Compressed Natural Gas (CNG)

Residents of Delhi and Mumbai are used to seeing auto-rickshaws painted a brilliant green. These auto-rickshaws use CNG or Compressed Natural Gas, and not petrol. And they are painted green because they are eco-friendly and don’t release dirty black smoke from their exhaust pipes.

What is Compressed Natural Gas(CNG)?

Compressed Natural Gas(CNG), is methane stored at high pressure. This is used as fuel in place of gasoline, diesel and propane(LPG).

Let us understand one thing about the word ‘compressed’ which means under pressure, ready to burst out, one might say. It’s how a wad of 100 rupee notes might pop out of a tin box that can actually hold only 70; they have been pressed in, to fit more and more. Whenever something is compressed, and there is even a little hole or outlet for release, the stuff will come rushing out. CNG comes rushing out of the land or water beneath which it exists, whenever someone drills a hole to extract it. It takes less time and money to extract CNG than it does to get the crude oil that gives us petrol.

Where is Compressed Natural Gas(CNG) found?

CNG maybe found above oil deposits or maybe collected from landfills or waste water treatment plants, where it is known as biogas.
It is made by compressing Natural Gas, which is made of methane, CH4, to less than 1% of the volume it occupies at standard atmospheric pressure.

Natural gas is also extracted from wells, it is cleaned and then stored in thick aluminum cylinders.

Properties of Compressed Natural Gas(CNG)

1. It is colorless and transparent.
2. It is odorless.
3. It is non-corrosive.
4. It is lighter than air ( which is why it must be collected quickly while extracting)
5. It burns only under certain conditions.

Burning of Compressed Natural Gas(CNG)

The burning of CNG is interesting. We know that oxygen is needed for things to burn. Now if there is 100 cc (cubic centimeters) of CNG and air mixed together, it will not burn if the CNG level is too high or too low. Less than 5cc of CNG in this mixture and it is too little to ignite. More than 15cc of CNG in this mixture and there is not enough oxygen for combustion to occur. This seems very safe – and also cheap – small quantities of CNG have to be mixed with regular air to run a car!

How does Compressed Natural Gas(CNG) work in automobiles?

When CNG reaches the combustion chamber, it mixes with air, is ignited and provides the necessary energy to the engine to move the vehicle.

Why is Compressed Natural Gas(CNG) better than Petrol or Gasoline?

1. CNG is cheaper than petrol or gasoline.
2. CNG reduces maintenance cost of vehicles, as the gas leaves no residue on engine parts, because of combustion.
3. CNG is more environmental friendly. It releases less exhaust emissions into the environment, by about 95% including carbon monoxide, carbon dioxide, nitrous oxide.

Another good thing about CNG is that when it is used in vehicles, the emissions from the exhaust create less damage than CO2 emissions. Thus, no black smoke and no poking ozone holes in the atmosphere! And since its non-corrosive, the metal does not rust.

Visit a petrol station (with an adult) that supplies CNG and ask how and where they mix air with the right percentage of CNG, so it will burn.

 For more environment related articles and videos, visit Environment for Kids category.