Why our heat engines do so little work

Heat engines within which a working fluid expands- for instance to push a piston down a cylinder- can only convert a fraction (Carnot coefficient) of the fluid's initial Q into mechanical (kinetic) energy W_mec. The rest is exhausted into the environment. This simplified calculation is approximately correct for dry air. When hydrocarbon fuels are burnt, their combustion gasses contain _G.H₂O. As such gasses expand, they lose P and T while doing W_mec until the _G.H₂O starts to condense. These gasses then stop doing W_mec because _L.H₂O shrinks as it condenses to _G.H₂O. They must be exhausted even though they still contain far more Q, mostly LQ, than was converted into W_mec in the engine.

This exhaust Q adds to global warming. The _G.H₂O released in the exhaust condenses to cloud if it is cooled- hence the clouds behind cars on cold days, vapor trails behind airplanes and over cooling towers of power stations (Fig.010). Existing heat engines waste about twice as much Q as they convert into W_mec