LPG vehicles

LPG is liquefied petroleum gas; a mixture of propane and butane which comes from oil refining and natural gas fields.

There are around 10,000 LPG vehicles in the UK and over 4 million LPG vehicles operating in the world.

Natural gas

Natural gas can be used in an internal combustion engine (ICE) in two forms: CNG or LNG.

• CNG is compressed natural gas, the same fuel you use for cooking, stored in the vehicle in a compressed form.
• LNG is liquefied natural gas, the same fuel you use for cooking, stored in liquefied form at low temperatures.

The fuel is stored under pressure in cylinders onboard the vehicle. It travels though a high-pressure fuel regulator located in the engine compartment before being injected into the engine’s combustion chamber at atmospheric pressure.

The UK’s first CNG bus was introduced in Bristol in 1996 and Southampton is one of a number of cities now operating CNG buses like the one below.

Fuel cells

Fuel cells produce energy in the form of electricity by mixing hydrogen with oxygen taken straight from the air. The only emission from a hydrogen fuel cell vehicle is of water.

Unlike normal engines, fuel cells do not rely on combustion to generate power. Inside the cell an electrode coated with platinum catalyst is used to split hydrogen into electrons (which create a usable electric current) and protons. The protons pass through a membrane and are combined with oxygen to create heat and water at a second platinum-coated electrode.

Although commercial use of fuel cells is limited, many car companies are developing fuel cell vehicles, like the Mazda car shown below.

Electric and hybrid vehicles

In electric vehicles, the conventional fuel system is replaced by batteries and electric motors. Vehicles may be derivatives of standard production models or purpose-built. Hybrid vehicles use a combination of a fossil fuel and an electric system, with electricity being used to power the vehicle at lower speeds and for stop-start driving in urban areas.

The most common battery type is the lead-acid battery, which provides a limited range. New lithium-ion battery technology, based on the same lightweight, high energy storage capacity power source used in notebook computers and top-end video cameras, is helping to make the long-range electric vehicle a viable proposition.

Unfortunately, cars like the Nissan Altra EV, shown above, which can travel 120 miles on a single £1.50 charge, are not currently available in Europe.