Timing and emissions

ijames

Active Member
Joined
Jun 1, 2001
Gofstbuick posted this link in another thread: http://franzh.home.texas.net/lean.html It gives a very nice chart showing what happens to the important gases (HC, CO, CO2, O2, NOx) as a function of air-fuel ratio. However, what about ignition timing? How does that affect things? My guess would be that more advance would give more complete combustion and a hotter chamber, so my guess is lower HC, CO, O2, and higher NOx and CO2. Anyone actually know the trends? In my experiments making an emissions chip for my car, it is amazing what a little load will do. Idling in park or neutral the best I could get the HC (without a cat) was about 400 ppm, and the CO I forget but maybe 0.2%. Drop the car in gear or rev it up to 2000 rpm and the HC fell to less than 100 ppm and the CO to less than 0.1%. Here in MD I face the IM240 dyno test so I really don't care about the no load idle, but friends in DE have a simple idle in park, then 2000 rpm in park, test and I want to know how to help them do better so I am hoping that the answer is in the timing map. Anyone?
 
Originally posted by ijames
My guess would be that more advance would give more complete combustion and a hotter chamber, so my guess is lower HC, CO, O2, and higher NOx and CO2.

That's it.
As far as trends, particular applications can vary.
 
Actually Carl, its been my experience since I started doing emissions testing some 15 years ago, that actually, advancing timing raises HC. I imagine, by the nature of the beast, and depending again on mixture, it would also raise NOx as well. CO however is as far as I have been instructed, and couldnt prove otherwise, is precisely a component of mixture. And I have never seen timing change CO.

Proof in the pudding? Well, one trick to getting a car thru emissions (no, I'd never do this) is to put the car into field service mode. Among other things, puts the car at a base timing so you can adjust it. Another trick was to pull the vacuum advance hose off. I've seen most everything as far as trying to get a car to pass over the years. Now, for NOx, since it is a product of combustion chamber temps (the temp at which the air splits off into different molecules (you're the chemist here, I dont remember what exactly, all I know if O splits off the N atom? )ANYWAY, advancing the timing, starts the burn event earlier, thus keeping the heat in the chamber longer, which heats the chamber MORE. Proof? Take a NOx readikng, then advance the timing, and retest. Retard and retest. Again, another trick, is remove some timing from the car. Get the chamber heat into the exh manifold where it can burn the HC's (a kind of natural catalytic converter if you will) and out of the combustion chamber.

This is just my experience in the real world, DOING emissions testing every day for years. Your results may vary, no warranty expressed, or implied. The people performing these stunts are professionals. Never try this at home. Use only with adult supervision.
 
So Jim, you see lower HC by retarding the timing? Was that with a cat or have you ever done it on a car without a cat? I've heard that putting the ecm into aldl mode by jumpering the top right two pins in the aldl connector, which is supposed to set the timing at a fixed 10 degrees has helped some pass over the years. I'm trying to get some guidelines before I pester my friend into letting me use his hc/co tester again and spend a Saturday burning chips :).
 
Carl,
I have question. If you ground the diagnostic link (with KOER), thus initiating fuel service mode, how well will the vehicle accelerate to 58mph, assuming MD is using a I/M240 test? How hard will it be to stay within the drive trace when timing is fixed?
I too am not a chemist (so by all means, correct me if I'm wrong), but NOx was explained as follows:the atmosphere is up of approx 79% nitrogen, 20.8% oxygen and the rest (kinda like gilligans island). Beyond 2500 degrees, free floating oxygen can combine with nitrogen. But the oxygen molecule can be in the form of O, O2, O3, etc.,,. Hence the "x" part of NOx, meaning an unknown oxygen part is combining with nitrogen. As Jim says, CO is really a guage af mixture, because it's partially burned fuel. Before catalytic converters, O2 could be used to determine rich or lean, because too much O2 (3.0% or higher was lean and 1% or lower was rich), but the cat completes combustion and therefore uses up the O2 (in the oxidation bed). CO2 another byproduct of combution (and H2O) determines whether the mixture is burning efficiently. I always look for 14.5% and higher, but again, the cat is involved (and will try to complete combustion).
 
Carl...I want to apologize in advance for this

So I am sorry for intruding on your thread but..............................................................................................

JOE!!! I NEED my car to pass. Come get it and don't bring it back till it passes or you set it on fire, whichever comes first! (At this point I don't know if I even care anymore... :D )
I have a July 27th appointment at DMV and I need this resolved first or they are going to be mad at me!.
Call me when you can.

Thanks Carl for the interruption.... Go on, continue, .... LOL :D



Bruce
WE4
 
Who's Joe? For that matter, who's gofstbuick? Whatever happened to real names?
 
Top