The Naked Scientists

The Naked Scientists Forum

Author Topic: De-nitrogenizing air.  (Read 5016 times)

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
De-nitrogenizing air.
« on: 20/08/2007 14:27:22 »
Anyone know a crude way of making air have a lower percentage of nitrogen?
i.e A method that an amateur could setup.

I ask as I'd like to experiment with feeding a car engine this way!


 

Offline rosy

  • Neilep Level Member
  • ******
  • Posts: 1018
  • Chemistry
    • View Profile
De-nitrogenizing air.
« Reply #1 on: 20/08/2007 18:10:01 »
Nitrogen gas is chemically pretty stable. Although nitrogen containing molecules are crucial to biology, relatively few organisms have evolved the ability to capture it and make it biologically available. I'm afraid the only way I know of extracting the stuff from air is to cool the air to below the boiling point of nitrogen (-196 oC ish), and then allow the liquid oxygen to boil off (b.p. about -182 oC). Pretty difficult without specialist cooling apparatus.

The other consideration is that if you take out the nitrogen you will (as is presumably your plan) create an oxygen rich atmosphere. If I recall correctly, in a 40 % oxygen atmosphere meat (and therefore human flesh), once ignited, will sustain burning. Which is not necessarily a good idea.
 

another_someone

  • Guest
De-nitrogenizing air.
« Reply #2 on: 20/08/2007 18:32:07 »
The other consideration is that if you take out the nitrogen you will (as is presumably your plan) create an oxygen rich atmosphere. If I recall correctly, in a 40 % oxygen atmosphere meat (and therefore human flesh), once ignited, will sustain burning. Which is not necessarily a good idea.

I ask as I'd like to experiment with feeding a car engine this way!

I don't see that burning flesh is going to be an issue here; but possibly burning metal might be.

The other problem is that if you are trying to feed it into a car engine to increase engine temperature, then I would imagine you need a fairly high throughput, and with relatively low energy cost.

I cannot see how these constraints can be met, but maybe that is just my limited imagination.
 

another_someone

  • Guest
De-nitrogenizing air.
« Reply #3 on: 20/08/2007 18:38:58 »
Nitrogen gas is chemically pretty stable. Although nitrogen containing molecules are crucial to biology, relatively few organisms have evolved the ability to capture it and make it biologically available. I'm afraid the only way I know of extracting the stuff from air is to cool the air to below the boiling point of nitrogen (-196 oC ish), and then allow the liquid oxygen to boil off (b.p. about -182 oC). Pretty difficult without specialist cooling apparatus.

Although it would probably not be any better than the above, but another means I could think of doing it would be to feed hydrogen and air into a fuel cell, collect the water from the fuel cell, and then use electrolysis to split the water into hydrogen and oxygen, and then feed the hydrogen back into the fuel cell.

The energy generated by the fuel cell could be used as part of the energy supply to later split the water, but it would be insufficient to do the job completely, so energy would still have to be pumped into the system from outside.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
De-nitrogenizing air.
« Reply #4 on: 20/08/2007 20:12:44 »
Anyone know a crude way of making air have a lower percentage of nitrogen?
i.e A method that an amateur could setup.

I ask as I'd like to experiment with feeding a car engine this way!

As Rosy wrote, it's very difficult.
A non-easy way could be this: at a certain temperature, I don't remember, something about 300 or 500C, metallic copper absorbs oxygen from air (to form CuO or Cu2O), which then releases at an higher temperature (~ 600C?).

Of course you want to remove nitrogen, but it's the same: you throw away de-oxygenated air and keep the oxygen!
« Last Edit: 20/08/2007 20:37:19 by lightarrow »
 

lyner

  • Guest
De-nitrogenizing air.
« Reply #5 on: 21/08/2007 23:32:41 »
If you just want to enrich the Oxygen content, pressurising the air can be pretty effective - superchargers do this and work very well at increasing internal combustion engine power.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8655
  • Thanked: 42 times
    • View Profile
De-nitrogenizing air.
« Reply #6 on: 22/08/2007 20:49:20 »
You will kill the engine but if you insist.
http://www.nda.ox.ac.uk/wfsa/html/u01/u01_009.htm
Have fun plugging it in.
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
De-nitrogenizing air.
« Reply #7 on: 23/08/2007 14:48:57 »
Thanks for your ideas everyone!

You will kill the engine but if you insist.
http://www.nda.ox.ac.uk/wfsa/html/u01/u01_009.htm
Have fun plugging it in.

- This sounds the most manageable for an amateur effort.
Although I'm quite aware that messing with IC engines is a serious business!

The reasons I'm interested in such a process has several themes:
firstly I'm currently running my (1960's) car with a smaller carb, which gives a leaner mixture & it works fine! However I'm aware I've probably increased my level of NOx in the exhaust. So, Idea 1: don't introduce nitrogen in the 1st place.
Second, weakening the mixture further or using a lower calorific fuel (get back to you this one!) plus a richer oxygen atmosphere should create an equal Bang in the cylinder (to a point - today's car engines use leaner burning mixtures anyway). Idea 2: remove the inert gas from the reaction - particularly as an old carburettor based car gives poor fuel/air mixing to start with.

