air and the vapor of some hydrocarbon (liquid) such as gasoline, kerosene or alcohol.

(b) OIL GAS formed by the distillation of some heavy, nonvolatile oil, or the distillation of tar or paraffine.

(c) NATURAL GAS obtained from natural accumulations occurring in subterranean pockets in various parts of the country.

(d) COAL GAS, made artificially by the distillation of coal, commonly called “illuminating” gas.

(e) PRODUCER GAS, some times known as “fuel gas,” produced by the incomplete combustion of coal in a form of furnace called a “producer.”

(f) BLAST FURNACE GAS, the unconsumed gas from the furnaces used in smelting iron, somewhat similar to producer gas but lower in heat value.

It should be noted that there is no essential difference between engines using a permanent gas or an oil as in either case the fuel is sent into the cylinder in the form of a vapor. In the case of oil fuel, the vapor is formed by an appliance external to the engine proper. In this book, the heat action of an engine using one form of fuel applies equally to the engine using another. The selection of a particular fuel for use with a gas engine depends not only upon its value in producing heat, but also upon its cost, the ease with which it meets the peculiar conditions under which the engine is to work, and its accessibility.

Neglecting for the moment, all of the items that do not affect the operation of the engine from a power producing standpoint, the principal requirement of a fuel is the production of a high temperature in the cylinder since the output is directly proportional to the temperature range. Since a very considerable mass of air is to be raised to this high temperature, the heat value, or CALORIFIC VALUE of the fuel in British Thermal units is of as much importance as the temperature attained in the combustion. The calorific value of different fuels vary widely when based either on the cubic foot or pound, and a considerable variation exists even among fuels of the same class owing to the different methods of production or to the natural conditions existing at the mine or well from which they originated. The principal elements of gas engine fuels, carbon and hydrogen, exist in many different combinations and proportions, and require different quantities of air as oxygen for their combustion because of this difference in chemical structure.

Since complete combustion is never obtained under practical working conditions, the actual evolution of heat and the actual temperatures are always much lower than those indicated by the CALORIMETER or heat measuring device. Besides the loss of heat due to imperfect combustion, there are many other losses such as the loss by radiation, connection, and slow burning, the latter being the principal cause of low combustion temperatures. From the statements in the foregoing paragraphs it will be seen that the theoretical or absolute calorific value of a fuel is not always a true index to its efficiency in the engine.

Complete combustion results in the carbon of the fuel being reduced to carbon dioxide (CO₂) and the hydrogen to water (H₂O), with the liberation of atmospheric nitrogen that was previously combined with the fuel, and some oxygen. The reduction of the fuel to carbon dioxide and water produces every heat unit available since the latter compounds represent the lowest state to which the fuel can be burned. Carbon however may be burned to an intermediate state without the production of its entire calorific contents when there is not sufficient oxygen present to thoroughly consume the fuel. Incompletely consumed carbon produces a gas, carbon monoxide, as a product of combustion, and a quantity of solid carbon in a finely subdivided state known as “soot.” Unlike the products of complete combustion, both the carbon monoxide and soot may be burned to a lower state with a production of additional heat when furnished with sufficient oxygen, both the soot and the monoxide being reduced to carbon dioxide during the process.

Fig. F-2. Sunbeam Engine with Six Cylinders Cast “En Bloc” (in one piece). At the Right and Under the Exhaust Pipe is the Compressed Air Starting Motor that Starts the Motor Through the Gear Teeth Shown on Flywheel. From “Internal Combustion.”

As the soot and monoxide have a calorific value it is evident that much of the heat of the fuel is wasted if they are exhausted from the cylinder without further burning at the end of the stroke. To gain every possible heat unit it is necessary to furnish sufficient oxygen or air to reduce the fuel to its lowest state. As the free oxygen and nitrogen contained in the fuel are without fuel value, their rejection from the cylinder occasions no loss except for that heat which they take from the cylinder by virtue of their high temperature.

With complete combustion the TEMPERATURE attained increases with the rate of burning, while the number of heat units developed remain the same with any rate of combustion. Because of the conditions under which the fuel is burned in the gas engine the fuel is burned almost instantaneously with the result that high temperatures are reached with fuels of comparatively low calorific value. With a given gas the rate of combustion is increased with an increase in the temperature of the gas before ignition and remains constant for all mixtures of this gas in the same proportion when the initial temperature is the same. The rate of combustion also varies with the composition of the gas, hydrogen burning more rapidly than methane. As a rule it might be stated that the rate of burning decreases with the specific gravity of the gas, the light gases such as hydrogen burn with almost explosive rapidity, while the heavier gases such as carbon dioxide are incombustible or have a zero rate of combustion. In practice an increased rate of burning is obtained by heating the charge before ignition by a process that will be explained later.

Another factor governing the output of an engine with a given size cylinder is the amount of air required to burn the fuel. The quantity of air necessary for the combustion of the fuel determines the amount of fuel that can be drawn into a given cylinder volume, and as we are dependent upon the fuel for the expansion it is evident that with two fuels of the same calorific value, the one requiring the least air will develop the most power. Since the air required to burn hydrogen gas is only one fourth of that required to burn the same amount of methane it is clear that more hydrogen can be burned in the cylinder than methane. This great increase in output due to the hydrogen charge is however, considerably offset by the greater calorific value of the methane.

Should the air be in excess of that required for complete combustion, or should a great quantity of incombustible gas, such as nitrogen be present in the mixture, the fuel will be completely burned, but the speed of burning will be reduced owing to the dilution. As the air is increased beyond the proper proportions the explosions become weaker and weaker as the gas becomes leaner until the engine stops entirely. Because of the fact that it is impossible in practice to so thoroughly mix the gas and air that each particle of gas is in contact with a particle of air, the volume of air used for the combustion is much greater than that theoretically required. A SLIGHT excess of air, making a lean mixture, increases the efficiency of combustion although it reduces the temperature and pressure attained in the cylinder. This is due to the fact that while the temperature of the mixture is lower than with the theoretical mixture the temperature of the burning gas itself is much higher. A mixture that is too lean to burn at ordinary temperatures will respond readily to the ignition spark if the temperature or pressure is raised.

(4) Compression.

In the practical gas engine the gas is not ignited at the beginning of the suction stroke by which it is drawn into the cylinder, but is compressed in the front end of the cylinder by the return stroke of the piston, and then ignited. The process of compression adds greatly to the power output of a given sized cylinder and increases the efficiency of the fuel and expansion. In order to understand the relation that the compression bears to the expansion let us refer to Fig. 2 in which C is the working cylinder, P the piston and G the crank. While the piston is moving towards the crank in the direction of the arrow A it draws the mixture, indicated by the marks x x x x x, into the cylinder, the quantity being proportional to the position of the piston. In this particular case let us assume that the area of the piston is 50 square inches and that the entire stroke (B) of the piston is 12 inches. To prevent confusion due to considerations of heat loss we will further assume that the cylinder is constructed of non-conducting material.

With the piston at the position H, midway between J and I, the volume D is filled with the explosive mixture at atmospheric pressure and a temperature of 500° absolute. Since D = 6 inches and the area of the piston is 50 square inches, the volume D is equal to 6 × 50 = 300 cubic inches, and the entire volume is 2 × 300 = 600 cubic inches. On igniting this mixture (at atmospheric pressure) the temperature will rise immediately, say to 1000°F with the piston at H. According to a law governing the expansion of gases, known as Gay-Lussac’s Law, the expansion v × T
t = V where v = the initial volume of the gas before ignition = 300 cubic inches; t = the temperature before ignition 500° absolute; V = the volume of the gas after expansion; and T = temperature after ignition = 1000° absolute. Inserting the values in numerical form we have as the final volume:—300 × 1000
500 = 600 cubic inches = the volume after expansion, or twice the original volume of gas. This means that the expansion is capable of driving the piston from H to I before the pressure is reduced again to atmospheric pressure. As the volume is expanded to twice that of the original volume at atmospheric pressure (14.7 pounds per square inch), the pressure against the piston before it starts moving will be 2 × 14.7 = 29.4 pounds per square inch.

Let us now consider the case in which the charge is compressed before ignition occurs and compare the expansion and pressure established with that produced by ignition at atmospheric pressure. To produce the compression the piston will travel through the entire stroke to the position I on the suction stroke filling the entire cylinder volumes of 600 cubic inches with the mixture. On the return stroke the piston stops at H, reducing the original volume of 600 cubic inches to 300 cubic inches, doubling the pressure of the gas. The initial and final temperatures will be considered as being the same as those in the first example, 500° and 1000°. From Gay-Lussac’s Law—v × T
t = V and substituting the numerical values 600 × 1000
500 = 1200 cubic inches, or the expanded volume will be four times the compressed volume, or four times the initial volume of the first case where the gas was ignited at atmospheric pressure.

