The correlation between the cylinder pressure and the ion current fitted with a Gaussian algorithm for a spark ignition engine fuelled with natural-gas–hydrogen blends

An investigation was conducted of the ion current characteristics at various excess air ratios λ in a spark ignition engine fuelled with natural-gas–hydrogen blends. The Gaussian mathematical method was employed to fit the pure ion current signal without a spark tail generated by the ignition discharge. The cylinder pressure was recorded, and the Pauta criterion static threshold was used to deal with the outlier errors in the testing data for given cycles. The results show that the spark tail and the ion current can be separated by fitting the ion current with the Gaussian method, and the fitted pure ion current includes the flame-front stage and the post-flame stage. The timing with respect to the flame-front peak exhibits an irregular variation with λ. The maximum current in the flame-front stage increases with increasing λ.The timing of the maximum current in the post-flame stage occurs earlier at the stoichiometric ratio than at other air-to-fuel ratios. The correlation coefficient between the ion cur...