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Further Light on

8th March 1932, Page 87
8th March 1932
Page 87
Page 87, 8th March 1932 — Further Light on
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Combustion in Oil Engines

tAN page 83 of our issue dated March let we gave a lldigest of the paper by Mr. C. D. Dicksee, of the Associated Equipment Co., Ltd., entitled "Some Problems Connected with High-speed Compression-ignition-engine Development." This paper was read at a joint meeting of II technical societies in London on March 1st. The chairman was Mr. Alan E. L. Chorlton, C.B.E., M.P., M.Inst.C.E., MA.Mech.E.

In opening the discussion, Dr. W. R. Ormandy entered a plea for fuel research in connection with oil on the same lines as those pursued a few years ego by Messrs. Ricardo, Tizard and Pye in regard to petrol, so that there might be available to the automobile industry authentic data which would assist both engineers and chemists. From his remarks dealing with combustion accelerators it would appear advisable that any research work should include such substances, as they will doubtless play an important part, particularly in areas in which fuel exists but is not of the required chemical composition. Dr. Ormandy stated that the fuels which crack most easily under the influence of heat have been found to give the best results as engine fuels.

Professor Cave-Browne-Cave gave some interesting data with regard to the addition of hydrogen to the air in oil engines. He stated that it had been found possible to add hydrogen to the extent of 25 per cent, of the calorific value of the fuel when the engine was running up to 70 lb. per sq. in. b.m.e.p., whereas with a b.m.e.p. of 60 lb. it was possible to add hydrogen up to the extent of 60 per cent. of the calorific value without causing knocking. The resultant smooth running and fuel economy were advantages.

He advocated pre-heating of the air, or the use of evaporative cooling, whilst a further scheme would be the burning in the ingoing air of small amounts of fuel. When this practice is adopted, the percentage of oxygen falls only from 23 per cent. to 22.6 per cent. of the air, so that it has a negligible detrimental effect.

This speaker stated that he had found the best starting to be obtained when the injection was retarded so as to ocaur at top dead centre, the fuel thus entering the air at the hottest point in the compression phase. In connection

with pre-heating of the air, his researches showed that an increase of temperature to the extent of 100 degrees F. was equivalent to increasing the compression ratio from 14 to 1 to 20 to 1.

Mr. le lirlesurer stated that the duration of the delay period depends upon the pressure and temperature of the air and upon the chemical composition of the fuel, whilst volatility is immaterial. In his view, turbulence is mot of primary importance, but its real value lies in its effect upon local temperatures.

Another speaker suggested that certain of the troubles in connection 7,-ith bearings in oil engines are due to. the higher rubbing speeds consequent upon the increased diameter of crankpins as compared with those of petrol engines.

Mr. Hutchinson suggested that it would be of advantage, particularly in the case of two-stroke-cycle engines, to design the combustion chamber to At the spray.

DE. S. J. Davies confirmed the remarks of Mr. le Mesurer with regard to the effect of turbulence.

Several speakers emphasized the importance of ascertaining the chemical constitution of the fuel, and that this was of greater value than the figures with regard to the distillation test mid ignition temperature. Dopes have been found to have varying effects; their action is not uniform, and it varies according to the class of oil employed. Exhaust odour was referred to by one speaker, and he stated that, so long as a fuel had good burning properties, no trouble arose on this score.

Throughout the meeting there was considerable support for Mr. Dicksee's view that "Diesel knock" is due to vaporization of the first portion of the fuel injected and the consequent rapid pressure rise following explosive, as opposed to the desired gradual burning.

On the afternoon of March 1st, prior to the reading of this paper, members of the various institutions were entertained by the Associated Equipment Co., Ltd, at Southall, when they had the opportunity for taking part in demonstrations of oil-engined vehieles of A.E.C. and KarrierGardner manufacture. An Armstrong-Saurer vehicle was also in attendance.


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