Data are presented to show the effects of inlet-air pressure, inlet-air temperature, and compression ratio on the maximum permissible performance obtained with a cylinder having a hemispherical-dome combustion chamber. The five aircraft engine fuels used have octane number varying from 90 to 100 plus 2 ml of tetraethyl lead per gallon. The results for each fule can be correlated by plotting the calculated end-gas density factor against the calculated end-gas temperature. Measurements of spark-plug electrode temperatures showed thta, with two spark plugs, cutting off the switch to one spark plug lowered the electrode temperature of that plug from a value of 1,365 degrees F to a value of 957 degrees F. The results indicate that the surface temperatures of combustion-chamber areas which become new sources of ignitiion markedly increase after ignition commences.

The results are given of an investigation of some of the limitations that now prevent increases in the temperature level of engine cylinder heads, and a review of previous work in the field is included to supplement these results. Attention was given, in particular, to the effects of fuel knock and surface ignition on cylinder temperatures and the effects of cylinder temperatures on performance. Data were obtained from a Wright C9GC air-cooled cylinder and from a Lycoming O-1230 liquid-cooled cylinder.

The flow of a compressible fluid past a sphere fixed in a uniform stream is calculated to the third order of approximation by means of the Janzen-Rayleigh method. The velocity and the pressure distributions over the surface of the sphere are computed and the terms involving the fourth power of the Mach number, neglected in Rayleigh's calculation, are shown to be of considerable importance as the local velocityof sound is approached on the sphere. The critical Mach number, that is, the value of the Mach number at which the maximum velocity of the fluid past the sphere is just equal to the local velocity of sound, is calculated for both the second and the third approximations.

Tests have been conducted with an air-cooled aircraft-engine cylinder to determine the effect on the knocking tendency of cutting out one spark plug when the engine is operating at or near the knock point with two spark plugs firing.