Table 1 Physiochemical properties of CNG vs gasoline and diesel

Octane/cetane number

120–130

85–95

45–55

Molar mass (g/mol)

17.3

109

204

Density at 15 °C (kg/m³)

215

750–765

830–950

Stoichiometric (Air/Fuel ratio)

17.2:1

14.7:1

14.6:1

Stoichiometric mixture density (kg/m³)

1.25

1.42

1.46

L.H.V. (MJ/kg)

47.5

43.5

42.7

L.H.V. of stoichiometric mixture (MJ/kg)

2.62

2.85

2.75

Combustion energy (MJ/m³)

24.6

42.7

36

Flammability limit in air (vol% in air)

4.3–15.2

1.4–7.6

1–6

Flame propagation speed (m/s)

0.41

0.5

–

Adiabatic flame temp. (°C)

1890

2150

2054

Auto-ignition temp. (°C)

540

258

316