Experimental study on jet ignition and combustion processes of natural gas

Pre-chamber-type ignition system can provide multiple ignition points, high ignition energy and strong turbulent disturbance, which are beneficial for the ignition and flame propagation of natural gas engines especially in lean-burn mode. The impacts of pre-chamber geometric parameters and premixed gas parameters on ignition and the consequent combustion processes were investigated with optical diagnostics in combination with pressure acquisition in a constant volume chamber. Experimental results showed that a larger pre-chamber orifice diameter caused earlier ignition timing and lower ignition position. When the ignition position was at the center of the main chamber, the flame propagation rate of the mixture and the pressure rise rate in the main chamber reached their highest values. The flame would quench when the orifice diameter was smaller than a certain value. Increasing the volume of the pre-chamber led to a retarded appearance timing of the jet in the main chamber, however, more combusting mixture and wider distribution range could provide higher ignition energy, resulted in a higher combustion rate. When the fuel/air equivalence ratio was increased in the pre-chamber, the ignition ability was enhanced and lean burn limit in the main chamber was expanded. The initial pressure and temperature of premixed gas played important roles in chemical reaction rate in the main chamber.