Flame Kernel Development and its Effects on Engine Performance with Various Spark Plug Electrode Configurations

Two constant-volume combustion chambers and a 2.3L SI engine were used to investigate the effects of spark plug electrode configurations on flame kernel formation and development, and on engine performance. The results showed performance differences between the spark plug types tested in terms of lean ignitability limit and 0-2% MFB time. Overall, the spark plugs with 0.6 mm diameter center electrode, referred to as Finewire spark plugs, were able to ignite the leanest mixtures and were the only spark plug type to demonstrate the lowest predicted 0-2% MFB times for both 0% and 20% EGR. The Schlieren images support the results of better ignitability confirming the fastest flame kernel development with Finewire spark plugs and demonstrating the benefits of J-gap design and fine center electrode. The results explain significant advantages in engine performance in terms of engine stability and fuel consumption rate. The difference becomes small as average equivalence ratio approaches 1.0 but it is likely to affect, at a reduced scale, engine performance even in the stoichiometric operating condition through spatial and temporal variations of air/fuel ratio in vicinity of the spark plugs.