Clearly, as mixture changes, so does ignition timing - which will have to be worked out as I go.  Also I have no wish to damage the engine through the process, but my gut feeling is if there is less fuel - less heat can be created.  I ought to mention that I am aware that weakening a car's mixture (slightly) has a tendency to make the engine hotter! - maybe someone could explain this to me also! (or should I start another thread..)
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
De-nitrogenizing air.
« Reply #8 on: 23/08/2007 15:45:25 »
The reasons I'm interested in such a process has several themes:
firstly I'm currently running my (1960's) car with a smaller carb, which gives a leaner mixture & it works fine! However I'm aware I've probably increased my level of NOx in the exhaust. So, Idea 1: don't introduce nitrogen in the 1st place.
In this case you shouldn't use nitrogen at all, that is, you should use pure oxygen (or the amount of NOx wouldn't reduce, possibly would increase); but then you'll have detonation (even if the amount of O2/fuel mix is little to prevent engine breaking/melting).
Quote
Second, weakening the mixture further or using a lower calorific fuel (get back to you this one!) plus a richer oxygen atmosphere should create an equal Bang in the cylinder (to a point - today's car engines use leaner burning mixtures anyway). Idea 2: remove the inert gas from the reaction - particularly as an old carburettor based car gives poor fuel/air mixing to start with.
It's better to reduce the compression ratio.
Quote
Clearly, as mixture changes, so does ignition timing - which will have to be worked out as I go.  Also I have no wish to damage the engine through the process, but my gut feeling is if there is less fuel - less heat can be created.  I ought to mention that I am aware that weakening a car's mixture (slightly) has a tendency to make the engine hotter! - maybe someone could explain this to me also! (or should I start another thread..)
What does "weakening" mean? It means to lean it? In this case the reason is that the combustion's speed is reduced, so the spark it's too delayed and the heat produced cannot be efficiently converted into mechanical energy, so the engine heats up; it could also burn through the pistons.
« Last Edit: 23/08/2007 15:51:53 by lightarrow »
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
De-nitrogenizing air.
« Reply #9 on: 23/08/2007 17:06:51 »
The reasons I'm interested in such a process has several themes:
firstly I'm currently running my (1960's) car with a smaller carb, which gives a leaner mixture & it works fine! However I'm aware I've probably increased my level of NOx in the exhaust. So, Idea 1: don't introduce nitrogen in the 1st place.
In this case you shouldn't use nitrogen at all, that is, you should use pure oxygen (or the amount of NOx wouldn't reduce, possibly would increase); but then you'll have detonation (even if the amount of O2/fuel mix is little to prevent engine breaking/melting).

I don't know why your inferring I could actually increase NOx's. I'm not planning on adding more nitrogen than air has to start with. Hence there's only as much as potential for NOx creation as there is free nitrogen available (in air).

Second, weakening the mixture further or using a lower calorific fuel (get back to you this one!) plus a richer oxygen atmosphere should create an equal Bang in the cylinder (to a point - today's car engines use leaner burning mixtures anyway). Idea 2: remove the inert gas from the reaction - particularly as an old carburettor based car gives poor fuel/air mixing to start with.
It's better to reduce the compression ratio.
Possibly, but this would involve messing with the fundamentals of the engine, which is not for me!

Clearly, as mixture changes, so does ignition timing - which will have to be worked out as I go.  Also I have no wish to damage the engine through the process, but my gut feeling is if there is less fuel - less heat can be created.  I ought to mention that I am aware that weakening a car's mixture (slightly) has a tendency to make the engine hotter! - maybe someone could explain this to me also! (or should I start another thread..)
What does "weakening" mean? It means to lean it? In this case the reason is that the combustion's speed is reduced, so the spark it's too delayed and the heat produced cannot be efficiently converted into mechanical energy, so the engine heats up; it could also burn through the pistons.
Yes, that makes sense. Thanks!
In that case more oxygen is likely to give a faster burn and counteract this! (?)
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8655
  • Thanked: 42 times
    • View Profile
De-nitrogenizing air.
« Reply #10 on: 23/08/2007 21:15:16 »
Without the N2 the flame burns hotter (because it doesn't waste energy heating N2).
The yield of NOx will rise with the temperature unless you totally remove the N2.
I guess you could try adding Ar or something.
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
De-nitrogenizing air.
« Reply #11 on: 24/08/2007 11:29:53 »
Without the N2 the flame burns hotter (because it doesn't waste energy heating N2).
The yield of NOx will rise with the temperature unless you totally remove the N2.
I guess you could try adding Ar or something.

Thanks. I see it now - heat is the key to NOx forming (around 1500C I've read). So short of there being no N2 around this is going to happen.

- Sorry to you 'lightarrow' for doubting you!

mmmm. I think I'll have to give this more thought!
The other option would to be to combine the method with water injection (with an emusifier) to create even higher expansion rates whilst lowering the temp.
 

The Naked Scientists Forum

De-nitrogenizing air.
« Reply #11 on: 24/08/2007 11:29:53 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums