Effect of Residual Gases on Autoignition 2,—Measurement of Autoignition Time†

Abstract

The effect of OH radical in residual gases was measured by making the residual gas with less OH concentration. The residual gas (2) with less OH was produced by burning of mixtures with CO as a main fuel, while the residual gas (1) with normal OH concentration was produced by burning of a stoichiometric n-C4H10 /air mixture. For both residual (burned) gases, a fresh stoichiometric n-C4H10 /air mixture was supplied into the combustion chamber in the late stage of expansion stroke, and then the mixtures between the residual and fresh gases were compressed to autoignite. Comparison between the autoignition times indicates that OH radical in the normal-OH residual gas (1) (residual-gas fraction of 40-50%) promotes autoignition to the same extent as the temperature just after the compression increases by 30 K.