Another LPG question

[Lutz]

I note from previous posts on the subject that those that have an LPG conversion do not apparently experience a noticeable drop in power compared to the standard petrol version. However, I have just read that the 2 litre Ford Focus sold over here with a CNG conversion drops from 145PS to 126PS. Is this specific to CNG or would it apply to LPG too?

 

[mcghee]

lutz.i run an lpg grand cherokee.in everyday driving there is no noticable power drop.however,at the top of the rev range there is a drop of about 10%.probably because gas burns hotter than petrol and so will begin to detonate earlier.most people cannot tell a 10% power differential on the road though.and in the case of the jeep with a 4litre engine,the top of the rpm range is never really needed.anyone with a spare 2hours could read through golpg.co.uk and learn more about lpg than theyl ever need to know.

 

[MONKEY1]

Lutz

I drove a Volvo V40 on LPG (BI-Fuel) for few weeks and noticed NO difference in power output or acceleration in was a quiet efficient car. . It was the visit nightly sometimes at best every other day to fill with LPG which was a pain the only good point was I think I ran up more clubcard points quicker.

Safeways/ Morrisons (supermarkets) run some trucks on CNG and they develop more BHP from the same power-plant 350 bhp vs 320bhp however that's down to the pump and ECU mapping I believe

Monkeys Husband

 

[mcghee]

yes the sytem of supplying gas to an engine was until recently similar to a carburettor.now theyre starting to use separate gas injectors and fully mapped fuel/ignition.which probably gives more power than petrol because the standard engine isnt mapped for power.if it was it would still return about 10% more power at the top end.its basically because gas is harder to ignite,its difficult to get enough ignition advance at high rpm so the power falls away.

 

[CliveV]

Craig is correct - a modern conversion that allows the engines "brain" to work out what fuel it is running on will reset the timing etc so as to get the best from whatever fuel you are running on.

My conversion is on a Carburettor model and so no fancy electronics. I set my timing as for the old 5 star fuel and it runs a treat - FAR better than it runs on current unleaded even with the timing altered to suit. So once again I believe this question is answered in part by LPG being higher octane therefore an intelligent modern engine will take advantage of this higher octane fuel and get more power out of it.

The lower calorific value of LPG helps ensure the clean emissions as it burns almost completely. Compare the smoke from a diesel and/or petrol fire, then compare the soot/smoke/smell from your caravan hob. I believe this to be a pretty good indication of how clean this LPG burns.

The Aussies have been getting cleaner emissions, more power and lower running costs from LPG injection systems in tandem with diesel on their big rigs. The LPG improves the efficiency as more diesel is actually burnt.

I always understood that a CNG system was very different to an LPG system - not least because you have to plug it into your gas system at home (or somewhere) and wait a long time (hours) for the fill up to be complete as the gas has to be compressed at the point of delivery.

HOWEVER! - I read that years ago so things may be very different now. I would be interested to hear.

I like the idea of filling up via my domestic gas system!

 

[DavidW1]

Lutz,

Don't know about the Focus and CNG is a closed book except that I know you need a heavy duty tank to accept the higher gas pressure but can speak for the Vectra 2 litre and presumably other Vauxhalls are similar

Figures from my Vectra 2.0 16v handbook state only a 1 bhp difference between petrol and gas and in practice the difference in running is imperceptable. I have run this car, a 140 SRI, for over a year and can honestly say the differences in performance are insignificant but are as follows: the change over to gas is set at 15 deg C coolant so in winter gas comes in after about 20 seconds after start and summer 5 seconds - in winter cold idle on gas is a bit lumpy. And that's it, switch between gas and petrol on the move and you can't feel any difference in smoothnes or power, pick up and acceleration is markedly similar but on gas I find there is more response at lower revs - this is borne out by hand book figures on max torque for LPG at slightly lower revs.

On towing I have tried petrol and gas for climbing hills and long motorway climbs and found no difference, pull away with gas or petrol is the same.

Of course there is one major difference and that is cost - the car regulary returns 25 mpg on gas which I think is acceptable for a 2 litre vehicle mainly used as a runabout on short journies of up to 200 miles a week. I don't know what it would do on petrol as it only gets a tenners worth every 3 or 4 months: put another way that's under

 

[Lutz]

I've just checked on the specs of the Zafira 1.6 petrol and 1.6 CNG and found that the power output is 105 vs. 97 respectively, so it would appear that there is a difference between CNG and LPG operation.

 

[Lutz]

Craig is correct - a modern conversion that allows the engines "brain" to work out what fuel it is running on will reset the timing etc so as to get the best from whatever fuel you are running on.

