One of the factors that has made the internal combustion motor so popular as a power plant for motor vehicle propulsion is the ability to operate satisfactorily on any form of hydro-carbon gas. This means that gasoline, kerosene, benzol, alcohol and other liquid fuels may be vaporized to form a gas that will produce power in the cylinders of the engine. The liquid fuels have a great advantage inasmuch as a relatively small supply can be carried in a container that is small compared to the total carrying capacity of the vehicle and that an extended radius of operation may be obtained without refilling the tank. The liquid fuels are easily handled and relatively cheap at the present time. Practically all of the internal combustion engines used in fire department service have keen designed with a view to using the liquids of high volatility such as gasoline. The very feature of quick evaporation and explosive power of gasoline vapor and air mixtures that make it a dangerous liquid and one subject to close regulation on the part of the insurance underwriters are the same that make it the most suitable of the liquid fuels for use with our modern vehicle engines.
Gasoline is obtained by distilling crude petroleum, which is a dark, evil smelling liquid that comes from subterranean deposits and is obtained in large quantities in Pennsylvania, Indiana, Texas, and Ohio. While crude petroleum is found in many parts of the world, the crude oil found in this country is said to yield more of volatile products such as gasoline, naphtha, etc., than petroleum of foreign origin. The process of purifying crude oil and of breaking it up into its constituent liquids is one of destructive distillation. During this process of refinement the oil is heated in large stills and gases are given off. These are collected and condensed in suitable cooling coils and are again turned to liquids. Naturally the substances having the lowest boiling points arc given off first. The crude oil is broken up into three main classes of products. The highly volatile classification includes gasoline and naphtha, while the light oils such as kerosene and light lubricants form the second class which comprises over 80 per cent, of the constituents of the c_____ oil. The third class or heavy oil and residuum include vaseline, petroleum jelly, tarry compounds and the mineral matter and impurities that was in suspension in the crude petroleum. Gasoline and substances closely relating to it comprise but 10 per cent, of the total. About 60 per cent, of the refined products is kerosene, 20 per cent, is light lubricating oil, while the remainder is composed of various heavy oils and greases.
The property of gasoline that makes it suitable for fuel is that it evaporates readily at ordinary temperatures and can be mixed with air to form a satisfactory explosive gas by very simple methods. The great demand that has existed for gasoline has produced a corresponding increase in cost, and efforts are being made to use other fuels which are more plentiful, such as kerosene. The chief difficulty which prevents the use of kerosene is that it will not vaporize readily at ordinary temperatures and it must be heated before it will evaporate sufficiently fast to form an explosive vapor. This makes specially constructed vaporizing devices and water or exibaust gas jacketed manifolds necessary. It is not possible to start an engine cold on kerosine as can be done with gasoline and where the kerosene is used it is necessary to carry an auxiliary tank filled with gasoline to permit one to make an easy start and heat the vaporizing device and manifold sufficiently to permit the use of kerosene.
• CopyriKhtcd by Victor W. Page.
Some efforts have been made in Europe to use benzol, which is derived from coal tar and is a bi-product of coal gas manufacture and also to burn alcohol. It is said that an engine will run fully as well on benzol as on gasoline and no auxiliary apparatus or special carburetor is necessary to use it successfully. The difficulties militating against the use of alcohol are its relatively high vaporizing point, which means that a preheating arrangement is necessary and as it has a lower thermal value than gasoline or benzol it requires an engine with a higher compression than practical with gasoline to burn it successfully. One advantage of alcohol that entitles it to serious consideration is that it is obtained from vegetable substances, so the raw materials are not only obtainable in all parts of the earth, but are reproduced each cycle of seasons and in some portions of the globe there is no cessation to the growth of vegetation. Many experts believe that alcohol will be the fuel of the future inasmuch as there will be a time when the deposits of crude petroleum will become depleted. At the present time the only serious efforts being made to use alcohol are in France and Germany.
