INCREASED ENGINE POWER

Timaru Herald, Volume CXLIII, Issue 20671, 9 March 1937, Page 2

INCREASED ENGINE POWER

FUELS FOR R.A.F. ’PLANES LOWER CONSUMPTION (From Our Own Correspondent) LONDON, January 12. Increase of aero engine power output by 30 per cent, is possible if fuels of “100 octane” anti-knock rating are employed, in the opinion of Mr F. Rodwell Banks, leading world authority on aviation fuels. The fuel at present generally used in the Royal Air Force and to some extent in commercial flying has a rating of 87 octane. which was introduced a few years ago and led to great advances in power output and economy of fuel consumption. Previously aero engines had burned “straight” spirit rating usually between 70 and 75 octane, which is about the same as the best petrol obtainable from roadside pumps by the motorist. Then research showed that admixture of other substances with the fuel, and especially of minute quantities of a compound called tetraethyl lead, greatly augmented the knock rating, or, in other words, enabled higher compression rations to be safely employed in the engine cylinders Increased compression ratios led directly to higher power output and lower fuel consumption.

All high-powered aero engines now in production are designed to burn fuel of approximately 87 octane rating. Now, following intensive research, the way is opqp for a fresh advance. All kinds of substances have been tested with straight spirit to ascertain the degree of octane rating obtainable with them. One of the better means has proved to be the addition of “isooctane” and tetra-ethyl lead, which gives up to 100 octane without introducing serious difficulties. Before long the Air Ministry will issue a specification for 100 octane fuel and supplies will become available for Service use.

Engine designers are turning their attention to the building of engines which shall be able to burn the new fuels with maximum efficiency. Mr Banks, in a paper read four days ago before the Institution of Petroleum Technologists, forecast that “100 octane” engines would develop along two distinct lines; “first, for those military or civil aircraft of short range, where fuel economy is relatively unimportant and a high degree of supercharge is required to obtain the maximum power possible for rapid climb or take-off with large loads and, perhaps, from small aerodromes. Secondly, for long-range work, for bombers and civil machines having to operate between far distant points, where fuel economy is of the greatest importance and where the maximum power may have to be sacrificed for a low fuel consumption.” He continued: “I think that the use of 100 octane fuel will be well worth while for the short-range civil aircraft, because even if it costs, say, three times the price of 87 octane fuel, the increased power available for take-off will allow a greatly increased pay load to be carried and more than compensate for the extra fuel cost.” Fuel Economy He expects remarkable reductions in fuel consumption. Engines burning 87 octane fuel on prolonged and exact test, have operated at a specific fuel consumption of 0.431 b. per horsepower per hour. For comparison, a compres-sion-ignition engine burning heavy oil consumes between 0.35 and 0.37 lb h.p. hr.; its superiority in this respect over the “petrol” engine is its chief advantage. Mr Banks considers that an engine designed to burn 100 octane fuel, having a compression ratio approaching 8 to 1, should attain a fuel consumption of not more than 0.381 b h.p. hr. in the immediate future, while within the next few years figures of the order of 0.32 to 0.351 b h.p. hr. should be obtained. The importance of this statement is that it indicates the probable eclipse of the heavy-oil engine for all military purposes and makes its use even problematical in commercial aeroplanes. Effect on performance of military aeroplanes is likely to be astonishing. Mr Banks, after examination of diagrams showing the “rate of climb” and “time to height” of a modern singleseat fighter burning 87 octane fuel, estimates that with 100 octane fuel and a constant speed airscrew a highspeed heavily loaded machine will be capable of maximum rate of climb of more than 4,000 feet a minute. From sea-level to the peak of Mont Blanc in less than four minutes! Incidentally, Mr Banks recalls that as long ago as 1927, British engineers attained a fuel consumption of 0.32 h.p. h.r.; the racing Napier Lion engine in that year’s Schneider Trophy seaplanes attained that figure, thanks to special cylinder design, use of the very high compression ratio of 100 to 1, and special fuel. That engine, according to Mr Banks, had the highest thermal efficiency cf any heat engine so far produced. He points out that the modern high powered American engine, which has larger cylinders and works at considerably lower speeds than comparable British units, is more “critical” to fuel quality than the equivalent British engines He adds: “Modern British engines are producing similar take-off powers to American engines, with somewhat smaller cylinder capacity and with a fuel which, on the average, is two octane numbers less than that generally used in the United States for the same purpose.” This is valuable authoritative evidence of the superior efficiency of the British aero engine.