INTERNAL COMBUSTION ENGINES.

Progress, Volume II, Issue I, 1 November 1906, Page 13

INTERNAL COMBUSTION ENGINES.

At the Royal Institution on August 5 Professor Bertram Hopkmson delivered the final lecture of his series on this subject. Professor Hopkmson said that in previous lectures he had described methods of regulation which were not satisfactory, but good regulation could be obtained by reducing the fuel supply if matters could be arranged so that the explosive mixture in the cylinder was stratified, consisting of practically pure air in one end of the cylinder and a strong mixture at the other. He would show by experiment what took place in the cylinder in these two cases, but he should point out that there was a practical difficulty with regard to this method of regulation because in the ordinary charging stroke of the gas engine the velocity of the entering gases was something like 60 miles per hour. It had, however, been successfully accomplished ixl the case of large engines, and there was reason to hope that it would be possible to work in this way with small engines. Apart from successful regulation there was this further advantage of obtaining strati"ication, that the piston remained cooler than under ordinary circumstances, and he need not say that the coolmg problem in the case of larger engines was a very serious practical question. Reference has already been made to the improved efficiency of the gas engine over the steam engine, and the economy of the gas engine could be improved by the adoption of any method which economised the loss of heat to the cylinder walls and that carried away in the exhaust. It was not possible to effect economies m regard to the loss of heat to the cylinder walls, except by making the engine larger, and therefore it was necessary to concentrate attention upon the "Heat carried away by the exhaust gases. To improve the efficiency of the gas engine m this connection it was necessary to secure a greater ratio of expansion which was accomplished by employing greater compression, the two things being, of course, definitely related to each other. In theory it was possible to reduce the temperature of the gases when they left the engine to any degree, but m practice there were definite limits to the extent to which gases could be compressed by reason of the danger of pre-igmtion. There were means, however, of preventing pre-igmtion ; for instance, water might be sprayed into the cylinder, and in that case the presence of the steam in all probability acted in preventing the gases from being prematurely ignited. By employing that and other devices it was possible to compress the gas to a volume as small as one-ninth of its original volume, and the economy of the engine could be improved to a point where over 30 per cent, of the total heat of the fuel was converted into mechanical work. The question as to whether the Otto or the two-cycle engine was the gas engine of the future had not yet been definitely settled, and he hesitated to prophesy.