CNG / LPG Engines

[RSmith]

CNG / LPG Engines. I know as much about these things as George Bush knows about global economics.

What kind of noise do they make? Can they be easily modified and how? How to do they stand up to their petrol / diesel counterparts?



Richard.

 

[HDi fun]

CNG / LPG Engines. I know as much about these things as George Bush knows about global economics.

What kind of noise do they make? Can they be easily modified and how? How to do they stand up to their petrol / diesel counterparts?



Richard.

Firstly, let's deal with road cars. 99.9% of alternative fuel cars will be petrol derivatives that have been converted to run on LPG. This can be a factory dual-fuel model, although aftermarket conversions are more common.

CNG is a very different beast, Saab, I believe, offers CNG compatible models now. CNG filling stations in the UK are very rare, LPG ones less so.

Noise wise they will sound just like the standard car running on petrol.

In the commercial HGV arena there's a growing number of operators who supplement diesel with CNG or LPG. This, I believe, is supplied in relatively low ratios compared to air (which contains oxygen, of course) and compressed along with the air. The diesel ignition process is still triggered by accurately timed fuel delivery. The idea is that less diesel is used because the compressed air/CNG provides optimum power with less use of diesel. Such an engine will sound like a diesel engine, although in 6 or 8 cylinder forms the overriding sound is that of the turbochargers anyway.

IF you are looking at the dual fuel aftermarket option then you need to start with a petrol car. Turbcharged ones are much more expensive to modify to operate on both fuels.

Start with a car that you plan to use for at least 100,000 miles to make the investment truly worthy.

 

[obi_waynne]

Fuel economy is not quite as good with these fuel types but the much lower initial cost more than makes up for this.

 

[aston]

I have one lpg (a vw camper) and owned a lpg grand cherokee in the past, sure the fuel is cheaper, after 4000 miles the conversion has paid for itself but to be honest it never runs right and therefore there is the hassle of going to the garage and then the expence of the mechanic. One installer told me the technology is just not quite right. However it feels great when you go to the pumps and fill up for £20 and the person next to you is looking at £50

 

[2fast2catch]

I had a vectra gsi (2.5 v6) running LPG, never had any problems with the LPG conversion.

you do need to have some petrol in the car as will normally need to start engine running petrol then swap to LPG after a couple of minutes.

running lpg affected the performance very slightly, had a bit more lag to it so used to switch back to petrol if i wanted to floor it for any reason.

best advice i can give is if your going to have a conversion done pay the money to do it properly, yeah it will be expensive but if your doing it due to doing high milage then it will pay for itself. plus having it done properly and getting all the certificates to prove it has been done properly will pay off when you go to sell (if you sell the car).

 

[aston]

much cheaper to buy a car allready converted as the lpg has no resale value

 

[2fast2catch]

much cheaper to buy a car allready converted as the lpg has no resale value

i found it does add a bit to the price of the car over here when it comes to sell - prob due to LPG being less than half the price of petrol

 

[RSmith]

Hi guys,

Okay... I probably should have given a bit more info. I'm trying to get a CNG engine imported from overseas to use in a one-off vehicle. I don't think it's a petrol to CNG converted engine. It's just a CNG engine off the factory line. Can I run a CNG engine on LPG? Or are they two completley seperate things?

 

[HDi fun]

You cannot run a CNG engine on LPG. The gases are radically different in terms of vapour point and saturated vapour pressure, despite the similarity in energy/unit mass of gas.

The injection systems are radically different in order to deal with this.

CNG filling stations are very rare in the UK which may further limit your options.