Kinetic study on the effect of di-tert-butyl peroxide and 2-ethylhexyl nitrate on the reactivity of toluene primary reference fuels

Fuel additives have shown to provide an important contribution to control the auto-ignition process of the homogeneous charge compression ignition (HCCI) and reactivity-controlled compression ignition (RCCI). In this work a kinetic modeling study has been conducted to study the effects of di-tert-butyl peroxide (DTBP) and 2-ethylhexyl nitrate (EHN) on the reactivity of toluene primary reference fuels (TPRF). The kinetic analysis at engine-like conditions showed that for TPRF, the first-stage heat release was similar for the two additives. However, in the case of EHN the OH precursor nitrous acid (common isomer HONO) was formed in significant amounts during the induction period which eventually lead to a faster high-temperature ignition. This was in contrast to primary reference fuels where the ignition enhancing effect of DTBP was more significant compared to EHN as a result of a more pronounced first-stage heat release when adding DTBP and a lesser amount of nitrous acid formed when adding EHN compared to a TPRF. Using a TPRF as gasoline surrogate fuel could reproduce the trends in RON as function of added EHN and DTBP for a commercial gasoline, indicating the importance to include fuel sensitivity (RON-MON) in a surrogate fuel.