It should be noted however, that while the expansion has been greatly increased by the compression, that this is not all gain, as equivalent work has been expended in compressing the charge. With the exception of doubling the fuel taken into the cylinder, and consequently doubling the output for a certain cylinder capacity, there has been no increase in fuel efficiency except that due to conditions other than the mere reduction in volume. In the second case the volume was increased four fold which resulted in a piston pressure of 4 × 14.7 = 58.8 pounds per square inch before the piston increased the volume by moving from H to I.

The work done by the engine on the charge in compressing is converted into heat energy causing a rise in the temperature of the gas. This would not be a loss as it would reappear as mechanical energy on the return stroke of the piston through its expanding effect on the gas. This heat would, in effect, be added to the temperature due to ignition, and the sum would produce its equivalent expansion. The temperature due to the combustion may be determined by reversing Gay-Lussac’s Law—

Where t = initial temperature; T = temperature combustion; P = pressure after combustion; p = pressure before combustion.

Because of the fact that the act of compressing the charge in the cylinder before ignition increases the temperature of the working medium, the compression will increase the speed of combustion and efficiency of the fuel as the rate of combustion increases with the initial temperature. This increased temperature due to initial compression of course results in a greater temperature range and output due to the increased rate of burning, and this rate of combustion may be varied for different fuels by changing the compression pressure. In a previous paragraph it was explained that the fuel efficiency was increased by a slight dilution or excess of air, and that while the temperature and pressure of the mixture were reduced by the dilution the temperature of the fuel was increased, provided that the inflammability was not decreased.

Compression affords a means of using dilute mixtures without loss of inflammability, as the heat gained by the compression restores the inflammability lost by the effects of dilution. Increased compression pressures increases the possible range of dilution, so that extremely lean gases and mixtures may be used with success with appropriately high compression. As an example of this fact we can refer to the engine using blast furnace gas, a fuel that is so lean that it cannot be ignited under atmospheric pressure. By increasing the piston speed, the heat of the compression can be made more effective as the gas lies in contact with the cylinder walls for a shorter time which of course reduces the heat to the jacket water.

(5) Efficiency and Heat Losses.

Up to the present time we have considered an engine in which there is no heat loss or loss from friction, but in the actual engine such losses are large and tend to materially reduce the values of heat and pressure to be obtained from a fuel with a given calorific content. Applying the rule for heat engines given in a previous section where the efficiency is—

We have the theoretical efficiency of a gas engine, neglecting friction, loss to the cylinder walls, and loss through the rejection of heat with the exhaust gas, equal to—

In substituting the numerical values in the above calculation it was assumed that the temperature of the burning mixture would be 1500° F above zero, and that the exhaust temperature would be as low as 60. Since the calculation is made from absolute zero, which is 460° below the zero marked on our thermometers, the temperature of the burning charge, T = 1500 + 460° = 1960° above absolute zero. Similarly the absolute temperature of the exhaust would be, t = 60 + 460 = 520° absolute. The application of the absolute temperatures will be seen from the calculation for efficiency. The value given, 73.5 per cent, it should be understood is the theoretical efficiency and is at least 20 per cent above the best results obtained in practice. The best record that we have had to date, is that established by a Diesel engine which returned 48.2 per cent of the calorific value of the fuel in the form of mechanical energy. In order that the reader may have some idea of the losses that occur in the engine, and their extent we submit the following table. These are the results of actual tests obtained from different sources and represent engines built for different services and of various capacities:

The remarkable efficiency of the Diesel engine is due principally to the extremely high compression pressure, which was from 500 to 600 pounds per square inch. When this is compared to the 60 to 70 pounds compression pressure used with automobile engines it is easy to see where the Diesel gains its efficiency. It is evident that as much depends on the manner in which the fuel is used in the engine as on the calorific value of the fuel.

(6) Expansion of the Charge.

When an explosive mixture is ignited in the cylinder with the piston fixed in one position thus making the volume constant, the increase of temperature is accompanied by an increase of pressure. If the piston is now allowed to move forward increasing the volume, the increase of volume decreases the pressure. Since in the operation of the gas engine the piston continuously expands the volume on the working stroke it is evident that there is no point in the stroke where the pressures are equal, and that the pressure is the least at the end of the stroke, it being understood of course that no additional heat is supplied to the medium after the piston begins its stroke.

This distribution of pressure in the cylinder in relation to the piston position is best represented graphically by means of a diagram as shown by Fig. 3, in which K is the cylinder and P the piston. Above the cylinder is shown the diagram HGDE the length of which (HE) is equal to the stroke of the piston shown by (BC). Intersecting the line HI are vertical lines, A, a, b, c, C, which represent certain positions of the piston in its stroke. The height of the diagram H G represents to scale the maximum explosion pressure in pounds per square inch, and the line HG is drawn immediately above the piston position B which is at the inner end of the stroke. To the left of the line HS is drawn a scale of pressures ML divided in pounds per square inch so that the pressures may be read off of the pressure curve GD. The line JI represents atmospheric pressure, and the divisions on ML, of course, begin from this line and increase as we go up the column. As an example in the use of the scale we find that the point F is at 50 pounds pressure above the atmospheric line JI.

We will consider that the clearance space AB is full of mixture at the point B, and that it is moved toward the left to the point C filling the space AC full of mixture at atmospheric pressure. The location of the piston on the diagram is shown by D and E. The opening through which the gas was supplied to the cylinder is now closed, and the piston starts on its compression stroke, moving from C to A. As the volume is reduced from AC to AB, there is an increase of pressure which is shown graphically by the rising line EF. This line rises gradually from the line JI in proportion to the reduction in volume until the piston reaches the end of the compression stroke at B, at which point the compression is at a maximum. The extent of this pressure is shown by the length of HF which on referring to the scale of pressure at the left will be found to be 50 pounds per square inch.

Ignition now occurs and the pressure increases instantly from the compression pressure at F to the maximum pressure at G which on referring to the scale will be found to equal 200 pounds. The actual increase of pressure due to ignition above the compression pressure will be shown by the length of the line FG which is equal to 150 pounds. As the pressure is now established against the piston it will begin to move forward with an increase of volume and a corresponding decrease in pressure, until it reaches the point C. This point at the end of the stroke is indicated on the diagram by D which by reference to the scale will be found equal to 25 pounds above atmosphere. An exhaust valve is now opened allowing the gas to escape to the atmosphere which reduces the pressure instantly from D to E on the atmospheric line. Expansion along the line GD is not complete as the pressure is not decreased to atmospheric pressure in the cylinder which means that there is a considerable loss of heat in the exhaust. In practice the expansion is never complete, but ends considerably above atmospheric pressure as shown.

Fig. F-3. Front Elevation of Curtiss “V” Type Aeronautical Motor. This is the Front View of the Motor Shown in the Frontispiece. See Chapter V for Description of this Type of Motor.

Complete expansion is shown by the dotted line GE which terminates at E on the atmospheric line. By following the vertical lines up from the points a, b, c, and d, the pressures corresponding to these piston positions can be found by measuring the distance of the curve from the atmospheric line, on the given lines a, b, c or d. To find the pressure at the position a, for instance, follow upwards along the line a to the point c on the curve, the length of the line ef from the curve to the atmospheric represents the pressure, which by reference to the scale ML will be found equal to 125 pounds. The pressure at any other point can be found in a like manner. Compression pressures may be found at any point by measuring from the atmospheric line to the compression curve FE along the given line. It will be noted that the combustion is so quick that the pressure rises in a straight line along GH, indicating that combustion was complete before the piston had time to start on the outward stroke. The expansion curves GE and GD are similar to the compression curve FE. With the actual engine the shape of the ideal card as shown by Fig. 3 is sometimes considerably deformed owing to the effects of defective valves, leaks, or improperly timed ignition.

Pressure curves of actual engines are of the greatest value as they show the conditions within the cylinder at a glance and make it possible to detect losses due to leaks, poor valve settings, etc. These curves are traced by means of the INDICATOR which is an instrument consisting of a small cylinder which is connected to the cylinder of the engine, and an oscillating drum that is driven to and fro by the engine piston. The piston in the indicator cylinder is provided with a spring that governs its movements and communicates its motion to a recording pencil through a system of levers. The spring is of such strength that a pressure of so many pounds per square inch in the cylinder causes the pencil to draw a line of a definite length, this line being equivalent to the pressure line GH in Fig. 3. A piece of paper is wrapped about the indicator drum, and the drum is attached to the piston in such a manner that it turns a certain amount for every piston position, the complete stroke of the piston turning the drum through about three-quarters of a revolution. Rotation of the drum traces the horizontal lines of the diagram and the movement of the piston draws the vertical lines, so the combined movements of the drum and piston records the pressures and piston positions as shown by Fig. 3.

