Page:International Library of Technology, Volume 93.djvu/124

 PRINCIPLES OF THE GAS ENGINE

THEORY OF OPERATION

WORK IN ENGINE CYLINDER

DEFINITIONS

1. The internal-combustion engine, of which all gas, gasoline, and oil engines are types, is a machine by means of which the heat of combustion of the fuel used may be transformed into work by the direct action of the products of combustion on the moving parts of the machine. Combustion takes place directly in the engine cylinder, and for this reason engines of this class are broadly termed internal-combustion engines. The term explosion engine is also often applied to this class of engine, since the combustion is so rapid that it resembles an explosion.

2. In the internal-combustion engine, the burning of the fuel results in gases of high temperature and pressure, which act directly on a piston, and by their expansion overcome the resistance of the piston, causing it to move, and thereby perform work. In gas-engine practice, this work is done on a piston that moves back and forth in a cylinder to which the air and fuel are admitted and from which the burned gases are discharged by means of suitable valves. In some forms of engines, work is done on one side of the piston only;