Effect of Gasoline Octane Quality and Hydrocarbon Composition on Afterrun

A survey of recent-model cars was made to evaluate their tendency to afterrun (continued running of the engine after the ignition is turned off) and to see what devices were used to control afterrun. The effects of idle operating conditions on afterrun were studied with two of the cars. Thirteen of the cars were used to evaluate the effects of gasoline octane quality and hydrocarbon composition on afterrun. The results of the studies give a good overall picture of how afterrun is affected by idle settings, octane quality, and fuel composition.