Effect of fuel property on the ignition and combustion characteristics of prechamber ignition

Recently, since international problems such as global warming, air pollution, and energy resource depletion are gradually becoming more serious, combined heat and power and cogeneration systems have been attracting a lot of attention since they can be used as low environmental load power generation systems (Agency for Natural Resources and Energy in Japan, Energy in Japan, 2003). A cogeneration system can recover an engine’s waste heat and provide both heat and electrical energy at the same time, resulting in a high total efficiency of 80%. In Japan, since 65% of the installed cogeneration systems are gas engines and about 49% of the total power generation capacity is fueled by natural gas, increasing the efficiency of natural gas engines, whose efficiency is currently about 40%, enhances the utilization of both heat and electrical energy, thus corresponding to various environmental and customer demands. One of the most effective ways for improving the thermal efficiency of combustion engines and reducing the harmful emissions of undesirable combustion products, such as nitrogen oxides, is the use of lean-burn techniques and exhaust gas recirculation (EGR) (Heywood, 2018). Although such methods have already been in practical use, they still face many technical problems, such as the substantial decrease in the burning velocity and the unstable combustion in the lean or diluted mixture region. To solve these problems, prechamber ignition systems are commonly used in gas engines to improve their inflammability and enhance the combustion characteristics in the lean or diluted mixture region. A prechamber ignition system has a small “prechamber” whose volume is less than 5% of the main chamber’s volume. The combustible mixture is first ignited in the prechamber, resulting in a torch flame that can burn a leaner mixture in the main chamber, where the torch flame is injected from the prechamber into the main chamber. Since the combustion characteristics in gas engines depend on the injected torch Riku YAMASHITA*, Satoshi WAKU*, Daisuke MORI*, Seiya UENO*, Kimitoshi TANOUE* and Yasuo MORIYOSHI** * Oita Univ. Dept. of Mechanical and Energy systems engineering 700 Dannoharu, Oita 870-1192, Japan E-mail: tanoue@oita-u.ac.jp ** Chiba Univ. Graduate School of Engineering 1-33 Yayoicho, Inage Ward, Chiba-shi, Chiba, 263-0022, Japan