Analysis of Combustion Characteristics and Efficiency Improvement of a Supercharged HCCI Engine Achieved by Using the Different Ignition Characteristics of Gaseous Fuels

摘要

This study focused on the use of a two-component fuel blend and supercharging as possible means of overcoming these issues of HCCI combustion. Low-carbon gaseous fuels with clean emissions were used as the test fuels. The specific fuels used were dimethyl ether (DME, cetane number of 55 or higher) that autoignites easily And exhibits pronounced low-temperature oxidation reactions, methane (cetane number of 0) that does not autoignite readily and is the main component of natural gas which is regarded as petroleum substitute, and propane (cetane number of 5) that is a principal component of liquefied petroleum gas. The results of previous investigations have shown that the use of a blended fuel of DME and methane produces a two-stage main combustion process under certain operating conditions, with the result that combustion is moderated. The mechanism involved in this process has been made clear by analyzing the exhaust gas using spectroscopic measurement methods and Fourier transform infrared (FTIR) spectroscopy. The aim of this study was to examine the potential for further expanding the region of stable engine operation and improving thermal efficiency, to investigate the effective use of gaseous fuels, and to clarify the effects of different types of fuel on engine operating characteristics. Toward that end, HCCI combustion experiments were conducted and chemical kinetic simulations were run to analyze combustion characteristics in detail. The results revealed that main combustion occurred in two stages with the use of a blended fuel of DME and methane, resulting in more moderate combustion. In contrast, a two-stage main combustion process did not occur with a blended fuel of DME and propane, though it was observed that the overall combustion process was delayed.