• THE INTERNAL-COMBUSTION BOILER.
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Is it Possible to Generate Steam Containing More Heat Calories Than Were Theoretically Contained in the Fuel Oil Employed to Convert the Water into Steam ?
By C. G. Conradi, M.I.Mcch.E., Author of "Mechanical Road Transport."
MITE article by Mr. Oscar Brunler in The Commercial Motor of February 17th again brings into prominence the claims of steam as a prime mover, whether for ordinary power purposes or for purposes of transport, and there are probably many like the writer who have a great regard for the senior power, and who feel that its partial eclipse is only temporary and that t will emerge again in a rehabilitated condition.
The success of steam for heavy vehicles has been considerable in spite of the handicap of weight and the griminess inseparable from boilers fired with solid fuel, but one cannot imagine the universal application of present-day designs of this type to road transport. At the other end of the seale we have small numbers of light machines being produced with flash boilers, the tout ensemble of which, however, is somewhat complicated. The simple steam engine and boiler have perforce had to have a quantity of accessory apparatus tacked on to them to make a feasible design, not only for touring car purposes, but even for goods'vehicle propulsion, with the result that the cost of production is high in comparison with that of the petrol car, and the power unit has lost its attractive simplicity. It is necessary to have feed-water heaters, superheaters, condensers and automatic control of the feed water, steam pressure and fuel feed, which, with the time required for starting up, leave the man in the street eold when you try to discuss steam cars with him.
Any means whereby a simple, Oman light piece of apparatus eouid be evolved which would supply the engine with steam as and when required, in the same Manner as the carburetter supplies the petrol engine, would give the steam vehicle a much needed fillip.
In this connection the boiler described by Mr. Brunler would, at first sight, appear to be an attractive proposition, but the claim that the boiler gives out more than is put into it makes one at once very critical, and it is surprising to find that this feature has received so much serious consideration by engineers and others, and unless we are prepared to drop the whole theory of the conservation of energy, there is nothing to be gained by trying to invent a ,new theory to support the claims made.
The inventor is, no doubt., convinced in his own mind that he has achieved such a result, but he produces no tests to substantiate it nor any calculations showing theoretically how it may be arrived at. Certain figures are given in the article in question, but no mention is made as to how -they were obtained, and, in any case, it does not appear to be an easy matter to measure with any degree pf accuracy the heat energy in the mixture of steam and products of combustion which -make up the output of the boiler. It is stated that the tar-oil used had a heat value of 8,662 calories per kilo. and this is rather a low figure, the average being at least 9,000, and it might be suggested /hat the figure given for the heat in the steam is more like what the calorific Nalue of to fuel should be. It would be interest ing to know how the heat in the steam and the products of combustion were separately measured as it i3 probable that some error has crept in here.
It would also appear that the power required to drive the. compressors has been. ignored altogether in the calculation, and, when we remember that in such a system all the air has to be compressed, the omission is a serious one. A rough estimation suggests that a loss of 10 per cent. will be incurred in the power required to drive the compressors, although some of the energy put into it during compression will be recovered from the expansion of the gases in the engine.
Taking the boiler unit as a whole, the thermal efficiency may be about 85 per cent., a figure which is certainlysan improvement on present practice, where a good result is, say, 75 per cent. The output of the new boiler, however, includes some 40 per cent, of incondensable gases, viz. carbon dioxide, nitrogen, etc., and this ll precltide its use with condensing engines and probably with most manufacturing processes, except -in cases-where the heating fluid is kept separate and does not come into contact with the materials being dealt with.
For general power purposes the system does not
appear commerciallyfeasible, and when considering it more particularly for mechanical` transport requirements, further difficulties suggest themselves as requiring solution by further tests. Many of the heavy as contain a certain small amount of ash and sulphur, and incomplete combustion at times, which it will be impossible wholly to avoid, will lead to deposits being thrown. down. These may collect on the burner or drop into the restricted space at the bottom of the water space, so necessitating cleaning out and perhaps faulty operation, whilst a concentration of the acid will take place, with corrosive results. The question of standing for varying periods during loading, etc., will affect the overall economy, as the stand-by, lasses will be comparatively heavy, the pressure will rise quickly and a continuous blowing-off appear to be inevitable.
The design is ingenious, even if the idea is not altogether novel, and, if the inventor can give more information on the practical operation of the boiler, it undoubtedly would be of considerable interest. A. more promising boiler design, perhaps, is one recently produced on a small scale by 'B' erhard Becker, of Wiemar, consisting essentially of a series of arched steam pipes into which water underlipressure is sprayed and instantly converted into steam. Contrary to expectation, reports state that no scale is being formed, and, so far as can be seen at present, no corrosion or burning out of the tubes is anticipated. For the highest overall economy, a closed circuit of some kind appears to be essential, and sight should not be lost of the suggestions put forward at various times for locomotive work.