challenges during the transitions the present invention differs from prior art transitions in stratified charge engines because in the present invention the fuel changes as well as the equivalence ratio it is known in the prior art to operate bi fuel engines in which transitions are made between two fuels such as between gasoline and propane or between gasoline and ethanol however most known fuels gaseous hydrocarbons liquid hydrocarbons and alcohols have a narrow range of flammability equivalence ratio roughly 0 65 lean limit and 1 7 rich limit compared with hydrogen fuel roughly 0 10 lean limit and 3 rich limit because most fuels cannot combust robustly at very lean equivalence ratios their stable lean operation occurs in a region in which high nox is produced thus most fuels except hydrogen are operated at stoichiometric i e equivalence ratio of 1 because very lean mixtures of hydrogen combust robustly the amount of nox produced is small allowing such lean operation without a great emission concern even though hydrogen can be combusted in a wide range of equivalence ratios in an internal combustion engine it is used in the 0 15 to 0 5 equivalence ratio range because when operating richer than 0 5 equivalence ratio harsh combustion and autoignition of the hydrogen results conditions which are to be avoided thus a bi fuel engine in which one of the two fuels is hydrogen when making a transition from hydrogen to gasoline a switch from an equivalence ratio of about 0 5 or leaner to 1 0 occurs in summary the present invention distinguishes between the prior art transitions between stratified lean operation and stoichiometric operation as discussed above in that both a transition in equivalence ratio and fuel type occurs the present invention distinguishes between the prior art bi.