Liquid fuels are carried in tanks conveniently disposed at various parts of the automobile depending upon the method of fuel supply to the carburetor. The stream line form of a number of the bodies on pleasure car ;hasses used by fire oliiefs make it possible to put the fuel container under the cowl just forward of the dash and back of the motor, as shown at Fig. 41. This permits of positive gravity feed to carburetor and reduces the length of pipe needed to convey the fuel. In some cars it is carried in a tank under the front seat or in a large oval or circular section tank back of the seat in roadster type automobiles. On some very powrful machines, where it would be difficult to store enough gasoline in a concealed tank a large container is carried at the rear end of the frame. The method of fuel storage shown at Fig. 41 has an important advantage in that thE flow of gasoline to the carburetor is by gravity and as the tank is carried so much highe.r than the vaporizing device there is not apt to be any failure of the •fuel supply as is the case when the pressure feed system is used. A typical pressure feed system is shown at Fig. 42. Here the tank is carried lower than the vaporizer and the fuel is supplied to the carburetor by virtue of air pressure in the gasoline tank. In order to secure pressure for an initial start a hand operated pump is provided at a point where it can be conveniently manipulated. As soon as the engine starts a small air pump driven by the motor will supply the air to the gasoline tank and no further pumping is necssary by hand as long as the motor is running. A pressure guage is interposed in the pipe line so the amount of air pressure in the tank can be readily ascertained at any time. The usual gasoline line communicates with the carburetor float chamber from the tank interior. A system of fuel supply devised recently makes it possible to place the gasoline tank at any convenient point on the chassis and it entirely eliminates the pressure piping, hand and engine operated pumps and other appliances necessary with the pressure feed system just described. The important element of the system is a small auxiliary gasoline tank which is interposed between the main container and the carburetor float chamber., The device is shown at Fig. 43 and comprises a small round tank about nine inches in depth and three inches in diameter which is intended to be mounted on the engine side of the dash. This tank is divided into two chambers, one above the other. A lead from the upper chamber is connected directly into the intake manifold, while another connection provides an anchorage for a pipe leading to the main gasoline supply tank. The lower chamber has a pipe connection which is connected with the carburetor in the usual manner. The intake stroke of the motor creates a vacuum in the upper portion of the tank and this vacuum or suction causes gasoline ‘to flow from the supply tank. As the gasoline flows into the upper chamber it raises a float which is connected by various links and levers to two valves. When the float reaches a certain height it automatically seats a vacuum valve which is attached to the pipe leading from the inlet manifold and at the same time opens an atmospheric valve which allows the gasoline to flow down into the lower compartment. The float in the upper chamber drops as the gasoline flows out and when it reaches a certain point it again reopens the vacuum valve and the process of replenishing the supply of liquid in the tipper chamber is continued. The lower chamber, which communicates with the carburetor is always open to the air, so that gasoline flows to the vaporizing device in quantities as required and with an even pressure.
In order to become explosive gasoline vapor must be combined with definite quantities of air and the process of mixing the vapor and air in proper proportions to secure rapid combustion is known as carburetion. Mixtures that are rich in gasoline ignite quicker than those which have more air, but these are suitable only when starting or when running the engine slowly. The best results are obtained when the proportions of one part gasoline vapor to five or seven parts of air as these mixtures produce the highest temperature when exploding and the most effective pressure in pounds per square inch of piston top area.
The form of carbureting device most widely used at the present time is shown in simple diagrammatic form at Fig. 44 and is known as the spraying type. This is because the fuel is drawn out of a stand pipe or jet in a fine stream which rapidly becomes a mist or vapor by mixing with the entering air stream drawn in through the air inlet as the piston descends on its charging stroke. A thorough amalgamation oi the gasoline and air is obtained because the spray or mist breaks up into minute particles which intimately mix with the air streams. The early or primitive forms of vaporizers in which the air stream was passed over or tiuough very volatile gasoline that was first used tor fuel would be entirely unsuitable for use today. In the first place there would be considerable difficulty in carbureting the lower grades of gasoline supplied at the present time by this method and then again it is doubtful it a modern lugn speed engine could be continuously supplied with gas o. proper consistency even it the very volatile gasoline was available.
