Thread: isuzu & LPG

Originally Posted by bee utey

Thank you but I'm afraid unless the d-gas owners who keep logbooks are all lying to me, they all achieve direct replacement of litres. How? Don't arsk me, I only report findings. I am talking about careful owners who do similar long trips at the same speed as before. Are there other factors applying here? Probably, but I will sit back and let you tell me where I am going wrong.

That is interesting...

Bowser metering has quite big error bars - however that should average out.

I suspect the difference may be due to the fact that the gas is switched off at idle and low temps...

Do you have any figures for customers who usually do long highway trips with heavy loads, vs those who usually drive in traffic?

There may also be an element of the placebo effect. We are also talking about a difference they should be seeing of 33% of 10-20% - so a reasonably small number.

EDIT - there may also be some confounding factors, such as efficiency increases caused by the adiabatic cooling of the LPG.

Originally Posted by isuzurover

That is interesting...

Bowser metering has quite big error bars - however that should average out.

I suspect the difference may be due to the fact that the gas is switched off at idle and low temps...

Do you have any figures for customers who usually do long highway trips with heavy loads, vs those who usually drive in traffic?

There may also be an element of the placebo effect. We are also talking about a difference they should be seeing of 33% of 10-20% - so a reasonably small number.

Most of the figures returned were without heavy loads on long trips. E.G Adelaide-Ceduna return, Adelaide-Melbourne, Adelaide-Newcastle return. I cheerfully admit I have a small sample size and would welcome more rigorous test results. City results are not conclusive so far as most owners report enjoying the improved acceleration to allow for exact comparism. One owner reported parity useage with a Rodeo 2.8TDi in the Adelaide Hills, and he is a very conservative driver. That was after I reduced the gas fuelling at his request as the extra power was embarrassing. (My first diesel, 3 years ago, learnt a lot)

Having observed low temp operation, LPG causes rough running and lotsa smoke, as per Dougal's test. I don't yet install low temp cutoffs but it sounds like a good idea. Something to do later. I instruct owners not to use LPG for full power until warm, which is of course good for a diesel anyway. By tuning the LPG delivery for the middle of the power band I waste as little as I can.

Just saw your edit, the ratio of LPG/air (0.4% by Dougal's calcs, 0.3% by mine) is chicken feed and the LPG is introduced as atmospheric pressure vapour in any case.

The real interest is not so much comparing gas on/gas off economy on the same vehicle. But comparing fuel consumption to similar vehicles used in similar ways.

Saving 2 litres/100km of diesel doesn't mean much if it was already using 2 litres/100km more than similar vehicles. But if it was already using similar to other vehicles it can.

Which is why I'd like to see tests done on a rolling road dyno. I'm frankly surprised that such tests haven't been published because if the claims made were true and proven, they would be a huge marketing point.

Originally Posted by bee utey

City results are not conclusive so far as most owners report enjoying the improved acceleration to allow for exact comparism. .

Thanks for all the info. However re the above - since you/we are interested in comparative fuel consumption, city driving/stop-start/fast acceleration is just as valid.

Originally Posted by isuzurover

Thanks for all the info. However re the above - since you/we are interested in comparative fuel consumption, city driving/stop-start/fast acceleration is just as valid.

Only once was I given city figures and I totally agree with you they would be good to have. Need to check their log books again!
People mainly like the extended range on trips, in the city one tends to switch off the economy nerve. I know I do.

Originally Posted by Dougal

The real interest is not so much comparing gas on/gas off economy on the same vehicle. But comparing fuel consumption to similar vehicles used in similar ways.

Saving 2 litres/100km of diesel doesn't mean much if it was already using 2 litres/100km more than similar vehicles. But if it was already using similar to other vehicles it can.

Which is why I'd like to see tests done on a rolling road dyno. I'm frankly surprised that such tests haven't been published because if the claims made were true and proven, they would be a huge marketing point.

this has been done


as per this page

Originally Posted by slug_burner

this has been done


as per this page

I can't see any fuel consumption numbers there???

A blind monkey with a spanner can get those sort of figures out of a VE injector pump.

Originally Posted by slug_burner

this has been done


as per this page

miracle of miracles - they get more range out of the same amount of diesel by adding another fuel source, plus re-tuning the engine to cater for more fuel gives more power... Sheesh anyone can improve the range of any car by putting another fuel tank on it... in terms of economy, gas is cheaper per joule that diesel, but in terms of energy, 1 joule of energy from gas = 1 joule of energy from diesel, it cannot chemically or physically be any other way.