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Old 10-06-2014, 12:26 AM   #11 (permalink)
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Originally Posted by serialk11r View Post
If it seems like it's working fine that's great to know, I'll keep that in mind for when I eventually get some engine tuning system. What does "surging" mean?
on my car the RPMs would start dancing...going up and down. it was quiet scary at first. it was caused by super lean conditions.

The dreaded engine surge - Automotive Service Professional

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Old 10-06-2014, 11:47 AM   #12 (permalink)
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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.
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Old 10-06-2014, 11:59 AM   #13 (permalink)
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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

Last edited by ever_green; 10-06-2014 at 12:05 PM..
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Old 10-06-2014, 01:39 PM   #14 (permalink)
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However in combination with pumping friendly drivebywire and over square engine operation it nets me good results
It also nets you more NOx production than a factory in China. Few people care about the side effects of engine mods, which is sad.
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Old 10-06-2014, 01:44 PM   #15 (permalink)
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It also nets you more NOx production than a factory in China. Few people care about the side effects of engine mods, which is sad.
Read my post above. I said I run 16:1 to control NOx which is why I'm not going leaner.

Also NOx is better than some of the emissions you get at other ratios such as CO.
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Old 10-06-2014, 02:49 PM   #16 (permalink)
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...this paragraph pretty much tells the tale:

"MAP and RPM

To achieve a certain amount of power there are a number of MAP and RPM combinations available to the pilot that will have the same result. The lowest SFC, however, is reached with the highest MAP and lowest RPM for that power setting. Low RPM reduces friction in the engine and improves the air intake (volumetric efficiency) and a high MAP also contributes to a good air intake (less restriction by the throttle valve). Limits are placed on MAP/RPM combinations by the engine manufacturer regarding the prevention of detonation. Just go by the book numbers and no harm is done."
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Old 10-06-2014, 04:12 PM   #17 (permalink)
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Read my post above. I said I run 16:1 to control NOx which is why I'm not going leaner.
I apologize for missing that.

Unfortunately, at 16:1, your 3-way catalyst is really only a 2-way catalyst, as it is useless at converting NOx when the AFR is lean.
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Old 10-06-2014, 04:14 PM   #18 (permalink)
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It also nets you more NOx production than a factory in China. Few people care about the side effects of engine mods, which is sad.
Depends on how lean?







My car passed my local emission with ease. In fact its a lot cleaner then my wife's 2012 Scion tc.
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Old 10-06-2014, 04:55 PM   #19 (permalink)
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Depends on how lean?
Remember, those charts represent pre-catalyst emissions. Sure, engine out NOx is significantly lower past 17:1, but at 17:1
a) the catalyst will do nothing to reduce NOx to near zero, which is what a catalyst does very well when running at 14.7:1 or less.
b) BSFC will likely be terrible anyway.
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Old 10-06-2014, 06:49 PM   #20 (permalink)
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...not many reciprocating aircraft engines using catalytic converters that I know of.

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