ABNORMAL COMBUSTION IN HIGH COMPRESSION SINGLE-CYLINDER ENGINES

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ABNORMAL COMBUSTION IN HIGH COMPRESSION SINGLE-CYLINDER ENGINES

YOUNG, R. W.

Abnormal combustion was encountered while investigating combustion chamber configuration in a high compression ratio single cylinder engine once initiated it manifested itself as an uncontrollable form of combustion occurring earlier and earlier in each subsequent engine cycle. This resulted in extreme engine power loss and a violent audible noise. It has been termed runaway preignition.An extensive investigation has been conducted to define, establish the cause, and determine a solution for this combustion phenomenon. This work has been done basically in two different single-cylinder laboratory engines. The combustion chambers were maintained essentially deposit free.The fundamental cause of runaway preignition has not been determined. It is promoted by engine design characteristics, such as high compression ratio and combustion chamber geometry. This form of abnormal combustion responds to engine speed, load, spark advance, and fuel-air ratio. It apparently occurs in the absence of conventional surface ignition. Although runaway preignition does not appear to respond to the octane quality of the fuel, it does respond to fuels of different chemical structure.The occurrence of this combustion irregularity in essentially deposit-free engines and the absence of its response to the octane quality of the fuel have predicated this investigation.