« НазадПродовжити »
Q. How much air is needed theoretically to insure the combustion of a pound of gasoline ?
A. In order to secure combustion of one pound of gasoline one should provide about 16 pounds of air; 10 pounds of air is needed to burn the carbon contents and about 6 pounds to insure combustion of the hydrogen.
Q. How much air is actually supplied to burn a pound of gasoline?
A. Owing to the presence of the inert element nitrogen which is the main constituent of air and which acts as a deterrent of burning, it is necessary to provide more than the 200 cubic feet of air that theoretical combustion calls for and to allow about twice this amount. This means that about 32 pounds of air are supplied to burn one pound of gasoline.
Q. What is the liquid measure equivalent of a pound of gasoline?
A. Approximately 1.25 pints of 63 degree Baumé test gasoline will weigh a pound.
Q. What is carburetion?
A. In order to be explosive, gasoline vapor must be combined with definite quantities of air. Carburetion is the process of mixing the gasoline vapor and air in proper proportions to secure rapid combustion. Mixtures that are rich in gasoline ignite quicker than those which have more air, but these are only suitable when starting or when running the engine slowly, as they are very wasteful of fuel. Mixtures vary from 1 part of gasoline vapor to 4 of air, to others having but 1 part of gasoline vapor to 13 of air can be ignited, but the best results are obtained when the proportions are 1 to 5 or 1 to 7, as these mixtures will produce the highest temperatures, the most effective pressure in pounds per square inch of piston top area and the quickest explosion. What we commonly call an explosion is merely an indication that the oxygen of the air has combined with the carbon and hydrogen of the gasoline rapidly enough so that this chemical union is attended by heat. The power produced in the automobile engine cylinder is really due to a rapid chemical combination.
Q. Describe a number of ways in which liquid fuel may be mixed with air to form an inflammable vapor.
A. Almost any device which permits a current of air to pass over or through a volatile liquid will produce a gas that will explode when compressed and ignited in the motor cylinder. In some carbureting devices the entering air is made to pass over the surface of wicks saturated with liquid gasoline or the liquid fuels may be injected into the entering air stream in the form of a fine spray or mist. In other constructions the fuel is injected directly into the engine cylinder.
Q. What is the present accepted method?
A. The form of carbureting device widely used at the present time is known as the spraying type, because the fuel is drawn out of a stand pipe or jet in a fine stream which rapidly becomes a mist or vapor by the suction effect of the entering air stream. The advantage of this construction is that a thorough amalgamation of the gasoline and air particles is obtained. Fig. 61.-Section of Vertical Cylinder The primitive forms of vapor
Fuel Injection Engine. izers in which the air stream was passed over or through the high grade or very volatile gasoline that was first used for fuel, would be entirely unsuitable for use today. In the first place they would not carburete the lower grades of gasoline supplied at the present time, and secondly, they could not supply the modern high speed engine with gas of the proper consistency fast enough even if high grade fuel was available.
Q. Describe the Diesel system.
A. A system of fuel supply developed by Dr. Diesel, a German chentist and engineer, is attracting considerable attention at the present time on account of the ability of the Diesel engine to burn low graue fuels such as crude petroleum. In this system, the engines are built so that very high compressions are used, and only pure air is taken into the cylinder on the induction stroke. This is compressed to a pressure of about 500 pounds per square inch, and sufficient heat is produced by this compression to explode a hydrocarbon mixture. As the air which is compressed to this high point cannot burn, the fuel is introduced into the cylinder head under still higher compression than that of the compressed air, and as it is injected in a fine stream, it is immediately vaporized because of the heat. Just as soon as the compressed air becomes thoroughly saturated with the liquid fuel, it will explode on account of the degree of heat present in the combustion chamber. (Figs. 61, 62.)
Q. What are the advantages of the injection method ?
A. The injection method of fuel supply has the important advantage of permitting the use of very cheap fuels which could not be utilized in ordinary forms of vaporizers on account of the high temperature needed to vaporize them.
Q. What are the disadvantages of injection engines?
A. Owing to the extremely high compression employed in injection engines, these must be made very substantial and strong, and this principle is suitable only for the comparatively slow acting power plants of the stationary or marine type. An injection engine is not as flexible as the electrically ignited carburetor supplied power plants used for automobile service, and this fact also militates against the injection principle for this use.
I ESSON SIX
TYPES OF CARBURETORS AND THEIR ACTION
Q. What are the simplest forms of carburetors?
A. The old patterns of evaporation or surface carburetors were the simplest forms of carburetion devices and the modified device in which wicks were used was but slightly more complicated.
Q. Describe action of evaporation or surface type.
A. This form of carburetor consisted of a simple tank or container for the liquid and the air was drawn in and across the surface of the gasoline in order that it might become saturated with the vapors constantly present at that po nt. These rich gases were drawn into the engine through a simple form of mixing valve which permitted the entrance of an auxiliary supply of air from the outside of the container to dilute the rich gas and make it of a proper composition to insure energetic combustion.
Q. Describe action of wick type vaporizer.
A. The wick form of carburetor is essentially the same in construction as the simpler surface type except that the mixing compartment through which the air flows is separated from the fuel containing portion by means of a wall of absorbent material, such as wicks, which feed the gasoline up into the mixing compartment by capillary attraction and by spreading it over more surface make it easier for the air stream passing over the wicking to pick up gasoline vapor.
Q. Describe action of bubbling type carburetor.
A. The bubbling type differs from the other simple forms previously described in that the air enters at the bottom of the device and bubbles through the liquid to reach the mixing chamber from which it is drawn to the engine cylinder.