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Today Liquid Petroleum Gas (LPG) or Autogas, as its more commonly known, is made up of 94% propane, 4% butane and 2% other petroleum by-products. It is produced as a light part of the oil refining process, or extracted from natural gas streams. It burns with very high carbon efficiency, producing little other than CO2 and water during combustion. About 60% of the supply of LPG comes from the separation of natural gas products, and 40% is a by-product from the refining of crude oil. LPG will offer a performance comparable to petrol, in top-end speed, acceleration and refill times.

The use of gas as an alternative road fuel has its roots in World War 2 when “town gas” was used, stored in canvas bags on the roofs of cars. After the War some countries went on to develop the idea further. The use of LPG as a road fuel for cars became common in Italy and Holland and today these countries lead the world in Autogas technology.

In the ’60s and ’70s LPG was becoming established in the UK but Government tax increases and the advent of small diesel engines meant that the industry never grew. We had to wait until the “Green Movement” in the ’90s before the Government would take the environmental issue seriously. In Italy and Holland this did not happen and the industry was allowed to develop.

The early LPG systems are often referred to as open loop systems and have no sophisticated negative feedback. They work in a very similar way to carburettors and are only used on pre ’90s vehicles.

In the ’90s the open loop system evolved into the closed loop system with the introduction of electronic control systems. This enabled autogas to be used on vehicles fitted with a catalytic converter in their exhausts. This system can still be used on some vehicles made prior to 2000 but is not normally recommended.

The latest Sequential Vapour Injection Systems now work alongside existing petrol systems. It leaves the existing fuel system in charge of monitoring and controlling the engine and uses the information from that to control the gas. The choice of fuel is controlled from a small switch on your dash board. Just by pressing the button you can change from petrol to gas and vice versa. This type of system is the one fitted to the majority of modern vehicles.

In the War some vehicles were adapted to run on ordinary household gas, which was not rationed. The car engines were modified and a large inflatable bag placed on the roof of the cars, The bag was some 3m long, 1m high and 2m wide today the gas is contained in a steel pressure vessel!!