Running your petrol car on liquified petroleum gas (LPG)
Last updated Wednesday 30 April 2008
Put your foot on the gas for cleaner motoring
Lower fuel duty means LPG costs about half the price of unleaded petrol at the pump, and it produces 15% less CO2. It also produces less energy than petrol so you need more of it, but on a typical dual-fuel vehicle doing 9,000 miles a year, your annual saving could be as much as £240 - soon making up for the cost of converting your engine.
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Saves 430kg per year for the average car
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Cost £1,400, saves £240 a year
In this article:
- How does it work?
- How will it make a difference?
- What's the debate?
- What's stopping me?
- How do I do it?
How does it work?
Pub Fact
- One diesel car produces as many particulate emissions as 120 LPG cars, according to the UKLPG
- There are currently estimated to be four million LPG-fuelled vehicles in Europe, with 140,000 of these on UK roads
- All the taxis in Tokyo and buses in Vienna run on LPG
LPG is a (relatively) carbon-lite mixture of propane and butane, produced either as a by-product of oil-refining, or from natural gas fields. At room temperature it's a gas, but under only moderate pressure it turns into a liquid, which means it can be transported and stored in much denser form.
Cars converted to run on LPG still have a petrol tank. A lever lets the driver select LPG or petrol operation, and a fuel gauge shows the remaining amount of both fuels.
For more information on LPG, see the UKLPG website.
How will it make a difference?
It will reduce your carbon emissions, for a start. According to the Energy Saving Trust (EST) and Calor, CO2 emissions from a car converted to dual-fuel will be 10% lower than when the vehicle runs solely on petrol. LPG is good for air quality all round, producing 80% fewer nitrous oxide (NO) emissions than diesel, lower methane emissions and zero particulates - though it can't match diesel for cutting CO2. In fact, EST estimates it produces 10% more.
You can also avoid noise pollution: an LPG-fuelled engine is about 50% quieter than a diesel one.
Financially, the sums add up too. You get fewer miles per litre with LPG than with petrol or diesel but there's less duty to pay so it's cheaper at the pump and works out cheaper overall, even factoring in mileage.
On top of that, some London drivers of LPG cars on the PowerShift register get the additional perk of a 100% discounted congestion charge. But check with Transport for London for updates on the law.
What's the debate?
In some ways, LPG is only a halfway house: it's not a renewable energy and as a by-product of commercial oil refining it relies on that emission-heavy industry. (You also continue to use petrol alongside LPG in your converted car.)
The financial incentive is diminishing, if only slightly, as fuel economy in petrol engines continues to improve. And LPG taxes are on the rise. Tax on LPG for road use increased by 2.25p in September 2006, reducing the differential between LPG and conventional road fuels by 1p.
There are also very small concerns about safety. The gas is highly flammable and accidents can happen, even though the tank is designed to take a major impact by altering shape instead of bursting. Currently, no LPG cars are allowed through the Channel Tunnel, although this is under review.
What's stopping me?
"The usual - expense. How much will it cost to convert?"
About £1,400, but on average you will save £240 per year on cheaper fuel.
"Can my car be converted?"
Probably (if it's a petrol car). Most petrol cars can be converted, though LPG is only really suitable for relatively young cars. Conversion is unrealistically expensive and technically tricky for diesel cars, and LPG is not a suitable fuel for heavy vehicles. Make sure a reliable company does the conversion (check on EST's PowerShift register).
Conversion may invalidate your manufacturer's warranty - but there are ways round that (see 'How do I do it?').
"What happens if I get stranded 100 miles from the nearest LPG supply?"
It's increasingly unlikely with LPG now available from at least 1,300 (one in nine) petrol stations across the UK - but in any case when the LPG tank runs dry your car will seamlessly switch to your petrol tank. Of course, you could run out of petrol too, but there's no helping some people. (See 'How do I do it?' for finding your nearest LPG station.)
An LPG car can admittedly be a pain at the pump (when you finally get there). Because there must always be a level of petrol kept in the car to ensure ignition, you have two tanks to refill, which may mean having to go to two different pumps.
"What about my pulling power!"
Well, it's true that LPG gives you a little less zip than petrol, and is unlikely - as Jeremy Clarkson would say - to "snap knicker elastic at several paces". But let's assume for a moment we're above all that.
In fact, even the most ardent petrolhead will be unlikely to notice the small loss of power (generally 5%) at full throttle when in gas-fuel mode in a dual-fuel car.
How do I do it?
- Calculate your potential savings on Drive LPG
- Make sure your car model is listed on the PowerShift Register if you want to apply for a congestion charge discount
- Get a quote for conversion and confirm whether it voids your warranty. Even if it does you can purchase an engine warranty for about £70-90 a year
- Drop your car off to be converted for two to three days; inform your insurer and the DVLA
- Check out the Energy Savings Trust's map to locate your nearest LPG refuelling stations, either at home or in Europe
- Many insurance companies do not charge an excess for LPGA-approved conversions - Drive LPG provides a list of these companies and full information on insurance
- Bone up on refuelling with LPG with the step-by-step guide at the DTI's Drive LPG campaign site
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Other advantages of LPG for automotive use include a much cleaner engine, the oil remains clear for many thousands of miles. This is due to the clean burn of the LPG, so rather than change the oils and filter, only the filter need be changed, also the abrasive components deposited in the oil are reduced, thus reducing engine wear. Now for the bad news. LPG burns hotter than petrol, this leads to more, not less Nox. It's high temperature burning of air, of which nitrogen is a constituant, that creates oxides of nitrogen (Nox) so I think the calim for lower Nox is based on poor science. Spark plug life can be reduced unless 'hotter' plugs are used, although these will be less suited for petrol use. I have seen a few engines which were designed to use unleaded petrol , running on LPG and suffering valve damage due to the heat. This is why you should occasionally run on petrol.
I run my Campervan on LPG, saves me money and reduces my impact on the planet. there are over 4 stations in my town alone selling LPG, so no shortage of supply!
Tricky to find it, but our LPG car saves a lot of cash as well as being better for the environment. xxx
© MMIX
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