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Aero-Engine Efficiencies

Published online by Cambridge University Press:  18 August 2016

A. H. Gibson
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Extract

By the efficiency of a petrol engine, one usually understands the thermal efficiency, or the ratio of the heat returned as work on the crank shaft, to the heat energy in the fuel. This efficiency is vitally important in an aero engine intended for long-distance work, since it directly affects the weight of fuel to be carried.

The necessity for a high thermal efficiency on the B.H.P. almost of necessity involves that of a high mechanical efficiency, that is it requires that the losses due to mechanical friction and to pumping losses shall be small.

But an engine may have a high thermal efficiency and yet have a comparatively low brake mean effective pressure. It may, owing to too small a valve area or to poor design of the induction system, only be able to draw a small weight charge into the cylinder, although it may use this very efficiently once it is in the cylinder.

Type
Research Article
Information
The Transactions of the Royal Aeronautical Society , Volume 3: Aero-engine Efficiencies , 1920 , pp. 3 - 38
Copyright
Copyright © Royal Aeronautical Society 1920 

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References

Note on Page 5 * Automobile Engineer Reprint. Iliffe & Sons, Ltd.

Note on Page 7 * The Fiat tests were carried out by Mr. E. G. Ritchie under altitude conditions. They indicate that θ diminishes as the height increases. In these tests θ was 3.2° at 17,500ft. and 4.3 at 10,000ft. The value of 6° under ground conditions has been obtained by extrapolation.

Note on Page 9 * In these tests the valve timing was :—Inlet opens 4° early; closes 62° late, Exhaust opens 60° early; closes 28°.late.