1. Advanced Engine System Development Team, Corporate Research and Development Division, Doosan Infracore, 489 Hwasu-dong, Injung-Ro, Dong-Gu, Incheon 401-702, South Korea e-mail:
2. Professor Department of Automotive Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 133-791, South Korea e-mail: