Reducing NOX emissions in gasoline engines. 1

[bayislandsdiver]

I am an automotive technician specializing in European performance cars including but not limited to Porsche, Mercedes, BMW, Jaguar, Volvo, etc..

In Houston, Texas the emissions testing for cars now includes a "dyno test" under load while measuring exhaust emissions.

The "dyno" runs at low speed during the test and tends to load the engine as if the vehicle was climbing a steep hill in high gear.

Some of the performance cars I am working on (Porsche, Turbo Volvo, Jaguar) have a hard time passing the NOX emission standard.

If I add a small amount of alcohol while the engine is running under load can it reduce the combustion temperature and reduce the NOX output?

As I have also been toying with a water injection system to increase mileage, wouldn't this water injection system also reduce the NOX?

Any comments on my questions, or any other thoughts or experience with this problem are welcome.

Bay Islands Diver

 

[HG350]

I'm guessing that if the alcohol has a lower adiabatic flame temp, then yes it could lower the overall combustion temperature which in turn can lower your NOx. Should be some literature on this in any book on combustion. If you can, run the engine at a certain RPM (preferably high)on usual fuel whilst recording the temp until a stabilized or steady state temp is reached. Then do the same experiment but this time once you ahve reached the steady state temp, add small amounts of alcohol to see if there is any change in temp. If the temperature drops by say 100 degrees then you'll probably have a reduction in NOx.

 

[DonClark92586]

I'm also desperate to know of a solution to lower NOX emissions. I have made all the usual repairs and checks and am to the point of using perhaps a fuel additive like alcohol. Does anyone have any experience with any substance that can be added to fuel to reduce NOX emissions? Feel free to contact me directly at "genghisdon@netzero.net" as well as post if you like. And Thanks much, Don ^

 

[drwebb]

Combustion chamber deposit buildup also adds to higher NOx output. High doses of some detergents such as Polyether-amine types can sometimes reduce these over the course of 300-600 miles. Some engine designs are much more prone to this than others.

Some types of detergents used in pump gas may increase CCDs. Alcohols at higher levels can also increase CCDs, so if you ran alcohol routinely rather than just to pass the test then it might temporarily mask the problem while making it worse.

You might ask around among other techs, as many 'cheats' have been devised to get around different emissions tests.

 

[schmidtj86]

Retarding the timing will probably help too, but it is a cheat. EGR will also reduce NOx. So will running richer. The problem is, most of these "solutions" are set from the factory. Maybe the standards are too strict and the decision makers should be alerted and perhaps exceptions can be made. I'm assuming the cars are all fuel injected and have 3-way cats, which usually means you're S.O.L. A good tune-up and clean combustion chambers, and a functioning O2 sensor, cat, and EGR are about all you can do.

 

[DonClark92586]

The vehicle is a 1982 GMC s-15 pickup. The engine was r&r'd about 2 years ago, but has been driven alot since.
Combustion chambers were cleaned, first using water through carb while engine was running, followed by GM's "top engine cleaner" again through carb (its carburated w/fixed jetting and a mixture solenoid as a booster), then removed plugs and poured directly in cylinders- two bottles / applications. Then Techroline fuel additive was added to the fuel and run through. The Cat converter is a week old and was removed when the above cleaning was performed and reinstalled after a couple hours running time. O2 sensor is also new. The EGR valve is 2 weeks old and the passage was cleaned with various chemicals and is open... proof of that is that the engine stalls when you manually squeeze open the EGR valve at idle. All the emissions solenoids are working and the vaccume going to the EGR valve appears to be sufficient. Spark plugs, wires, cap and rotor are all new (a couple weeks ago). The truck runs fine, no error codes are stored on the computer, and all emissions measurements except NOX are good. Timing looks good, although I need to check to see if the harmonic balancer has slipped. Other than that, I don't see what more I can do to fix it. I'm at 2200 for NOX, and I need to get down to 1500 or so at most, and the smog guy's printout says around 550 is the average. If the balancer has slipped, could those few degrees timing make the NOX that bad? I'm told that overly milled heads might do this, but it passed smog two years ago, although I'm also told that they changed the smog test for my area in S. California. Anybody have any ideas? They just gotta have a fuel additive out there for this... anybody?
Thanks, Don

 

[patprimmer]

High compression, a lot of spark advance, lean mixture, low octane fuel all help to make NOx.

I would be checking fuel quality and ignition timeing, and possibly cam timeing. Do this by physically finding TDC and clearly marking it Regards
pat

 

[schmidtj86]

If you retard the timing some (5-10 degrees), i gaurantee you'll pass the NOx sniffer w/dyno loaded test. IF they do timing check though, you might be in trouble. Heck, retarding the timing will also help HC's, if you were close on those.

 

[JoeyHughJorgan]

Don,

Did a recent up-jet on a similar class of vehicle. 3 number drill sizes later & the fat lady sang.
Differences like nite & day - factory jetting was just too dang skinny. We went from gross polluter to clean as ODB-II, according to the tech.

