THE DIESEL ENGINE

Evening Post, Volume CXXIII, Issue 108, 8 May 1937, Page 28

THE DIESEL ENGINE

PROGRESS IN THE AIR

AN ENGINEER'S TALK

An illuminating' survey of the advantages and disadvantages of com-pression-ignition engines . for civilian and military aviation is contained in a paper by Mr. F. M. Owner, which was read to . a meeting ■ of the Manchester Association of Engineers. Mr. Owner, a well-known British aeronautical engineer, is equally definite about good and bad points.

He emphasises the comparative freedom from fire risk of the compressionignition, or Diesel, engine. "Apart from the lesser danger of the fuel itself," he says, "the Diesel exhaust temperature is much lower; hence the surface temperature of the exhaust manifold is reduced, thus lessening the chance of ignition ' of lubricating oil, which constitutes a very real danger with an exhaust system temperature of 500deg Centigrade or over." Above a certain temperature lubricating oil is just as dangerous, as vola-

■-■■■- ■■•.,■ * - tile.spirit. Reduced fuel consumption of the' Diesel, measured, in. the weight of fuel consumed to ..produce one horsepower for an hour, he regards as. ah advantage of diminishing importance. He says: "Consumptions of the order of 0.451b per h.p. hour.are being-regu-larly achieved on petrol, engines using 87-octane (high anti-knock- rating) fuel,.'and this may eventually be reduced to 0.4 per, h.p. hour with 100----octane fuel." This is, the .latest' form of volatile fuel to become available for use in military and, commercial aero engines; it increases power, output by some 30 per cent, from a given size of engine' and greatly reduces specific fuel • consumption.

Trustworthiness, , Mr. Owner considers superior in the piesel engine. "There can be no questidn ■ that. the fuel pump is inherently a more reliable device than the magneto." Finally, the Diesel-causes no radio interference, and Diesel' fuel costs less.

The foregoing advantages are more interesting to : civil than to military flying. In 1937, civil ,' aviation must still, use engines adapted.from engines designed primarily for ; military, purposes. "A modern aero engine," states Mr..Owner, "niay cost up to a quarter of a million: sterling to develop to the quantity production stage, and 'outputs of civil engines are too small as yet to bear this overhead." He adds that for military 'use the Diesel ■ engine has serious disadvantages. It will not give the high power1 for take-off that a "petrol" engine does. He assesses the possible take-off Diesel output as 75 per. cent, of that of the equivalent 87----octane engine and only 65 per cent: of the equivalent 100-octane. engine. This means that the load to'be lifted is limited,' which, incidentally,: is .a disadvantage in civil as. well-as in military flying; payload depends largely on the take-off qualities of. an aeroplane. . : '. r?

Although specific weight of the com-pression-ignition aero engine has been much reduced in- recent;- years/ it is stiirabout 30 'per cent, more than the weight of the, corresponding;,"petrol" engine, and,, in Mr. Owner's view, is not likely to'catch up.