section_path: Types/Heat engine/Non-combusting heat engines
section_name: Non-combusting heat engines
paragraph_text: Non-combusting heat engines
  
  Some engines convert heat from noncombustive processes into mechanical work, for example a nuclear power plant uses the heat from the nuclear reaction to produce steam and drive a steam engine, or a gas turbine in a rocket engine may be driven by decomposing hydrogen peroxide. Apart from the different energy source, the engine is often engineered much the same as an internal or external combustion engine.
  
  Another group of noncombustive engines includes thermoacoustic heat engines (sometimes called "TA engines") which are thermoacoustic devices that use high-amplitude sound waves to pump heat from one place to another, or conversely use a heat difference to induce high-amplitude sound waves. In general, thermoacoustic engines can be divided into standing wave and travelling wave devices.
  
  Stirling engines can be another form of non-combustive heat engine. They use the Stirling thermodynamic cycle to convert heat into work. An example is the alpha type Stirling engine, whereby gas flows, via a recuperator, between a hot cylinder and a cold cylinder, which are attached to reciprocating pistons 90° out of phase. The gas receives heat at the hot cylinder and expands, driving the piston that turns the crankshaft. After expanding and flowing through the recuperator, the gas rejects heat at the cold cylinder and the ensuing pressure drop leads to its compression by the other (displacement) piston, which forces it back to the hot cylinder.