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Aviation History
1937
1937 - 1271.PDF
MAY 13, 1937. FLIGHT. This view of a Jun kers Ju.86 shows the clean installation of its Jumo 205 Diesels. DIESEL PROBLEM A Brief Review of the CJ. Situation as it Affects Aircraft By CAPT. ANDREW SWAN, B.Sc, A.M.Inst.C.E., A.F.R.Ae.S. INTEREST in the compression-igni tion engine for aircraft has waxed and waned several times during the past eighteen years. So far as this country is concerned, a certain amount of experimental work has been done throughout, but while this type of engine has its adherents, the general view of its future in aviation is one of some uncertainty. On the other hand, intensive preoccupation with the petrol engine may account for some lack of interest. No doubt there are important technical difficulties to be overcome and penalties attached to its use, as otherwise few could dispute the desirability of an aircraft engine which is more economical in fuel than the petrol engine, uses an inherently cheaper fuel of plentiful supply, has A reduced fire risk, and operates without the complication of electrical ignition. In the notes that follow, endeavour will be made to out line the progress and problem of the compression-ignition engine and at the same time to indicate the con temporary development of the petrol engine, so that the promise of the former may be measured in terms of the achievement and the further promise of the latter. The Four-stroke Compression-ignition Engine. —In 1927 H. B. Taylor published the results of his work at the Royal Aircraft Establishment on a single-cylinder compression-ignition engine. This had a bore of 8in., a stroke of nin., and ran at speeds up to 1,200 r.p.m., so that the piston speed was comparable with that of current petrol engine practice. The fuel consumption under moderate load conditions was as low as 0.37 lb. per b.h.p./hr., and was exceedingly attractive in comparison with the consumption of petrol engines at that time. There appeared J?EW authorities are better fitted to discuss the Diesel question than is Captain Swan. As head of the Engine Department of the Royal Aircraft Establishment, Farnborough, he has been able to study and assist the develop ment work on C.I. engines in this country. In the accompanying article he views the situation concisely and in its true perspective, setting out the qualities and shortcomings of what has been called the Cinderella of aero engines against those of the petrol unit. to be a saving of fuel of at least 25 per cent. The brake mean effective pressure was much less than that in current petrol engines, and the power out put was, therefore, relatively low. In consequence, a larger engine would have been required for a given total power output. In addition, the high pressures at the commencement of the expansion stroke necessitated a strengthened design. These two fac tors, the low power output and the high maximum pressure, make the chief contribution to the heavier weight of this type of engine. Never theless, it is clear that for a given flight endurance the total weight of engine and fuel is the important factor, and not the weight of the engine alone, and there must be some range above which it should be advantageous to use a compression-ignition engine instead of a petrol unit. The cylinder used for this experimental work was a large More commercial Junkers with their economical heavy-oil Jumos. SruSSM I
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