[this_is_tom]

So, i am not a chemistry student (i study civil protection in europe) and part of my thesis involves doing chem work. My faculty doesn't have a lab and my thesis advisor told me to figure it out... But anyway that is not why I am here.

The stuff i am supposed to do is - measure how much NO2 is in car exhausts gases (data i found was mg/km and that is useless), then recreate the concentration and test if mixing it with LPG will cause it to ignite.

My questions are: What simple method can i use to measure the concentration? I found epa 7 and that is not possible. Is There a 'standard' method for testing ignition? Is There a quantifiable limit to 'iniciation' of LPG?

I am sorry for any mistakes and the simple english, its not my first language.

[Enthalpy]

Welcome, Tom!

I had never-ever imagined traces of NO₂ could ignite LPG. It would take hard experimental evidence to convince me. Not only because of the extreme dilution: NO₂ ignites amines, and if no amine is present, it may ignite unsaturated bonds, but these are rare in LPG.

Sensors exist to measure an NO₂ concentration. As individual electronic parts to build a circuit around them, or as a complete apparatus.

The mg/km give you an idea of the NO₂ concentration in the exhaust gas. Take some reasonable consumption in L/100km, convert to moles of C and H, and to moles of combustion products, remembering that air is mainly N₂. Or take the engine's volume and rotation speed. This tells you how many mol/km of exhaust gas, which you can compare with the mol/km of NO₂, and deduce the concentration. Not perfectly accurate because the proportion of NO₂ varies a lot depending on the engine's effort, but already the power-of-ten may give you an idea.

When experimenting what concentration ignites LPG, I suggest to test a very wide range, because the exhaust concentration may very well be 10³ or 10⁶ smaller than the ignition limit. Don't forget to add a few additional causes: warm weather, sunlight, sand aerosol, fine particles.

[this_is_tom]

Thanks for them answer. I did some more research and came up with a plan on how to sample the NO2. Would you please take a look? NO2 reacts with water forming HNO3 and that in water forms NO3- and that i can measure. Does that make sense? Would that work? I know i need to calculate the conversion rate of NO2 to HNO3 but i already found some examples.

One question is, how do i know i dissolved all of the NO2?

[chenbeier]

The problem ist NO₂ soloubility is only middle to poor. And the reaction with water gives 2 NO₂ + H₂O => HNO₃ + HNO₂.

A mixture of nitric and notrous acid. Better is to use sodiumhydroxid as solvent. But also here you will have mixture of nitrate and nitrite.

[this_is_tom]

thank you, that was really helpful. I found a lot of info thanks to that. I found the saltzman method and I have more questions.

I found this Indicator Solution

1. Weigh out 5.0 g of anhydrous sulfanilic acid and add to a 1-L volumetric flask.
2. Add 500 mL of nanopure water.
3. Add 140 mL of glacial acetic acid.
4. Using a stir bar, stir the solution until the sulfanilic acid dissolves. This takes approximately 30 min.
5. Weigh out 0.020 g of N-(1-naphthyl)-ethylenediamine dihydrochloride and add to the volumetric flask.
6. Dilute to the mark using nanopure water.

my question is: compounds in step 1 and 5 are there to make it change color after the sampling right?

if so, do I get NO2-, NO3- or both?
and could I use those Nitrite/nitrate aquarium test kits just to get the ball park or would the acetic acid interfere?

[chenbeier]

The receipe is an indicator which gives a red colour with nitrite.  Also indication of reducing nitrate to nitrite.

https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Sigma-Aldrich/Datasheet/1/73426dat.pdf

[Enthalpy]

https://www.google.com/search?q=NO2+sensor