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Compressed Natural Gas

Environment | 6-12 yrs | Interactive, Learning Pod

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.

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.

Natural gas is also extracted from wells, it is cleaned and then stored in thick aluminum cylinders.
Let us look at some of the properties of CNG –
1. It is clear i.e. 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.

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!

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.

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