HEAT ENGINE

A method for converting heat to mechanical work including providing incoming heat transfer fluid (HTF) at a first temperature to a mixing chamber, providing incoming compressed gas at a second temperature to the mixing chamber, enabling the gas and the HTF to mix, producing a gas- and- HTF mix, enabling the HTF in the gas- and- HTF mix to heat the gas and isotherma l expansion of the gas in the gas- and- HTF mix, limiting volume of the gas-and-HTF mix, thereby increasing pressure of the gas and causing acceleration of a flow of the gas-and-HTF mix, causing the gas-and-HTF mix to eject through a nozzle, thereby converting the heat of the HTF to kinetic energy, and using the kinetic energy to produce mechanical work. Related apparatus and methods are also described.