(G) very economical diesel

Sorry guys but I think there is a misconception about the diesels here...now, I'm no tech but I DO know that the longer a machine takes to warm up the MORE efficient it is.

EVEN modern petrol injection engines which are now called 'lean burn' still require a richer mixture in a cooler cylinder, before, when you used to have carburettors the engine used to dump fuel into the manifold when cold and when you pulled the choke (Hence that horrible fuel smell you got on early morning starts years ago!) It's NOT so bad on modern day petrols but is still glaringly inefficient this is because petrols have much less of a 'compression ratio' than diesels. Petrol 10 to 1 (variable) whereas diesel 20 to 1 (constant).

Compression ignition Diesel is not inefficient when cold because of the the high compression ration about...3000ibs per square inch. This causes the fuel to be already extremely hot and thats why its called 'compression ignition'; does not need a spark plug the glow plug is there to warm the viscous, thicker fuel before it enters the head.

On full or part throttle, diesel uses the ONLY the amount of fuel that is necessary for that amount of power but a petrol will reduce it's compression ratio and the mixture will become richer (more fuel less air) otherwise you'll stall, petrol is only at it's maximum efficiency when you're 'flat out'...(full compression ratio).
Petrols also wash the lubricating oils off the cylinder because petrol is a solvent and if its rich and not fully vapourised then it will dissolve the lubricating oil leading to engine wear, hence the shorter petrol life span in comparison to diesel.

Manufacturers use all their expertise and resources to improve this universal inefficiency problem with petrols, clever ECU calibrations, mixtures, all sorts but diesel is STILL more efficient because of it's basic and rather simple operating principles.

The ONLY element to a diesel engine which can make it negligibly less efficient when cold is the Diesel Particulate Filter and the Catalyst, which require full operating temperature to feedback to the engine more efficiently. However this part is heated FAR quicker than the engine itself because it's an exhaust management element, and exhaust leaves the engine piping hot from start.

So don't worry if you're pottering along in your 1.3 which I will be in the next 48 hrs and after 10 miles you're still not up to temperature. You will NOT be burning more fuel ( as you would be in a petrol,) you are in fact witnessing the miracle of a super efficient engine!

I now apologise if I have any of my facts wrong, I DO know that petrol injection technology and engine management systems have come a long way and I am pleased to hear high MPGs for the 1.2s however I feel that it is a common misconception that diesels behave in the same way as petrols whilst getting up to temperature and I thought I might try to explain it....Sorry if I'm mistaken in some areas.

Well said about the cold efficiency Baerius! I knew I wasn't talking rubbish. You managed to put very eloquently just what I was thinking...

I will defo be posting my mpg on here soon....can't WAIT!

Mine is currently showing an average of 70.3mpg. Just as well with the fuel shortages up here.

Cheers

D

70.3...that's...well....beautiful

Er....I'm supposed to be getting mine on Friday, they 'sort of' promised me a full tank o diesel....don't think I'll be getting that now! Fuel shortage just when I take delivery of my car...tsk