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Junk_Enginerd
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[*] posted on 7-4-2020 at 08:12
Nitromethane torch?


I had an idea I wanted to check for feasibility and safety... I've gotten really into making torches lately. They're crucial for a lot of the metalworking I do, but making and improving torches has become a hobby in itself to be honest.

One problem common to all the torches I've made is that one eventually comes to the point where the gas stream speeds exceeds the flame front speed, and it goes out. This point is usually before I'm satisfied with the heat output.

Of course, adding oxygen solves both the heat output and the flame speed, but I'd like to keep going the path of air aspirated torches and see where it takes me. As a challenge, or just for fun.

So I thought of nitromethane. As I understand it, it contains quite a bit of oxygen already. Enough to burn even without adding air. Burning it stoichiometrically with air requires significantly less air than other fuels. Less air means that I can burn more fuel before the speed of the mixture exceeds the flame front speed. This in turn should mean I can burn more fuel in the same volume, and therefore get either a hotter flame or at least one that will heat things faster. That would be my first question... Is this correct?

One thing that has me worried though, is the "can burn without oxygen"-part. So far I haven't needed to worry about any explosions happening with torches. Fuel needs air to burn, so it's not going to burn until it exits the can it's stored in. To what extent is this still true with nitromethane? Since it is widely used in racing and hobbies like rc cars, I assume it can't just deflagrate through the fuel line and blow the whole thing up, at least not easily.

If I were to make a torch, what do I need to avoid? Is it a monumentally stupid idea to make a torch that's based on boiling the fuel to make it gaseous? Under what conditions would it deflagrate without air? Is detonation a concern?

I have tried to google around but nitromethane torches do not seem to be a thing as far as I can see.
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[*] posted on 9-4-2020 at 22:52


I do not know if nitromethane torch has some advantages over usual gas- air torches. If you wanna hi temp torch, you may use the mix of toluene+tetranitromethane. But these compounds must be mixed in some proportion- the excess of tetranitromethane makes such a liquid very sensitive and powerful explosive.



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Sulaiman
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[*] posted on 10-4-2020 at 00:04


Is HEAT or TEMPERATURE the main concern ?

If it is heat then you could make several jets that converge ?
or https://en.wikipedia.org/wiki/Meker%E2%80%93Fisher_burner




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[*] posted on 10-4-2020 at 00:18


Interesting idea. Now NM is a decent monopropellant and a potent explosive, so do read up on proper handling. But if they can use it in engines I don't see why a torch wouldn't work.



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[*] posted on 11-4-2020 at 10:35


Quote: Originally posted by Sulaiman  
Is HEAT or TEMPERATURE the main concern ?

If it is heat then you could make several jets that converge ?
or https://en.wikipedia.org/wiki/Meker%E2%80%93Fisher_burner


Heat, or more exactly power/volume. The 2000°C temperature that a propane torch supplies is enough for anything I can imagine needing to heat, except maybe for arc furnace type reactions. But, in the end, a propane torch is pretty damn weak in a metal- and glass working context. Takes forever to heat things up, unless the flame is impractically large, and will usually not heat anything but the tiniest pieces to more than 800°C ish.

Converging flames might be an alternative route to investigate. Thanks for the tip!
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[*] posted on 11-4-2020 at 10:49


Quote: Originally posted by caterpillar  
I do not know if nitromethane torch has some advantages over usual gas- air torches. If you wanna hi temp torch, you may use the mix of toluene+tetranitromethane. But these compounds must be mixed in some proportion- the excess of tetranitromethane makes such a liquid very sensitive and powerful explosive.


Uh huh okay, lets see...

TNM forms extremely powerful explosive mixtures when fuels are added in stoichiometric proportions. Many of these mixtures show sensitivity to impact even higher than that of nitroglycerine.[13]

TNM reacts with moisture at elevated pH to produce trinitromethane (nitroform) which reacts easily with metals to form highly unstable and explosive salts.


Ahh I'm noping out of that lol. Most would call me reckless to the point of being an idiot, except I actually do have certain boundaries that I do not cross. I can deal with flames, molten metals going everywhere, toxic things... But things that go unpredictable and risk getting violently surprise-explosive when not carefully watched and treated absolutely properly isn't for me. It did lead me to some interesting reading though, so thank you for that.
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[*] posted on 11-4-2020 at 10:54


Quote: Originally posted by Fulmen  
Interesting idea. Now NM is a decent monopropellant and a potent explosive, so do read up on proper handling. But if they can use it in engines I don't see why a torch wouldn't work.


