Bi-fuel engine using hydrogen

A method is disclosed for making a transition from fueling an engine with hydrogen to another fuel. That other fuel may be gasoline, a gasoline and alcohol mixture, or gaseous fuels, as examples. The other fuel has the capability of providing higher BMEP than the hydrogen because of better air utilization and because the other fuel occupies less volume of the combustion chamber. Because a desirable equivalence ratio to burn hydrogen is at 0.5 or less and a desirable equivalence ratio to burn other fuel is at 1.0, when a demand for BMEP that leads to a transition change from hydrogen fuel to the other fuel, the amount of air supplied to the engine is decreased to provide more torque and vice versa. During a transition in which liquid fuel supply is initiated, it may be desirable to continue to provide some hydrogen, not leaner than 0.1 hydrogen equivalence ratio.