bear on their design has made it possible to obtain a surprising degree of endurance from light and seemingly fragile constructions.
The same, with regard to lightness and endurance, may be said of automobile engines. Economy of weight is here of the first importance, as a heavy motor necessitates building the remainder of the vehicle accordingly. Complete automobiles are built to weigh much less per horsepower than even the lightest stationary engines, and engines of over 100 horsepower have been put in racing automobiles weighing not more than 2,204 pounds, which is the present limit of weight for racing machines.
In nearly all American automobile engines, gasoline is used. In Europe, several concerns have built successful kerosene engines for motor vehicles; and, in France and Germany, alcohol or a mixture of alcohol and benzine has been used experimentally with considerable success, although in France alcohol can hardly as yet be considered a serious commercial factor.
CHARACTERISTICS OF AUTOMOBILE ENGINES
2. Nearly all automobile engines are of the four-cycle type. Although a number of manufacturers have experimented with the two-cycle engine, only a few have turned out commercially successful engines of this type. Owing to the high compression, heavy flywheel, and considerable structural rigidity required by the Diesel kerosene-oil engine, it has been found altogether unsuited to automobile service.
The typical automobile engine has from one to four cylinders, is small and compact, and is of light weight and high speed. The maximum power of single-cylinder engines is about 10 horsepower, and four-cylinder engines are built as small as 10 or 12 horsepower. The compression is from medium to high, and some sort of a float-feed carbureter is employed. The inlet valve is sometimes automatic, and sometimes mechanically operated; the latter type predominates. The engine is controlled almost exclusively by
