In message , IMM
writes

"Michael McNeil" wrote in message
. com...
Grunff wrote in message

Efficiency? A mute word here. A diesel returns higher mileage because a
litre of diesel has a higher CV than petrol, no other reason.


No.
Diesel engines are more efficient for two reasons:
1) Higher compression ratio & higher cylinder pressures are
thermodynamically more efficient.
2) Lower "pumping losses" at part load, i.e. a petrol engine spends most
of its life gasping to draw in air against a partial vacuum due to the
restricted (throttled) inlet. A diesel has free flow air inlet (ignoring
turbos & EGR for simplicity).

--
Steve