Influence of charge constituents on the cycle-by-cycle variations of DME HCCI engine

Homogeneous Charge Compression Ignition (HCCI) engine has the potential to achieve lower NOx and PM emissions with high thermal efficiency. However the operation region is limited by knocking. Combustion phasing retard is one of the methods to avoid knocking. However, excessive retard happen unstable combustion. This study explores how the cycle-by-cycle variations of HCCI engine are affected by charge constituents, which includes air, fuel, cold EGR and re-breathing EGR (hot EGR). The engine was fueled with Dimethyle Ether (DME). The experiments were conducted in a single-cylinder HCCI engine equipped with two-stage exhaust cam for re-breathing EGR and four throttle valves. In this study, it is important to detect each gas volume and temperature every cycle because combustion phasing depends on the in-cylinder mass averaged temperature. Therefore the engine included fast-response sheath thermo couples located near the exhaust valve to quickly measure the exhaust gas temperature and re-breathing EGR temperature and fast-response laminar flow meter to measure cycle-to-cycle intake air and cold EGR flow rate.