300 THE GAS ENGINE 



to convert it to a spray in the carburetor. The inflowing 

 air evaporates the fine particles of liquid and a gas mixture 

 results. Fuels like kerosene which do not vaporize so readily 

 at ordinary temperatures, should be heated before they are 

 admitted to the carburetor, in order to develop maximum 

 power. 



The mechanical devices for admitting gas and air to the 

 carburetor, for regulating the inflow of explosive mixtures 

 to the piston, for removing the burned gas, and for the 

 numerous other necessary steps in the development of 

 maximum power in a gas engine cannot be discussed here. 

 For such details the reader is referred to books on gas engines. 

 (See reference list at end of chapter). For the present pur- 

 pose, however, a brief description of fuels, their properties 

 and sources, may not be out of place. 



220. Crude Petroleum. — Crude petroleum is the source of 

 gas engine fuels. It is usually a heavy, dark, oily liquid 

 with peculiar characteristic odor, and found in porous rocks 

 at a depth of 300 to 3700 feet below the earth's surface. The 

 decomposition of organic matter within the earth is supposed 

 to be the origin of it. Since petroleum is an inflammable 

 liquid it can be used in the crude state as a fuel, but not of 

 course in a gas engine. To obtain the greatest value from 

 this material it is necessary to separate it into its various 

 components. This can be readily accomplished by fractional 

 distillation, since petroleum is essentially a mixture of par- 

 affine hydrocarbons of very many kinds. There are other 

 compounds in some petroleum, but in the better grades of 

 Pennsylvania oils from which the refined products are most 

 easily made, these compounds are present in very small 

 amounts and need not be considered. 



The paraffine hydrocarbons have as empyrical formula 

 C n H 2n +2 and run from methane, CH 4 , to hexacontane, 

 C 6 oHi22, from gases through liquids to solids. The more 

 carbon atoms in the molecule the greater the density and the 

 higher the boiling point. Without going into the details of 

 the distillation process it is sufficient to say that the crude 

 petroleum is charged into large stills and heated, the various 

 hydrocarbons coming off at different temperatures. By 



