Combination of multiple combustion modes in a gas engine system using dedicated EGR

Although HCCI combustion has high thermal efficiency, it has difficulties such as controlling its ignition timing and combustion. This study proposed a method to make HCCI combustion in gas engines possible, combining dedicated EGR, SI combustion, and HCCI combustion, i.e. multiple combustion modes engine system. In a DEGR system, one cylinder runs with a premixture of rich fuel and air to reform the part of its exhaust gas into hydrogen and carbon monoxide, which are introduced to other cylinders and promote combustion. In this study, the exhaust gas was introduced through a bypass from rich SI cylinder to HCCI cylinder. In the experiments, conditions of high thermal efficiency and combustion characteristics were investigated. It was revealed that DEGR made HCCI combustion possible on a condition that HCCI combustion was impossible. The more the DEGR rate was, the higher the thermal efficiency was, and the thermal efficiency reached a maximum value when the equivalence ratio of rich SI combustion was adjusted. We proposed the adjustment of premixed gas amount in Rich SI cylinder as a means of improving thermal efficiency, and it was successful.