I don’t believe diesels are more efficient. Diesel fuel has more BTUs per gallon than gasole and therefore more miles per gallon. It makes use of a more powerful fuel.
Thanks for the feedback, I'm not really much of a car guy, so I don't keep up on these things. But I do know about performance in steam power stations, hence my desire for normalized performance measures.
Gasoline engines are typically only 25% efficient while diesel engines can convert over 30% of the fuel energy into mechanical energy. The common margin is 40% more MPG for an efficient turbo diesel. Diesel engines are more efficient because they have much higher compression ratios 20:1 for a typical diesel vs. 8-10:1 for a typical gasoline engine. The life of a diesel engine is generally about twice as long as that of a gasoline engine, due to the increased strength of parts used, also because diesel fuel has better lubrication properties than gasoline. Another reason the diesel cycle is more efficient is because there is no ignition system to energize. As for the higher price of diesel fuel, that is due simply to a higher tax structure. Diesel fuel actually costs less to produce because it is refined less than gasoline. Now do you believe?
Doesn’t the fact that diesel engines run “cold” mean they lose less energy to waste heat?