Зображення сторінки
PDF
ePub

LESSON FIVE

THEORY OF CARBURETION AND ITS APPLICATION

Q. What is combustion a manifestation of?

A. Combustion always indicates a chemical combination between certain elements which have a great attraction or affinity for each other.

Q. Is combustion always rapid?

A. Combustion may be very slow as well as extremely fast.
Q. Give an example of slow combustion.

A. The rusting of metals or the rotting of wood, cloth and similar materials are examples of slow combustion.

Q. Give an example of rapid combustion.

A. Burning gas, wood, coal or oil are examples of rapid combustion.

Q. Give an example of instantaneous combustion.

A. The explosion of gunpowder or of the compressed gas in the automobile engine cylinder may be considered as practically instantaneous combustion.

Q. What is a vacuum and could anything burn in vacuo?

A. A vacuum is a space in which there is no air or other gas present. A vacuum may be nearly complete, but it is almost impossible to obtain a perfect vacuum. If a burning candle is placed under the receiver of an air pump and the air exhausted from the chamber in which the candle burns, it will be noticed that as the degree of exhaustion becomes greater, the flame burns dimmer until it finally goes out.

Q. What is necessary to support combustion?

A.

Combustion cannot take place unless air or the element oxygen of which it is partly composed is present.

Q. What is gasoline composed of?

A. Gasoline is composed of carbon and hydrogen. The former is a solid material while the latter is the lightest known gas. When combined chemically, owing to the great affinity that exists between them, they will form a liquid if mixed in the correct proportions.

Q. How much of each element is there in gasoline?

A. The ordinary gasoline used for fuel is said to contain 84% carbon and 16% hydrogen.

Q. What is air composed of?

A. Air is composed of oxygen and nitrogen.

Q. Which element supports combustion?

A. The oxygen has a great affinity or combining power with the two constituents of the hydrocarbon liquids, and it is the oxygen which supports combustion. Nitrogen is an inert gas that is mixed with the air in order to act as a deterrent and prevent too rapid combustion.

Q. How much oxygen is needed to burn carbon?

A. One pound of carbon requires two and one third pounds of oxygen to insure its combustion.

Q. How much air is needed to burn a given weight of carbon?

As air is composed of one part of oxygen to three and one half portions of nitrogen by weight, for each pound of oxygen one needs four and one half pounds of air. It requires about ten pounds of air to burn one pound of carbon.

Q. Has air any weight?

A. While one does not consider air as having much weight, fourteen cubic feet of air at a temperature of 62 degrees F. will weigh about a pound.

Q. How much oxygen is needed to burn a given weight of hydrogen?

A. One pound of hydrogen requires 8 pounds of oxygen to burn it. This means that 6 pounds of air will be needed to insure combustion of the hydrogen component of gasoline.

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

F

T

and air particles is obtained. Fig. 61.-Section of Vertical Cylinder Fuel Injection Engine. The primitive forms of vaporizers 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.

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]

Fig. 62.-Sectional View of Horizontal Type Two-Stroke Stationary Fuel Injection Motor

Q. Describe the Diesel system.

A. A system of fuel supply developed by Dr. Diesel, a German chemist and engineer, is attracting considerable attention at the present time on account of the ability of the Diesel engine to burn low grade 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 hydro

« НазадПродовжити »