Since the movement of the indicator piston represents the pressures in the cylinder to scale it is possible to compute the power developed in the cylinder as the output in mechanical units is equal to the product of the average force acting on the piston multiplied by the speed of the piston in feet per minute. This product of the force and velocity (known as “foot pounds per minute”) divided by 33,000 (one horse-power = 33,000 foot pounds) gives the output of the engine, in horse-power.

As the pressure on the piston fluctuates throughout the stroke, it would be wrong to consider the force, in the calculation for power as being equal to the explosion pressure, and so the effective pressure is taken as being the average of all the pressures from the point of explosion to the exhaust. The average pressure or “mean effective pressure” as it is called is computed from the indicator diagram by dividing it into a number of equal parts along the horizontal line, adding the lengths of the pressure lines such as CH, CF, etc., and dividing the total length by the number of the lines. After the average height of the diagram is thus determined, the average length is multiplied by the scale of the indicator or the pressure that is shown by it per inch.

Fairbanks-Morse Gasoline Pumping Engine. Pump is Gear Driven From the Engine Crank-Shaft at Reduced Speed.

Knowing the mean effective pressure, the total pressure on the piston, or the force is found by multiplying the area of the piston in square inches by the average pressure per square inch. This product is multiplied by the piston speed in feet per minute and is divided by the product of the number of strokes to the explosion and the quantity 33,000. Should there be more than one cylinder the result is multiplied by the number of cylinders, and this is multiplied by 2 in the case of a double acting engine. Stated as a formula this rule becomes:

It should be specially noted that the area of the piston is given in square inches and the stroke of the piston in feet. The number of revolutions per minute, R, is multiplied by two in order to obtain the number of strokes, as there are two strokes per revolution. When the engine governs its speed by dropping explosions to meet varying loads, the quantity C should be omitted and the explosions counted.

Due to the fact that the incoming charge of the mixture is expanded by the heat of the passages, a full charge computed at atmospheric temperature is never obtained in the cylinder and for this reason the gas should be kept as cold as possible before entering the passages in order to obtain the maximum output. Friction due to restricted passages and valve openings also reduces the amount of mixture available. Small exhaust valves and pipes prevent the gases from escaping freely to the atmosphere and produces a back pressure on the piston which cuts down the effective pressures. All of these items are recorded by the indicator and makes it possible to make alterations that will increase the output of the engine.

Because of the reduced atmospheric pressures at high altitudes the output and compression are reduced for every foot of elevation above sea level. As the weight of the atmosphere is reduced, less mixture is drawn into the cylinder. Taking the output of the engine as 100 per cent at sea level, it is reduced to less than 62 per cent at an elevation of 15,000 feet.

CHAPTER II
FUELS AND COMBUSTION

(7) Combustion.

The phenomenon called combustion by which we obtain the heat energy necessary for the operation of the internal combustion engine is a chemical combination of the air with the fuel. This process results in heat and some light which is equal in quantity to the energy required to separate the fuel compound into its elements or to build it up in its present form from the original elements. If the process is comparatively slow, the compound is called a fuel, if it is instantaneous it is called an explosive. Some substances produce mechanical force through an instant, without the evolution of much heat, due to the disintegration of an unstable compound. The effect of the latter type of which dynamite is an example is static, that is to say, it is not capable of producing power, but only pressure. For this reason, compounds having an instantaneous effect without the ability to produce the pressure through a distance, or an expansion, are not considered as suitable fuels for a heat engine.

A fuel is essentially a substance which is capable of generating heat, which is a form of energy, and not static pressure. The heat engine is an instrument which transforms this energy into power which is again dissipated into heat through the friction of the engine itself and by the load that it drives. This is an illustration of the physical law that “energy can neither be created nor destroyed,” that is, the heat energy developed by the fuel is converted into mechanical energy which is again transformed into heat energy through friction.

It should be understood that fuel belongs to that class of substances that will not burn nor evolve energy under any temperature, pressure, or shock, without an outside supply of oxygen. This is the characteristic property of all fuels used with the internal combustion engine. Each element, such as carbon and hydrogen, in a compound fuel, develops a certain definite amount of heat during their complete combustion, and at the close of the process certain compounds are formed that represent the lowest chemical form of the compound. To restore the products of combustion to their original form as fuel would require an expenditure of energy equal to that given out in the combustion.

While all substances that are capable of oxydization or combustion can be made to liberate heat energy, it does not follow that all of them can be successfully used as fuels. A fuel suitable for the production of power must be cheap, accessible and of small bulk, and must burn rapidly. Such fuels must also be products of nature that require no expenditure of energy in their preparation or completion.

Fig. F-4. Fairbanks-Morse Producer Plant and Engine, Connected for Operation.

In practical work, the natural fuels are coal, mineral oils, natural gas, and wood, which are compounds of the elements carbon and hydrogen. When these fuels are burned to their lowest forms the products of combustion consist of carbon dioxide and water, the first being the result of the oxydization of carbon, and the latter a compound of oxygen and hydrogen. In solid fuels, such as coal, a portion of the compound consists of free carbon and the remainder of a compound of carbon and hydrogen known as a HYDROCARBON. In liquid fuels there is little, if any, free carbon, the greater proportion being in the form of a hydrocarbon compound. Natural gas is a hydrocarbon compound.

It should be noted that a definite amount of oxygen is required for the complete combustion of the fuel elements, and that a smaller amount of oxygen than that called for by the fuel element results in incomplete combustion, which produces a product of higher form than that produced by the complete reduction. The product of incomplete combustion represents a smaller evolution of heat than that of the complete process, but if reburned in a fresh supply of oxygen the sum of the second combustion together with that of the first will equal the heat of the complete oxydization. When pure carbon is incompletely burned the product is carbon monoxide (CO) instead of carbon dioxide (CO₂).

Carbon completely burned to carbon dioxide produces 14,500 British thermal units per pound of carbon, while the incomplete combustion to carbon monoxide evolves only 4,452 British thermal units, or less than one-third of the heat produced by the complete combustion. Theoretically one pound of carbon requires 2.66 pounds of oxygen to burn it to carbon dioxide. On supplying additional oxygen, the carbon monoxide may be burned to carbon dioxide and the remainder of the heat may be recovered, or 10,048 British thermal units. When a hydrocarbon, either solid, liquid or gaseous is burned with insufficient oxygen, solid carbon is precipitated together with lower hydrocarbons, and tar. In an internal combustion engine the precipitated solid carbon is evident in the form of smoke.

Since the carbon and hydrogen elements of a fuel exist in many different proportions and conditions in coal and oil, different amounts of oxygen are required for the consumption of different fuels. It should also be borne in mind that a greater quantity of air is required for the combustion of a fuel than oxygen, as the air is greatly diluted by an inert gas, nitrogen, which will not support combustion. Because of the impossibility of obtaining perfectly homogenous mixtures of air and the fuel, a greater quantity of air is used in practice than is theoretically required.

In a steam engine the fuel can be used in any form, solid, liquid, or gaseous, but in an internal combustion, it must be in the form of a gas no matter what may have been the form of the primary fuel. Fortunately there is no fuel which may not be transformed into a gas by some process if not already in a gaseous state. The petroleum products are vaporized by either the heat of the atmosphere or by spraying them on a hot surface. Coal is converted into a gas by distilling it in a retort or by incomplete combustion. The heat energy developed by a gas when burning in the open air depends on its chemical combustion, but its mechanical equivalent in power when burned in the cylinder of the engine depends not only upon its composition but upon the conditions under which it is burned as stated in the chapter devoted to the subject of heat engines.

(8) Gaseous Fuels.

While the calorific values of the different gases given in the accompanying table are approximately correct for gases burning in the open air at atmospheric pressure they develop widely different values in the cylinder of an engine because of the effects of compression and preheating. The table serves, however, as an index to the relative values of the fuels under ordinary conditions without compression. While natural gas has nearly eight times the calorific value of producer gas in the open air, its actual heat value in the cylinder is only about 45 per cent greater. While acetylene has an exceedingly high calorific value and explodes five times as fast as gasoline gas, it develops only 20 per cent more power in the same cylinder. Another item affecting the value of a gas is the rate at which it burns, which is in part a characteristic of the fuel and partly a factor of the conditions under which it is burnt. This subject is treated of in the chapter devoted to the heat engine.

The calorific value of a gas may either be computed from its chemical composition or by burning it in an instrument known as a calorimeter. A gas calorimeter consists of a small boiler or heating tank which is carefully covered with some non-conducting material so as to prevent a loss of heat to the atmosphere. The gas under test is burned in the boiler whose extended surface catches as much of the heat as possible and transfers it to the water in the boiler. The weight of the water heated and its temperature are taken when a certain amount of the gas has been burned (say 100 cubic feet), and from this data, the heat units per cubic foot of gas are computed.

