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Hydrogen can be readily used in spark-ignition engines as a clean alternative to fossil fuels. However, a larger burning velocity and a shorter quenching distance for hydrogen as compared with hydrocarbons bring a larger cooling loss from burning gas to the combustion-chamber wall. Because of the large cooling loss, the thermal efficiency of a hydrogen-fueled engine is sometimes lower than that of a conventionally fueled engine. Therefore, the reduction of the cooling loss is very important for improving the thermal efficiency in hydrogen-combustion engines. On the other hand, the direct-injection stratified charge can suppress knocking in spark-ignition engines at near stoichiometric overall mixture conditions. Because this is attributed to a leaner end gas, the stratification can lead to a lowered temperature of burning gas around the wall and a reduced cooling loss.

Homogeneous charge compression ignition (HCCI) combustion enables higher thermal efficiency and lower NOx emission to be achieved in internal combustion engines compared with conventional combustion systems. Adjusting the proportion oftwo fuels with different ignition properties is an effective technique for controlling ignition timing in HCCI combustion. The authors have proposed a new HCCI combustion engine system fueled with dimethyl ether (DME) with a high cetane number and methanol-reformed gas (MRG) with a low cetane number in previous research. In the system, both DME and MRG are to be produced from methanol by onboard reformers utilizing exhaust heat from the engine. The research has shown high thermal efficiency of the system over a wide operable range of equivalence ratio. MRG effectively controls the timing of the second stage heat release by the high temperature reactions in HCCI of DME to expand operable range of equivalence ratio and engine load.

Homogeneous charge compression ignition (HCCI) combustion enables higher thermal efficiency and lower NOx emission to be achieved in internal combustion engines compared with conventional combustion systems. Adjusting the proportion of high cetane number fuel and high octane number fuel is an effective technique for controlling ignition timing in HCCI combustion. The authors have proposed a new homogeneous charge compression ignition combustion engine system fueled with dimethyl ether (DME) with high cetane number and methanol-reformed gas (MRG) with high octane number in previous research. In the system, both DME and MRG are to be produced from methanol by onboard reformers utilizing exhaust heat from the engine. The research has shown high thermal efficiency of the system over a wide operable range of equivalence ratio.