This paper demonstrates the first successful use of factorial statistical analysis in quantifying the effect of ignition system parameters on lean operation of a fast burn single cylinder engine. Ignition parameters investigated include plug type, plug number, ignition system, plug location, and ground electrode orientation with respect to the mean swirl generated flow direction. System performance is quantified by analyzing the coefficient of variance of the peak cylinder pressure and the 0-10% mass fraction burn time for various parameter combinations.
To confirm the results from the factorial analysis technique, data from spark angle sweeps at constant flowrates are presented for the basic system and for two promising candidates that were selected from the factorial experiments. These candidates, a multi-ground electrode plug and a surface-air gap plug combined with more ignition energy, are shown to improve engine operation at lean gas-to-fuel ratio.
Finally, a simplified thermodynamic engine model is utilized to predict what specific fuel consumption (ISFC) is attainable with stable operation at lean gas-to-fuel ratio. The value measured at the MBT+1% ISFC level, using the surface-air gap plug and more ignition energy at about 22:1 gas-to-fuel ratio, is found to be within experimental error of the predicted value.