Steam Engines

Steam engines use a constantly burning fuel to boil water, which is forced into a cylinder as steam, and the pressure forces the piston within that cylinder outward.

Steam engines aren't used in passenger vehicles today because they are too large and inefficent for that particular type of transportation. Some early attempts at personal transport attempted to produce a vehicle with a miniature steam engine, but most were often lacking power and often inefficent.

Steam Engines: History & How They Work (by Real Engineering)