On 05/03/17 20:15, Chris Green wrote:
ARW wrote:
On 05/03/2017 18:06, charles wrote:
In article ,
Chris Green wrote:
charles wrote:
I have been driving a diesel car for nearly 30 years (not the same one).
Originally bought for 400 mile runs up the motorway and kept because I
still do regular motorway runs - the 400 mile one is down to 2 or 3 time a
year,

Isn't that the one sort of journey where a diesel is very little if
any more economical than a petrol engine? Diesels win on economy for
stop start driving, hence the London taxi.

general round the local area 44mpg, motorway 56mpg - I doubt if any cars do
that.



My Scudo van does about 44MPG to and from work (usually nice clear A
roads and B roads and a 20 mile journey). About 30 to 35MPG around town
and about 25MPG on the motorway. I can improve the motorway MPG if I
slow down to less than 90MPH.

I *think* if you compare a diesel at a steady 70mph on the motorway
with a similar powered petrol engine at the same speed there's very
little to choose between them. It *used* to be that the petrol engine
was more economical but maybe the pressure to make better diesel
engines has meant that they've caught up.

It's a great pity that the 'lean burn' developments of petrol engines
petered out.

Diesels have always been more economical mostly because of the higher
temperatures and pressures in the combustion chamber.

Only at full smoky throttle when the air fuel ratio was at its lowest
did they start to chew fuel, and turbocharging fixed that.

When was the last time you saw a petrol powered commercial vehicle of
more than 3 tonnes?

Lean burn stopped because of NOx emissions.

Petrol engines are at their most efficient at higher throttle settings
as well. Diesels like to be a tad over tickover to be really parsimonious.



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