Do you have any suggestions for where I could find anything to read up on? The required precautions to take are vague at best, and of course mostly aimed toward motorsport and/or hobby uses. It certainly doesn't include boiling it in a pressurized container and setting it on fire as far as I've seen lol. One could argue that's exactly what happens in an engine, but you know... it's not quite the same after all. I guess the major difference is that I might want to boil it to create a gas before combusting it, and that's not quite what it experiences in a vehicle tank...
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[*] posted on 11-4-2020 at 12:03


How about spraying it into a current of very hot air to vaporize it?

I bet it would ignite spontaneously if you sprayed it into air heated to paint-stripper gun type temperatures. (450-550 C)

Force air through a stripper gun with a more powerful fan (or blower) and into a small nozzle to get the velocity up (as long as total mass flow through the gun is about the same nothing should burn out. You'll just need higher pressure in the casing to maintain the mass flow through the small nozzle)) then spray in the nitro (in the tube after the nozzle, not into the stripper gun) with something like a fuel injector nozzle. Maybe water cooling for the fuel line/injector to play it safe (safe?).

Edit: And flame front speed might be less important with all those little boiling droplets igniting on their own all over the place.

I think however you do end up doing this that efficient combustion will be important as working in a cloud of nitric acid vapors would be a real drag.

It just occurred to me that I don't know how much air one of those guns puts out. You probably want a lot of liters per minute for glass and metal work. It could make a cheap proof of concept though.

[Edited on 11-4-2020 by SWIM]




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[*] posted on 11-4-2020 at 23:03


Quote: Originally posted by SWIM  
How about spraying it into a current of very hot air to vaporize it?

I bet it would ignite spontaneously if you sprayed it into air heated to paint-stripper gun type temperatures. (450-550 C)

Force air through a stripper gun with a more powerful fan (or blower) and into a small nozzle to get the velocity up (as long as total mass flow through the gun is about the same nothing should burn out. You'll just need higher pressure in the casing to maintain the mass flow through the small nozzle)) then spray in the nitro (in the tube after the nozzle, not into the stripper gun) with something like a fuel injector nozzle. Maybe water cooling for the fuel line/injector to play it safe (safe?).

Edit: And flame front speed might be less important with all those little boiling droplets igniting on their own all over the place.

I think however you do end up doing this that efficient combustion will be important as working in a cloud of nitric acid vapors would be a real drag.

It just occurred to me that I don't know how much air one of those guns puts out. You probably want a lot of liters per minute for glass and metal work. It could make a cheap proof of concept though.

[Edited on 11-4-2020 by SWIM]


Huh yeah that's an interesting concept. I've been wanting to try something along those lines for a while anyway, but with other liquid fuels. A hot air gun puts out way more air than I'd need for a torch, no problem. I've no feel for it on a numerical level(liters/minute-wise) but based on my experience I would say a typical hot air gun would be good for at least 30 kW of hydrocarbon combustion. With nitromethane needing less air I guess probably 50-60 kW? I think the ballpark I want to be in is similar to a small-medium oxy acetylene torch, which I'd estimate to be in the 6-8 kW range.

But as you say, I'd need pressure/velocity for mixing action, direction and probably some venturi effect. It's likely safest to pressurize the air rather than the nitromethane, yeah. But... probably if I went through the trouble to find high conc. nitromethane I might as well do it properly. I could build a simple hot air gun and ditch the fan completely, I can't see any kind of fan providing enough pressure anyway. Instead I'd run it off compressed air directly, and just have simple closed loop PID circuit regulate the air temp with a resistive heating element running off 230 VAC...

You gave me some cool inspiration, that's all I'm ever looking for lol, thanks!
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[*] posted on 12-4-2020 at 01:32


Quote: Originally posted by Junk_Enginerd  
not quite what it experiences in a vehicle tank...


I agree, there are some very crucial differences.

I don't know much about NM or liquid fueled rockets, but I do remember that Clark mentions NM monopropellants in "Ignition!". That book doesn't go into the finer details, but it's free, pretty darn hilarious at times and a must-read for anyone interested in energetics.

Either way, I would consult the rocket scientists on this one. NM has been studied as a monopropellant probably since long before WWII, so chances are much of it is declassified by now. Look for data on regenerative cooling, this is where they use the fuel to cool the combustion chamber and nozzle.





