CNG vs LPG
CNG or Compressed Natural Gas is mainly composed of Methane while LPG or Liquefied Petroleum Gas is mainly composed of propane, butane and other gasses.
Another major difference is that LPG is in liquid form under high pressure. At normal temperature and pressure this is a gas. CNG on the other hand does not become a liquid even at high pressure. To liquefy it the temperature needs to lower than -164 degrees.
Compressed Natural Gas, after it is extracted, only needs to be filtered a little and pressurized. It may be used as fuel even before the filtration process. Liquefied Petroleum Gas on the other hand is generally a bi-product of the drilling process or the refinement of crude oil.
CNG is lighter than air, hence, in case of a leak from a tank or a pipeline it can immediately go higher up in the air and disperse quickly making it very safe. LPG on the other hand is twice heavier than air and will accumulate around the area of the leak making it very volatile and dangerous. To detect the leaks quickly ethanethiol is added to the gas so that its powerful odor can easily be picked up.
The pollutants released into the atmosphere by CNG upon combustion are far less than LPG mainly due to the fact that the CNG consists of mainly methane only.
In the US LPG is far more popular as Auto fuel than the CNG. There are numerous certified installers for LPG kits on to a conventional car or truck. There are estimated to be more than 270,000 LPG vehicles in the US. While CNG vehicles are still less, Honda Civic has recently been launched in the CNG version and more auto makers are trying to catch up. In countries like Brazil, Argentina, Italy, India, Pakistan, Thailand, China and Iran CNG is much more popular than LPG as auto fuel and has a higher availability at filling stations.
Summary:
1. CNG or Compressed Natural Gas is mainly composed of Methane while LPG or Liquefied Petroleum Gas is mainly composed of propane, butane and other gasses.
2. CNG is mainly Methane at a very high pressure while LPG is Propane, Butane and other gasses.
3. CNG remains in gas form even at higher pressure while LPG liquefies.
4. While LPG is usually a bi product of the drilling or the refining process, the CNG is extracted as it is and supplied with minimum of processing.
5. CNG is a much cleaner fuel and very popular abroad while in the US LPG is quite popular.