Observations on the Two-stroke Oiler
Page 25
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yOU published in your issue dated May II a Jettef. from .Mr. C. B. M. Pale, chief engineer, • Petters; Ltd., also a short article entitled " Are the Days of the FOur-stroke. Numbered? " by A:Q.M.S. Frogley, R.E.M.E. Bah concerned a letter of mine which appeared on April .13 and in Which I referred to the smoking propensities of the two-stroke-cycle oil engine...
Treating first with the communication from Mr. Dale; my contention regarding the babit.of this type of emitting smoke was in connection with the -normal orthodox design and not to special models such as that' built on the Kadenacy system.
I have no reason at all to doubt Mr. Dale's assertions that he obtains smoke-free running when employing the latter, also that engines employing this principle can give a consumption of 0.371 lb. per b.h.pa-hour, but the very fact that it was necessary to employ this special method to obtain these results, satisfactory as they may be, proves my assertion to be Correct regarding the. ordinary type of two4stroke.• I think it safe to say that no normal type of engine using the two-stroke principle will ever show a consumption as good. as that quoted by Mr. Pale. ,
The 'Kadenacy system was, of course, worked out and designed with the very object of eliminating theSe serious drawbacks: It took many years of patient research . work by M. Michel Kadenacy so to imProve the twostroke type that it could show a performance equal to the four-stroke unit. His main efforts were directed to eliminating the impurity Of the air charge, also the nigh internal temperatures, and to do this he used what might be called "ballistic principles." .
In his system the evacuation of the exhaust gases froth the cylinder is an entirely separate process front the .introduction of the fresh-air charge: Briefly, the system comprises a special design of the exhaust ctrifics and of the whole exhaust system, so that the effect • is given, at least in theory, of suddenly expelling the exhaust gases•in a body and in a way siini-• lar to that of a shell being fired out of a gun barrel: There is a momentary partial vacuum formed between the time of the evacuation of these gases and the intro, duction of the fresh air.
• Kadenacy System Gives Excellent Results
The system is cleverly thought out, and, in certain circumstances, especially with the junkets opposed'piston type of engine, it does give extremely • good results, but it is not yet so widely known or employed as is the ordinary two-stroke cycle. I feel tare that Mr. Ottaway, of London Transport, was also referring to the more normal engine when be said that it was apt to .
Only the re8uAs of the future can tell us whether the Kadenacy• method: of obviating -the drawbacks ..of the ordinary twd-stroke engine will eventually enable it to attain a leading place as .apower unit kir road-transport
vehicles. . .
I a.ppreciate Mr. Dale's kind promise to demonstrate to
• me his smokeless example of this new type, and I shall be glad to see ,this when I sin next in the Loughborough district. . . . •
As regards the remarks made by A.Q.M.S. Frogley, I
and afraid that he has gained a wrong impression of nly ideas asto the future of engiir design for road-transport „vehicles. I certainly do not believe that the present design Of' petrol and oil engine is likely to remain unaltered for ever.
My views are as follow:—(1) The high-class, designed oil engine, not of mass production, will eventually eliminate the petrol engine for road'transport, with the exception of units employed on cars and small and light vans. What has been done in this country during the past few years seems to me to be ample proof of this contention.
(2) The four-stroke engine will never be superseded by the two-stroke for road vehicles, unless some unexpected . and radical method be found to reproduce in the latter the same efficientcycle of exhaust and recharge as is found in the four-stroke type. Such improvements should also. be of a type easy to incorporate in existing units.
This appears to be a difficult, if• not impossible, problem.
(3) That in consideration of the marvellous progress made in the past five years or so in the Use and application of wireless; I cannot avoid the impression that, in the near futu're, radio power may be niade-aVailable for 'transport purposes. . This may seem fantastic, but so did so many other things which have been perfected and put into useful service since 1940.
-War DemandUnlike Peace Requirements Concerning the General Motors two-stroke unit, which Frogley has found to be so efficient and of which he has had much experience, I would like to ask him to bear in mind the two distinct demands for power units, i.e., those for •urgent War .services and the others for peace-time commercial work. For the former, it is necessary rapidly to produce huge quantities, with many replacement units and full mserves of spare parts, but without several stipulations as to thermal efficiency or economy in fuel consumption.. This is the very type of -use to which this particular, engine was most suited. For commercial .Work in peace-tithe, w.e want something different—A British, thdrinally efficient engine with low fuel consumption,. capable of running 150,000 iniles or more without needing new parts•or much in the way Of overhauling.. Our high-class four-stroke engines
comply with these requirements. .
I consider that the author. made a mistake when he claimed that perfect scavenging is performed -by means of the blower and that, conkquently, the thermal efficiency is very high. Actually, the power required to drive a blower greatly reduces the hope of obtaining any high 'overall efficiency. This seems to be proved by the consumption figureswhich General Motors gives with its performance. charts in its catalogues.The best fuelconsumption figure 'appears to be. some 0.45 lb. per b.h.p.-hour at 1,400 r.p.m.; at 2,000 r.p.m„ it rises to nearly 0.50. Oar most efficient British four-stroke units show 0.367 lb. per b.h.p.-hour at their best, and about 0.385 at very high.revs. . Thus, they are about 0.1 lb, better per 13.11.p.-hour, which is quite a big saving, and on a year's mileage of, say, 30,000, represents quite a
lot of money in fuel, .