3 ms·
Lean/Stoichiometric is one thing, you still can (in theory) have perfect combustion on that part of the axis. Running very rich will increase both NOx and CO, f
by sudosysgen 4y ago
Lean/Stoichiometric is one thing, you still can (in theory) have perfect combustion on that part of the axis. Running very rich will increase both NOx and CO, for example.
- bumby 4y agoIt's a bit more complicated than just air-fuel ratio. The primary mechanism in NOx formation is combustion chamber temperature, while the primary mechanism in CO formation is incomplete combustion of HC. If you look at most emission maps, the NOx is decreasing rapidly while CO is relatively flat or increasing. My main point is that combustion is complicated and not as simple as "just do this thing to reduce all emissions". It's often a balancing act, which is why European regulations may be more favorable to diesels than American regulations and the opposite is true for gasoline.
- sudosysgen 4y agoI definitely agree that within reasonable combustion regimens it's a balancing act. However, when you run your fueling extremely rich like someone that is rolling coal, NOx is going to be higher than in any reasonable tradeoff, because if the irreversible damage to the catalytic converter. It will be far worse than any conceivable lean air mixture.
- bumby 4y agoAh, ok, I'm tracking your perspective now, thanks for continuing the conversation. Yes, I wasn't really speaking to the damage to the catalytic converter. But I think you may have it reversed? Under lean conditions, the Rh2O3 layer in the cat reacts with the Al2O3 to create an inactive oxide. This degrades the ability for NOx reduction.
- sudosysgen 4y agoUnder very rich conditions, unburnt fuel will combust in the catalytic converter, drastically increasing the temperature and greatly speeding up oxidation, which degrades its effectiveness with regard to all pollutants, including NOx, and oftentimes pretty dramatically.
- bumby 4y agoHigh temps in the catalytic converter can sinter the precious metals, reducing the surface area of catalytically active surfaces, but I believe the effect is much more pronounced in CO and HC activation. The conversion of NOx is much more constant.
- sudosysgen 4y agoAh, I was under the impression this wasn't the case, so you're probably right. Do you have a source I could refer to?
- bumby 4y agoInternal Combustion Engine Handbook by van Basshuysen and Schafer. My edition is rather old (2004) so there may a newer one with different info as diesel and emission tech has changed a bit in the last 20 years.
- sudosysgen 4y agoThank you! I'll take a look and try to find a more up to date source if possible.