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# question for methane gas

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## question for methane gas

(OP)
if we say methane gas has 5% LEL/LFL fuel concentration mix in air ....so how much percent of air need to burn the methane gas.

### RE: question for methane gas

U want to explode it or burn it?

CH4 + O2 + O2 +O2 => CO2 + H2O + H20 + H2O + H2O
1 methane to 3 oxygen
air is 28% O2,
so that's 3O2/0.28 = roughly 1 methane to 10 air

If you're trying to find the amount of methane in a mix that is needed to a reach LEL atmosphere, then 100 x 0.05 = 5 methane and obviously 95 Air => 5 cubic feet to 95 cubic feet of air, 5 gallons of methane to 95 gallons of air, etc., etc.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

### RE: question for methane gas

CH4 + 2O2 --> CO2 + 2H2O

Good luck,
Latexman

### RE: question for methane gas

(OP)
u say burning or explode .. what is the difference .and how can you
make it burn or explode.

got a match?

### RE: question for methane gas

What the guys are trying to get you to understand is that if the mixture is between the LEL and the UEL and you supply an ignition source (anything that is greater than 1,000°F), ignition will happen. Whether that results in a fire or an explosion is just a matter of containment. If the combustion gases can expand without [near field] limit, then you have a fire. If the combustion gases are contained and can't expand then you have an explosion.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

### RE: question for methane gas

David, i thought the difference between burn, explode and detonate were is "flame propagation speed". In the range cm/sec it burns, if its in the m/sec range it explode - and above the speed of sound it detonates. I mean - you can have an explosion or a detonation in "open air" (think of a fuel gas bomb e.g.)

You can mix air with methane without being able to ignite it. Where i live they now make city gas this way. City gas has lower heat of combution pr. volume unit than natural gas. In order to avoid having to replace a lot of gear they simply mix in som air than lowers the heat of combustion to a similar value.

There is an "ideal mixture of methane and air between LEL and UEL. At this value (or close) the mixture will explode not burn. E.g. with a internal combution morotr. If your mixture is to lean or to rich (altough within LEL/UEL) you get poor combustion with low performance and lots of soot/smoke whatever.

Best regards

Morten

### RE: question for methane gas

The only "open air" explosion that I've ever studied is called a BLEVE (Boiling Liquid Expanding Vapor). In that scenario, the flame is adequately contained by the liquid. The whole flame speed is about a propensity to explode (e.g., C4 burns so fast that the combustion gases can't get out of their own way).

My kid is a bomb tech, I'll ask him this morning and let you know.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

### RE: question for methane gas

(OP)
what i understand you say .. if methane
has 5% LEL and 15% UEL (gas mix in air)
and between them is 10% .....so this mean
the 10% has more explosion than 5% and
15% (LEL & UEL )...is it correct.

### RE: question for methane gas

Bottom line - if you have a valve - turn it on slowly - light it and then up the release. Done all the time...

Think of your gas stove. It fires right off. If you suppress the ignition and gas spreads through the house and "hits" the pilot light in water heater - GA-BOOM

### RE: question for methane gas

taregg,

Your questions lead me to believe you want to know how to optimize the explosive force of a methane/air mixture. What is your application or concern?

Good luck,
Latexman

### RE: question for methane gas

taregg,
I don't think that anyone has ever said that before in the history of saying stuff. I see some minor differences in flame temperature as you go from LEL to UEL, but the differences are really small.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

(OP)
thank you

### RE: question for methane gas

Almost certainly between them, although I can't say exactly where. Offhand it seems that being close to stoichiometric, or a little bit richer, would be the best.

From an internal combustion engine point of view, the most power is created for a given amount of air when the amount of fuel is slightly greater than the stoichiometric ratio would give. How much richer depends on how well things mix, how hot the surrounding surfaces are, etc. This results in a condition where all the oxygen is reacted, but you don't have so much fuel left over that you "soak up" lots of the released heat. Having no leftover fuel means that you have leftover O2, since the molecules don't actively seek each other out but instead rely on chance encounters to react.

In the sense of "most powerful explosion" there is likely another factor at play, and that's how fast the flame will propagate (which can dictate what pressure is achieved within your container). It's not necessarily the case that the mixture which releases the most energy during combustion will also achieve the highest pressure, as your container may change shape/size during the process, or you may lose some of your reactants through various leak paths, either way favoring faster burns. There may be some air/fuel ratios which will tend to self-ignite when the pressure and temperature get high enough but before the flame actually arrives, resulting in multiple flame fronts and faster combustion.

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