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Exhaust Turbo charger Progress T HE oil engine equipped with an

19th November 1954
Page 36
Page 36, 19th November 1954 — Exhaust Turbo charger Progress T HE oil engine equipped with an
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exhaust turbocharger has earned a high reputation for reliability and economical running as an industrial unit, but is regarded by a number of leading research engineers as unsuitable for road vehicles. Its first cost is high and, judged by established designs, its response to throttle movement, is slow, whilst the low-speed torque is poor, which are the operational disadvantages normally cited.

The turbo-blower possesses the characteristic that the power required to drive it is derived from a source of energy that is otherwise entirely wasted, unless it be used for heating. There are no attendant mechanical losses and the gain in power output, being in part a function of energy restoration, is obtained with a lower specific fuel consumption than can be provided by any other means.

Given that the first cost were not prohibitive and the disadvantages mentioned could be eliminated, it would probably be adopted by many makers of commercial-vehicle engines. The exhibition at Earls Court of two turbo-blown vehicle engines and the demonstration of a doubledeck bus fitted with an exhaust-supercharged unit caused many transport engineers to reconsider the potential merits of such engines for road use.

The slow-response disadvantage of the turbocharger is one which must be obviated, before -itis acceptable for vehicle-engine use, and the performance data of the new units will be awaited with interest; recent announcements regarding mechanically driven compressors giving a high supercharge at low speeds, and therefore a high torque, and reduced supercharge at high speeds, thus avoiding excessive piston temperatures, may offer a stimulating challenge to their development and progress.

The justification of the higher first cost of the turbo-blown industrial unit is often determined by the increase in power output, a gain of 50 per cent. being generally considered as a qualifying figure. No output-improvement standard has, as yet, been advanced for the vehicle engine.

The life of an industrial engine on the average exceeds the life of a vehicle engine by a fairly wide margin, because it is less dependent upon external factors. The replacement of a passenger or goods vehicle may be decided by the wearing properties of the chassis components, and sometimes by the necessity of taking advantage of design improvements in auxiliary gear or of body features which are more up to date or stylish.

For these reasons the length of service required of the engine, as distinct from the period between major overhauls, is limited and an increase in first cost must be recovered in a shorter time than is the case with units employed for generating, pumping, and so on. A saving in space and weight is, however, more important when the engine -is installed in a vehicle, and in this application the supercharged engine scores_ There have not been any commercial applications of two-stroke engines fitted with exhaust turbines. Such a unit would be of -particular interest in that high back pressure is not a disadvantage. The turbo-charger would -restore power lost because of back pressure, which could be increased by raising the capacity of the blower until all the -power was absorbed. The blower would then become a power turbine fed by a piston-engine gas generator.

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