Influence of Reformed Gas Composition on HCCI Combustion of Onboard Methanol-Reformed Gases

Adjusting the proportion of two fuels with different ignition properties is an effective technique for controlling ignition timing in homogeneous charge compression ignition (HCCI) combustion. One of the authors has proposed an HCCI combustion engine system fueled with dimethyl ether (DME) with a high cetane number and methanol reformed gas (MRG) with a high anti-knock property in the previous research. Both DME and MRG are to be produced from methanol by onboard reformers utilizing the exhaust heat from the engine in the system. The research has shown that adjusting the proportion of DME and MRG effectively controlled the ignition timing and load in HCCI combustion of the two fuels. High overall thermal efficiency has been shown over a wide operable range.

While the MRG used in the research was the thermally decomposed methanol, which consists of hydrogen and carbon monoxide, methanol can be reformed into various compositions of hydrogen, carbon monoxide and carbon dioxide. The present paper aims to find the optimum MRG composition for the HCCI combustion engine system in terms of the ignition control and the overall thermal efficiency. The influence of MRG composition on the characteristics of ignition, combustion, engines efficiency and waste heat recovery is experimentally analyzed.

The results show that an MRG model gas having a larger hydrogen amount has a higher effect of ignition control but a lower effect of waste heat recovery. The highest overall thermal efficiency is expected by using MRG by the thermal decomposition, while MRG by the steam reforming with the highest hydrogen fraction brings the highest output because of the strong ignition control.