My conversion is on a Carburettor model and so no fancy electronics. I set my timing as for the old 5 star fuel and it runs a treat - FAR better than it runs on current unleaded even with the timing altered to suit. So once again I believe this question is answered in part by LPG being higher octane therefore an intelligent modern engine will take advantage of this higher octane fuel and get more power out of it.

The lower calorific value of LPG helps ensure the clean emissions as it burns almost completely. Compare the smoke from a diesel and/or petrol fire, then compare the soot/smoke/smell from your caravan hob. I believe this to be a pretty good indication of how clean this LPG burns.

The Aussies have been getting cleaner emissions, more power and lower running costs from LPG injection systems in tandem with diesel on their big rigs. The LPG improves the efficiency as more diesel is actually burnt.

I always understood that a CNG system was very different to an LPG system - not least because you have to plug it into your gas system at home (or somewhere) and wait a long time (hours) for the fill up to be complete as the gas has to be compressed at the point of delivery.

HOWEVER! - I read that years ago so things may be very different now. I would be interested to hear.

I like the idea of filling up via my domestic gas system!

From what I've seen when CNG cars are being filled up, it doesn't take any longer than filling up with LPG. I'm just curious about the practical differences between LPG and CNG because LPG is not widely available over here but CNG is.

 

[DavidW1]

I've just checked on the specs of the Zafira 1.6 petrol and 1.6 CNG and found that the power output is 105 vs. 97 respectively, so it would appear that there is a difference between CNG and LPG operation.

I think you are rite, CNG must be less wassaname in it's burn - CliveV or Robjax claim to have the lowdown on all that stuff so maybe they wiil have a theory.

 

[emmerson2]

I think engine size may also be a factor regarding power loss. My experience with a 3.5 efi and now 4.2 efi has been that there is no noticeable difference between gas and petrol. When you've got 200 bhp to play with, 5 or ten percent isn't going to make any difference. I can't rememeber who said it, but"there aint no substitute for cubic inches" ( or centimetres).

 

[RogerL]

It appears that there's a significant difference between LPG and CNG so recommendations based on LPG aren't helpful.

 

[CliveV]

That is my understanding as well Roger

 

[rob_jax]

Hi,

Agree with Lutz, it's the same here in Holland - most if not all new dual fuel cars are CNG fuelled. A few years ago you could order a CNG or LPG based vehicle from VOlvo, Opel, etc., but not any more - I've only seen CNG offered for two years.

In the past, LPG was easier to install, CNG required more expensive installations (high pressure tank) and was slower to fill at the tank station. But those differences have disappeared, and if you have the right compressor it's theoretically possible to refill your tank from the house gas cooker.

One reason for the switch in Holland is that LPG is made from crude oil, so it doesn't significantly increase the amount of fuel produced from a barrel of crude - there is an amount of LPG in crude oil extracted during the development phase of the oil field - but to make more LPG requires the refinery to crack the naphtha fraction (petrol) and that just loses energy.

Whereas CNG is natural gas (Methane) - and there are very large gas fields off the Dutch coast.

Robert

 

[354]

very close now to getting a V6 Fronty which if all goes well will be converted to LPG. Question is what is the current cost of LPG per litre and is there any differense in power / consumption with the van on the back.

My other concern is how do you find a reputible convertor , any recomendations would be appreciated on the outer London herts / Essex area

 

[emmerson2]

Caan't recommend any one in you're area, but check out boostlpg. As Iv've said on various posts, ther is no significant difference in performance. The difference is in your POCKET and if you want to be GREEN in the CO2 saving.

This compuiter can't spell when I've been out for lunch!! Does anyone else have this problem?

 

[DavidW1]

very close now to getting a V6 Fronty which if all goes well will be converted to LPG. Question is what is the current cost of LPG per litre and is there any differense in power / consumption with the van on the back.

My other concern is how do you find a reputible convertor , any recomendations would be appreciated on the outer London herts / Essex area

Go for an LPGA approved installer that can issue an LPGA cert for insurance - main price diff will be wether you have inboard or underslung tank. Go for underslung if you need the space inside and sequential injection which is backfire free. I paid

 

[DavidW1]

Just been on the LPGA site and they list about a dozen installers for Essex and Herts - some with websites so plenty of info and choice and they are all LPGA registered.

 

[354]

Well from the postings here and the feed back I have recieved elsewhere all going well I think I have been converted (hope I dont regret it) . Going to have a test drive it a potential new vehicle next week and have had a quote of

 

[CliveV]

Hi Del

Only thing I would repeat here is that make sure the installer is LPGA registerred and that you get the "certificate of conformity" - this makes getting insurance easier because you MUST inform your insurer that the car is modified.

With the certificate this is NOT a problem - without one it very much can be.

Like the idea of the joint tank - i will be interested to here how that goes.

Merry Christmas and a cheaper traveling 2006!!