Experimental investigation on effect of misfire and postfire on backfire in a hydrogen fuelled automotive spark ignition engine

This study investigates the effect of misfire and postfire on backfire in a hydrogen-fuelled automotive spark ignition engine. Backfire is a preignition phenomenon and the flame propagates toward the engine's intake manifold during the suction stroke. Postfire is a post-ignition phenomenon occurring in the exhaust manifold during the exhaust stroke and the flame propagates towards the exhaust manifold or backflow to the combustion chamber or combined both. Misfire occurs when cranking the engine (starting), fouled spark plug, and unoptimized spark timing. Several misfire cycles lead to an increase in the accumulation of unburnt hydrogen-air charge inside the cylinder and 13% hydrogen leaves the exhaust manifold resulting in postfire occurrence in a subsequent cycle. The postfire in the current cycle acting as an external ignition source for the preignition of the accumulated hydrogen-air charge results in backfire in the immediate next cycle. The misfire, postfire and backfire stall the engine operation due to a drop in indicated mean effective pressure. The experimental data indicates the backfire limiting equivalence ratio (BLER) should decrease with an increase in the engine speed as the equivalence ratio varies from 0.91 at 2000 rpm to 0.4 at 4900 rpm. As too advancement of spark timing increases the probability of misfire leading to postfire and backfire, the engine must be operated at backfire limiting spark timing to avoid misfire, postfire, and backfire occurrence. An important point emerged from this study that misfire without postfire does not lead to backfire occurrence. Physical mechanisms and mitigative measures for misfire, postfire and backfire are discussed in detail.