Abstract
Keywords:
HCCI, DME, Methane, Low-temperature Reaction, Cool Flame, Formaldehyde, Spectroscopy
Abstract
Homogeneous charge compression ignition (HCCI) combustion can achieve thermal efficiency equal to that of diesel engines and also reduce nitrogen oxide (NOx) and particulate matter (PM) emissions simultaneously, something that has not been possible to accomplish with diesel engines. On the other hand, because HCCI combustion is dependent on many chemical reactions in the process leading to ignition, it currently has the drawbacks that the compression ignition operation range of HCCI engines is narrow and that the ignition timing is difficult to control. Various methods of controlling HCCI combustion have been proposed, including varying the compression ratio, varying the intake air temperature, and using a mixture of two fuels having substantially different ignition characteristics. In this study, a diesel engine was operated on the HCCI combustion process by supplying dimethyl ether (DME; CH3OCH3) as the test fuel. Experiments were conducted under varying compression ratios and also with a two-fuel blend prepared by adding methane to DME for HCCI operation. An analysis of the experimental results showed that varying the compression ratio and adding methane respectively influenced the ignition timing, i.e., the manifestation of low-temperature reactions and high-temperature reactions. In addition, it was found that engine operation with relatively high power output was obtainable by adjusting the compression ratio and the amount of methane added.