1929-01-01

Combustion Control by Cylinder-Head Design 290016

DETONATION and shock, the two principal barriers to increased compression, are subject to a degree of control which can readily make possible the use of compression ratios in the neighborhood of 6-1 on commercial fuel without objectionable effects and without sacrifice of output.
Since detonation depends primarily upon the temperature attained by the residual unburned gas, it can be controlled by combustion-chamber design which intensifies the heat transfer from the unburned gas to the walls.
The shock tendency, which originates in the pressure-time characteristic of combustion, can be controlled only by deliberate incorporation of the desirable anti-shock characteristic in the chamber design by a method of calculation which is explained in detail. To obtain smoothness without loss of power, the volume of charge must be so distributed with respect to the firing position as to obtain as nearly as possible uniform acceleration in the rate of pressure rise up to the maximum rate, without excessive increase in the explosion time.
No definite empirical rules for chamber proportions can be laid down which will cover the wide range of variation in individual requirements. Each case calls for an independent application of the fundamental principles if maximum results are to be obtained from the design.
Discussers of this paper report the results of their attempts at combustion control with several of the leading manufacturers of motor-cars and engines. Various speakers express appreciation of Mr. Janeway's analytical approach to the problem. Elasticity of engine and chassis parts and their effect on sensible roughness are brought out, and questions are raised as to the influence of roughness on durability and the effectiveness of rubber mountings and connections in suppressing the results of roughness.

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