The device shown at Fig. 44 is a float feed carburetor in which the fuel is automatically maintained at a definite level in the standp.pe or spraying nozzle. This level is reguiated so the liquid does not overflow t lie standpipe and the fuel will be drawn into the air stream only when subjected to the suction effect or the vacuum created by the piston movement. The level is maintained to a definite height by a simple mechanism consisting of a ball valve attached to a cork or hollow sheet metal float. When the level in the float chamber falls below a predetermined point the float will fall as well and will unseat the ball valve and permit gasoline to run into the float bowl througn the pipe at the bottom of that part. As soon as the level again reaches the proper point it raises the float with it and the ball valve shuts off the fuel opening in the bottom of the float bowl. While the device shown would furnish an explosive vapor the carburetors at present used incorporate a number of detail improvements and refinement in construction such as automatic compensation for different degrees of engine suction and regulating means to control the flow of air and gasoline and thus vary the mixture proportions for most efficient engine operation. It is also necessary to provide some form of throttle valve to regulate the amount of mixture supplied the engine. This in turn regulates the engine speed and power output.
In a carburetor of the simple type outlined at Fig. 44 as the suction increases the amount of gasoline drawn into the mixer augments proportionately. This would result in the mixture being excessively rich at high engine speeds when the suction was greatest and very thin on low engine speeds when the suction was less on account of the fixed air opening. In practical service the conditions should be reversed, i. e., a rich mixture is needed for starting and a weaker mixture containing more air is more economical and better for engine operation at high speeds. In order to promote a positive flow of fuel from the spray nozzle when the engine is turned over slowly to start, as by hand cranking, it is customary to constrict the air passage at a point corresponding to the top of the jet as shown in the various forms of carburetors outlined at Fig. 45. This insures a high velocity of air past the top of the spray nozzle even at low engine speed, whereas with a straight mixing chamber wall as at Fig. 44, the entering air stream at low engine speed might not be sufficient to pick up enough fuel to form a readily ignited mixture.
While constricting the carburetor air passage in the manner shown makes for easy starting. it also promotes a much more energetic suction at high engine speeds than would be the case with a straight wall type. This makes it necessary to provide some auxiliary means by which additional air may be admitted to the mixture to dilute it. A carburetor including a constricted mixing chamber and means of supplying auxiliary air is termed an automatic carburetor because the compensation for mixture richness is performed by automatic air valves rather than by positive mechanical means under control of the operator. In Europe the automatic form of carburetor, such as is so widely used in this country, is not popular and the forms used in England. France and Germany usually involve manual control of the auxiliary air intake passage.
Owing to space limitation it is not possible to describe all types of carburetors that have received general application. The forms shown and described, however, are typical designs that may be considered representative of standard construction. If the reader will study the illustrations at Fig. 45 it will be apparent that in all cases the mixing chamber and float chamber are concentric, i. e., the mixing chamber is in the centre of the float chamber and surrounded by the float regulating the height of the gasoline in the spray nozzle. This concentric arrangement is of distinct value. Consider a simple form of carburetor as shown at Fig. 44 installed in the car so the float chamber is toward the front of the chassis. It will be apparent that when ascending hills the compartment carrying the float will be higher than the top of the spray nozzle. This means that the gasoline will overflow and that the mixture will be too rich. When descending a hill the conditions are reversed because the float chamber is lower than the spray nozzle and the mixture will be thin. Similarly as the car sways from side to side there would he a change in the fuel level in the spray nozzle if the float bowl was carried in line with the mixing chamber and at its side instead of ahead of it. When carburetors using separate float and mixing chambers are used the accepted method of installation is to place the float bowl beside the mixing chamber so that it will not be affected or the float level vary by climbing or descending hills. With the concentric arrangement of float and mixing chambers there is not apt to be much variation in the level of fuel in the standpipe.
The carburetor shown at Fig. 45-A is the Schebler Model L and is an automatic, concentric float type in which the amount of fuel entering the motor is controlled by a needle valve which is operated by mechanical linkage from the throttle. As the throttle is moved to permit more gas to flow to the motor the needle valve which is raised and lowered by a cam will alter the mixture proportions according to the engine speed. The main air inlet is at the bottom of the float bowl, while the auxiliary air flow is controlled by a poppet valve of the usual type. This is held against its seat by a compression spring which is provided with a regulation so that the valve travel and the amount of auxiliary air admitted will depend upon the spring pressure tending to keep the valve seated. The float in this device is of cork and controls a needle valve by a simple lever of the first class which changes the upward movement of the float to a corresponding downward movement of the needle valve controlling the fuel supply opening.
