Investigating the Behavior of Natural Gas Flame in a Spark Ignition Engine

Heat release rate process in SI Engines is directly related to the flame propagation in the combustion chamber. In this study, by simulating natural gas combustion in SI Engines using CFD software, flame behavior is investigated near the wall. Experimental tests were performed for various engine speeds and spark timings. The engine simulation was done and the results were validated with experimental data at various engine operating conditions. The results were in good agreement with the corresponding experimental data. Results show that by keeping the spark plug out of the geometric center of the cylinder, the concentric spherical propagation assumption of flame is not true. The walls near the flame prevent its propagation and its shape deviates from the spherical shape. Finally, it can be concluded that, natural gas turbulent flame propagation occurred in three stages: 1- The initial propagation of flame with high acceleration, in which 15% of the fuel is burned with a high rate of H.R.R. 2- Colliding of the flame with the floor of the piston, H.R.R continues with almost constant rate, in which 30% and 50% of the fuel is burned for the off-centered and centered spark plug location, respectively. 3- Deceleration of flame propagation after colliding with the side walls, in which 55% and 35% of the fuel is burned for off-centered and centered spark plug location, respectively.