Typically hydrogen engines are designed to use about twice
as much air as theoretically required for complete combustion.
At this air/fuel ratio, the formation of NOx is reduced
to near zero. Unfortunately, this also reduces the power output
to about half that of a similarly sized gasoline engine. To
make up for the power loss, hydrogen engines are usually
larger than gasoline engines, and/or are equipped with turbochargers
or superchargers