Article published in Dawn newspaper
http://www.dawn.com/2001/10/27/letted.htm
Use of CNG in vehicles
THIS refers to Sobia Zareen’s letter, captioned “CNG use in vehicles” (Oct 24). It is really heartening to see that people are becoming more and more aware of the environmental problems and share their ideas to control wide spread air pollution.
CNG has been promoted as clean fuel that helps in reducing air pollution caused by toxic exhaust emissions of petrol driven engines (as most of us know it). But if you do some research and study CNG in detail the so called ‘clean fuel’ doesn’t appear to be so “clean”. The exhaust gases that are emitted during combustion process of an engine can be significantly lowered if the combustion is complete. Unfortunately the fuel is not completely burned and if the engine is not properly tuned, the improper combustion increases the density of emissions.
Now if you use CNG in place of petrol, the gases like carbon monoxide, carbon dioxide, etc are significantly reduced, but a far more dangerous emission is released due to presence of methane in the CNG. Methane, ethane, propane and butane all present in the CNG, cause much less pollution then petrol but gas powered engines emit ultra fine particles that penetrate deep into the human body and cause respiratory diseases and can also instigate cancer. An editorial published in Dawn (Aug 9, 2000) captioned ‘CNG dangers’ has all these details.
Another commonly ignored danger of CNG is the possibility of explosion. CNG is stored at very high pressure of around 3200psi in cylinders. These cylinders can easily explode in a collision or by a spark near a leaking cylinder. So it’s like carrying a bomb with you on the road. The claims by cylinder manufacturers can’t be justified as the strength of these cylinders is measured in controlled lab conditions that don’t even come close to the actual incidents on the road.
CNG is very explosive. It’s a poor man’s bomb. CNG is safe in a non-spark and non-collision world, but if is released and allowed to mix with air, and at the same time there is a spark, the sub-zero temperature suddenly increases and the volume expands 1000 times and such a sudden increase in pressure bursts even the strongest container and huge fireball results. The government should take very firm steps to check this CNG gimmick, which can result in an uncontrollable security problem in future.
CNG is also harmful for engines not designed for this fuel. Common cars like we have in Pakistan are designed to run on leaded fuel. These cars need special fuel conditioners to run on unleaded or low lead fuel and the introduction of CNG, which is a dry fuel, damages the engines specially the valves seats. This process of valve seat recession takes sometime during which a consumer thinks that the savings through use of CNG are substantial and when the engine breaks down the cause is unknown and blamed on something else and the poor user continues using CNG not knowing the same thing will be repeated very soon.
It is advisable that conversion to any alternate fuel should be done very carefully.
ZAHEER A. MALIK
Karachi