Characteristics
CNG is a non toxic GAS liquid at -259 °F -162 °C which ignites at 1350°F 732°C. The octance number is 120. It may be inflamed having a share of 5.3 to 15% in air.
Methane has only 42.4% of the density of air and thus is ligther and may disappear in case of leackages. The lower heating value is 50,020 kJ/kg. Ignition energy is 0.29 mJ.
Natural gas may consist of:
- Methane CH4 70-90%
- Ethane C2H6 0-20%
- Propane C3H8
- Butane C4H10
- Carbon Dioxide CO2 0-8%
- Oxygen O2 0-0.2%
- Nitrogen N2 0-5%
- Hydrogen sulphide H2S 0-5%
- Rare gases A, He, Ne, Xe trace
CNG quality may be expressed with the
- Wobbe Index
- Methane Number MN80 (Volume percent hydrogen atoms / carbon atoms)
OR
More detailed:
- C3or higher <=3%
- C6 or higher <=0.2%
OR
even more detailed:
- Hydrogen <=0.1%
- Carbon Monoxide <=0.1%
- Oxygen <=1%
- Intert gases (sum of CO2 and N2) 1.5-<=4.5%
- Sulfur <=16ppmv
- Water: the dewpoint shall be at least 5 K lower than the 99% winter design temperature
- Particulate Mater: no dust, sand, dirt,gums, oil injurious to the filling stations
- Odorant should be detectable at 20% of the lower limit of flammability
In Germany two CNG-grades ar offered depending on the sources for natural gas:
- H-gas 87 - 99,1 Vol.% CH4 and 10,0 - 11,1 kWh/m3 lower heating value
- L-gas 79,8 - 87 Vol.% CH4 and 8,2 - 8,9 kWh/m3 LHV
More Info
more in German...
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