Chemical Aspects of Combustion
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QTUDENTS of the chemical aspects
of the combustion of fuels in petrol, oil and producer-gas engines, will find much to interest them in " Applied Chemistry for Engineers" by Eric S. Gyngell, Ph.D. B.Sc., which has recently been published by Edward Arnold and Co. The relation between mixture strength and flame speed and its effect on combustion in an engine are clearly defined as well as the effects
Of interest, in particular, to producer-gas engineers, is the statement that the presence of water vapour increases the flame speed of mixtures of carbon monoxide and air. This seems to suggest that some useful information might be derived by experimenting with the injection of steam into the air-gas mixing valve.
That important term " octane number " is explained. Its significance in relation to fuels for petrol engines is indicated by the fact that a fuel which has an octane number of 100 gives a consumption of 230 cc. per h.p. hour, whereas one of 73 octane number involves a consumption of 325 cc. per h.p. hour, an increase of practically 40 per cent. The comparative power output is represented by the figures 777 for the former and 608 for the latter. It is, however, emphasized that there is no advantage in using a petrol of high-octane number in a medium or low compression ratio engine. High compression is necessdrY if advantage is to be derived from the use of these high-grade fuels.
In fuels for compression-ignition engines, a sinlilar means for measuring fuel quality is its cetane number. The author describes, in detail, the process of combustion for oil engines. and gives these figures for comparative consumptiOn: a fuel ratio of I to 14 on load and 1 to 70 on idling. The figures are significant as supporting the contention so often made, that Much of the. economy of oil-engined vehicles is due to the fact that they consume. littlefuel when idling and on low load.