Over square operation and Specific Range

[mechman600]

Originally Posted by Old Tele man

...not many reciprocating aircraft engines using catalytic converters that I know of.

True. That's not what I was implying.
Neither do airplane engines run past 17:1. Even 16:1, for that matter.

[gone-ot]

Originally Posted by mechman600

True. That's not what I was implying.
Neither do airplane engines run past 17:1. Even 16:1, for that matter.

...but, pilots can (accidentally or stupidly) lean engines out to 16-17:1, something that we automotive drivers cannot (realistically) do.

[iveyjh]

I'm stupid then.

[gone-ot]

Originally Posted by iveyjh

I'm stupid then.

Huh? Are you able to actively control the A/F-ratio of your Honda and Chevy engines while you're driving? Do you have access INTO the ECM's and their software coding and mappings?

[serialk11r]

At 16:1 you are definitely not limiting NOx emissions. NOx conversion efficiency falls dramatically with excess oxygen and by the time you're at 16:1 most of the NOx you send to the cat is not converted, so that's actually the setting where you'll be producing maximum NOx.

Personally I'd attempt to run 17-18 because the lowered combustion temperature would reduce the NOx a little, and the excess air should help increase efficiency a bit. I also don't believe NOx is as big of a deal as the EPA says it is, because they let all those diesel trucks roll along the road producing far more NOx than a passenger car ever could while tightening our NOx emissions to <10 ppm. Your gas stove probably emits more NOx than your car does, and it emits it directly into your house.

Obviously if the engine is stumbling at those AFRs then it doesn't work. Maybe you need some hotter spark plugs?

[iveyjh]

Originally Posted by Old Tele man

Huh? Are you able to actively control the A/F-ratio of your Honda and Chevy engines while you're driving? Do you have access INTO the ECM's and their software coding and mappings?

Yes I do, it's called an Apexi Fuel/Air Controller Safc or Vafc.

[mechman600]

Originally Posted by serialk11r

all those diesel trucks roll along the road producing far more NOx than a passenger car ever could

Diesel trucks are down to 0.2 g/hp-hr, from 1.2 in 2007, 2.5 in 2002, 5.0 in 1994. That's as close to zero that EPA cares about for now. It would be interesting to get an equivalent unit of measure for the automotive side to compare.

[j12piprius]

Originally Posted by ever_green

Overview
For a naturally aspirate engine this means that you basically cannot exceed ~2900 RPM at sea level if you want to stay in oversquare engine operation. This is because at sea level atmospheric pressure is roughly 29 in-hg and 2900RPM/100 = 29. So for my driving I set 2900 RPM as my redline, but to keep the limits softer and add room for error i usually set 2500-2700 as the limit. I have also programmed MAP in in-hg for my scangauge to ensure i'm always operating in an "over square" fashion.

I'm curious how oversquare applys to Dfco and Eonc, vs DWL, which it sounds like is the main application.

I've been using abs kPa on the Ultragauge, which as far as I can tell doesn't have a reading for inHg. Standard atmosphere is 101.3 kPa, 29.92 inHg and 14.696 psi. The following would be relative to using kPa readings, i.e. 10 MAP ~ 300 rpm.

100 > 2992 rpm
90 > 2700 rpm
80 > 2400 rpm
70 > 2100 rpm
60 > 1800 rpm

What about accelerating, when MAP can be considerably higher relative to rpm, for example 1500 to 1800 rpm and 27 Hg ( 90 kPa ); is that acceptable or should MAP trend towards the 100:1 ratio?

[serialk11r]

Originally Posted by mechman600

Diesel trucks are down to 0.2 g/hp-hr, from 1.2 in 2007, 2.5 in 2002, 5.0 in 1994. That's as close to zero that EPA cares about for now. It would be interesting to get an equivalent unit of measure for the automotive side to compare.

Assuming 200g/kWh BSFC that's ~1/750th of the fuel mass emitted as NOx, or about 1/3000th of the exhaust gas (about 3 oxygens per carbon gives you the right mass ratios), which would be 333ppm. I believe the standard for gasoline engines is now under 5ppm, considering how it says the "average" for NOx at smog tests is like 2-4ppm. That would be in line with 1mg/mile or so.

Besides, most of the diesel powered vehicles are not new. Most of the ones I see make all the air along the street unbreathable as they pass by, which even a de-catted car doesn't do.

[mechman600]

Not quite.
When I monitor NOx sensor values on a 2010+ 15L diesel, engine out NOx is around 300-400 PPM at max load (EGR engine). After SCR NOx (out of the exhaust stack) stays around 5-20 PPM at cruise and goes up to maybe 80 PPM at max load.