Experimental investigation on backfire occurrence, duration and termination in a hydrogen-fueled automotive spark ignition engine

The present study investigates the occurrence, duration, and termination of backfire in a hydrogen-fueled automotive spark ignition engine. Backfire is a pre-ignition phenomenon that originates from the cylinder and the flame travels towards the intake manifold of the engine during the suction stroke. A high-speed camera was used to capture the real-time backfire images during the engine running. The simultaneous acquiring of the intake manifold and in-cylinder pressure was used to define the origin, duration, and termination of backfire. The probability of backfire occurrence rises with the increase in torque at constant speed, the increase in speed (at constant torque), high equivalence ratio, and the increase in torque with the decrease in speed (at constant brake power). The critical exhaust gas temperatures (EGT) identified for backfire initiation are in the range of 765 degrees C to 955 degrees C for speeds from 2000 rpm to 4900 rpm. A correlation of backfire occurrence number (BON) for the prediction of backfire occurrence was developed using experimental results, where BON greater than or equal to zero, indicates backfire occurrence. The backfire is characterized using backfire ignition delay, expansion, convergence and termination. The average backfire propagation velocity calculated using high-speed images is found to be 179.3 m/s corresponding to a Mach number of 0.52 at an equivalence ratio of 0.5 and hence, backfire under varied speed can be characterized as deflagration. Simultaneous acquiring of pressure was found reliable approach for calculating backfire propagation velocity. Lastly, backfire was suppressed using forced air induction at a reactant velocity of 4.5 m/s. This study's results could be useful for the prediction of backfire occurrence and backfire velocity in hydrogen-fueled engines.