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

(105) Principles of Carburetion.

The carburetor is a device for converting volatile liquid fuels, such as gasoline, alcohol, kerosene, etc., into an explosive vapor. Besides vaporizing the liquid, the carburetor also controls the proportion of the fuel to the air required for its combustion. The mixture produced by the carburetor must be a uniform gas and not a simple spray to accomplish the best results for complete and instantaneous combustion. Proper combustion cannot be attained with any of the fuel in a liquid state as all of the fuel contained in a liquid particle cannot come into contact with the consuming air. It is of the utmost importance to have the air and fuel in correct proportions so that the fuel may be completely consumed without danger of interfering with the ignition by an excess of air.

With few exceptions modern gasoline carburetors are of the nozzle type in which the liquid is broken up into an extremely fine subdivided state by the suction of the engine piston. This fine spray is then fully vaporized or gasified by the heat drawn from the surrounding intake air that is drawn through the carburetor and into the cylinder on the suction stroke. Owing to the low grade fuels now on the market and to the constantly varying atmospheric conditions it is seldom possible to obtain a perfect vapor in the correct proportions, and for this reason much heat is lost that would be available were the mixture perfect.

Carburetors for automobiles and boats vary in detail from those used on stationary engines due principally to the difference in matters of speed. A stationary engine runs at a constant speed which makes adjustment comparatively easy, while automobile engines have a wide range of speeds and loads making it very difficult to maintain the correct mixture at all points in the range. The difference in the fuel and air adjustments for varying of speeds marks the principal difference between stationary and automobile carburetors. There are many types of successful carburetors on the market, so many in fact that we have room for the description of only three or four of the most prominent, but we will say that the well known carburetors are based on the same principles and differ only in matters of detail.

A cross-sectional view of the well known Schebler Type D carburetor is shown by Fig. 116, and is of the type commonly used on automobile motors and boats.

MODEL “D”
Fig. 116. Cross-Section Through Type “D” Schebler Carburetor.