As a British thermal unit is the amount of heat required to raise the temperature of one pound of water through one Fahrenheit degree (at about 39.1° F.), the total heat per cubic foot of gas as observed by the calorimeter is equal to the weight of the water multiplied by its rise in temperature in degrees, divided by the number of cubic feet of gas burned in the calorimeter. Since a British thermal unit is equal to 778 foot pounds in mechanical energy, its mechanical equivalent is equal to the number of British thermal units multiplied by 778.

Another difference between the actual and theoretical results obtained is that due the perfect combustion in the calorimeter and the imperfect combustion in the engine. Since some gases require more air for their combustion than others, less of the first gas will be taken into the cylinder on a charge than the latter, which tends still further to balance the heating effect of rich and lean gases in the cylinder.

(9) Gasifying Coal.

Coal Gas or Illuminating Gas is generated by baking the coal in a closed retort or chamber out of contact with the air so that no combustion takes place either complete or incomplete. The hydrocarbon gases and tars are set free from the coal as permanent gases and are then piped to a gas holder after going through various purifying processes to remove the tars, oils, moisture and dust. The free or solid part of the coal remains in the retort in the form of coke, which is again burned for fuel.

Because of its high carbon content, coal gas burns with a yellowish-white flame and is extensively used for lighting purposes, hence the name illuminating gas. In many ways coal gas is an ideal fuel for power purposes as it has a high calorific value (650–750 B.T.U. per cubic ft.), is supplied by the illuminating company at practically a constant pressure, and is uniform in quality. Its only drawback is its comparatively high cost.

This gas is always obtained from the city service mains as its preparation is too expensive and complicated for the gas engine owner. Because of its cost, the use of coal gas is restricted to small engines.

(10) Water Gas.

Water gas is made by blowing air through a thick bed of some coal that is low in hydrocarbons until the coal becomes incandescent, the gases that are formed are allowed to escape to the atmosphere. At this point a jet of steam is blown into the incandescent bed, which is broken up into its elements, oxygen and hydrogen, by the heat of the fuel. As there is no air present the oxygen combines with the carbon of the fuel to form carbon monoxide while the hydrogen goes free. Both of these gases, carbon monoxide and hydrogen, are collected and supplied to the engine. The production of water gas is intermittent, as the steam blast cools down the fuel bed, and requires further blowing before more steam can be passed. While this gas has a lower heating value than coal gas, it is much cheaper to make and all of the coal is consumed in the process.

Water gas is high in hydrogen and is too “snappy” for gas engines; the hydrogen places a limit on the allowable compression.

For each thousand feet of water gas generated, approximately 24 pounds of water are required.

By the introduction of hydrocarbons or vaporized oil, illuminating value is given to water gas, this process is called carburetion. Carbureted gas is not usually used for power, as it is expensive, and is not proportionately high in heating value.

(11) Blast Furnace Gas.

Many steel companies are utilizing the unconsumed gas of the blast furnaces for power.

Blast furnace gas is of very low calorific value, rarely if ever, exceeding 85 B.T.U. per cubic foot. This allows of very high compression, which greatly increases the actual power delivered by the engine.

A smelter produces approximately 88,000 cubic feet of gas per ton of iron smelted.

Blast furnace gas is so lean that it cannot be burned satisfactorily under a boiler; the high compression of the gas engine makes its use possible.

(12) Producer Gas.

Producer gas which is generated by the incomplete combustion of fuels in a deep bed is the most commonly used gas for engines having a capacity of 50 horsepower and over, because of the simplicity and economy of its production. While producer gas has been obtained from practically every solid fuel, of which coal, coke, wood, lignite, peat, and charcoal are examples, the fuel most generally used is either coal or coke. While producer gas is much lower in calorific value than either natural or illuminating gas it gives admirable results in the gas engine and is a much cheaper fuel than coal gas in units above 50 horse-power capacity. The fuel is completely burned to ash in the producer without the intermediate coke product that exists in the manufacture of coke.

A producer consists of three independent elements as shown by Fig. F-6; the PRODUCER or generator (A), the steam boiler (B), and the SCRUBBER or purifier (C). The incandescent fuel (F) in the form of a cone lies on the grate bars (G) at the lower end of the producer. Above the burning fuel is a deep bed of coal (D) which reaches to the top of the producer at which point it is admitted to the bed through the charging valve or gate (H). The gas resulting from the combustion in the producer is drawn out of the tank through the gas outlet pipe (E) by the suction of the engine. The air for the combustion is drawn up through an opening in the ash pit (J) by the engine.

When the oxygen of the air strikes the incandescent fuel on the grate it combines with a portion of it forming carbon dioxide (CO₂) which is an incombustible gas, but on passing through the burning fuel above this point, one atom of the oxygen in the CO₂ recombines with the fuel forming the combustible gas—carbon monoxide (CO). Because of the distilling effect of the heat in the bed, the volatile hydrocarbons of the coal are set free and mingle with the CO formed by the combustion. The producer gas consists, therefore, principally of CO, with a certain proportion of the volatile hydrocarbons of the coal such as marsh gas, ethylene, and some oil vapor.

Since the hydrocarbons are easily condensed on coming into contact with the coal walls of the piping, to form trouble making tars and oils, they must either be washed out of the gas in the purifier or passed again through the high temperature zone to convert them into permanent gases. In the usual producer, the hydrocarbons are reheated, as they form a considerable percentage of the heat of the gas. After the volatile constituents are reheated, the gases pass through the boiler (B), which absorbs the heat of the gas in generating steam, and from this point the gases enter the scrubber where the dust and the residual tars are removed. The scrubber, which is a sort of filter, is an important factor in the generating plant, for if the dust and dirt were allowed to pass into the cylinder of the engine it would only be a question of a short time until the valves and cylinder would be ground to pieces.

When the steam from the boiler is allowed to flow into the ash pit of the producer and up through the incandescent fuel, the heat separates the water vapor into its two elements, oxygen and hydrogen. The oxygen set free combines with the carbon in the coal forming more carbon monoxide, while the hydrogen which is unaffected by the combustion adds to the heat value of the gas. The last additions to the combustion due to the disassociation of the steam are really what is known as “water gas.” A limited amount of steam may be admitted continuously in this manner without lowering the temperature of the fuel below the gasifying point, and its presence is beneficial for it not only provides more CO and hydrogen but produces it without introducing atmospheric nitrogen. The steam is also a great aid in preventing the formation of clinkers on the grate bars. Since the air used in burning the fuel in the first reaction contains about 79 per cent of nitrogen, which is an inert gas, the producer gas is greatly diluted by this unavoidable admixture, which accounts for its low calorific value.

Fig. F-6. Diagram of Suction Gas Producer Showing the Generator, Boiler and Washer.

While the air required for the combustion of the fuel is drawn through the producer by the suction of the engine in the example shown (SUCTION PRODUCER), there is a type in common use called a PRESSURE PRODUCER in which the air is supplied under pressure to the ash pit by a small blower, which causes a continuous flow of gas above atmospheric pressure.

Gas producers are divided into two classes: suction producers and pressure producers. The suction producer presents the following advantages:

1. The pipe line is always less than atmospheric pressure, hence no leaks of gas to the air are possible.

2. The regulation of the gas supply is automatic.

3. No gas storage tank is required.

4. The production of gas begins and stops with the engine.

5. Uniform quality of gas.

The suction producer is limited to power application and cannot be used where the gas is to be used for heating, as in furnaces, ovens, etc., or where the engine is at a distance from the producer, unless pumped to its destination.

The pressure producer does not yield a uniform quality of gas, hence requires a storage tank where low quality gas will blend with gas of higher calorific values and produce a gas of fairly uniform quality.

The pressure producer is adapted to the use of all grades of fuels, such as bituminous coal and lignite.

Anthracite coal contains little volatile matter and is an ideal fuel for the manufacture of producer gas, while bituminous coal with its high percentage of volatile matter and tar, requires more efficient scrubbing, as these substances must be removed from the gas.

On starting the producer shown by Fig. 6, the producer is filled with the proper amount of kindling and coal, and a blast of air is sent into the ash pit by a small blower, the products of combustion being sent through the by-pass stack (K) until the escaping gas becomes of the quality required for the operation of the engine. The by-pass valve is now closed, and the gas is forced through the scrubber to the engine until the entire system is filled with gas. When good gas appears at the engine test cock the engine is started, and the blower stopped, the gas now being circulated by the engine piston. The volume of gas generated by the producer is always equal to that required by the engine so that no gas receiver or reservoir is required. Because of the friction of the gas in passing through the fuel, scrubber and piping, its pressure at the engine is always considerably below that of the atmosphere, which of course reduces the amount of charge taken into the cylinder. Because of the weak gas and the low pressure in the piping, it is necessary to carry a much higher compression with producer gas than with natural or illuminating gas.

