Abstract
This paper presents three general types of combustion which occur in homogeneous mixtures of explosive gases (preflame oxidation, normal burning, and the explosive wave) and reviews available experimental evidence as to the combustion processes which actually occur in spark-ignition engines. Oxidation is detected optically by changes in absorption spectra and chemically by analysis of samples removed from the combustion chamber. The progress of flame away from the spark plug has been followed by visual, photographic, and electrical means, with simultaneous measurements of pressure development. Spectra of visible radiation and measurements of infra-red radiation, obtained through windows in the cylinder head, assist in analyzing combustion phenomena. The characteristics of preignition and knock are understood, but the exact mechanism of knock remains obscure.
