Quote:
Originally Posted by pgfpro
IMO Internal combustion of mixtures leaner than stoichiometric produces products at lower temperature, and with less dissociation of the triatomic molecules CO2 and H2O.
EGT numbers may read higher when you run leaner than stoichiometric, but this is because you are running a incorrect amount of ignition advance. Leaner A/F will always have a slower flame speed so you will have to adjust ignition advance to utilize the power and keep the heat/power in the engine cylinder and not at the exhaust port. |
it's not that simple...yes leaner AFR is cooler, theoretically...Going leaner than 14.5:1 has a dramatic effect on flame propagation and flame front speed but as you mentioned timing needs to adjust for it. i know timing is important but i was already hitting the maximum limit of ignition timing at 50* ... and this was using EGR as well. Not to mention excessive timing cause engine pinging or knock which i experience in lean high timing situation. The quality of the burn suffers a lot once you go leaner than 14.5:1, at least for my car and 16:1 is the limit in my opinion for a proper burn and good mileage. Also it's not always a good idea to 'keep the heat inside the engine'. specially in a high compression compact pentroof combustion chamber.
So going leaner requires more timing but this is not often possible because:
- you can hit the possible ECU limit for max IGN
- you will experience engine detonation, knock or pinging
- Timing is very sensitive to quality and AKI of fuel used
- High timing and lean conditions develop tremendous amounts of NOx
- Engines can surge in lean conditions
- Causes loss of power