5. Hybridization benefits, optimizing efficiency and pollutants

5.1 Energy efficiency of heat engines

The main operating parameters of heat engines are the exchange time with the "hot and cold sources" and the load or mass of working fluid involved. For combustion engines, this translates into operating speed and the quantity of fuel burned per unit of time or per cycle.

When the exchange time is longer, i.e. at low engine speeds, heat exchanges with the walls are, in relation and all things being equal, greater than at high engine speeds. Energy efficiency is therefore degraded at low speeds by the relative importance of heat exchanges. At high speed, losses linked to the transfer of the working fluid increase (turbulence and pressure drops), again in relation to the other items involved in the overall energy balance....