The efficiency of a producer is from 75 to 85 per cent, that is, the producer will furnish gas that has a calorific value of an average of 80 per cent of the calorific value of the fuel from which it is made, the remaining 15 to 20 per cent being consumed in performing the combustion. This is far above the efficiency of the furnace in a steam boiler, as an almost theoretically exact amount of air can be supplied in the producer to effect the combustion, while in the boiler furnace about ten times the theoretical amount is passed through the fuel bed to burn it. Heating up this enormous volume of air to the temperature of the products of combustion consumes a large amount of fuel and reduces the efficiency of the furnace considerably. Because of the reduction in the air supply, a gas fired furnace is always more efficient than one fired with coal. Producer gas with 300,000 British thermal units per thousand cubic feet, and oil having 130,000 British thermal units per gallon will result in 1,000 cubic feet of gas being equal to about 2.30 gallons of fuel oil.

If the gas is to be used for heating ovens or furnaces in connection with the generation of power, the character of the fuel will be determined to a great extent by the requirements of the ovens and by the type of producer used, as each fuel will give the gas certain properties. Thus gas used for firing crockery will not be suitable for use in open hearth steel furnaces, as the impurities in the various fuels may have an injurious effect on the manufactured product. The cost of the fuel, cost of transportation, heat value, purity, and ease of handling are all factors in the selection of a fuel.

The size and condition of a fuel is also of importance. Exceedingly large lumps and fine dust are both objectionable.

Wet fuel reduces the efficiency of the producer, as the water must be evaporated, this causing a serious heat loss.

With careful attention a producer gas engine will develop a horse-power hour on from 1 to 1¼ pounds of anthracite pea coal, and in many instances the consumption has been less than this figure. The efficiency in dropping from full load to half load varies by little, one test showing a consumption of 1.1 pounds of coal per horse-power hour at full load and 1.6 pounds of coal at half load. Producer gas power is nearly as cheap as water power, in fact the producer gas engine has displaced at least two water plants to the writer’s knowledge. According to an estimate made by a well known authority, Mr. Bingham, it is possible for a producer gas engine to generate power for only .1 of one cent more per K.W. hour than it is generated at Niagara Falls.

According to the United States Bureau of Mines,

“The tests in the gas producer have shown that many fuels of so low grade as to be practically valueless for steaming purposes, such as slack coal, bone coal and lignite, may be economically converted into producer gas and may thus generate sufficient power to render them of high commercial value.

“It is estimated that on an average each coal tested in the producer-gas plant developed two and one-half times the power that it would develop in the ordinary steam-boiler plant.

“It was found that the low-grade lignite of North Dakota developed as much power when converted into producer gas as did the best West Virginia bituminous coals burned under the steam boiler.

“Investigations into the waste of coal in mining have shown that it probably aggregates 250,000,000 to 300,000,000 tons yearly, of which at least one-half might be saved. It has been demonstrated that the low-grade coals, high in sulphur and ash, now left underground, can be used economically in the gas producer for the ultimate production of power, heat and light, and should, therefore, be mined at the same time as the high-grade coal.

“As a smoke preventer, the gas producer is one of the most efficient devices on the market, and furthermore, it reduces the fuel consumption not 10 to 15 per cent, as claimed for the ordinary smoke preventing device offered for use in steam plants, but 50 to 60 per cent.”

(13) Producer Gas From Peat.

The production of gas from peat having a low water content (up to about 20 per cent) for use in suction gas engines has already met with considerable success in Germany, but for a number of years efforts have been made to utilize peat with a water content as high as 50 to 60 per cent and thus eliminate the costly process of drying the raw material.

Difficulties have been encountered in preventing a loss of heat through radiation and other causes, and in getting rid of the dust and tar vapors carried over by the gases to the engine; but great strides have been made recently in overcoming these obstacles. Peat with a water content up to 60 per cent has been found to be a suitable fuel. Owing to its great porosity and low specific gravity it presents a large combustion surface in the generator, so that the oxygen in the air used as a draft can easily unite with the carbon of the peat.

Fig. F-7. German Producer for Generating Producer Gas from Peat.

One of the great difficulties is to eliminate the tar vapors that clog up many of the working parts of the engine. The passing of the gas through the wet coke washers and dry sawdust cleansers does not appear to have thoroughly remedied the evil. Efforts were therefore made to remove the tar-forming particles of the gas in the generator itself or to render them harmless. That of the Aktien-Gesellschaft Gorlitzer Maschinenbau Ansalt und Eissengiesserei of Gorlitz, was displayed at the exposition at Posen in 1911. The gas from the generating plant was employed in a gas suction engine of 300 horse-power used to drive a dynamo for developing the electric energy for the exposition. The fuel used was peat with a water content of about 40 per cent. The efficiency and economy results obtained were very promising.

The advantages claimed for the Gorlitz engine are that the sulphurous gases and those containing great quantities of tar products are drawn down by the suction of the engine through burning masses of peat and thus rid of their deleterious constituents. The air for the combustion purposes is well heated before entering the combustion chamber, thereby producing economical results. It is claimed also that the gas produced by its system is so free from impurities that the cleaning and drying apparatus may be of the simplest kind.

In Stahl und Eisen, an abstract is given of a paper by Carl Heinz describing a peat gas producer, built by the Goerlitzer Maschinenbauanstalt. We are indebted to Metallurgical and Chemical Engineering for the translation of this paper:

Air and fuel enter the producer at the top, and the gas exit is in the center of the bottom so that the air is forced to pass through the center of the producer, decomposing the volatile matter into gases of calorific value. The moisture which is present in the peat fuel in considerable quantities must be taken into consideration. For its decomposition which passing through the hot-fire zone only a certain amount of heat is available. It is, therefore, important that the heat from the gasification be fully utilized.

There are two kinds of heat losses in a gas producer, due to radiation and to the sensible heat of escaping gases. Both these amounts of heat, however, are utilized according to the special design of this producer. The air circulates first through the lower conduit and comes so in contact with the warm scrubber water. A part of the air which has been preheated is carried upwards through the pipe A in the center of the producer where it is thoroughly preheated by the hot gases and enters then the air superheater B in which the temperature rises to a still higher degree.

The other part of the air passes through the feet of the producer into an air jacket which envelops the whole shell of the producer and enters finally the producer by the reversing valve C on top of the producer. In this way the outer surface of the producer is maintained at a temperature hardly higher than that of the surrounding air. The escaping gases are cooled down so far that the gas outlet into the scrubber may be touched by hand. All ordinary heat losses are thus made use of in the gasification process.

If there is a large excess of moisture in peat, the process is somewhat modified by regulating both air supplies in such a way that the gasification in the upper part of the fuel-bed takes place in two directions, one downwards and the other upwards.

It seems that a content of 80 per cent moisture and 20 per cent dry fuel in the peat is about the limit permitting evaporation of the water, but it is, of course, impossible to obtain in this case a gas of calorific value.

The modification of the process for very wet fuel is as follows:

When the fire on top of the fuel bed appears to disappear, the heater opens the stack and valve D. Valve C is then closed, to prevent air from entering on top. The preheated air enters by D causing a down draft combustion due to the suction of the gas engine and an upward combustion due to the draft in the stack. The moisture is evaporated and escapes through the stack. When the fire has burned through at the top, the valve is switched over. The bad smelling gases rising from the scrubber enter the producer together with air and are there consumed.

In commercial use at the exhibition in Posen the whole plant worked continuously day and night and cleaning of the gas engines was necessary only every three months. Slagging of ashes is done during the operation of the producer, without any nuisance from dust.

The highest percentage of moisture in peat gasified was 50 per cent. The fuel consumption per horse-power hour is 2.2 lb. (1 kg.) of peat. Careful tests made by Prof. Baer, of Breslau, showed that with a cost of peat of $1 per ton the kw-hour at the switchboard costs 0.15 cent.

(14) Crude Oil Producers.

The development of the crude oil gas producer, for which there is great demand, in oil regions remote from the coal field, has been exceedingly slow but it is believed that definite progress has recently been made along this line. The most recent notes on this subject relate to the Grine oil producer. In this type steam spray is used for atomizing the oil which is introduced into the upper part of the generator where partial combustion takes place. The downdraft principle is then applied and the hydrocarbon broken up and the tar fixed by passing through a bed of incandescent coke. Mr. Grine reports that a power plant using one of these producers has been in operation a year in California. With crude oil as a fuel costing 95 cents per barrel, or 2.3 cents per gallon, the plant is reported to develop the same amount of power per gallon of crude as is ordinarily developed by the standard internal combustion engine operating on distillates at 7 cents per gallon. Including the cost of fuel, labor, supplies, interest, depreciation and taxes, Mr. Grine states the cost per b.h.p. hour to be 0.76 cents for a plant of 100 h.p. rating.

