As a hydrogen/air fuel mixture is quicker to ignite with a faster burning rate than gasoline, an important issue of hydrogen internal combustion engines is to prevent pre-ignition and backfire. In a rotary engine each pulse of the Otto cycle occurs in different chambers. The rotary has no exhaust valves that may remain hot and produce the backfire that occurs in reciprocating piston engines. Importantly, the intake chamber is separated from the combustion chamber, keeping the air/fuel mixture away from localized hot spots. These structural features of the rotary engine enable the use of hydrogen without pre-ignition and backfire.