Hybrid cars: driving by Diesel and electric power

How to calculate one litre Diesel to electric power? Why are hybrid cars so fuel saving? What costs 1 kWh mecahnic energy for mobility?

Full power - partial power - cold engine

A modern Diesel engine can produce at ideal conditions 4 kWh mechanical energy. But the every day usage of a car is significant different from ideal conditions. The ideal conditions are also different from an energy saving driving style. Quantity discount, less Diesel per kWh at full power. Who glides softly uses much less kWh, but each kWh has to be paid with more Diesel.

Minvan below 3 litre at constant efficiency

Let's take a typicall minvan with modern Diesel engine. I hope 2,8m² front area, cw=0,35, 1800 kg weight and 1% rolling resistance and 38% efficiency to the wheel on the street are typical values.

For real 180km/h shows teh calculation 82,5 kW power demand and 12,06 l/100km. The same calculation for 60km/h shows 5,72 kW power demand and 2,51 l/100km. Wow! A minivan as a 3 litre car! But this is not the reality, because the eingine has at low poer demand less efficiency. At warm engine will sohw up 4 to 4,5 l/100lkm on the fuel economy instrument. It's even with a tmpomat hard to find out, because even 0,2% uphill would increase the power demand by 10%.

Cold engine, low power demand, 1/3 efficiency

Constant 60km/h with a cold engine in winter, and the fuel economy instrument shows 7,5 l/100km. One pays per kWh mechanical energy 3 times the price compared to full power with warm engine on the high way.