(15) Operation of Producers.

A good producer operator is simply a good fireman, he must know how to keep a uniform bed of coal and how to draw the fire. While there are many thousands of men running producer plants without previous mechanical training, there are now but few steam engineers running steam engines of the same capacity but what have had at least two years’ training and sufficient mechanical knowledge to pass an examination and obtain a license. While a considerable amount of skill is necessary to obtain the best efficiency from a producer, it is a knack that is easily acquired in a short time by “sticking around” the plant. Skill in operating a producer consists chiefly in keeping the right sort of a fire without damage to the lining by poking down ashes and clinkers. When a new plant is installed, the manufacturer generally sends an instructor to operate the plant for a short time so that with a few days running in his hands any man with ordinary intelligence can overcome the difficulties which arise from time to time.

While there are many types of producers, the main difference will be found in the character of the draft, that is whether it is up, down, or crossways. Down draft producers are generally used with bituminous coals, as the tars and oils that emanate from the coal are drawn through the fire which converts them into a permanent gas, and avoids the difficulty of removing great quantities of the tar from the producer. An up draft producer will not do this as the gas is drawn directly into the mains without coming into contact with the fire. This would result in considerable expense due to the frequent cleaning. Anthracite coal which does not contain much tar can be used successfully in an up draft producer.

A compromise between the up draft and down draft producer is had in the DOUBLE ZONE producer, which “burns the candle at both ends” as it were, a fire being at both the top and bottom of the producer. Nearly any class of fuel may be used with this type.

It should be remembered that a hot fire and fuel are required for the manufacture of gas, and that the ash pit and grate must be kept clear of the ashes and clinkers that not only reduce the temperature of the fire, but also reduce the gas available at the cylinder by increasing the friction. Shaking down and cleaning out will in nearly every instance start a bucking producer into operation.

When operating under full load a much hotter fire is required than when operating under a reduced load, or the producer will not furnish the necessary gas. According to the size of the producer, the depth of the incandescent fuel will run from 30 inches in the large sizes to 15 inches in the smaller. After being charged up, suction producers will continue to give gas in sufficient quantities with the bed at half this depth. This is only possible with a hot producer, and when no fuel is being fed, as the feeding of a cold charge will reduce the output. A steady depth of fire should be kept to maintain a uniform quality of gas.

In suction producers careful watch should be kept for leaks, as the gas being below atmospheric pressure gives no outward signs of dilution. If water seals are used in the system they should be given careful attention. When using coals that are rich in tar or hydrocarbons, or with fuels that have much fine dust, considerable trouble is had with some types of producers due to “caking” or to the adhesion of the coal particles to the walls of the producers or to their adhesion to one another. In the latter case the “stickiness” of the fuel prevent the proper feed. This difficulty may often be overcome by a change in the rate of feeding or by regulating the depth of the incandescent bed.

Porosity of the fuel, and the rate at which the air is supplied to the producer determines the depth of the incandescent bed. Particular care should be taken that the blast or draft occurs evenly over the fire surface, and that no holes occur in the fire which will cause more rapid combustion in one spot than in another. Neglect of this precaution not only causes a waste of fuel but often results in the fuel “arching” and preventing further feed. The producer should be so proportioned that at full load, the rate of combustion does not exceed 24 pounds of fuel per square foot of producer area per hour.

In his researches, Professor Bone (Iron and Steel Institute, May, 1907) has shown that up to 0.32 lbs. of steam per lb. of coal can be completely decomposed in a producer, but that, from 0.45 lbs. to 0.55 lbs. should be used, approximately 80% more.

Now, in considering the question of the proper proportion of steam for the production of gas for power purposes we must bear in mind that as much heat as possible should be utilized in the producer itself. Some manufacturers of plant go so far as to state that as much as 1 lb. of steam per lb. of coal should be used, but we are safe in saying that 0.5 lb. to 0.7 lb. should be the figure for a power plant. The common practice is to use a blast saturation of 55% whenever the clinkering character of the coal renders it possible. This figure corresponds to about .57 of steam per lb. of coal gasified.

It is of the utmost importance that the proportion of steam and air should be constant, and the best figure being determined, it should not be varied to any degree. It is equally important that the fuel depth should be left constant. By this I mean that not only should the coal in the producer be kept at a specific level, but the position of the fire on the ash bed should be kept as near as possible a fixed point. Ashes should be drawn at regular intervals, or, if desired, continuously by mechanical means.

Further, the supply of air and steam should be regularly distributed, so that the velocity of the gases through the fuel shall be as nearly as possible regular across its whole area.

In some cases the by-products of a producer, such as ammonia, tar, etc., have a commercial value, and if a large amount of gas is generated it will sometimes pay to select a fuel that is rich in these particular substances.

(16) Coal.

Coal which is the basis of producer gas, is composed generally speaking of the combustible matter, moisture, ash and sulphur. The combustible element may be subdivided into the HYDROCARBONS, OR VOLATILES, and the solid fixed carbon. The exact composition of coal is generally given by what is known as PROXIMATE analysis, which analysis divides the constituents of the coal into five groups, viz.: MOISTURE, VOLATILES, FIXED CARBON, ASH, and SULPHUR. Ultimate analysis resolves the coal into its ultimate chemical elements, such as hydrogen, carbon, nitrogen, sulphur, etc., and being a difficult and tedious process it is not much used.

The proximate analysis gives all the necessary information and takes less time to perform.

The CALORIFIC VALUE of a fuel may be calculated from its analysis, or may be determined by means of the CALORIMETER from a sample of the coal; the latter method is the most reliable. Table gives approximately the calorific values, and the proximate analysis of several representative coals from various sections of the country. The values given in the table are not exact, as the coal from each locality varies considerably in quality, but the figures will indicate what may be expected from each type of coal.

Connellsville, Pa., Coke has a calorific value of approximately 13,000 B.T.U.’s per pound, contains no volatile matter, and has an approximate content of 10% ash. Coke is a valuable fuel for the gas producer, but is rather expensive. It is clean and the absence of volatile matter reduces the “scrubbing” problem to a minimum.

Small coal such as buckwheat and pea contain a much higher percentage of moisture than given in the table, running from 5% to 10% higher than the given values.

Bituminous coal is high in hydrocarbons or volatiles which condense easily and form tar. If the tar is not removed or converted into a permanent gas, it will clog the passages of the producer and the engine and cause trouble.

The removal of the tar and ash from a gas is called SCRUBBING, and is performed by a device much resembling a filter. Anthracite coal and coke are low in volatiles or hydrocarbons, and therefore do not cause trouble with tar deposits.

A high percentage of volatile matter also causes trouble by the tar cementing the particles of fuel together. This interferes with the proper action of the producer.

Fuels having a high percentage of ash call for perfect filtering or “scrubbing” as such fuels will fill the gas passages with dust. Dust should be kept out of the engine at all costs, for the dust even in a quantity will cause wear in the cylinder.

Depending on the quality of the fuel, bituminous coal will produce about 4½ pounds of ammonia and 12 gallons of tar with about 5% of sulphur.

Anthracite coal will produce approximately six pounds of tar, and two pounds of ammonia with traces of sulphur.

Loose Anthracite coal requires approximately 40 cubic feet of storage space per ton of 2240 pounds and weighs about 56 pounds per cubic foot (market sizes).

Loose Bituminous coal requires approximately 45 cubic feet of storage space per ton of 2240 pounds, and weighs about 52 pounds per cubic foot in market sizes.

Dry coke requires approximately 85 cubic feet of storage space per ton of 2240 pounds, and weighs about 26 pounds per cubic foot.

(17) Fuel Oils.

Crude oil, a natural product, is the base of the fuels most commonly used in internal combustion engines, especially in the smaller sizes. From this compound the following derivatives are obtained by the process of distillation, a separation possible because of the different boiling points of the various oils. As each derivative or DISTILLATE has a different boiling point, the temperature of the crude oil is maintained at the boiling point of that product that is desired, and the resulting vapor is condensed. The following list is not anywhere near complete for there are several hundred distinctly different distillates, but it contains those that are of the most interest to the engine man.

• 1. Crude Oil.
• 2. Gasoline.
• 3. Naphtha.
• 4. Solar Oil.
• 5. Kerosene.

The specific gravity of the crude oil as obtained in the field will range from 12° to 56° Beaumé scale. The crude from Pennsylvania will average 40° Beaumé while that from Texas will average 20°. The accompanying table will give the calorific values and general properties of the principle liquid fuels. It should be noted that the weight or density of the liquids is given in terms of specific gravity or Beaumé scale, in which the SPECIFIC GRAVITY of the fuel is the ratio of its weight per unit volume to the weight of an equivalent volume of water. The specific gravity of a liquid is generally determined by an instrument known as a HYDROMETER which consists of a glass tube sealed at both ends carrying a graduated scale on the upper portion of the stem, and a ballast weight of shot or mercury at the bottom.

