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Gas Engines

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-294

2025-11-26

1092

In a gas engine the motive power is the expansion caused by the explosion of a mixture of gas and air in a cylinder. The expanding gases work against a moving piston as the expanding steam does in a reciprocating steam engine. The cycle of operations in a four-stroke or four-cycle engine is briefly as follows (Fig. 1):

On the first, outward, stroke of the piston the inlet valve is opened and a mixture of gas and air enters the cylinder through the inlet. On the return stroke the mixture is compressed. When the piston begins its third stroke, which is the second outward stroke, the gas is exploded by an electric spark and expands, and on the fourth stroke the outlet valve is opened and the products of the combustion are driven from the cylinder through the outlet. The third stroke is the only one from which power is obtained. In the two-cycle engine the mixed gases enter the crank case B through the port A, Fig. 2, when the piston C is at the top of its stroke during which the gas in the cylinder D is compressed. The spark explodes the gas, driving the piston downward and compressing the gas in the crank case. The gas from the crank case passes through the transfer port as shown by the arrows, and forces the exploded gas out of the exhaust port E. Both ports are closed as the piston begins its upward motion and the rest of the stroke completes the compression.