Also, may seem pretty basic here, but ..... is your Cat up to full operating temp prior to I/M 240 test ?? (a recent test of mine aborted due to low exhaust temp - AFTER 30 minutes on I-10 Freeway). Guess we can't be too prepared these days. Once it warmed, however, things were fantastic: CO was ZERO !! (hi & low range), NOx <5% of limit, both ranges (on the above-rejetted '83 E-150).

Correct on emission limits changes there. The standards in SCAQMD get tougher every 4 yrs, I believe.

 

[toytech]

Have you tested pre-cat? A lot of aftermarket cats are not up to snuff when reducing NOX, for a commonly failing model such as yours, I would recomend a catalyst rated for a much heavier vehicle to get a good life span and effective reduction. That carb I believe is adjustable for dwell angle and the internal throttle position switch is also adjustable (has a big effect on timing).

 

[FreeWheel]

No one really addressed your water injection question and I do not know the answer either but it is not uncommon to find water injection on natural gas turbines as a NOx reduction measure to meet state set limits.

 

[toytech]

Water injection will reduce nox in the same manner that an egr valve does, by cooling combustion temperatures somewhat. It will also remove carbon from the chambers over time, reducing compression.

 

[tonyseno]

Perhaps adding a mix of hydrogen and oxygen to the air/fuel mix with an automotive hydrogen generator will reduce the emissions. I think I saw one one ebay motors.

 

[toytech]

Was it next to the electric supercharger?

 

[tonyseno]

Don't know about electric supercharger but heres the link:

http://pages.ebay.com/ebaymotors/index.html?ssPageName=ML01

 

[DonClark92586]

Update on the 1982 GMC S-15 with 2.6 V6. Because the timming mark measured off, I bought a new harmonic balancer (comparison also revealed it was off also- about 2 degrees)and I installed that and retimmed the engine. Just for sport, I threw in some off the shelf octane booster. Unfortunately, the NOx remained just over 2050 ppm, down from around 2200, but short of the acceptable 1550 (and for reference, the average vehicle like mine measures around 550 ppm according to smog database.) At this point, I had exhausted every possibility I (and many others) can think to check or repair, and without firm information on a fuel additive, a low tech solution was adopted. The smog guy, believe it or not, experienced what I can only describe as empathy for me after so many failed attempts. Didn't think it was possible?... Me neither, but it happened. Empathy... it had to be. Out of no where, a paper clip jumped into the diagnostics connector in the vehicle placing the computer in test mode and the NOx dropped like a rock. Down to about 435 or so and all other measures looking about as good. It passed like it was a new car, which isn't far from the truth anyway. So there you have it... the solution. That bit of wizzardry is sure to save you a ka-jillion dollars on your next smog test. This creative solution reminds me of when I used to work in aerospace, for many reasons that there is too little space here to share. Anyway, thanks everyone, and feel free to write if anyone does come up with an &quot;easier to cheat&quot; fuel additive- and consider marketing the stuff and making serious cash. Good luck DonClark@mchsi.com

 

[JoeyHughJorgan]

Sine me up fer haff-a-duzzin o' them clip thangz.
;-)

 

[ShaunT]

Not that you are interested anymore since you got pretty beat up on the smog test, but try a fresh timing chain.

Shaun Tiede ULTRADYNE Arlington,TX

 

[enginead]

If the cars are fitted with three way catalysts then it's either: not enough catalyst to reduce all the NOx to N2 and O2 or (more likely) the closed loop biasing being too lean. Three way cats have a very low tolerance to running lean (less than 1% lean will drop converter efficiency to ~20%) but a fairly broad tolerance to running rich (2-3% before significant CO or HC breakthrough). Hence manufacturers 'bias' the fuelling slightly rich to ensure that on aged catalysts there is little or no breaskthrough of NOx. One way to check this is to measure the rear O2 sensor voltage using the appropriate scan tool. If it's reading ~0.2V at steady state speed and load then the mixture entering the catalyst is too lean (it should read ~0.6V). If this is the problem it's difficult to 'fix' as this is something that is calibrated during the development phase of the vehicle so you need specific tools. The two main options (if available) are to retard the spark or introduce EGR both of which will reduce engine out NOx emissions significantly.

 

[bayislandsdiver]

FreeWheel, RE: water injection on natural gas turbines to reduce NOx for State emissions, don't forget to let everybody know that after the &quot;State test pass&quot; the water injection system is allowed to be removed from the gas turbine to run without it until the next &quot;test&quot; by the State.

P.S. I like the way you think, bayislandsdiver.



enginead,

On your outlook on a good 3 way cat, I believe that a good functioning cat, if the engine is running too rich, can produce exess NOx in the cat while burning it?

Isn't the temperature in a functioning cat, that has enough extra unburn't fuel, and enough oxygen to lite it high enough to produce NOx?

bayislandsdiver