FALMMABILITY CALCULATION 1

[Jasmine2000]

How can I calculate flammibility of gasoline vapor by knowing vapor pressure, UEL and LEL, and total pressure?

 

[dcasto]

Flammibility is not an analog number, its discrete, yes it is or it isn't. We call theupper range or the area where if the air mixture is too rich to support combustion, the Upper Explosive Limit. And on the oppisite end, where there is not enough fuel, lower explosive limit.

 

[Flareman]

Jasmine2000

Are you asking whether a mixture with air is flammable?
The normal values given for LEL (lower explosive limit, almost too much air) and UEL (upper explosive limit, almost not enough air) are given for a condition of 25 degC at atmospheric pressure and represent the volume percent of the flammable gas in the gas air mixture.

If you have an equilibrium mixture at atmospheric pressure, and you know the vapor pressure of the flammable component, that pressure, divided by the atmospheric pressure tells you the percent of gas. You can then see whether it comes between the LEL and UEL and hence is a flammable mixture.

However, it is not adequate to apply this blindly at any pressure and temperature without properly understanding flammability because flammability varies non-linearly with total pressure and temperature. The common use of easy values for flammability gives a false impression that it is an absolute property. Unfortunately that is not the case. The absolute property is the intrinsic energy level of the molecule and its stability relative to the potential products of combustion. The conventional method of using LEL and UEL is just a convenient shorthand way (which usually works) to get a good idea about what might occur "normally" and without having to do complex calculations.

Try your local Technical Library for two relatively old publications by the US Bureau of Mines, Bulletin 503 and Bulletin 627 (by Zabetakis) both of which will give you a "feel" for flammability.

David