What is LPG (autogas)?
LPG (liquefied petroleum gas), also called autogas, is a fuel made of propane and butane. It is a by-product of natural gas extraction and oil refining. Because it liquefies under moderate pressure, a useful amount can be carried in a vehicle tank.
Composition
Autogas consists mainly of propane (C3H8) and butane (C4H10). The mix is not the same everywhere: propane vaporises reliably even in the cold, while butane is sluggish in frost. For that reason, autogas in many countries contains more propane in winter than in summer. If you fill up in another country, you may get a slightly different blend than at home, which modern systems normally cope with without problems.
How does an LPG system work?
A car with an LPG system has two fuel systems: the original petrol tank and an additional gas tank. The main components of the gas system:
- Gas tank: usually a cylindrical tank in the boot or a toroidal tank in the spare-wheel well. It is filled to only about 80 percent so the gas has room to expand.
- Vaporiser (reducer): turns the liquid gas into vapour and reduces the pressure. It is heated by the engine coolant.
- Injectors: feed the gas in measured amounts into the intake.
- Control unit: converts the petrol injection times into gas injection times and switches between fuels.
- Filler and lines: filled through a standardised connector, see filling connectors and adapters.
The engine normally starts on petrol and switches to gas automatically after a short time, once the vaporiser is warm enough. A switch lets you go back to petrol at any time. That petrol is also your reserve if there is no gas station nearby.
Naturally aspirated, turbo, direct injection
The classic system with vaporised gas suits naturally aspirated engines well. For engines with direct petrol injection there are systems that inject some petrol as well or that inject the gas as a liquid. Not every vehicle is equally easy to convert; more under LPG conversion.
LPG from the factory
Besides retrofitting, some manufacturers offer vehicles with an LPG system from the factory. A well-known example is Dacia's ECO-G range. Which models are available changes over time, so check the manufacturers' current price lists.
LPG, natural gas and heating gas: do not mix them up
LPG is not the same as natural gas (CNG). Natural gas consists mainly of methane, is filled as a gas at very high pressure and needs different stations and tanks. Bottled gas for heating or barbecues is chemically similar but must not simply be put into a car tank.
The map of LPG stations shows where you can fill up near you. Our database currently holds more than 7,300 stations.