RECENT improvements in techniques and instrumentation plus further data on rapid chemical chain reactions have made possible a clearer picture of the chemical reactions in engines. This paper describes the present knowledge of the changes in the fuel-air mixture prior to combustion, the effect of these changes on knock, and the method by which antiknocks function.
Knock is controlled by the preflame reactions occurring prior to fuel combustion. These reactions are very complex, but the specific reactions causing knock seem to be simple, probably involving very fast reactions initiated by combinations of only hydrogen and oxygen. Hydrocarbon structure affects the rate of accumulation of enough of the hydrogen-oxygen species to cause knock.
Tel slows the later stages of reaction, probably by deactivating the hydrogen-oxygen groups. The active antiknock species seem to be either lead oxide or metallic lead.