THE FUTURE OF THE HEAVY-OIL ENGINE.
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A Summary of an Important Paper Read Before the Members of the Institution of Automobile Engineers and the Discussion Thereon.
HAVING. regard to the recent rise inthe price of Petrol it was appropriate that Mr. A. E. L. Chorltou,
• of William Beardmore and Co.. Ltd., should read a Paper entitled "The Heavy-oil Engine on Road and Rail" before the -Institution of Automobile Engineers,. in London, on March 5th.
In the opening portioit of the paper he expressed the view that the heavy-oil engine would first he applied to heavy-haulage work, and that its wideruse is destined for
the future rather than the present. •
Diesel engines Work on the constant-pressure cycle, and the fuel is injected directly into the compressed .air in the cylinder at the end of the compression stroke,. when tin! air temperature ignites it.
Unlike the true Diesel, when the engine is of the smallcylinder, high-speed type employing airless injection of the oil, it runs substantially on the constant-volume Cycle
and high maxima are obtained which demand a heavierand More e„xPensive engine than when petrol is the fuel; The first cost of a compressionPrnition engine is 'about three times greater Than the 'corresponding petrol engine.
Methods of vaporization of heavy fuels, to enable them to be employed in a carburetter type engine, were said to --have a limited value, owing to the pre-heating of the charge causing a reduction of the induced. volume. • The compression ignition engine, „ designated. by the anthor _the xenitr," will run on fuels varying from .710 specific gravity to .95, that is, from aviation petrol le boiler-fuel oil.
Belief was expressed that the one-cell pattern of engine wmld, in time, supersede the two-cell or Ackroyd Stuart class, Improvements in .fuel-injection pumps may do inueli t.) further this development. Reference -was made to a. flash-valve type of pump used on Beardmore engines and designed to eliminate the seated valve.'
A component of vital importance is the atomiser. This generally consist of a: pepper-castor nozzle with fine holes, in some caseshaving .a spring-loaded valveseated i111111ediately behind •it. .Essential 'features of the performance of the.atomiser,are that, in conjunction with the pump,' it must give • sharp, penetrating, fine sprays reaching the confines of the .combustion chamber -without interference, yet close enough to make effective use of all the air present.
For road work stouter transmission parts are required in conjunctionwith the heavy-oil engine, and an electrical drive has many merits. For starting purposes a powerful motor and glow-plugs may be used. Steam meting, is advantageous and is likely to be developed.
• In constructing a heavy-oil engine the following parts require alteration to withstand the higher pressures imposed upon them, as compared with the petrol-power unit :— The crankshaft should have a greater hearing area, the pistons need thicker crowns, Langer skirts, more rings' and larger gudgeon pins, whilst the connecting rods must have lerger ends and be of heavier section. The crankcase needs to be stouter, as do the cylinder heads and main bearings; the flywheel must .be heavy to aid starting.
• In the case of petrol engines the fuel cost is about equal to that of repairs and maintenance ; with the -Diesel, feel and repair costs are in the ratio of 9 to 63. During. the discussion which followed the reading of the paper, Mr. Wiudeler suggested that coal-oil be added to the range of commercially available fuels advocated by the author. The next speaker, Mr. W. A. Tookey, referred to 'a. iittniSh invention which provided for the vaporization of heavy •fuels. Although the idea had certain defects, it was pdssible, in his view, to obtain useful resulte with
vaporizers. According to Mr. Tookey, an engine -which gives 250 b.h.p. at 1,000 r.p.m. is now undergoing tests ; details will be made public later. Reference was made to the policy of the oil companies ; several of the speakers pointed out the possibility Of a rise in the price of heavy oils so soon as the demand showed an increase.
Wing-Cominander Cave-Browne-Cave spoke of the appli cation of the heavy-oil engine to aircraft. He did not think that the difference in the relative weights of the two engines was so serious as the author made out. An important point in favour of the heavy-oilmotor is its fuel economy at reduced power. If it were possible to eliminate the hang-fire at the beginning of burn:rig, control meld be by injection regulation only.
Mr. Challouer regarded the utilization of cheap fuel, as secondary to the need for making engines capable of
burn
ing a wide range of liquids, Mr. Milligan pointed out the increased difficulty iu gear-changing with a Diesel owing to the poor engineo3peed control. ILs also stressed the safety of the fuel used as an important factor. Dr. W. R. Orniandy suggested that tar-oils were not wholly desirable as fuels ; he also 'CI:mud that Russian crudes gave better running than those' from other sources. With regard to injection, pumps, he stated tin case cif a Bosch design which gives three-quarters of a cubic millimetre of oil per injection at 2,000 r.p.m. with an error of about I per cent, during many hours' running.
Mr. G. M. Junner raised the point of obnoxious exhaust .fumes, and stated that 'difficulty had been experienced with police in Germany on this score. In one case a con-. cern suggested that a purchaser should employ a petrol engine for town work and a Diesel for the country. Part ' of the trouble due. to fumes-might be that users employed, unsuitable fuels. In his experience heavy-oil engines were quiet under load, but clattered when running light.
Mr. Wardman entered a plea for the development of coal-oil in this country. Mr. M. Platt touched upon the possibilities of air-cooling. In his opiunn, undue attention was paid in the paper to explosionpressure as a basis of comparison of stresses in petrol and heavy-oil engines; owing to the comparatively high rates of rotation of the modern Diesel the inertia stresses are more iroportant.
In his reply the author pointed out that, as the traespoet engine rims at reduced power very often, the inertia stresses are not so important as if full throttle be always required.