CNGV, it means Compressed Natural Gas for Vehicles 
The exhaust pollution of vehicle in city becomes the problem seriously due to heavy
traffic in nowadays. Compare with petrol and gasoline, the CNG is economic fuel
and more clean fuel as well. It has been paid much more of attention by government
of all of the countries in the world due to it is related with environmental
protection. 
Using the compressed natural gas (CNG) as the fuel of vehicle (CNGV) instead of petrol,
gasoline has been acceptable by most of the countries that are not lack of
natural gas.
 As per record, 4200 CNG filling stations have been established and 5700000 sets
of vehicle are using CNG as fuel already in the world, and the quantities are increasing
day by day. 

As per the practice and analysis, following are the some data for better understanding:
1. Main advantage of Compressed Natural Gas Vehicle (CNGV):
Gas of CO will be reduced by 90%, Carbon hydrogen compound will be reduce by 70%,
Nitrogen and oxygen compound will be reduced by 40%, CO2 will be reduced by 20%,
without pollution of lead. So it is really low pollution fuel than oil.
2. Operation cost reduced:
   As normal, heat value of 1M3 natural gas equivalent to 1.13 liter of Gasoline,
cost of one liter of gasoline is much higher than of 1 M3 of natural gas. 
3. Compare with motor driving, CNGV has the advantage of longer duration in running,
shorter time for filling. 
4. The modification for CNGV from use oil is very cheap and easy.
5. CNG cars are much more safety than use of oil:
Gasoline is much more volatilized and the point of set fire is 430 ??,but natural
gas the point  of set fire is 650 ??. Gravity of natural gas is less than air so
in case it has some leakage it will be floated to air quickly; 
The cylinders for filling CNG must be tested under the pressure of 4 times of its
working pressure, the mechanism of explore proof is mounted on the CNG cylinder
to protect the cylinder from explore in case of accident such as collision or turn
over. It is much more safety than use of oil! This conclusion have been made
by Italy who has observed with their 30 years running experience and made by U.S.A
who has investigated with ??CNGV?? sample examination. 
6. Present technology of CNGV in China:
Since 1980??s China has invest a large amount of capital to study and develop the
CNG and CNGV technology and has reached successful. Now the technology entered
its fourth generation, so the technology is advanced level and CNG stations have
been establishing in quick speed to protect the environment.