Ammonia from Exhaust?

[john_pifer]

Yesterday I backed my WRX into the garage like I always do. I got a little close to one of my bicycles, so I got out and bent over to look between rear quarter panel and the wall to check how close I was. The car was still running, and I got an unmistakable whiff of ammonia coming from the exhaust. I've never smelled ammonia coming from the exhaust of any vehicle.

Did a quick search, and found where someone else had the same thing and asked about it, and one of the replies suggested that Shell puts some kind of nitrogen additive into their gasoline, which could be causing it. I do try to use Shell gas. As a matter of fact, I'd just filled up at a Shell station (always 93 octane).

A question for you chemists: Could certain oxides of nitrogen give off the smell of ammonia? Aren't these oxides of nitrogen the very compounds that are deemed to be harmful to the atmosphere and/or promote greenhouse effect, and aren't they the exact compounds that the EGR system and catalyzers are designed to dispose of?

Something else, which, I'm not sure has any bearing on this, is that I'd just come home from running the car pretty hard on some curvy, hilly backroads for a couple of hours, enjoying my new set of Continental ExtremeContact Sport Tires. So, everything had definitely reached operating temp and been kept there for a while.

The thought crossed my mind that this could also be the result of the interaction of exhaust gas products with the catalyst. But, again, I've never experienced an ammonia odor coming from the exhaust of any engine.

Anyone else experienced this?

 

[Linctex]

Originally Posted by john_pifer
.....one of the replies suggested that Shell puts some kind of nitrogen additive into their gasoline, which could be causing it. I do try to use Shell gas. As a matter of fact, I'd just filled up at a Shell station (always 93 octane).



I have never heard anyone come up with a REAL DEFINITIVE answer to what exactly this so-called "Nitrogen" additive actually is.....

 

[Garak]

I'd wager it were some sort of amine.

 

[StevieC]

I used Shell V-Power exclusively before I had my fuel paid for by my employer in the form of a corporate gas card and not reimburse indirectly. I never noticed this smell from the exhaust and would frequently come out of the house in the morning with the back end of the vehicle near the steps I would go down to get to it. It just smelled like normal exhaust to me. Perhaps it reacts differently with different catalytic converters?

 

[Dyusik]

NAME CAS NUMBER CONCENTRATION %
Gasoline 8006-61-9 100%
Ethanol 64-17-5 0 - 10%
Toluene 108-88-3 0 - 10%
Benzene 71-43-2 0 - 2%
Cyclohexane 110-82-7 0 - 1%
Ethylbenzene 100-41-4 0 - 3%
Naphthalene 91-20-3 0 - 1%
N-Hexane 110-54-3 0 - 5%
1,2,4 - Trimethylbenzene 95-63-6 0 - 8%
Xylenes 1330-20-7 0 - 10%
Cumene 98-82-8 0 - 0.5%
No nitrogen in these

 

[MolaKule]

Most likely from PEA in the fuel but many oil additives are aminic, meaning they contain NHx molecules.

Ammonia is a compound of nitrogen and hydrogen with the formula NH3.

 

[john_pifer]

Well, now that I've noticed it, I'll continue to monitor this, and I'll try to remember to check it if I use a different brand of fuel (which I have to do sometimes on trips when there's not a Shell around; my 2nd choice is BP, which still has their premium labeled "Amoco Ultimate", which, 10-12 years ago, held the top spot as "best gas". Heck, I remember when they had the clear window with the 3 little red balls in the gas pump handle so you could "verify" it was actually clear. It was. I could tell when putting it into my motorcycle gas tank. I don't think it's still the same formula anymore, though).

I use PPPP 10W-30 oil only, and have since the first oil change at 2200 miles.

 

[john_pifer]

Originally Posted by MolaKule
Most likely from PEA in the fuel but many oil additives are aminic, meaning they contain NHx molecules.

Ammonia is a compound of nitrogen and hydrogen with the formula NH3.



I remember reading here that PEA is the active ingredient in fuel system cleaners like Gumout & Techron.

Any comment on how much PEA Shell V-Power contains?

What about in other brands' premium gasoline?

 

[edhackett]

Ammonia is a normal part of the emission profile of a catalyst equipped vehicle. The hot catalyst facilitates the formation of NH3 from the hydrogen in the fuel plus the nitrogen in the air. It wouldn't be a stretch to believe that amine additives could increase the levels.

The amount of NH3 produced will vary with the specific operating conditions of the engine. Richer mixtures and low sulfur favor NH3 formation.

NH3 was a standard analysis for our emission studies. It was a pain to analyze at low levels because the ammonia in your breath would contaminate the samples. With our most sensitive methods (down to 5 parts per billion), you set up the run and left the lab. Ammonia containing cleaning products were forbidden in the building.

Ed

 

[john_pifer]

Originally Posted by edhackett
Ammonia is a normal part of the emission profile of a catalyst equipped vehicle. The hot catalyst facilitates the formation of NH3 from the hydrogen in the fuel plus the nitrogen in the air. It wouldn't be a stretch to believe that amine additives could increase the levels.

The amount of NH3 produced will vary with the specific operating conditions of the engine. Richer mixtures and low sulfur favor NH3 formation.

NH3 was a standard analysis for our emission studies. It was a pain to analyze at low levels because the ammonia in your breath would contaminate the samples. With our most sensitive methods (down to 5 parts per billion), you set up the run and left the lab. Ammonia containing cleaning products were forbidden in the building.

Ed


That's really interesting, Ed. Thanks for posting.

This car is TGDI - reckon the mixture is richer at idle than a PFI engine? I know the Subaru FA20 DIT engine is infamous for diluting the oil with fuel, which, of course, gets even worse the more you idle.

Not sure on the sulfur content of Shell fuel. I know there's been a trend for several years to decrease the amount of sulfur in diesel. But has sulfur in gasoline ever really been a problem?

I remember being in the back seat of my parents' car with my grandfather (an old-school mechanic, b. 1919, RIP) when I was a little boy and smelling that sulfurous, rotten egg smell, and him telling me that meant the car ahead of us was running rich. I didn't know what it meant at the time; now I do. But I do wonder - when a car runs rich and I smell that sulfur (hydrogen sulfide, I'm guessing?), is it because there is a lot of sulfur in the gas, or is it a reaction of certain gases with the catalyst?

 

[edhackett]

Originally Posted by john_pifer

But I do wonder - when a car runs rich and I smell that sulfur (hydrogen sulfide, I'm guessing?), is it because there is a lot of sulfur in the gas, or is it a reaction of certain gases with the catalyst?


Yes, hydrogen sulfide, formed in the catalyst from sulfur and hydrogen in the fuel. The same conditions that favor NH3 formation favor H2S formation. Sulfur preferentially reacts with the catalytic sites, reducing NH3 formation.

For a number of model years Toyotas were notorious for H2S smell when running rich, such as climbing a hill. There was quite a grade on the road to my work. If you smelled H2S there was a 90% chance you'd pass a stinky Toyota a few cars ahead.

Ed