Fuel Design Concept for Robust Ignition Process in Compression Ignition Engines (Second Report)

- Application to Optimize Methane-based Blends for High Speed/load Operation-

Abstract

The authors proposed a fuel design concept for an HCCI engine to optimize a profile of heat release and achieve a robust ignition process. The concept was validated by engine operation tests using methane-based dual-component fuels at a low speed and a low load in the previous study, and has been done at a high speed and a high load in the present study. Methane/ethane demonstrates a lower COV of IMEP than those of methane/propane, methane/n-butane and methane/isobutane, when the timing of 50 % heat release is set at the same crank angle in the expansion stroke. It is because according to 0-dimensional chemical kinetic computations, ethane indicates a higher heat release rate in the late stage of an ignition process than propane, n-butane and isobutane do. Methane/ethane also demonstrates a lower knocking intensity than those of the other dual-component fuels, when the timing of 50 % heat release is set at the same crank angle close to the knocking limit. Methane/ethane indicates a lower gradient of the heat release rate immediately before the heat release rate reaches the peak value, which moderates the pressure rise rate and suppresses knocking.