Combustion-Chamber Deposition and Knock 530239

THIS paper discusses a number of factors involved in the problem of octane-number requirement increase due to combustion-chamber deposits. A laboratory single-cylinder engine test procedure, which evaluates the effects of various fuel and oil factors, is presented with data showing its correlation with passenger-car operation under light-duty, city-driving conditions.
The influence of engine operating conditions during accumulation of deposits and the importance of engine conditions selected to evaluate the magnitude of the requirement increase are illustrated. It is indicated that organic materials formed from both fuel and oil are of major importance in deposit formation.
Data are presented which show that tel added to pure hydrocarbons of different chemical types may have different effects. It is shown that the carbon/hydrogen ratio of leaded pure hydrocarbons influences the amount and composition of the deposit formed. Among leaded commercial gasolines there appears to be little effect of changes in hydrocarbon composition, although there is a trend toward smaller requirement increase as fuel endpoint is reduced.
Similarly, removal of heavy ends from lubricating oils tends to lessen requirement increase, and the magnitude of this effect is dependent on the contribution of the fuel to the organic portion of the deposit. Maximum effects are observed when clean-burning leaded isooctane is used as the fuel.
Combustion-chamber design and deposit location influence the magnitude of the requirement increase.


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