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Petrol Possibilities

11th December 1959
Page 41
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Page 41, 11th December 1959 — Petrol Possibilities
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Which of the following most accurately describes the problem?

THE development of new techniques in combustion-chamber design may well open up a fresh field of progress in petrol engines that at present exists largely in the imagination of advanced technicians. The production of -highly efficient petrol engines could redress the lack of balance between the availability of the fighter-fraction fuels and the supply of the heavier distillates. The interests of oil-engine makers would not necessarily be threatened by this development, because extremely high compression ratios would require crankcase scantlings of the compression-ignition-engine type to resist the greater stresses.

ft is claimed that a relatively modest increase in compression ratio from 8 to 1 to 11 to 1 has reduced fuel consumption by a quarter, and there is promise that overall fuel consumption might by this means be halved within the foreseeable future. It would, however, be essential to develop a means of operating the unit on commercial-grade petrol, without serious loss of performance, if it were to be competitive with an oil engine.

By using costly fuels of high octane rating it has been possible to raise compression ratios to the point where the peak-load efficiency of a petrol engine equals the maximum efficiency of a typical oil engine. The efficiency at lower loads'and speeds —a matter of great importance to the majority of commercial-vehicle operators—of the most advanced design of petrol engine envisaged by some authorities would, however, compare unfavourably with that of the oil engine. Indeed, many experts believe that equality in peak-load efficiency between petrol and Oil engines will never be reached.

A Critical Limit

One of the main difficulties in fully exploiting the known possibilities of raising the compression ratio is that a reduction in the size of the combustion chamber below a critical limit involves an increase in the surface-volume ratio, which seriously impairs efficiency. So far, experiments have been conducted on existing types of power unit adapted to operate at very high compression, but the gains might well have been even greater had the engines been designed from the start as highcompression units.

Work done by. the British Internal Combustion Engine Research Association with petrol engines having constant-pressure pistons proves that a substantial part-load advantage is offered by automatic ratio control, and it may be assumed that the unit would run satisfactorily on commercial fuel with only a small loss in peak performance. Progress in ratio control could close the gap between the consumption rates of petrol and oil engines if a combustion chamber were designed to provide a compression ratio in the region of 20 to 1 which did not impair combustion by virtue of its poor shape.

In using a constant:pressure piston it would also be necessary to evolve a means of compensating for any reduction in the quenching effect of the squish area. If these conditions were satisfied the unit might be more economic than art oil engine. Certainly, its power output per litre should substantially exceed the current average.

Despite the existence of the petrol engine for some 70 years, relatively little is still known of the mysteries of combustion. Its future development depends largely on a more profound understanding of what goes on inside the cylinder head at high compression ratios. This is a matter for concentrated research, which might well be combined with a study of the combustion characteristics of engines designed to operate on a variety of fuels.

Stimulant and Tranquillizer

ACCORDING to Mr. A. B. Waring, president of the .n.Motor Industry Research Association, the British motor industry spends more than £20m, a year on research and development. This may seem a large figure, but American expenditure is placed at £200m. a year. This is a measure of the competition which British makers must face, despite an almost overwhelming burden of taxation.

Most of their investment,in research and development is on their own account. The work done centrally for the benefit of the whole motor industry and its customers all over the world is conducted on a shoestring. M.I.RA.'s annual revenue is f200,000, of which £60,000 comes from the Government through the agency of the Department of Scientific and Industrial Research. Although hampered by a lack of funds. M.I.R.A. have already rendered great service, and they are embarking on a new five-year plan of research into many important phenomena.

In view of the confession last week by Mr. Reginald Maudling, President of the Board of Trade, that he was sometimes alarmed by the extent of Britain's dependence on the motor industry for its daily bread, one might expect that the Government would be more generous in their support of its -central research organization. He could help to sustain Britain's motor exports and set his mind at rest by increasing Government aid for the research and development on which the continued prosperity of a key industry rests.


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