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Dear all

First of all, I lack knowledge of LEL and UEL. What I know, below LEL, or 100%LEL (5% by volume), methane is too little to burn, so a flame cannot happen. And above UEL% (15% by volume), the mixture is too rich to burn or explode.

At what concentration of methane does burner support proper combustion (good air-fuel ratio) and at what point the fuel become rich and can cause an explosion?

Thanks for your help.

Aida Hannah


Hello Aida, it depends...

There is most certainly a theoretical stoichiometric ratio for methane/air mixtures, but that provides little more than a starting point.

Also, the above-noted may not necessarily be the ideal ignition ratio...

Your reference to a "burner" suggests continuous combustion rather than cyclic, but is this at near-atmospheric pressure [such as in a boiler furnace] or at an elevated pressure [such as in the combustion chamber of a gas turbine]?

Properly graduated and matching adjustment of fuel admission valves and air admission dampers or equivalent is commonly achieved using flue gas analysis, and the optimum excess air ratio is determined by the application, burner style, fuel composition, firing rate, primary and secondary air temperatures, etc., etc.

More information leads to better answers.


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

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