Which of the following is not used as a rocket fuel?
Liquid Nitrogen is a liquid at very low temperature (-417 degrees Farenheit). At normal temperature it is a gas. So, fill your tank with liquid nitrogen. Then let it into your engine, where the heat from the the outside air turns the liquid nitrogen into a high-pressure gas and expands and can harness the expansion to push a piston, just like you harness the expansion of high-pressure burning gasoline. Meanwhile, the cold engine must draw in heat from the atmosphere to warm it back up.