cooljustin

Firstly, I googled, read & read again on some of the info that I could excavated in archive, but there are still not enough information regarding LPG conversion on W12.

Let me explain why I've come across the LPG conversion concept.

1. High octane gas price in my country is relatively high compared to other countries. (USD 2.2 ~ $2.4 per litre)

and there is a high chance of it going even higher near future, whereas the LPG price about a half of that price.

2. Not all of drivers(citizens) are allowed to modify their vehicles from petrol to LPG. Only a minority group of people including taxi drivers(companies manufacture LPG powered cars for taxi drivers), disables and war veterans. My father got involved in fighting for the U.S. in Vietnam so I am allowed for such privilege.

What I am really afraid is that, am I going to lose a true W12 feeling & NA power once I convert the A8L into an ordinary LPG powered car?

Is there any risk for blowing the cylinder head or gasket or other misfortunes involving engine troubles or malfunctions due to excessive heat?

If I go ahead with the LPG conversion, I think I will become the first LPG powerered A8L owner(W12) in the country.

There is one W12 which went through a CNG conversion and the owner seems quite happy with the outcome.

I am attaching some pics of this CNG converted A8.

I really don't like how they drilled on the engine but they say it was inevitable. I also have to get a set of open air-filters to replace the stock enclosed box since there isn't much space to accommodate LPG conversion parts.

It's really ruining the engine bay look though...

mishar

First thing is if it could be done with W12. It has to be incorporated into very sophisticated system. Next question is how much it would cost. Than, you will loose some power and burn more fuel (15% - 20%), so it offsets savings to about 30%. Now, installation price, average millage you drive and 30% of a gas price will give you how long it would take to pay itself and start saving.

I believe that you have to go to certain pumps to fuel and you will have big tank in your trunk.

In my opinion driving W12 and saving on fuel doesn't go together. Diesel would be quite a different story, but there is no such conversion.

twentysevenlitres

I want to know what Country you are in that offers such conversion restrictions??

Anyway Mishar's info is a bit 1990's...

LPG has come a long way in recent times:

First of all, there are two types of LPG conversion that you can consider for such an engine:

1. Vapour Injection
2. Liquid Injection

(There is a third system called a vapour ring which is a venturi-ring that sits in the intake in-front of the throttle-body, but they are very old fashioned, very inefficient and are prone to back-fire and other nasty things in high-tech engines. They will also suffer from insufficient power through-put for your engine - just think of it as a very inefficient carburettor).

Vapour Injection:

• Came into common use in the 1990's
• Looks very similar to the "CNG" system in those photos
• Requires a fitting to be tapped into the inlet manifold above the inlet valve/s (just like a fuel injector for port injection) with hoses feeding back to a distribution housing near the liquid/vapour converter.
• Results in a 0-5% power loss (nearly inpercetable)
• Results in around 20-30% greater fuel use (which is of course offset by cheaper fuel cost).
• Cheaper conversion cost (in Australia, about $4000 minus a government rebate of about $1500)

Liquid Injection

• Came into common use in the mid 2000's.
• Feeds liquid LPG right up to the inlet manifold.
• Requires the fitting of an electronically controlled "Gas Injector" into the inlet manifold right above the inlet valve/s (again, just like a port injector).
• This system will look bulkier than vapour injection, but is superior in power and economy.
• Uses cars own computer with a piggy-back system to control gas injection.
• Results in 5-10% power GAIN.
• Results in 10-20% greater fuel use (again, offset by cheaper fuel).
• Much more modern and more efficient system
• More expensive conversion cost (in Australia, about $6500 minus a government rebate of about $1500)

Engine:
LPG has a greater RON than unleaded petrol, but gets slightly less work out of the fuel, which explains the greater fuel use.
LPG is also much cleaner in emissions than petrol (mainly why I'm surprised by your Country's restrictions)
Engine longevity is not effected.
Often runs cooler due to cooler air/fuel mix as a result of LPG being cold. Will require spark plugs 1-2 temp ranges cooler than ones you are running on petrol (not vital, but will achieve optimum running).
In fact, LPG does not create as much carbon deposits as petrol, and has less impact on oil contamination. Oil looks cleaner longer - you can see it! Potentially this could lead to longer oil-change intervals, but in practice, just keeps the oil in better condition within the service interval.

Complexity:
The conversions aren't that complicated. Mainly they consist of the tank and fuel lines (which are pressurised), with a converter under the bonnet (hood) somewhere (for liquid-gas conversion for the vapour system) and feed lines to the inlet manifold. The liquid injection systems don't even use a convertor, and do it all at the injector.
An electronics black-box will interrupt the fuel injectors and control solenoids for LPG flow, or in the case of liquid injection redirect the injector signal to the LPG injector, and if required trick the ECU to prevent injector or engine faults.
A filler port will need to be installed somewhere, often it can be incorporated into the existing fuel filler flap.
Just be aware that the fuel pump (petrol) will still run the whole time and keep the fuel rail pressurised, so keep plenty of petrol in the tank.

LPG Tanks:
LPG will require the installation of a fuel tank in the boot (trunk).
However, modern donut tanks can be installed into the spare wheel well, minimising impact on boot storage (though obviously impacting on carriage of the spare wheel). These will be restricted to about 60 usable litres (LPG tanks can only be filled to about 80%, due to pressure problems with thermal expansion), with a range restriction based around that amount of fuel.
A larger in-boot tank can be installed behind the rear seats. 80+ usable litres in these tanks, but do take away boot space. You will still have access to spare wheel well though. I would recommend removing carpet before installation, otherwise the rear portion will get bolted down! This type of install will also restrict access the the fuel-pump (just something to consider).


