What does cng stands for and …

CNG stands for Compressed Natural Gas.
Since CNG is a clean burning fuel, combusting it leaves little or no residue compared to gasoline or diesel. Thus, the damage to the pipes and tubes of the vehicle’s engine is greatly reduced.
There is also less particulate matter that can contaminate the motor oil. This results to longer periods in between maintenance procedures such as tune-ups and oil changes.
CNG also has a high ignition temperature of about 1163 degrees Fahrenheit and a flammability rating of approximately 5 to 15% gas in air. This reduces the risk of fire if and when a leak happens.
 CNG is also lighter than air and will simply dissipate into the atmosphere in the case of leaks. Meanwhile, gasoline or diesel will pool in the ground when there is a leak which results to a very dangerous fire hazard.
 Lastly, CNG is a non-toxic fuel that does not pose any danger of contamination to ground water.