Running your petrol car on liquified petroleum gas (LPG)

Last updated Wednesday 30 April 2008

Put your foot on the gas for cleaner motoring

Cleaner, greener and cheaper than petrol, LPG could prove a quick and painless conversion if you drive a petrol car.

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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Photo: Running your petrol car on liquified petroleum gas (LPG)

Saves 430kg per year for the average car

89 Bloomers are doing this

CO2 reduction 2 out of 5

Cheapness 4 out of 5

Popularity 2 out of 5

Cost 1,400, saves 240 a year

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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.

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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.

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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.

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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.

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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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Baz, Shrewsbury 2009-02-17

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.

Alan, Hull, East Yorkshire 2009-01-09

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!

grayster, United Kingdom 2008-11-09

Tricky to find it, but our LPG car saves a lot of cash as well as being better for the environment. xxx

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Glossary terms used on this page
Air pollution
Air pollution usually refers to the presence of any chemical or particulate that alters the normal make-up of our atmosphere, causing direct threats to human health (such as breathing difficulties) or longer-term damage through its effects on our planet's ecosystem. Pollutants include smoke and dust, nitrogen oxides, methane, and the fumes from aerosol sprays and other solvents. Industrial processes and transport are major contributors to air pollution, but it can also be caused by natural processes such as forest fires and volcanoes. See also acid rain.
CO2, or carbon dioxide, is made up of the elements carbon and oxygen. It exists quite naturally in our atmosphere, as part of the carbon cycle. Everyday processes in the plant and animal world both add CO2 to the atmosphere and take it out. However, because it is a greenhouse gas - meaning it affects the temperature of the earth - the exact level of CO2 is important. Burning fossil fuels releases CO2 into the atmosphere, hence the anxiety that extensive use of these fuels is causing climate change.
Carbon is the fourth most common chemical element in the universe, and carbon compounds - in other words, carbon chemically combined with other elements - are the basis of all known life forms on earth. Pure carbon appears in many apparently diverse forms, from diamond to graphite to charcoal, but it is much more commonly found in substances such as coal, oil, natural gas, wood and peat that we use for fuel. When we burn these substances to provide energy - either directly in our homes as heat, or in power stations to produce electricity - the combustion process produces 'oxides' of carbon, including the gas CO2.
Ordinary diesel, like regular petrol, is refined from oil but it is a thicker, heavier liquid with a higher 'energy density' - meaning it offers better fuel economy. On the down side, unless you buy an air filter, diesel exhaust is a significant source of particulates and other sources of air pollution. A type of diesel not derived from petroleum is increasingly widely available, commonly referred to as biodiesel.
Emissions are the CO2 (and other greenhouse gases) produced by energy use, usually calculated and stated as an annual tally: also referred to as your carbon footprint. Your personal emissions can be direct - such as the gas you personally use to heat your home or the petrol you burn to power your car - or indirect - meaning the energy use that has gone into the products or services you buy. The latter, such as the emissions caused by the manufacture of your new TV, or the packaging your food comes in, are also referred to as embodied emissions.
Fuel duty
Fuel duty is the tax the government levies on fuel used for transportation, imposed at the point of sale.
Fuel economy
How many miles a vehicle will travel for each litre of fuel used.
Liquid petroleum gas (LPG)
Liquid (or 'liquefied') petroleum gas (LPG) is a mixture of butane, propane and other light hydrocarbons produced either as a by-product of oil refining or from natural gas fields, and used as a vehicle fuel with lower CO2emissions than petrol. At standard temperature and pressure, it's a gas but the mixture can be cooled, or subjected to moderate pressure, and is then transformed into a liquid for ease of storage and transportation. LPG is used in dual-fuel vehicles, where it operates alongside a conventional petrol tank. It is also used in heating appliances.
Methane is a hydrocarbon, the main component of natural gas and among the six greenhouse gases to be curbed under the Kyoto protocol. As a greenhouse gas it is estimated to have a warming effect about 25 times as great as CO2. (Compared to CO2 its effects are greater but last for a shorter period). As a fuel, it is used in electricity generation and in the form of compressed natural gas it can be used as vehicle fuel. Methane is produced during the decomposition of many materials in landfill, while about 16% of methane emissions are caused by livestock's digestive processes.
Nitrogen oxides
Nitrogen oxides are compounds of nitrogen and oxygen, two elements that do not normally react with each other but will do so during high temperature combustion – such as in a car engine. Examples include nitric oxide (NO) and nitrogen dioxide (NO2), which contribute to air pollution, and nitrous oxide (N2O), which is a major greenhouse gas. Although its warming effect is far less than CO2, it persists in the atmosphere for far longer, so measured over 100 years its impact is 298 times greater.
Oil refining
Oil refining is the process of taking crude oil and turning it into fuels such as petrol and diesel. Crude oil varies in its composition, consisting of hydrocarbons and other organic compounds containing nitrogen, oxygen and sulphur. Refining oil requires energy and releases air-polluting chemicals. However, the majority of the CO2 produced by oil is emitted only once it has been turned into fuel and then burnt.
Particulates - sometimes referred to as particulate matter or just particles - are tiny pieces of dust, soot and other materials suspended in the atmosphere. These can be produced naturally, by volcanoes or forest fires for example, but are also caused by incomplete combustion of fossil fuels, particularly from diesel engines. Because diesel is a denser fuel than petrol, it needs more oxygen for all its hydrocarbons to react completely, and the unburnt carbon - soot or black smoke - is emitted through the exhaust pipe.
A car enthusiast; often used to describe those who are most reluctant to limit their car use or petrol consumption.
Renewable energy
Renewable energy comes from natural sources that can be replenished and not permanently depleted - such as biomass, hydro-power, geothermal heat, solar power, wind power, and wave and tidal power - and most of which do not produce CO2emissions. They are unlike fossil fuels, which took millennia to form and cannot be replenished. navigation


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