Waste heat
A turbosteamer is a term used by BMW to describe a combined cycle engine. Waste heat energy from the internal combustion engine would be used to generate steam (see Waste Heat Recovery Unit) for a steam engine which would create supplemental power for the vehicle. The turbosteamer device is affixed to the exhaust and cooling system. It salvages the heat wasted in the exhaust and radiator (as much as 80% of heat energy) and uses a steam piston or turbine to relay that power to the crankshaft. The steam circuit produces and of torque at peak (for a 1.8 Straight-4 engine), yielding an estimated 15% gain in fuel efficiency. Unlike gasoline-electric hybrids, these gains increase at higher, steadier speeds.