The hydrometer is floated in the liquid to be tested, and the lower the specific gravity, the lower the hydrometer sinks, and vice versa. The specific gravity of the liquid is read directly from the graduation on the stem that are on a level with the surface of the liquid under test. As in the case of thermometers, hydrometers are all graduated in two different scales, the specific gravity scale and the Beaumé scale. The specific gravity scale reads at 1.00 when floated on distilled water, and the Beaumé at 10.00 when floated on the same liquid.

A difference in temperature affects the density of a liquid, hence all hydrometers are graduated for a standard temperature of 60°F unless otherwise specified. For a difference of 10°F there is a variation of one degree gravity in the Beaumé scale, and for a difference of 20°F in temperature there is a change of one degree on the specific gravity scale. If the temperature differs from 60°F, the corresponding correction should be made in the reading.

To convert the Beaumé reading (B) to terms of the specific gravity scale (S) use the following formula:

It will be noted that the petroleum products contain an enormous amount of heat energy, nearly 25% more than that of the same weight of pure carbon. It will also be noted that the lighter products such as gasoline, kerosene, etc., have more heat per pound but less per gallon than the heavier oils. This is rather confusing at first, but as will be seen after deliberation that the heavier fuel is the most economical since the least is used per horse-power, and is bought by the gallon. The calorific values given in the table are obtained by a calorimeter, and are burnt in the open air, and consequently have a different heating value when under compression in the cylinder of the engine.

In all cases the liquids are vaporized before being introduced in the cylinder, the more volatile liquids such as gasoline being converted into vapor at atmospheric temperature, and the heavier non-volatiles by being sprayed into a heated vessel or preheated air. The percentage of liquid fuel contained in a cubic foot of air vapor mixture depends on the temperature, the boiling point of the liquid and upon the pressure and humidity.

Gasoline consists principally of compounds of the methane series, the one representative of gasoline being Hexane (C₆H₁₄). It requires 15.5 pounds of air for combustion theoretically and about 10 per cent. more in practice. The formation of gasoline vapor produces a drop in temperature of 50°F, and should be heated 100°F above the atmosphere for the best results. The volume of air required for the combustion is about 192 cubic feet. With alcohol at 20 cents per gallon and gasoline at 12½ cents the number of B.T.U.’s for one cent in the case of alcohol is 3594 and 9265 in the case of gasoline. In the engine the difference is not so great owing to the difference in compression pressures.

(18) Tar for Fuel.

Because of the increasing interest in the Diesel type engine and the low grade fuels that it has made possible, we quote the specifications laid down by Dr. Rudolph Diesel, the inventor, before the English Institution of Engineers.

(1.) Tar-oils should not contain more than a trace of constituents insoluble in xylol. The test on this is performed as follows:—25 grammes (0.88 oz. av.) of oil are mixed with 25 cm.³ (1.525 cub. in.) of xylol, shaken and filtered. The filter-paper before being used is dried and weighed, and after filtration has taken place it is thoroughly washed with hot xylol. After re-drying the weight should not be increased by more than 0.1 gr.

(2.) The water contents should not exceed 1 per cent. The testing of the water contents is made by the well-known xylol method.

(3.) The residue of the coke should not exceed 3 per cent.

(4.) When performing the boiling analysis, at least 60 per cent. by volume of the oil should be distilled on heating up to 300° C. The boiling and analysis should be carried out according to the rules laid down by the Trust. (German Tar Production Trust on Essen-Ruhr.)

(5.) The minimum calorific power must not be less than 8,800 cal. per kg. For oils of less calorific power the purchaser has the right of deducting 2 per cent of the net price of the delivered oil, for each 100 cal. below this minimum.

(6.) The flash-point, as determined in an open crucible by Von Holde’s method for lubricating oils, must not be below 65° C.

(7.) The oil must be quite fluid at 15° C. The purchaser has not the right to reject oils on the ground that emulsions appear after five minutes’ stirring when the oil is cooled to 8°.

Purchasers should be urged to fit their oil-storing tanks and oil-pipes with warming arrangements to redissolve emulsions by the temperature falling below 15° C.

(8.) If emulsions have been caused by the cooling of the oils in the tank during transport, the purchaser must redissolve them by means of this apparatus.

Insoluble residues may be deducted from the weight of oil supplied.

Coal tar oil is the distillate of the tar obtained from gas works, from which all valuable commercial materials such as aniline have been removed. Coal oil tar is also known as creosote oil and anthracene oil, the heat value of which is not quite 16,000 B.T.U. per pound.

(19) Residual Oils.

Residual oil is the residue left after the lighter oils have been distilled from the petroleum, which before the advent of the Diesel engine were useless. Residual oil which was hardly fluid at ordinary temperatures has been successfully used in the Diesel and semi-Diesel types of engines, by preheating it before admission to the inlet valves. The enormously increased demand for gasoline has resulted in a great increase of the formerly useless residual oil so that it is possible that the demand for gasoline will make the production of the residual great enough so that it can be seriously considered as a fuel.

(20) Gasoline.

Gasoline is by the far the most widely used fuel for internal combustion engines because of its great volatility and the ease with which it forms inflammable mixtures with the air at ordinary temperatures. Another point in its favor is the fact that it burns with a minimum of sooty or tarry deposits, without a disagreeable smell with moderate compression pressures and without preheating through a wide range of air ratios. Gasoline is a product of crude oil from which it is obtained by a process of distillation, and as it forms but a small percentage of the crude oil it is rapidly becoming more and more expensive as the demand increases. Some Pennsylvania crude oils will yield as much as 20 per cent of their weight in gasoline, while the low grade Texas and California crudes very seldom contain more than 3 per cent.

When considered as a term applying to some specific product, the word “Gasoline” is a very flexible expression as it covers a wide range of specific gravities, boiling points, and compositions, the latter items depending on the demand for the fuel and the taste of the manufacturer. Since the specific gravity of gasoline is a factor that determines its suitability for the engine, at least in regard to its evaporating power or volatility, it is graded according to its density in Beaumé degrees as determined by the hydrometer. According to this scale gasoline will range from 85° to 60° Beaumé, and even lower, although 60° is supposed to mark the lowest limit and to form the dividing line between gasoline and naphtha.

The density of the gasoline in Beaumé degrees is an index to the volatility, for the higher the degree as indicated on the hydrometer, the higher is the volatility at a given temperature, consequently a high degree gasoline will give a better mixture at a low temperature than one of a low degree. In cold weather all gasoline should be tested with a hydrometer when purchased to insure a grade that will be volatile enough for easy starting when the engine is cold. In cold weather the gasoline should not be lower than 68°, and for the best results should be above 72°, at least for starting the engine. Good gasoline should evaporate rapidly and should produce quite a degree of cold when a small amount is spread on the palm of the hand, and it should leave neither a greasy feeling nor a disagreeable odor after its evaporation.

The high gravity gasoline is of course the most expensive, as there is less of it in a gallon of the crude oil from which it is made; gasoline of 76° Beaumé being approximately 15c. per gallon in carload lots, while naphtha of 58° Beaumé brings 8½c. per gallon.

The calorific value of gasoline increases as the gravity Beaumé decreases per gallon; 85° gasoline having approximately 113,000 B.T.U. per gallon while 58° naphtha has an approximate value of 122,000 B.T.U. per gallon. The calorific value remains nearly constant per pound for all gravities.

It should be remembered that heat is absorbed in evaporating gasoline as well as in evaporating water, and that effects of cold weather are greatly increased by the amount of heat absorbed, (or cold produced) by the vaporization of the fuel. While the heat absorbed by evaporating a given quantity of gasoline is only .45 per cent of that absorbed by an equal amount of water, it is a fact that this heat must be supplied from some source to prevent a reduction in the vapor density. In starting the engine, the heat of evaporation is supplied by the atmosphere, and should the temperature of the air be below that required for a given vapor density, the engine will refuse to start.

By the use of two tanks and a three way valve, it is possible to use two grades of fuel: one tank containing high gravity gasoline, and the other low gravity; the high gravity being used for starting the engine in cold weather, and the cheaper, low gravity, being used for continuous running after the engine is warmed up—the change of fuels being made by throwing over the three way valve.

The VAPOR DENSITY of gasoline vapor is the ratio of the weight of the vapor compared with the weight of an equal volume of dry air at the same temperature. If the weight of a cubic foot of gasoline vapor is divided by the weight of a cubic foot of air at the same temperature the result will be the vapor density of the gasoline vapor. Compared to air, the gasoline vapor is quite heavy so that if a small quantity of gasoline is poured on the top of a table, the vapor will flow over the edge of the table and drop to the floor where it will remain until it has united with the air by the process of diffusion. Experiments have shown that pure, dry gasoline vapor has a density of about 3.28, or in other words weighs 3.28 times as much as an equal volume of dry air. This weight of course is the weight of pure vapor which is considerably heavier than the mixture of vapor and air that is used in the cylinder of the engine.

