Higher Compression : Better Fuels • into nto the Future
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A DOPTION of higher compression tA ratios would, as mentioned by Mr. Brunner, lead to greater fuel economy, but would not the improved fuels necessary to meet the higher compression ratios be so much dearer than present-day fuels that any estimated gains would be a loss to the operator?
No, said Mr. T. A. Boyd, of the Research Laboratories Division, General Motors Corporation. Past experience had shown that the gains in octane number had, on the whole, been accomplished with a decrease in fuel prices. In the light of that experience it did not seem unrealistic to anticipate that future increase in octane number would not add as much to the cost of the fuel as would be returned in the form of the improvement in miles-pergallon.
Greater .Efficiency
In pushing back the barrier of knock far enough to permit Of higher compressions and higher efficiencies, the most promising path was the one already being followed. This was that of the Otto-cycle engine using petrol as fuel. Improvements could be made both in the engine and the fuel, and engine builders would certainly continue to take every possible advantage of mechanical factors, that would reduce octane requirements. The opportunity to further that progress, by extending the important gains which had been made along the fuel route, would be a major one.
In the past 20 years the economy of the average American vehicle had gone up from 29 to 41 ton-miles-per-gallon, accompanied by an increase of the compression ratio from 5 to 1 to 7 to 1, and an increase in octane number from 60 to 78. Half of this gain in tonmiles-per-gallon had been secured by mechanical or physical means, or as a result of refinements in design, one of the principal used being a leaner airfuel ratio under load conditions, or during part-throttle operation.
Substantial increases in octane number would probably be required to allow the engine manufacturers to go to a 10-to-1 or 12-to-1 compression ratio which might be desirable for efficiency, Mr. E. V. Murphree, president of the Standard Oil Development Co. had said.
Further improvements were possible, Mr Boyd continued. Much yet n20 OMEWHAT conflicting with Mr.
Boyd's views concerning engine factors, was the opinion expressed by Professor J. J. Brocze, Director of the Royal Dutch Shell Laboratory, at Delft, Holland. The motor industry, as a whole, he said, had been rather lax in exploiting to the full the anti-knock quality of fuels. It was not the trivial matter of increasing the compression ratio to the point where the engine began to knock and then to ask for more octane, but of improving its temperature control and its breathing so as to obtain better performance at the knock limit.
Recent engine developments had shown more understanding, however, and performances were being obtained on fuels of quite normal octane levels that, years ago, would have called for special fuels.
Looking into the future, Professor Broeze said that an amazing refinement had been obtained at the present lowlevel of production cost, yet one doubted whether really serious complications that could not be reduced to a matter of low-priced accessories could be at any time successful. In this connection the author referred to fuel injection instead of the normal system of carburation, supercharging in place of an increase in bore size or engine speed, and oil cooling-systems instead of a combination of bearing metal and heavy-duty oil that enabled one to pass the short period of maximum temperatures with ambiguity.
He, therefore, envisaged a slow development tending towards standard
would be thoroughly practical. Nevertheless, advances in that direction had already been made and the means for making further improvements in octane number were known
,By the full application to a typical crude oil of processes of refining now in use commercially, it was possible to convert 60 per cent, at least into petrol having a research octane number clear of 94_ That result was, as yet, merely one which it was possible to achieve with existing techniques, but it was not one which had been achieved generally. .
The part that changes in engine factors (mechanical octane number) had already contributed to increases in compression ratios, was considerable and might be added to. Nevertheless, the possible magnitude of such effect appeared to be smaller than the known influence of fuel structure, supplemented by the knock suppressing effect of tetraethyl lead.
Transmission systems of the automatic type, which did not permit the engine to run at low speed during fullthrottle operation could, however, lower octane requirements to a considerable degree.
ization. Generally speaking, one might expect that, according to conditions of austerity or prosperity and under the influence of the field of forces between the petroleum industry and the automobile industry, the octane level would be stabilized, but never would it move fast no matter what pressure was applied so long as no radical new technology, applicable to really bigvolume production, was developed.
Much had already been achieved with regard to engine life. A cure for wear would, at the same time, open wide perspectives for engine development both with regard to petrol and oil units. There was no reason for having huge bulky engines, excepting for the fact that wear affected the smaller parts to a greater extent and reduced them to scrap at a faster rate, sometimes too fast to be economical. The wear factor excepted, the small engine had it on all counts.
Wear and Ring Sticking Development of the oil engine was still dominated by two bottlenecks: its wear rate and ring sticking. The latter had been much lessened since the more general use of detergent oils, but only latterly had it been realized that ring sticking was related, not only to piston temperature and the cleanliness of combustion, but also to sulphur content in the fuel. Immediately this was appreciated the attacks on this trouble and on wear converged and led to decisive results which were now available for ready application.
Hence, one of the main glimpses of the future was the emergence of the oil engine from its restraint; henceforth it might be developed further for it was no longer hindered by any other limit than that imposed by the endurance of the materials of which it was made.