In the present study, a single-cylinder four-stroke SI engine was operated with LPG (C4H10/C3H8, 70:30), hydrogen and methane mixture (H-2/CH4, 30:70). Experiments were conducted at excess air ratio between 0.8 and 1.5. Spark timing was varied from 14 to 35 degrees CA BTDC under a constant load of 6 Nm at 1400 rpm. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.