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[*] posted on 12-4-2020 at 17:47


Quote: Originally posted by Junk_Enginerd  
[ I could build a simple hot air gun and ditch the fan completely, I can't see any kind of fan providing enough pressure anyway. Instead I'd run it off compressed air directly, and just have simple closed loop PID circuit regulate the air temp with a resistive heating element running off 230 VAC...

You gave me some cool inspiration, that's all I'm ever looking for lol, thanks!


Suppose you heat the air to 1000C then use it in a propane torch. I would expect that to increase the flame temperature from the typical 1,100C by at least 500C. Engineering the torch would be the problem.




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[*] posted on 13-4-2020 at 14:16


Quote: Originally posted by wg48temp9  


Suppose you heat the air to 1000C then use it in a propane torch. I would expect that to increase the flame temperature from the typical 1,100C by at least 500C. Engineering the torch would be the problem.


But then you need more air because it now occupies a bigger volume.
And why use air really ? 70% nitrogen will be heated along the way for nothing that's a lot of wasted heat :)

I really dont see the appeal of using NM in a torch. It might make a cool looking flame but not as hot as the majority of easily available fuels.
C2H2 burns bright and hot because of carbon. Want more heat ? chose a fuel with a better C ratio than NM.




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[*] posted on 13-4-2020 at 20:49


The reason NM would make it hotter is that you need less external air to burn it. As in you can use a lot more of it, and only need enough air to oxidize part of it. That means that for each megajoule of heat released, you have less nitrogen there to dissipate the heat. Yes, it will be a little hotter than methane burning in air, but it's a total waste, especially since it won't be nearly as hot as methane burning in oxygen. One suggestion is preheat the air. Another is use a more carbon rich fuel.

Would you mind using a preheated stream of carbon vapor as the fuel?




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[*] posted on 14-4-2020 at 00:04


Quote: Originally posted by Herr Haber  

And why use air really ?


Idunno, because it's free?




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[*] posted on 14-4-2020 at 00:06


Quote: Originally posted by Junk_Enginerd  
Quote: Originally posted by caterpillar  
I do not know if nitromethane torch has some advantages over usual gas- air torches. If you wanna hi temp torch, you may use the mix of toluene+tetranitromethane. But these compounds must be mixed in some proportion- the excess of tetranitromethane makes such a liquid very sensitive and powerful explosive.


Uh huh okay, lets see...

TNM forms extremely powerful explosive mixtures when fuels are added in stoichiometric proportions. Many of these mixtures show sensitivity to impact even higher than that of nitroglycerine.[13]

TNM reacts with moisture at elevated pH to produce trinitromethane (nitroform) which reacts easily with metals to form highly unstable and explosive salts.


Ahh I'm noping out of that lol. Most would call me reckless to the point of being an idiot, except I actually do have certain boundaries that I do not cross. I can deal with flames, molten metals going everywhere, toxic things... But things that go unpredictable and risk getting violently surprise-explosive when not carefully watched and treated absolutely properly isn't for me. It did lead me to some interesting reading though, so thank you for that.


Yeah, I didn't mean that you have to make such experiments. It was only a piece of information. Moreover, TNM is toxic like mustard gas. I read about an incident in Germany, it was if I'm correct, in 1923. They used the aforementioned mix to get hot flame. The percentage of components was given in grams. Once laboratory assistant mixed up grams and milliliters. Due to the hi-density of TNM, it was not the same as if grams had been used. Well, in short words. 20+ were killed immediately.




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Junk_Enginerd
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[*] posted on 14-4-2020 at 01:05


Quote: Originally posted by wg48temp9  

Suppose you heat the air to 1000C then use it in a propane torch. I would expect that to increase the flame temperature from the typical 1,100C by at least 500C. Engineering the torch would be the problem.


Yep. That's why i've been meaning to try it, should be interesting. But you're not gonna get away from the basic power sum of it...

If I want an 8 kW torch for example, and I have a 3 kW propane torch, adding 2 kW of electricity to that is probably not going to add upp to more than 5 kW in the end. Engineering is the smallest hurdle for me, personally. It's what I do all day after all. Chemistry is my weakest area...

Quote: Originally posted by Herr Haber  
Quote: Originally posted by wg48temp9  


Suppose you heat the air to 1000C then use it in a propane torch. I would expect that to increase the flame temperature from the typical 1,100C by at least 500C. Engineering the torch would be the problem.


But then you need more air because it now occupies a bigger volume.
And why use air really ? 70% nitrogen will be heated along the way for nothing that's a lot of wasted heat :)

I really dont see the appeal of using NM in a torch. It might make a cool looking flame but not as hot as the majority of easily available fuels.
C2H2 burns bright and hot because of carbon. Want more heat ? chose a fuel with a better C ratio than NM.


