1. Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Republic of Korea, Environmental Parts Research and Development Center, Korea Automotive Technology Institute, 74, Yongjung-ri, Pungse-myun, Chonan, Cheungnam 330-912, Republic of Korea, and Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551