A priming lever is provided on top of the float bowl consisting of a pin or plunger that may be depressed so it will force the float down and raise the needle from its seat and allow gasoline to flow into the float chamber higher than the normal float level. This causes flooding at the jet and the excess gasoline provides a mixture that makes for prompt starting. The amount of gasoline sprayed into the mixture may be regulated by an adjustable needle valve, the point of which is adapted to vary the spray nozzle opening.
The carburetor shown at B is used on the Pierce-Arrow automobiles and is an automatic form having the popular concentric float and adjustable spraying nozzle. The float is a hollow sheet metal form and is connected to the needle valve by the usual lever. The gasoline supply from the tank must pass through a fitter screen before it can enter the float compartment. A feature is the barrel throttle valve, the interior of which really forms a supplementary mixing chamber. The throttle is surrounded by a water jacket through which warm water is bypassed from the engine cylinder before discharging it to the water-cooling arrangement. The heat thus obtained makes for more perfect vaporization of low grade gasoline. Another feature of merit is the form of auxiliary air valve provided. Two reed valves are used which are controlled by flat springs, one having slightly greater tension or pressure than the other. As the engine runs slowly both valves remain seated but as the engine speed increases the augmenting suction due to greater throttle opening causes the lighter reed to open which is folllowed progressively by the heavier reed when the maximum amount of auxiliary air is needed to dilute the mixture. The usual form of needle valve is provided to regulate the opening of the spray nozzle A.
Still another form of automatic carburetor differing in that the auxiliary air is supplied to the mixture by ball valve is shown at Fig. 45-C. The main air intake communicates directly with the mixing chamber which is constricted at the spray nozzle in the usual manner. The auxiliary air enters through a number of circular openings controlled by floating balls, which are so arranged that they can lift from their seats but cannot become displaced.
The action of these ball valves is progressive, as they lift from their seats in order as the motor suction increases. The air entering through the openings flows directly into the mixing chamber where it dilutes the rich gas drawn from the spray nozzle. It will be noticed that the spray nozzle is enlarged at the upper portion to form a well which becomes partially filled with gasoline while the motor is idle. This results from the level in the float chamber being set somewhat higher than the top of the small opening in the jet. This gives a rich mixture for starting and after the motor speed increases to a certain point the gasoline is sprayed through the jet in the usual manner, the well remaining dry. The jet adjustment or gasoline regulation is by the usual form of needle valve.
While most carburetors use a single spray nozzle, some forms employ two or more jets. The Stromberg arrangement is shown at Fig. 46-A. The design is such that of the two nozzles the primary nozzle is used alone at low speeds, while the secondary nozzle is only brought in action at higher speeds when more fuel is needed. In some multiple jet carburetors, the nozzles are brought into action progressively when the throttle is opened as at a certain point the primary nozzle with its small spraying orifice cannot supply fuel enough and then the secondary nozzle is brought in action and contributes its quota of fuel to compensate for the augmenting demand of the engine. In the carburetor shown the float chamber is at one side of the mixing chamber and has a glass wall. The float needle that regulates the gasoline supply to the float compartment passes through the centre of the hollow metal float and closes the opening when the float reaches its proper level. Two levers are used, the inner ends being attached to the needle while the outer portions rest on the float. As is usual practice the flow of mixture to the engine is controlled by a butterfly valve placed in the mixing chamber directly over the constricted portion in which the main jet C is located. The secondary jet J comes in operation only when the speed of the motor increases to such a point that the suction is great enough to open the auxiliary air valve and allow the air stream to brush by the auxiliary or secondary jet. The automatic air valve is of the usual mushroom or poppet type.
A form of carburetor in which no auxiliary air valve is provided is shown at Fig. 46 B. The usual concentric float and adjustable jet construction are followed. A supplementary standpipe for starting and slow running enables the designer to dispense with auxiliary air valves of the usual pattern. The gasoline enters the float chamber through the connection A and passes into the float compartment through the strainer F and the usual needle valve controlled passage. A standpipe J communicates from the well at the base of the spray nozzle M and when the throttle is closed the gasoline is drawn into this standpipe through the plug K which is provided with a small hole communicating into the intake manifold. After the motor has been started and the throttle is opened, the air stream entering through the annulus N nullifies the effect of the slight suction in standpipe J and all the gasoline supplied the mixture is drawn through the main jet M.
Editorial Note: The next discussion will describe battery and magneto ignition methods.