The very large percentage of heat absorbed by the water-jacket should point out to the ingenuity of inventors the first problem to be attacked, viz., how to save this heat without wasting the lubricant or making it inoperative; and in the solution of this problem, I look for the most important improvement to be expected in the engine. The most obvious contrivance would be some sort of intercepting shield, which would save the walls of the cylinder and the rings of the piston from the heat of the ignited gases. I have just learned that something of the kind is under trial. Another solution may possibly be found in the employment of a fluid piston; but here we are placed in a dilemma between the liquids that are decomposed and the metals that are oxidized at high temperatures. Next, the loss by radiation - 15 per cent. - seems large; but this is to be attributed to the fact that the inside surface of the cylinder is at each inward stroke exposed to the atmosphere - an influence which contributes to the cooling necessary for lubrication. The remaining 15 per cent., which is carried away by the exhaust, is small compared with the proportion passing away with the exhaust steam of a high-pressure or the water of a condensing engine.
As the water in the jacket can be safely raised to 212° Fahr., the whole of the jacket heat can be utilized where hot water is required for other purposes; and this, with the exhaust gases, has been used for drying and heating purposes.
With such advantages, it may be asked: Why does not the gas-engine everywhere supersede the steam-engine? My answer is a simple one: The gas we manufacture is a dear fuel compared with coal. Ordinary coal gas measures 30 cubic feet to the pound; and 1,000 cubic feet, therefore, weigh 33 lb. Taking the price at 2s. 9d. per 1,000 cubic feet, it costs 1d. per lb. The 30 cubic feet at 630θ give 19,000θ all available heat. Although good coal may yield 14,000 units by its combustion, only about 11,000 of these reach the boiler; so that the ratio of the useful heat is 11/19. The thermal efficiency of the best non-condensing engine to that of the gas-engine is in the ratio 4/22. Multiplying together these two ratios, we get (11 / 19)×(4 / 22) = 44 / 4.28. That is, speaking roughly, 1 lb. of gas gives about ten times as much power as 1 lb. of coal does in a good non-condensing engine. But at 18s. 8d. a ton we get 10 lb. of coal for 1d.; so that with these figures the cheapness of the coal would just compensate for the efficiency of the gas. As to the waste heat passing away from the engine being utilized, here the gas-engine has no advantage; and, so far as this is concerned, the gas is about eight times dearer than coal.
The prices of gas and coal vary so much in different places that it is hard to determine in what cases gas or coal will be the dearer fuel, considering this point alone.
But there are other kinds of non-illuminating gases - such as Wilson's, Strong's, and Dowson's - which are now coming into use; and at Messrs. Crossley's works you will have an opportunity of seeing a large engineering factory employing several hundred mechanics, and without a chimney, in which every shaft and tool is driven by gas-engines supplied by Dowson's gas, and in which the consumption of coal is only 1.2 lb. per indicated horse power. The greatest economy ever claimed for the steam-engine was a consumption of 1.6 lb.; and this with steam of very high pressure, expanded in three cylinders successively. Thus in a quarter of a century the gas-engine has beaten in the race the steam-engine; although from Watt's first idea of improvement, nearly a century and a quarter have elapsed.
As regards the steam-engine, it is the opinion of competent authorities that the limits of temperature between which it works are so restricted, and so much of the heat is expended in producing a change of state from liquid to vapor, that little further improvement can be made. With respect to gas-engines, the limits of temperature are much further apart. A change of state is not required, and so very great improvement may still be looked for. It is not impossible even that some of the younger members of our body may live to see that period foretold by one of the greatest of our civil engineers - that happy time when boiler explosions will only be matters of history; that period, not a millennium removed by a thousand years, but an era deferred perhaps by only half a dozen decades, when the use of the gas-engine will be universal, and "a steam-engine can be found only in a cabinet of antiquities."Discussion.
The President said this was a very delightful paper; and nothing could be finer than Mr. Lane's description of the conversion of heat into power, and the gradual growth of theory into practical work.
Mr. W. Foulis (Glasgow) agreed that it was admirable; but it required to be read to be thoroughly appreciated. When members were able to read it, they would find Mr. Lane had given a very clear description of the elementary principles of thermo-dynamics in their relation to the gas-engine and the steam-engine. There was very little in the paper to raise discussion; but Mr. Lane had made exceedingly clear how the present loss in a gas-engine was occasioned, and had also shown how, in the future development of the engine, the loss might be saved, and the engine rendered more efficient.
Mr. H.P. Holt (of Messrs. Crossley Bros., Limited) said he could indorse everything Mr. Lane had said. He had found the paper most interesting and instructive even to himself, though he had some little practical experience of gas-engines, and was supposed to know a little about them. He did not pretend to be able to teach other people; but if he could say anything as to indicator cards, or answer any questions, he should be happy to do so. (He then described the indicator diagram of the atmospheric gas-engine.) In this engine the proportion of the charging stroke to the whole sweep of the piston was about 10 per cent.; and as the charge drawn in consisted of about 10 per cent. of gas, about 1-100 of the total sweep of the piston was composed of the gas.