Influence of mock reformed gas by over-rich SI combustion on HCCI combustion fuelled by methane

Abstract

HCCI combustion is effective for improving thermal efficiency of a gas engine, but it has problems such as control of the ignition and combustion. To solve the problem, availabilities of dedicated EGR technique are considered to control its ignition and combustion. Dedicated EGR involves reforming fuel into H₂ or CO by running a single or more cylinder with rich mixture and supplying the exhaust gas directly into other cylinders. In this study, the effect of dedicated EGR on methane HCCI combustion was investigated by experiments. As a result, when equivalence ratio of rich SI combustion or EGR ratios increase, the ignition timing of HCCI advances and combustion becomes steep. The advanced ignition timing is caused by an increase of H₂ mole fraction in the intake gas. In addition, the possibility of controlling the ignition timing, which is strongly concerned with the thermal efficiency of a HCCI engine, by dedicated EGR was discussed. It was shown that the ignition timing linearly depends on H₂ mole fraction in the intake gas.