Elements of heat-power engineering by unknow

Author:unknow
Language: eng
Format: epub
Tags: Heat-engines, Thermodynamics
Publisher: New York, J. Wiley & sons; [etc., etc.]
Published: 1912-03-25T05:00:00+00:00

CHAPTER XXVI.

INTERNAL-COMBUSTION ENGINES (cont.).

Efficiency, Performance, and Power.

219. Efficiencies of Otto Four-Stroke Cycle Engines, (a) Not only does the thermal efificiency of the Otto cycle engine theoretically vary with the ratio of compression, increasing as the final volume is decreased with respect to the initial volume, but real engines also show a similar gain. The rapid improvement in the efficiency of this type of engine during the past twenty years has been largely due to this increase in compression pressure. It is well shown by the following table:*

(b) It should not be assumed, however, that by an indefinite increase of compression pressure the thermal efficiency of the real engine can be raised without limit. For even if the tendency of the fuel to preignition could be overcome, calculations based upon actual performances show that with the Otto type of engine the maximum practical thermal efficiency would probably be attained with a compression pressure of from 250 pounds to 300 pounds per square inch.

Blast-furnace gas engines operating with compression pressure as high as 200 pounds have given thermal efficiencies on the brake of 32 to 34 per cent. But the tendency with this fuel is * The Gas, Petrol and Oil Engine, D. Clerk, page 243. 443

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