Fuel & gas properties

Properties using Metric Unit

Property Units Natural Gas Propane Butane
Chemical formula CH4 C3H8 C4H10
Molecular weight kg/k/mole 16 44.10 58.12
Boiling point of liquid at atmospheric pressure °C -161.6 -42.1 -0.5
Specific gravity of vapour (Air=1) 0.6 1.53 2.09
Specific gravity of liquid (Water=1) 0.6 0.512 0.58
Density of vapour 1.5 1.95
Density of liquid at 20°C 0.505< 0.575
Volume occupied/mass of liquid litre/tonne 1957 1743
Calorific value at 20°C MJ/M3 38.7
MJ/litre
MJ/kg
Latent heat of vapourisation kJ/kg 358 372
Wobbe index 50.13 81.12
Specific heat – liquid 0.60 0.58
Liquid weight kg/l
Vapour volume from 1 litre of liquid at 20°C M3
Vapour volume from 1 kg of liquid at 20°C M3
Vapour pressure at 20°C kPa g
Vapour pressure at 38°C kPa g
Compustible limits % gas in air 5-15 2.2-9.6 1.9-8.6
Amount of air to burn 1 M3 of gas M3 9.78
Ignition temperature in air °C 612-622
Maximum flame temperature in air °C 1964
Auto ignitition temperature °C 470 410
Critical temperature °C 96.7 152.1
Critical pressure kPa g 42.5 38.0
Octane Number 100 Over 100 92

Properties using Imperial Unit

Property Units Natural Gas Propane Butane
Chemical formula CH4 C3H8 C4H10
Molecular weight
Boiling point of liquid at atmospheric pressure °F -256.7 -44 32
Specific gravity of vapour (Air=1) 0.6 1.53 2.00
Specific gravity of liquid (Water=1) 0.6 0.51 0.58
Density of vapour
Density of liquid at 60°F
Volume occupied/mass of liquid lbs/ton
Calorific value at 60°F BTU/ft3 1012 2516 3280
BTU/gal 91690 102032
BTU/lb 21591 21221
Latent heat of vapourisation BTU/gal 712 785 8.8
Wobbe index 1317 2034 2034
Specific heat – liquid BTU//lb/°F
Liquid weight lbs/gal 4.24 4.81
Vapour volume from 1 gallon of liquid at 60°F ft3 59.0 36.39 31.26
Vapour volume from 1 lb of liquid at 60°F ft3 23.6 8.547 6.506
Vapour pressure at 60°F psi 92
Vapour pressure at 100°F psi 176 37
Compustible limits % gas in air
Amount of air to burn 1 M3 of gas ft3 5-15 2.2-9.6 1.9-8.6
Ignition temperature in air °F 9.53 23.86 31.02
Maximum flame temperature in air °F 1200 920-1020 900-1000
Auto ignitition temperature °F 3568 3595 3615
Critical temperature °F 878 770
Critical pressure
Octane Number 100 Over 100 92
All values are approximate.