Ah, but the heat also increases the flame velocity, so it's not quite that simple. The volume is not a problem as long as you can increase the gas flow speed without having the flame burn out.

Duh, air is everywhere and it's free. The only real alternative is oxygen, and it's surprisingly expensive and a hassle to refill.

I've made diesel torches which I suppose should be a quite high C ratio fuel, no? They're not that great. The energy in the fuel and the temperature of the flame is barely relevant. Delivering lots of heat boils down to being able to burn a lot of fuel in a constrained volume at a high rate, which in turn ultimately boils down to flame speed. NM needing less air means removing a major component of the gas flow, and thus being able to burn more faster.

Quote: Originally posted by Vomaturge  


Would you mind using a preheated stream of carbon vapor as the fuel?


Been there, done that. ;)

The problem with a carbon arc torch is that it makes a goddamn mess. It sprays carbon over everything, shit gets oxidized to crap since it doesn't supply a reducing atmosphere like a flame does, and it's pretty difficult to control exactly where the heat goes. Plus you have to use a welding mask which is bothersome.

Another issue is that suitable carbon electrodes are a little more difficult to find than I'm comfortable with. I can extract them from carbon-zinc batteries, but you only get 4 rods. They are consumed in 10-15 minutes of active use. Such a battery is $3-4, and what's worse is they're getting increasingly difficult to find as they're replaced with more modern alkaline batteries. Haven't been able to find a retailer that sells proper welding carbon electrodes to anything but businesses.
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[*] posted on 14-4-2020 at 04:20


Quote: Originally posted by Fulmen  
Quote: Originally posted by Herr Haber  

And why use air really ?


Idunno, because it's free?


But if you're looking for heat, it's 70% inert ;)

When I wrote that I was just having fun thinking about the thousand of conversations I've had with carbide lamps enthousiasts. I got about 80 in my limited collection.
A couple of years ago I received thousands of burners, looked up a lot of information, had enlightening talks.

The lesson: our ancestors were geniuses :)




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[*] posted on 14-4-2020 at 08:04


I know, I know. But the fact is that many gases are prohibitively expensive in smaller amounts. If you can get around the need for O2 by using NM, why not?



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[*] posted on 14-4-2020 at 14:50


Here are some fuel flame temperatures.

Gasoline provides about 42–44 MJ/kg, whereas nitromethane provides only 11.3 MJ/kg, meaning You will need even more fuel to heat up the mass.

It has a flame temperature of about 2,400 °C, given it has most of the oxygen contained, blowing air would not increase the temperature by a lot.

My brother is into RC, and the fuel he uses has only 25% NM, which is considered a high percentage. (Rest is 7% lubricant and methanol), it might be not because of explosion hazard, but rather to keep the tiny engine in solid state.

This does not look like a good deliverer of energy. But it might look cool!




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[*] posted on 15-4-2020 at 04:39


Quote: Originally posted by TheMrbunGee  

Gasoline provides about 42–44 MJ/kg, whereas nitromethane provides only 11.3 MJ/kg, meaning You will need even more fuel to heat up the mass.

It has a flame temperature of about 2,400 °C, given it has most of the oxygen contained, blowing air would not increase the temperature by a lot.



Yup, the more oxidized the fuel = less heat.

But that said, a torch working on the same principle as those alcohol burners that you have to pre-heat could work and have a decent size looking grey flame without the need for oxygen.




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[*] posted on 15-4-2020 at 08:25


Nitromethane also seems like a particularly poor choice of fuel for a torch simply because of its potential for autodecomposition:

CH3NO2 >> H2O + CO + 1/3 N2 + 1/3 NH3 + 285.8 kJ/mol

I had initially looked up acetonitrile, based on the similarity to cyanogen, but its flame temperature is unremarkable. Acrylonitrile on the other hand might boast a somewhat hotter flame (data unavailable; math hard). But it's already difficult to beat acetylene with a flame temp of 2500 C in air.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 15-4-2020 at 12:08


I think oxy-acetylene would burn so much hotter than nitromethane that the addition of nitromethane would have little value. It would also be a significant challenge to add a liquid fuel to a gas mixture, and it might reduce the effectiveness of the gas mixture.

Plus, nitromethane is so expensive and hard to come by, it would be much better used to sensitize ammonium nitrate or make PLX type explosives for blasting purposes, but it’s your money!
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