Dampness, or the presence of water vapor in the air reduces the quantity of gasoline vapor taken up by the air, but only by a small amount, the maximum difference being only about 2 per cent. Since it is very likely that the water vapor is broken up into its original elements, oxygen and hydrogen, by the heat of the combustion it is likely that there is no heat loss due to the vapor passing out through the exhaust. The principal trouble due to dampness is the mixture of water and liquid gasoline caused by the condensation of the water vapor.

All gasolines and oils contain water to a more or less degree, hence provision should be made for the draining of the water which collects in the bottom of the tank. Water in liquid fuels is the cause of much trouble.

Water in gasoline may be detected by dropping scrapings from an indelible pencil into a sample of the suspected fluid. If water is present in any quantity the gasoline will assume a violet color.

In filling a supply tank with gasoline, a chamois filter or chamois lined funnel should always be used, as the chamois skin allows the gasoline to pass but retains the water and impurities contained therein. There are many funnels of this type now on the market.

The rate at which gasoline burns depends on the amount of surface presented to the air by the fluid, for a given quantity of gasoline burns faster in a wide shallow vessel than in a deep jar. Since a spray of minute particles presents an enormously greater surface than the liquid its burning speed is correspondingly greater, and as a true vapor has an almost limitless area, its speed is much greater than that of the spray, the combustion under the latter condition being almost instantaneous. Besides the question of subdivision of the liquid, the rate of combustion also depends on the intimacy of contact of the vapor with the air and on the pressure applied to the vapor as previously explained under the head of “COMPRESSION” in another chapter.

CARBURETING AIR, or producing an explosive mixture of gasoline vapor and air is accomplished by two different methods, first by passing the air over the surface of the liquid, or by passing it through the liquid in bubbles; second by spraying the liquid into the air. The latter is the method most generally in use at the present time, the spray being formed by the suction of the intake air upon the open end of the spray nozzle. The vapor density of the mixture thus formed depends on the suction of the air and upon the nozzle opening, either of which may be varied in the modern carburetor to vary the richness of the mixture.

As a suggestion to the users of gasoline we append the following remarks.

Gasoline vapor will readily combine with air to form explosive mixtures, at ordinary temperature. This property at once makes it the most suitable fuel and the most dangerous to handle.

Never fill tanks or expose gasoline to the air in the presence of an open flame, or do not attempt to determine the amount of gasoline in a tank with the aid of a match. There are a number of people who have successfully accomplished this feat, and a very great number who have not.

Be very sparing in the use of matches around a gasoline engine; there are such things as leaks.

Always carefully replace the stopper or filler cap in a gasoline tank after filling. Never use the same funnel for water and gasoline, and avoid any possibility of water finding its way into the tank.

If you do succeed in igniting a quantity of free gasoline, do not attempt to extinguish the fire with water. Pouring water on burning gasoline spreads the fire. Extinguish it with earth or sand, or by the use of one of the dry powder extinguishers now on the market.

Water may be removed from gasoline by placing a few lumps of desiccated calcium chloride in the tank, the amount depending on the quantity of water.

Calcium chloride, has a great capacity for absorbing water, and in a short space of time will absorb all of the moisture contained in the tank.

The best way to introduce the chloride is to wrap the lumps in a sheet of wire gauze and lower into tank with a wire, the wire allowing it to be easily removed when saturated with water.

(21) Benzol.

Benzol has been used to some extent in Europe as a fuel, its use being due to the rapidly increasing cost of gasoline.

Benzol is a distillate of coal tar, and is a by-product of the coke industry. In England benzol brings approximately the same price as gasoline (called petrol), but benzol proves economical for the reason that it develops more power per gallon.

Benzol is not as volatile as gasoline, but is sufficiently volatile to allow of easy motor starting.

Benzol is also used for denaturing alcohol.

(22) Alcohol.

Alcohol is of vegetable origin, being the result of the destructive distillation of various kinds of starchy plants or vegetables. Starch is the base of alcohol.

As a fuel, alcohol has much in its favor, as it causes no carbon deposit, has smokeless and odorless exhaust, can stand high compression, and requires less cooling water than gasoline, as the heat loss is less through the cylinder walls, and for this reason it is more efficient fuel than gasoline.

At the present time the price of alcohol prohibits its general use. In order that alcohol equal gasoline in price per horse-power hour, it should sell for 10c. per gallon, the price of gasoline being 15c. per gallon.

Alcohol can be used in any ordinary gasoline engine with readjustment of carburetor and the compression.

The nozzle in the carburetor has to be of larger bore for alcohol than for gasoline, and the compression for alcohol in the neighborhood of 180 pounds per square inch.

The inlet air should be heated to about 280°F for alcohol fuel; approximately 6% of the heat of the alcohol is required for its vaporization. Alcohol is much safer to handle than gasoline owing to its low volatility.

90% alcohol has a calorific value of 10,100 B.T.U. per pound, its specific gravity being .815.

WOOD, or METHYL alcohol is made by distilling the starch contained in the fibres of some species of wood (Poisonous).

GRAIN, or ETHYL alcohol is the result of the distillation of the starch contained in grains, potatoes, molasses, etc. ETHYL, or GRAIN alcohol rendered unfit for drinking by the addition of certain substances, is called DENATURED ALCOHOL. The process of denaturing does not affect the calorific value of alcohol to any extent.

(23) Kerosene Oil.

Kerosene is a fractional distillate of crude oil which has a considerably higher vaporizing temperature than gasoline. It does not form an inflammable mixture with the air at ordinary temperatures, but is vaporized in practice by spraying it into a chamber heated to above 200°F. Kerosene forms a greater percentage of crude oil than gasoline and as there has been less demand for it up to the present time it is much cheaper. Pennsylvania crude oil produces only 20 per cent of gasoline while the kerosene contents will average nearly 42 per cent according to figures at hand.

Kerosene has a very high calorific value per gallon, 8.5 gallons of kerosene having the same heating effect as 10 gallons of gasoline. Because of its high calorific value and its low cost per gallon, many types of engines have been developed for its use during the last few years, several of which have been very successful. Before the advent of the modern kerosene engine much difficulty was experienced with the fuel because of its high vaporizing temperature and its tendency to carbonize in the cylinder, but as the price of gasoline continued to rise, the inventive genius of the gas engine builder overcame these troubles so that the kerosene engine is now as reliable as any form of prime mover.

Kerosene Vaporizer on Fairbanks-Morse Engine. The Engine is Started on Gasoline and When Hot, the Kerosene Feed is Turned on.

Any gasoline engine will run on kerosene, after a manner, if the engine is thoroughly heated to insure the vaporization of the kerosene, and if the fuel is heated in the carburetor. Such an arrangement is make-shift, however, and is not productive of good results in continuous service. If kerosene is to be used as a regular fuel, a kerosene engine should be used to avoid vaporizing and carbonizing difficulties as well as the sooty, offensive exhaust, and the loss of fuel represented by the soot.

Many kerosene engines are arranged to start on gasoline, and, after becoming heated, have the running feed of kerosene admitted through a three way valve. The gasoline feed is then stopped.

The above arrangement admits of easy starting in all weathers and temperatures.

In the Diesel engine there is no evaporating of fuel, and no deposits of carbon because of the high temperature of the combustion chamber. With engines that draw the mixture of vapor and air into the cylinder there are several methods of applying heat to the liquid, and the combustion of the vapor thus formed is perfected by the injection of water into the combustion chamber. It has been found by experiment that a small amount of water vapor introduced into the cylinder of a kerosene engine makes the engine run more smoothly and prevents a smoky exhaust and carbon deposits in the cylinder. The water is introduced into the cylinder through an atomizer in the form of a mist or fog, the particles of water being in a very finely subdivided state.

Kerosene Vaporizer on Fairbanks-Morse Vertical Engine. Started on Kerosene Directly by Heating Vaporizer with Torch.

The deposits of free carbon (soot) caused by the “cracking” or decomposition of the kerosene vapor before ignition, due to the high temperature of the cylinder, are burnt to carbon dioxide by the oxygen of the water which is also set free by the heat of the cylinder. This produces an odorless gas (CO₂) which indicates complete combustion. Besides the increase of fuel efficiency due to the water vapor, the cylinder is more thoroughly cooled and is more efficiently lubricated because of the reduction in temperature.

CHAPTER III
WORKING CYCLES

(24) Requirements of the Engine.

In order that an internal combustion engine shall operate and develop power continuously the following routine of events must occur in the cylinder in the following order, no matter what the type of engine.