While I agree that diesel engines are more efficient in energy conversion then gasoline engines I dispute the statement that difference is like 37% to 18%.

I can't find a quick source of data here but I seem to remember that when I was going through the internal combustion part of my mechanical engineering courses I learned that gasoline engines were 20-25% efficient in non stationary operation and about 30-35% when operated stationary. Stationary here means operating at a constant power output level and rotation speed.

Diesels were typically 5-10% more efficient in the same roles.

Often marketeers will add efficiency points due to the fact that a liter of diesel contains more energy then a liter of gasoline. They do this as most people are only interested in the fuel costs (per liter of gallon) of a given fuel. However these imaginairy efficiency %'s are not scientific and are indeed very misleading. They have no meaning whatsoever outside of fuel cost calculations.


Wouter