Propane has an air fuel ratio of 15.5 : 1

Propane (LP) 	
By Mass: 15.5 : 1 	
By volume: 23.9 : 1 	
Percent fuel by mass: 6.45%

Stoichiometric air-fuel ratios

Propane Boiling Point -44°F
Weight of 1 Gallon Liquid Propane 4.24 Lbs at 60°F
Specific Gravity of Propane Gas 1.52 at 60°F
Specific Gravity of Liquid Propane .51 at 60°F
BTU per Gallon of Propane Gas 91,547 at 60°F
BTU per Lb. of Propane Gas 21,591
BTU per Cu Ft of Propane Gas 2,516 at 60°F
	
Propane Boiling Point - Water boils at 212°F meaning that it becomes a gas at this temperature whereas water is still a liquid at 200°F. Propane is a liquid at -50°F and boils at -44°F. In other words, at 10 degrees below zero, propane is well past its boiling point. What does this mean to ordinary people like us? It means that propane is cold enough freeze your skin (and tissue underneath) to the point of severe damage.


Specific Gravity of Propane Gas - One cubic foot of propane weighs .1162 lbs. and one cubic foot of air weighs .07655. Dividing .1162 by .07655 equals 1.52. What does this mean? Propane is heavier than air and will seek the lowest space available.

Specific Gravity of Liquid Propane - One gallon of propane weighs 4.24 lbs. One gallon of water weighs 8.33 lbs. Dividing 4.24 by 8.33 equals .51. This means propane is less dense than water (lighter than water) and will not sink in water, so to speak.


BTU - As defined, a British Thermal Unit is the quantity of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It takes about 143 BTU, or .0016 gallons of propane, to melt one pound of ice (at 32°F). Most all installation requirements and decisions revolve around BTU ratings and demand.  


Propane Combustion Characteristics
Lower Limit of Flammability 2.15
Upper Limit of Flammability 9.60
Flash Point -156°F
Ignition Temperature in Air 920-1020°F
Maximum Flame Temperature 3595°F
Octane Number Over 100
	
Propane limits of flammability - The lower and upper limits of flammability are the percentages of propane that must be present in an propane/air mixture. This means that between 2.15 and 9.6% of the total propane/air mixture must be propane in order for it to be combustible. If the mixture is 2% propane and 98% air, there will not be combustion. If the mixture 10% propane and 90% air, combustion will not occur. Any percentage of propane in a propane/air mixture between 2.15% and 9.6% will be sufficient for propane to burn. However, an improper air/gas mixture can produce Carbon Monoxide (CO) that is a deadly product of incomplete combustion.


Flash Point - The flash point is the minimum temperature at which propane will burn on its own after having been ignited. This number states that below -156°F, propane will stop burning on it's own. In other words, if the outside air temperature is -155°F, propane will burn on it's own. If the outside air temperature falls to -157°F, propane will no longer burn on it's own. However, if a source of continuous ignition is present, propane will burn below - 156°F.

Ignition Temperate in Air - This number states that propane will ignite if it reaches a temperature between 920-1020°F. If propane is heated up to a temperature between 920 and 1020°F, it will ignite without needing a spark or flame.


Maximum Flame Temperature - A propane flame will not burn hotter than 3595°F.


Octane Number - Without presenting a chemistry lesson, the Octane number of propane being over 100 means that it is a very engine friendly fuel.


Propane 
LFL/LEL in % by volume of air: 2.1
UFL/UEL in % by volume of air: 9.5 to 10.1
Flash point 480 °C
Minimum ignition energy in mJ expressed at percent by volume in air
0.25 @ 5.2% (in pure oxygen 0.0021)
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The Flammable Range (Explosive Range) is the concentration range of a gas or vapor that will burn (or explode) if an ignition source is introduced.

Below the explosive or flammable range the mixture is too lean to burn and above the upper explosive or flammable limit the mixture is too rich to burn. The limits are commonly called the "Lower Explosive or Flammable Limit" (LEL/LFL) and the "Upper Explosive or Flammable Limit" (UEL/UFL).

The lower and upper explosion concentration limits for some commonly used gases are indicated in the table below. Some of the gases are commonly used as fuel in combustion processes.

"Lower Explosive or Flammable Limit" (LEL/LFL) (% by volume of air)
Propane 

"Upper Explosive or Flammable Limit" (UEL/UFL) (% by volume of air)
Propane 10.1