The use of hydrogen as an engine fuel has a great potential for reducing exhaust emissions. With the exception of a little amount of hydrocarbon emissions originating from the lubricating oil, NO, is the only pollutant emitted. The special properties of hydrogen compel much more study on hydrogen internal combustion engines (ICEs). Studying and analyzing the behavior of hydrogen ICE and its sensitivity to controllable parameters can help designers to have better understanding over hydrogen characteristics and its combustion in an ICE. In this paper, firstly a quasi-dimensional two-zone thermodynamic model of an SI hydrogen ICE is developed and validated by experimental data. The model is used as an engine simulator. Spark advance (SA), air to fuel ratio and valve timing are selected as the main effective and controllable parameters on engine emissions and performance characteristics. Valve timing parameter is defined as the intake and exhaust valves' lift, opening time and duration. Secondly, the effects of variation of the mentioned three parameters on emission and performance characteristics of the modeled engine are illustrated. Finally, the reasons of the engine behavior and characteristics under variations of these parameters are fully discussed. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.