1. Fuels and Power Technology Research Division, Faculty of Engineering, University of Nottingham, NG7 2RD, U.K.
2. Current address: Department of Chemical & Environmental Engineering, Faculty of Engineering, University of Nottingham, Nottingham, NG7 2RD, U.K.
3. Innospec Limited, Oil Sites Road, Ellesmere Port, Cheshire, CH65 4EY, U.K.