SILENCING THE NOISY EXHAUST
The waste of energy is clearly evident in the exhaust pipe of an internal combustion engine. The gases after doing their work on the piston rush out with such velocity as to produce a sharp explosive sound. The noise of the exhaust is highly objectionable in automobiles and must be overcome, but instead of utilizing the boisterous energy of the escaping gases and getting a little more useful work out of them, means are provided for hushing their noise. This is done by passing them through a series of baffles which reduces the pressure of the gases before they are discharged into the atmosphere. By letting the gases expand gradually instead of bursting suddenly into the atmosphere the noise of the discharge is reduced. However, this must not be done at the expense of the engine power. Unless the gases pass quickly through the muffler they will choke and retard the exhaust and make the engine do useless work in driving them through. Even the best of mufflers will use up nearly 5 per cent of the engine power. The energy that escapes at the exhaust is not the only loss. All the heat that radiates from the engine represents just so much wasted energy. In our water and air-cooled systems we deliberately abstract heat from the burning gases and throw it away. If we had materials that would stand the intense heat of burning gases and enable us to conserve all the heat developed in the cylinder we could use our fuels much more economically.
Many attempts have been made to utilize the wasted heat of internal combustion engines, but they have not met with any considerable degree of success, with the exception of the invention of William Joseph Still. This engine, which was the result of many years of patient work, was first made public in a paper read before the Royal Society of Arts in London, May 26, 1919, and when it was shown that the new engine had developed an efficiency of 38 to 41 per cent it was realized that here was a remarkable advance over any other machine for turning heat into power.