(a)Introductory.—The paper deals with experiments carried out in the engineering laboratories of the University of Manchester on a Crossley solid-injection oil engine in which small quantities of hydrogen or coal gas were introduced along with the air supply to the engine.

(b)Range of Investigation.—Three series of trials were run with hydrogen, each at a different load, namely, 53·4, 39·4, and; 24·4 b.h.p. The maximum amount of hydrogen used was slightly more than 3 per cent. by volume of the air supply, corresponding, at the lightest load, to some 14 per cent, by weight of the oil fuel supply.

Three corresponding series of trials were run using coal gas in place of hydrogen, the maximum volume of gas employed being 5 per cent. of the air supply. At the lightest load this corresponds to approximately 2·4 times the weight of fuel oil used.

(c)Conclusions.—Such quantities of hydrogen or coal gas can be used satisfactorily in the type of engine considered. No trouble was experienced due to pre-ignition or other causes, and the engine appeared to run more sweetly when gas was being used.

When running at constant load and speed, the admission of small quantities of gas appears to cause combustion to take place at a slower rate, giving a lower maximum pressure and more burning down the expansion stroke. The thermal efficiency is in consequence slightly reduced, while the heat-losses to exhaust are increased.