Present day machines usually burn fuel, then transfer the heat from burning to working vapor to create high pressure vapor. Then this high pressure vapor pushes a piston in a cylinder to produce power. After that, the working vapor is dumped to the outside environment. This method of producing power has three big drawbacks. First, it requires fuel which is very expensive to create heat. Second, because it dumps the working vapor after producing power, most of the heat created from burning is lost. Third, because pistons and cylinders have to bear high temperature and pressure, it is expensive to make.