LPG and CNG were the first alternative fuels to be widely adopted for use in the UK.
These are most commonly used in dual-fuel (or bi-fuel)
mode alongside conventional petrol through use of an additional fuel tank often
located in the boot of the vehicle.
Their popularity was encouraged by the government's Powershift scheme which provided grants
to cover the conversion cost from petrol or diesel. Other attractions included a hefty
tax subsidy which almost halved the cost of the fuel and for Londoners, a congestion charge of zero.
What is it?
LPG or Liquid Petroleum Gas is a mixture of propane and butane and produces a very clean burn
with reduced CO2 output when compared to petrol cars and a substantial reduction in fine particle
and noxious output compared to diesels. LPG can be stored as a liquid at atmospheric pressure
through mild compression meaning that a large volume can be stored in a small tank.
Firstly, CNG needs to be stored at a very high pressure (around 200 bar)
and secondly it doesn't achieve the density that LPG manages in liquid form. This high pressure requirement means that a very robust tank is needed and its lower density results in the tank being two to three times bigger than that of the equivalent LPG.
CNG or Compressed Natural Gas is much less common in the British Isles than LPG even though it provides an increased reduction in emissions.
The popularity of LPG over CNG is the result of two physical differences between these fuels.
Most current UK production petrol cars can be converted to LPG. The cost of this is around £1700. Diesel conversions
are more expensive as more complex alterations are required to the engine.
New Green Fuels
When the Powershift scheme finished in 2005 the interest in LPG and CNG started to wane and manufacturers switched
their attention to the new breed of biofuels. Ethanol which is produced from sugar and starch crops
is the most widespread and is usually found in flexible fuel vehicles or FFV.
Flex-fuel vehicles use a single tank which normally takes a blend of 85% ethanol and 15% ordinary petrol.
This ratio accounts for the fuel name - E85. Petrol cars can be easily modified and although there is no loss in performance, economy suffers due to the lower
energy properties of ethanol.
The green credentials of biofuel might seem somewhat shaky when it's revealed that CO2 emissions are slightly higher than
petrol. The environmental impact however only becomes apparent when looking at the big picture. Ethanol is derived from plants
so the amount of C02 emitted during combustion is offset against the CO2 absorbed during growth.
This can reduce emissions by as much as 70% over petrol.
UK Production Vehicles
LPG and CNG cars are now found mainly in the second-hand market with Proton, the Malaysian manufacturer, one
of the few producers of a brand new dual-fuel petrol/LPG car. The family orientated GEN-2 ecoLogic comes in a choice of 4 door saloon or
5 door hatchback.
Biofuel cars with flex-fuel engines are much more common and there are production models available from
Ford, Saab, and Volvo. Volvo, which has a history of using alternative fuels
such as LPG and CNG in its production cars has the biggest range:
C30 1.8F, S40 1.8F, V50 1.8F, V70 2.0F, V70 2.5FT, S80 2.0F and S80 2.5FT.
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