All About Engines

The Oil Engine 233 in a gas engine the compression must not be too high lest the heat produced should cause a premature explosion. In the Hornsby-Ackroyd engine this was actually allowed to occur—not prematurely, but at the right moment. The heat of the chamber, added to the heat produced by compressing the mixture, was sufficient to cause explosion, so that when once the engine had fairly started the lamp could be re- moved. Successive explosions afterwards kept the combustion chamber sufficiently hot. No further heating was required. There was no hot tube, no delicate and complicated coil or magneto to get out of order, no accumulators to run down just when they were wanted, no sparking plugs to get clogged up : just the combustion chamber, alternately warmed up by the explosion and cooled down by the spray of oil. Surely one of the simplest and most beautiful applications of a scientific principle to a practical purpose that was ever made! The oil was delivered by a, pump which, driven at half the speed of the engine, delivered at each stroke exactly the quantity required for one charge. The only valve, therefore, was that for the exhaust, and it was operated by a cam and rocking lever exactly as in the gas engine. Apart from the com- bustion chamber or the end of the cylinder and the single valve, there is nothing to distinguish this engine from a gas engine in appearance or construc- tion. For small powers they are in competition to- day, and but for the increase in price of oil which has taken place in recent years, the competition