Influence of intermediate temperature heat release on autoignition reactivity of single-stage ignition fuels with varying octane sensitivity

This study investigates the effects of intermediate temperature heat release (ITHR) on autoignition reactivity of full boiling range gasolines with different octane sensitivity through intake temperature and simulated exhaust gas recirculation (EGR) sweeps in a homogenous charge compression ignition (HCCI) engine. To isolate the ITHR effects, low temperature reactivity was suppressed through the use of high intake temperature and low intake oxygen mole fraction. For quantification of ITHR, a new method was applied to the engine data by examining the maximum value of the second derivative of heat release rate. Combustion phasing comparisons of fuels with octane sensitivity showed that fuel with less octane sensitivity became more reactive as intake temperature and simulated EGR ratio decreased, while fuel with higher octane sensitivity had a reverse trend. For all of the fuels that were tested, the amount of ITHR increased as the intake temperature and oxygen mole fraction increased. These ITHR trends, depending on octane sensitivity, were almost identical with the trends of combustion phasing, showing that ITHR significantly affects fuel autoignition reactivity and determines octane sensitivity. ? 2020 Published by Elsevier Inc. on behalf of The Combustion Institute.

Automated summary

This study explores the effects of intermediate temperature heat release (ITHR) on the autoignition reactivity of full boiling range gasolines with different octane sensitivity in a HCCI engine. It was found that ITHR significantly affects fuel autoignition reactivity and determines octane sensitivity. The amount of ITHR increased as intake temperature and oxygen mole fraction increased, with different fuels showing distinct reactivity trends based on octane sensitivity.