LPG, or Liquid Petroleum Gas, is an old substitute for pure petrol, although to run as a dual fuel vehicle, a car needs to be converted to cope with the differing fuels. LPG was first found in 1910 during the evolution of the refining process.
LPG is a generic name for mixes of hydrocarbons – typically propane or butane that have been compressed by 120psi which turns them into a liquid. This means that the gas needs to be contained in a strengthened tank in the car. For safety, a sulphur based chemical (Ethyl Mercaptan) is added so that a leak can be detected because it stinks of rotten vegetables!
LPG has been used for decades in vehicles as an alternative fuel source as it is a byproduct of the oil refining process and is a good source to use rather than be wasted. In Australia, LPG can be found as natural gas in fields off the West Australian coast, in fact according to the Australian LPG industry web site, over 75% of Australian LPG is found naturally.
There are some positive and negatives of using LPG. Firstly, due to its lower density than petrol, engines will burn more in comparison to petrol to get the same power output – up to 20% more, so to compensate, many Governments put a lower tax on the fuel. This means that amongst other reasons, LPG is much cheaper than unleaded fuel. Today, Fuelwatch.com.au, which is based in Western Australia, has an average price for ULP at 116c per litre whilst LPG was 81c. The gap between the two fuels has actually shrunk over the past few years by about 20c a litre.
Talking of Government intervention, the Australian Government had a rebate to help motorists convert to LPG. Like many policies it was heavily subscribed and the conversion companies couldn’t keep up with demand, then the Government realised that too many people were converting and they were losing their tax, so it was wound back. Subsequently, very few conversions have been done in the past few years. It also didn’t help that vehicle manufacturing is about to die in Australia so locally built LPG cars are no longer available and no manufacturer sees a market to import them.
Another positive is that LPG produces much less pollution than petrol – about 20% less carbon dioxide, which is good for the environment, although it is still a fossil fuel that requires energy consumption to extract, refine and transport to the retail outlet.
It has a Research Octane Number of between 90 and 110, which is similar to petrol and as I said earlier, cars need some extra bits to manage the LPG:
- New filler components and piping needs to be fitted to cope with the pressurised liquid.
- New tanks are fitted that are strengthened for safety with pressure release valves.
- A converter is used to turn the liquid back to a gas at atmospheric pressure which send the gas to:
- A mixer, that is a form of carburettor that mixes the gas with air ready to be sent to the cylinder for compression and ignition.
Some new cars that are pure LPG based and not flex or dual fuel use a form of fuel injection that mixes the gases and then pushes it into the cylinder. Ford for one, went down that path in Australia.
Recently, I wrote about water injection to improve the performance of petrol engines and a similar idea is used for diesel cars. Namely, injecting LPG with the diesel improves the combustibility by about 25%, so with a bigger bang comes bigger power! It works by improving the ignition of the oxygen in the cylinder when it is compressed.
So, LPG is another option for motorists today, however the economic benefits are being gradually reduced from petrol or diesel and many fuel stations are removing their LPG bowsers because they aren’t selling enough. What I find interesting is that with all the bad press with diesel, the LPG industry isn’t stepping up their campaigns to increase sales and take more share from the two main power sources. With hybrid cars being able to use a variety of fuels, you would think that a revised marketing plan might actually work.