Department of Mechanical Engineering, K. N. Toosi University of Technology, Tehran, Iran
In this paper, the performance of a natural gas HCCI engine is studied through a thermodynamic model including detailed chemical kinetics. It is shown that as hydroxyl radical has important effects on natural gas combustion, it is possible to quantify SOC with hydroxyl concentration variations. Meanwhile the influence of using formaldehyde as an additive on the engine characteristics has been investigated. Results show that it is possible to change the engine working limits using this additive. Lower autoignition temperature of formaldehyde causes advanced combustion in natural gas HCCI engine. In TIVC = 410K case, adding 5% formaldehyde would lead to more than 10 CA advance in SOC. Furthermore, there is an optimum additive content for each operating condition, which leads to higher output work and power. It is also shown that the air/fuel mixture will ignite earlier using this additive so it is conceivable to reduce inlet mixture temperature resulting in better performance due to higher volumetric efficiency.