Influence of Hydrogen and Carbon Monoxide on HCCI Combustion of Dimethyl Ether 2002-01-2828

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. 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. While the MRG consists of hydrogen and carbon monoxide, the effects of the two on the ignition of DME have not been separated yet.

This research experimentally investigated each influence of hydrogen and carbon monoxide on HCCI of DME. To separate the effects of the two on the ignition, HCCI combustion of DME-H₂ and DME-CO were compared in a single cylinder engine. The results of the analysis show that both hydrogen and carbon monoxide have the positive effect of retarding the beginning of the second stage heat release. The results also show that hydrogen more largely affects the heat release in HCCI of DME than carbon monoxide does.