Investigation on ionization current characteristic in a spark ignition engine fueled with natural gas natural gas hydrogen bends and gasoline was conducted Blind Source Separation (BSS) de noising method is employed to separate the ionization current signal from the interference of spark tail generated by ignition discharge Cylinder pressure was recorded and local temperature at spark plug gap is calculated using AVL FIRE simulation code Results show that the simulated cylinder pressures are in good agreement with those of measured and the spark tail and ionization current can be separated using BSS method Front flame stage and post flame stage in ionization current can be used to analyze the combustion characteristics of natural gas hydrogen blends De noised current shows that the appearance of front flame stage and post flame stage (including the peaks in the stages) fueled with natural gas is postponed and compared with that fueled with gasoline and the appearance of front flame stage and post flame stage advance with the increase of hydrogen fraction in natural gas hydrogen blends In addition the amplitude of ionization currents in both front flame and post flame (including the two peaks) fueled with natural gas gives lower values compared with those fueled with gasoline and hydrogen addition can increase the amplitude Maximum post flame current shows similar trend to maximum cylinder pressure and it has good correlation between the timing of maximum post flame current and the timing of maximum cylinder pressure High correlation coefficient between maximum post flame current and maximum pressure is presented (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved