Chemical reaction analysis of auto-ignition behavior for mixed fuel of cyclopentane and paraffin

Abstract

Knocking due to auto-ignition of fuel greatly hinders the performance enhancement of gasoline engines. Since general gasoline is a mixture of many substances, its knock resistance depends largely on the combination of substances contained. Therefore, it is important to comprehend the chemical reaction process up to ignition in mixed fuels. This study performed various analyses of the detailed chemical reaction process for the case where cyclopentane, a representative of naphthene, is mixed with paraffin. The main purpose of this analysis is to discover a mechanism that enhances the antiknock effect by combining fuels. Analysis of the detailed reaction process suggests that in some cases cyclopentane suppresses the subsequent reactions by consuming the OH produced by paraffin during the initial low temperature oxidation. Therefore, mixing cyclopentane into paraffin greatly extends the ignition delay time by suppressing the subsequent exothermic reactions. When added in a low fraction, the ignition suppression effect exceeds that of the general octane booster toluene. On the other hand, analysis of the detailed reaction process under high mixing ratio conditions showed that cyclopentane has an ignition promotion effect. The reason for this phenomenon is that cyclopentane lowers the ignition temperature because it accumulates a large amount of H2O2 as an intermediate product after the initial reactions. Furthermore, H2O2 advances the ignition reactions by generating OH in the subsequent reactions. Additionally, due to the changing behavior of the low-temperature oxidation reaction, the effect of cyclopentane mixing also changes with the temperature range. In other words, cyclopentane has the opposing effects of suppressing and promoting ignition, which results in a complicated phenomenon that changes depending on the mixing ratio with paraffin and temperature.