Many engine manufacturers claim the most efficient operating points in their specifications. An engine efficiency map BSFC (brake specific fuel consumption) is much more detailed. Then engines can be compared to each other to find the best one for a particular application. The calculations below are more instructive than precise. In simple terms the chemical energy in the fuel is converted into useful mechanical power or heat.
Using the Kohler data as typical, the 34 kilowatts into the engine, produces 13.2 kilowatts of useful power. The rest is wasted heat. The important point for YankeeDiesel is how much of the wasted heat can be converted into useful power. Obviously the heat exhausted as steam is not useful. That steam goes out the exhaust pipe of a car. When cars are cold, the steam condenses in the exhaust pipe and is seen as water dripping out. The 10 kilowatts as heat from the engine block is not available. But the 8 kilowatts as hot exhaust gases is available. If just ¼ of that wasted 8 kilowatts is converted, the engine efficiency increases by 6%.