Combustion-Chamber Deposits and Octane-Number Requirement

RESULTS of an investigation directed toward determining why deposits increase antiknock requirement are discussed here. Data are presented which indicate that substantially 100% of the increase in octane-number requirement caused by deposits results from a combination of thermal and volume effects.

An analysis procedure is given which indicates that deposit-thermal effects may result entirely from the heat that is stored in the deposits. Thus, the deposits absorb heat during the combustion process in one cycle and transfer it to the fresh charge during the intake and compression portions of the next cycle.

The findings reported in this paper show that those engines with the smallest area of combustion-chamber surface, for a given displacement, would be expected to have the smallest thermal effects and hence should have minimum deposit effects.