A liquid nitrogen vehicle is powered by liquid nitrogen

Liquid nitrogen

Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...

, which is stored in a tank. The engine works by heating the liquid nitrogen in a heat exchanger

Heat exchanger

A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...

, extracting heat from the ambient air and using the resulting pressurized gas to operate a piston or rotary engine. Vehicles propelled by liquid nitrogen have been demonstrated, but are not used commercially.

Liquid nitrogen propulsion may also be incorporated in hybrid systems, e.g., battery electric propulsion and fuel tanks to recharge the batteries.