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i seem to be a bit confused on what it means when nitrogen burns in a rocket mass heater

 
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i talked to my grampa and he told me that nitrogen the gas cant burn, is it that organic nitrogen can burn or am i missing out on something?
 
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Connor, this is a really good question and I don’t have a good answer.  As far as I know, nitrogen will not burn or oxidize exothermically.  Many nitrogen compounds such as nitrous oxide and nitrogen tetroxide make great oxidizers, but I don’t think of them as burning/oxidizing.  I would really like to hear someone more knowledgeable on this, but it’s a great question.

Eric
 
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I'm pretty sure that wood fires don't normally get hot enough to produce any meaningful amounts of NOx. I think you need well over 1200C before that happens.
 
Eric Hanson
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Phil,

I tend to agree.  Also, would higher pressures also be needed?  Just a thought.

Eric
 
Phil Stevens
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Internal combustion is a big source of NOx, and that requires compression so that could be a factor. N in the fuel is also a contributor in the case of some coal and low quality heating oil. Wood is clean by comparison.

[Edited to add] NOx Wikipedia says "At high temperatures, usually above 1600 °C (2900 °F), molecular nitrogen (N2) and oxygen (O2) in the combustion air dissociate into their atomic states and participate in a series of reactions."
 
connor burke
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I remember hearing or reading about some folks doing some really effeicent rocket mass heaters where it could get up to those temperatures and i read them when oxygen and nitrogen combined a little bit of energy is released which would help support combustion. And a good while ago I think I remember reading something about a methane atmosphere or a nitrogen atmosphere and what would happen if you put oxygen into the atmosphere and if I remember right you had something that was like a reverse Flame and I think there may have been a lab testing component to it.
 
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Unlike other reactions, that release energy (heat, light, sound, etc) this one actually absorb energy. This makes it unlikely to happen in nature.

But technically Oxygen react with nitrogen to produce nitrogen(II) oxide. This reaction takes place at the high temperature[about 2000°C(without catalyst) ;
1200-1300°C(with catalyst)), an overpressure and in the presence of a catalyst. In this reaction, the catalyst can be platinum, manganese(IV) oxide. https://chemiday.com/en/reaction/3-1-0-694

After NO is from, if left by itself it will break back down into separate nitrogen and oxygen molecules, giving off heat. But usually this unstable NO will react with something to become stable.
 
Eric Hanson
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S,

Thanks for the specific reply.  Thankfully your chemistry knowledge is vastly more advanced over my own.  I knew that N2O and NO4 were both pretty powerful oxidizers, therefore I surmised that they would not casually react with oxygen and if they did, they would require extra energy to do so.  So again, thanks for providing us with that specific information.

Eric
 
S Bengi
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The chemical composition of wood varies from species to species, but is approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen/sulphur, and 1% other elements (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight. https://en.wikipedia.org/wiki/Wood

So yes while nitrogen in the air might not readily react with oxygen to for oxides, the amino acids/proteins in the plant do react/decompose to ammonia via deamination and amines via decarboxylation. Which then turns into NOx. Most of it then turns into regular nitrogen gas that makes up 78% of the atmosphere.

Checkout the figure below for a bit more info.


 
connor burke
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Thanks for the replies y'all!
 
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For what it's worth, my experience with NOx is in the automotive industry and it's a huge topic surrounding diesel engines in particular. NOx os thought to be a HUGE noxious pollutant, and while most people think of diesel smoke/soot as the emissions problem with diesels that really is just the smallest portion of the pollutant that is of concern.  If you've ever been around older vehicles, gas or diesel, and the exhaust almost burns your eyes and has an acrid almost acidic smell to it, that's NOx. In gasoline engines, it occurs when the fuel mixture is too lean, and combustion temperatures get so high, free nitrogen in the air starts burning.  Better fuel management systems on vehicles like fuel injection and oxygen sensors have really helped bring NOx down in gasoline vehicles.  In gasoline vehicles, engine rpm is determined by how much air enters the engine via a throttle plate, and the fuel amount is adjusted to match the air input.

On a diesel however, the engine is allowed all the air it can possibly get, and engine rpm is controlled strictly by the amount of fuel allowed to be injected into the cylinder.  This creates an almost "too lean" mixture all the time, raising combustible temperatures and burning free nitrogen in the air creating NOx. They combat this several ways.  They use exhaust gas recirculation, or egr to add already combusted air into the intake of the engine to combine with with fresh air to fill the cylinder. This combusted air is inert and cannot add to the combustion process, effectively cooling the cylinder.  Since around 2008, they have added diesel oxidation catalysts in the exhaust system that spray urea (diesel exhaust fluid or def)into a bed of precious metals that makes a chemical reaction to bind NOx into a different substance.  

I would say anything that can get hot enough can burn nitrogen for sure! I dont think most rocket stoves get that hot, but only a gas analyzer could really tell.
 
connor burke
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eric "free nitrogen in the air starts burning" is the bit im having trouble with the folks above are saying that the conversion of n to NO2 takes energy out of the environment. is NO2 able to release a small amount of energy that would add to the heat the rocket mass heater releases? i heard somewhere that rocket mass heaters can get hot enough for NO2 to form.
 
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The most efficient rocket mass heaters may be able to get up to temperatures that form NOx; this does not mean that that reaction releases energy. Designing a combustion core that gets to around 2000-2200F but not a lot hotter will give excellent efficiency yet not risk forming NOx. NOx temperatures pose a risk to the material of a core, in that it takes very specialized and expensive refractory materials to resist those extreme temperatures without melting, shrinking, cracking, or otherwise degrading. Firebrick rated for 2300F is common, 2600 or 2700F is obtainable but more expensive. Any firebrick or other material rated for less than 2000F is unsuitable for an efficient core as it will degrade fairly quickly and need repair or replacement within a few years.
 
connor burke
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100% i figured id ask around to see if anyone had heard differently and thanks for telling me about the different levels of firebrick that's something I hadn't realized was a thing
 
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