wasted in the first method is saved. The gas will continue to burn until the oxygen in the air contained in the cylinder is exhausted, the heated gases expanding and performing work as in the first case. The method illustrated in Fig. 4 has a still further advantage. The contents of the cylinder are heated much more rapidly, and a larger amount of work can be done in a given time.
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14. Instead of allowing the gas to burn as it enters the cylinder suppose that the latter is filled with an explosive mixture of gas and air and that the mixture is ignited, or fired, by an electric spark at g, Fig. 5. The mixture explodes and the resulting pressure performs work on the piston. A much more rapid expansion is produced by this means than by the methods already mentioned. By employing a long cylinder, a greater proportion of the heat may be transformed into work, since the gases cannot escape
until the pressure is very low.
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15. A still further improvement is made by filling the cylinder in Fig. 5 with an explosive mixture and compressing it before ignition or firing. Suppose the cylinder to be filled with a mixture of gas and air, and the piston then forced down until the mixture is compressed into a space of, say, one-third of its former volume, and ignited by means of the electric spark. The explosion pressure is much higher than if there had been no compression, and the average pressure during the motion of the piston will also be much higher, and consequently more power can be obtained from
