Liquefied Petroleum Gas

Liquefied petroleum gas (LPG) is a combination of several hydrocarbons. The main component is propane (chemical formula C3H8) with smaller amounts of ethane and butane.

Q. Which Cars Can Use LPG?

LPG may be used within a modified internal combustion engine. The majority of cars and car-derived vans which operate on LPG are conversions which can work in bi-fuel mode, i.e., the engine is able to operate on gas or petrol. The older bi-fuel conversions usually did not perform effectively as the engine was optimised for petrol operation. However, recent versions use electronically controlled gas-injection systems.

The great advantage of bi-fuel operation is that vehicles become less reliant on an LPG refuelling infrastructure and you can use them in areas where gas is not available. Bi-fuel cars do not achieve the full emission benefits offered by LPG because a compromise in engine tuning is necessary for both fuels.

Used alongside a spark-ignition engine, LPG can be added to the airflow or injected into the cylinder in liquid or gaseous form. The gas mixes instantly with air, enabling a fuller combustion than that with conventional liquid fuels. In many respects, the engine performance of present bi-fuel and dedicated LPG vehicles are similar to that of conventional cars. Using LPG has several advantages, including an extended engine life due to reduced engine stress and burn characteristics. Conventional (petrol) catalytic converters are used by the majority of bi-fuel cars. On the other hand, dedicated LPG vehicles use catalysts which are optimised for the gas, lowering vehicle emissions more so.

The most significant difference between gas and conventional cars is the method of fuel storage. You need a pressurised tank because LPG is a gas at room temperature. The fact that LPG liquefies under moderate pressure is a reason why it is popular over other gaseous fuels. The gas/liquid mixture is normally stored in cylinders at about 10 bar. For car conversions, LPG tanks are cylindrical and located within the boot space or doughnut-shaped to fit into the recess, usually occupied by the spare wheel.

As they are pressurised, these tanks are much heavier than conventional fuel tanks in the same range. Even though these tanks are of a similar volume to petrol/diesel tanks, they can be problematic for bi-fuelled vehicles as two tanks need to be accommodated. This results in the weight of the extra cylinder slightly increasing the fuel consumption and somewhat reducing the size and weight of luggage which can be accommodated.

Liquefied petroleum gas is known to be a tried-and-tested green car fuel. Presently, there are 4 million plus vehicles using LPG in Holland, Italy, the former Soviet Union, Australia, Japan South Korea, Canada and the USA. Here in the UK, there are 100,000 plus LPG vehicles in use. The majority of LPGs are cars and light-duty vans and many of them are bi-fuel.

Q. What do LPG cars feel like to drive?

An LPG car drives very much like a conventional car. The controls are on the whole the same: the starting, engaging as well as stopping the engine are all as per a normal car. The key additions include a switch which is normally located on the dashboard or by the gear lever, enabling the driver to choose LPG or petrol operation, as well as a fuel gauge which highlights the remainder of both the fuels left.

Q. How do I refuel a LPG car?

Once the car in position, you need to connect a flexible hose between the dispenser and the car; this locks into place creating a sealed system. You pre-select the amount of LPG that you need prior to the gas being dispensed automatically. Please note that it is considered advisable to get a person who knows what they are doing to go through this procedure with an LPG car owner. It soon becomes second nature and, with a few attempts, becomes like conventional fuels.

Previously, the main problem with using LPG in the UK is that there were only a handful of refuelling stations. However, that is not the case any more; there are currently 1,200 LPG filling stations in the UK; approximately 10% of all refuelling stations provider LPG.

Q. Is an LPG Car Better for the Environment?

In comparison with petrol cars, greenhouse gas emissions from LPG cars are lowered by the gas' low carbon content, which more than balances the comparatively high fuel consumption of LPG cars (litres per mile), which is about 30% more than for petrol. Taking into account carbon dioxide emissions, tests highlight that bi-fuel LPG cares account for approximately a 15% reduction of life cycle greenhouse gas emissions (per km) in contrast to petrol cars.

LPG cars also produce fewer emissions.

Q. How much does an LPG Car Cost to Own?

Certain ownership costs for LPG cars are more than petrol ones, due mainly to their more expensive purchase price if new and due to the cost of conversion of an existing car. The purchase prices/conversion cost is between £1,200-£2,000. You can also save about £50 on the road tax. The depreciation rates for LPG cars are also considered to be lower than the petrol equivalent.

Q. How much do LPG cars cost to run?

The main reason for opting for LPG cars has been the lower fuel costs as opposed to environmental reasons.

LPG is to be found retailing at about 45p/litre. Please note that the energy density of LPG is about a third less than that of petrol. Hence, a greater volume is needed. Given the energy content of LPG and the extra amount of fuel required, the price of LPG is about 60p a litre or 30% less than petrol.

There is a further incentive in London as you only pay an annual £10 congestion charge for an LPG car. Given the £8 daily congestion charge, this means you could save yourself £2,000 p.a.

Q. Where can I buy a LPG car?

The suppliers of LPG cars are to be found on the Energy Saving Trustís Powershift Register. There are LPG cars manufactured by well known companies like the Ford (Focus), Citroen, Vauxhall's 'dual-fuel' cars (Astra, Corsa, Vectra and Zafira), Nissanís Primera, Mitsubishiís Colt as well as Peugeot and Rover.

In terms of after-sale conversions, lots of companies will convert your petrol car to LPG. Make sure that you choose a company listed on the PowerShift Register, or recommended by the Liquefied Petroleum Gas Association.