Misc:
Also, CNG systems are quite suitable for diesel - loads of Buses around the world use CNG as a fuel.
In Australia and the UK there is a growing market for "Dual Fuel" Diesels using LPG as a supplementary fuel to diesel (ie both are used simultaneously - diesel igniting the LPG). Requires quite complex fuel management and I think is only suitable for common-rail diesels. Cleans up emissions, increases range and reduces running costs.

That "CNG" system on the W12 in the photos looks suspiciously like a Vapour injection LPG system. Are you sure it's CNG? I've never heard of car CNG systems... LPG is much more efficient in terms of fuel storage.

And finally - Of course LPG requires specific pumps at a petrol station... It's a totally different fuel!
Pumping time is a bit slower than petrol, but only around a minute longer to fill the tank. I can only imagine that CNG must take about 20 mins!
Just make sure you have one nearby to make it worth your while.
Don't fret about long road trips either, as nearly all LPG conversions are "Dual Fuel", meaning that when you run out of Gas, you run on Petrol!
(By the way, Aussie's don't call petrol "Gas", because we have been running cars on actual GAS (LPG,which is butane/propane) for 40 years!)

mishar

Well, if it has to be long, mainly useless to the OP and partly inaccurate in order to be 21st century than I am glad that mine is oldish.

cooljustin

Many thanks for your advice Mishar. I think Mr. Marty didn't mean to offend you sir, but LPG (or LPI) conversion has vastly improved over the past years. Nowadays, a lot of LPI modified cars are equipped with a donut tank which can be nicely accommodated in the space for a spare tire.


Initially I wrote about a page full of replies and explanations about LPG regulatory measures and things but pressed the wrong button and oops, it's all gone. So I will keep it short.

1. as Mishar kindly noted, I need to carefully calculate the break-even point for spending a lump sum of money for a LPG or LPI to be more precise conversion. It will cost me about 4grand (USD) which is relatively cheap but I hardly use my A8L since I commute to work by subway.

2. Money is not a big issue nor availability of LPG stations but I am more concerned about possible risks involved in LPG system in the long-term.(MY A8 has a mileage of about 70,000km, pretty low for its age).
i.e. excessive heat in the engine bay leading to blowing up head or head gasket etc.

Regarding Marty's few dubious outlook, Yes, I talked to the guy and even test-drove the vehicle, it is a CNG-converted A8 W12, very rare thing.

But this is not what I pursue since there is absolutely not spare space in the boot after accomnmodating a huge CNG tank.



But the vehicle provides super-a-like drivability compared to the original petrol status and more efficient in terms of gas- consumption mileage.

I am from Korea and unlike petrol LPG is not comprising of any taxes (i.e. VAT and education tax(weird huh.. yep we pay education tax for a liter of petrol)
that is why only a minority group of people are granted for LPG or LPI vehicles.

finally what I am looking at is the LPI conversion (the latest tech) and I think I am going to bite the bullet and go ahead with the conversion.

I will come back and let you know the outcome (hopefully positive though )

Many thanks for your two cents gentlemen.

aTOMic

Justin,
I have learned a lot from the A8Parts forum; there are a lot of guys there who have done this! Surprised at all the advantages, best of which is the elimination of the carbon buildup problem on the FSI engines.

Tom

snapdragon

"Are you sure it's CNG? I've never heard of car CNG systems.."

Virtually all the cars in Iran are CNG as they have 400 years worth of gas supplies.
It is 10 cents a litre. It is just like lpg, but never becomes a liquid.
The CNG stations look like gas stations but with a shipping container sized compressor with big radiators and fans compressing the gass at one corner..

In fact, here's one being filled.
http://www.autoblog.com/2012/09/10/c...wner-fills-up/

parkrog2

Here in Utah CNG is cheap $1.35 per gallon. Can even fill car from home gas line. NO Taxes. Many conversions plus tax credits for EPA certified installs. Big for pickups and suv because of tank size.

twentysevenlitres

No I didn't, sorry Mishar.

I actually meant to draw attention to the Dual Fuel Diesels that are getting around now for Mishar's benefit, but got carried away with the rest of my post...

Anyway, In Europe, they've started doing a few diesel cars, but in Oz it's still mainly Utes and a few SUV's. I can only imagine the engine management gets a bit complicated when you try to get the ECU to deliver less diesel through the injectors.

Cooljustin,
At least as far as LPG is concerned (in Australia, LPG is correct terminology) I wouldn't be concerned with under bonnet or engine temperatures - in fact heat aids the liquid to gas conversion required before combustion can take place.
If using a vapour system, it will have an under-bonnet converter which actually uses coolant from the car's cooling system to heat the unit.
However, the latest technology is definately liquid injection, and this delivers a very cool charge to the inlet port.

Cars in Australia have been running on LPG for over 40 years. Problems are very few and far between provided the conversion is done properly.

cooljustin

Thanks for your great knowledge in LPG conversion. I will give it a try then. I also heard that our A8 engines are more resilient to stress and overheat than other brands or aren't we?

Apart from driving around town, even if I don't wonder around and just stay in my garage while the car is running, I can sense that it just devours my bloody (excuse my language) expensive high octane fuel, gurgling into its cylinders.

We normally use our vehicle for commute but it also serves a wide array of purposes while pulling over to the side of the road, you know what I mean..

Regarding aTOMic's suggestion, many thanks I have already visited the forum yet still haven't found any useful information about LPG conversion on W12. But I will keep diggin~ thanks.