A carnot engine operates between two heat reservoirs at temperatures th and tc. an inventor proposes to increase the efficiency
by running one engine between th and an intermediate temperature t and a second engine between t and tc using as input the heat expelled by the first engine.
The efficiency of the first Carnot engine is n1 = 1 - Th/T The efficiency of the second Carnot engine is n2 = 1 - T/Tc The total efficiency of the engines put in series is n = 1 - Th/Tc <span />
