Abstract
Exhaust hydrocarbon concentration reductions were determined for a revised design of spark ignition engine piston having a much narrower top land. Hydrocarbon concentrations with the revised design were 47 to 74 % lower than the production design, depending on engine speed and load. These results demonstrate the sizable reductions in exhaust hydrocarbon emission that are possible when the piston-bore-ring crevice volume is essentially eliminated. However, durability of the present design, while adequate for laboratory experiments, would be un-satisfactory in passenger car service.

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