05-17-2020, 11:38 AM
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#1 (permalink)
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Cyborg ECU
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18:1 AFR is "cleaner"?
So, assuming the catalyst is fully warmed-up, doesn't a graph such as this indicate that an AFR of 18:1 is better for emissions than stoich? I realize we can only be in lean burn under light throttle and load conditions. Nonetheless, at 18:1 only 02 is higher than at 14.7:1. That seems gooder for everybody. So 18:1 is simply better, no? Why aren't all cars in lean burn under light load and part throttle and steady cruise on freeways?
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.
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05-17-2020, 11:58 AM
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#2 (permalink)
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Master EcoModder
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Probably because of the nox spike at 16:1. They appear to be concerned about the nox most.
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05-17-2020, 12:21 PM
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#3 (permalink)
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Cyborg ECU
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Quote:
Originally Posted by me and my metro
Probably because of the nox spike at 16:1. They appear to be concerned about the nox most.
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That makes sense, but at 18:1 NOx is lower than at stoich and much lower than 16:1. So assuming an efficient catalyst, less NOx going into the catalyst means less coming out the tailpipe, no?
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.
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05-17-2020, 02:58 PM
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#4 (permalink)
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Corporate imperialist
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The EPA declared war on NOx and the government want us all to buy more gallons of fuel.
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05-17-2020, 03:24 PM
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#5 (permalink)
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Cyborg ECU
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Quote:
Originally Posted by oil pan 4
The EPA declared war on NOx ...
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Again though, at 18:1 AFR, this chart suggests NOx is lower than at 14.7:1 and so is CO2. Why isn't 18:1 lean burn common place in contemporary cars? Or is it maybe common and not touted like in the old days of the 90s and early 00s?
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.
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05-17-2020, 03:47 PM
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#6 (permalink)
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home of the odd vehicles
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Quote:
Originally Posted by California98Civic
Again though, at 18:1 AFR, this chart suggests NOx is lower than at 14.7:1 and so is CO2. Why isn't 18:1 lean burn common place in contemporary cars? Or is it maybe common and not touted like in the old days of the 90s and early 00s?
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That graph is assuming you don’t have a cat,
Given the circumstances today it’s likely because of two things
1. We never did it so it’s impossible (hear that a lot)
2. Emissions controls (not represented by the graph) reduce Nox below the graph,
the unfortunate part is because we are laser focused are a single pollution percentage we rather burn more fuel and make more pollution in grams per mile.
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05-17-2020, 03:56 PM
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#7 (permalink)
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Corporate imperialist
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Oh its too difficult for obsolete binary O2 sensors to detect and maintain 18:1 and it was decided that stoich was cleaner not with actual science, but with politics.
And most importantly it burns more fuel.
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1984 chevy suburban, custom made 6.5L diesel turbocharged with a Garrett T76 and Holset HE351VE, 22:1 compression 13psi of intercooled boost.
1989 firebird mostly stock. Aside from the 6-speed manual trans, corvette gen 5 front brakes, 1LE drive shaft, 4th Gen disc brake fbody rear end.
2011 leaf SL, white, portable 240v CHAdeMO, trailer hitch, new batt as of 2014.
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05-17-2020, 04:06 PM
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#8 (permalink)
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Somewhat crazed
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Doesn't the cat have overtemp isses when too much air is introduced?
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05-17-2020, 04:09 PM
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#9 (permalink)
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Cyborg ECU
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Quote:
Originally Posted by rmay635703
... 2. Emissions controls (not represented by the graph) reduce Nox below the graph,
... we rather burn more fuel and make more pollution in grams per mile.
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I am aware that the graph assumes no CAT. But if the exhaust in cleaner going in, it'll be cleaner coming out, assuming a properly efficient CAT, right? Am I wrong about that? Cleaner in, means cleaner out?
This all would suggest that modifying a car to run lean at 18:1 is likely cleaner than stock. Hondas like the VX and HX and the Insight all did lean burn from 1992-2006 and they had the best or almost best emissions ratings (LEV, ULEV, and such). Those lean burn systems relied merely on ECU tuning, a wideband O2, and a knock sensor, IIRC. Not a super high bar.
I guess I am surprised because I thought the LB engines had higher NOx, but that is no necessarily true, unless something is still missing from this picture.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.
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05-17-2020, 04:14 PM
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#10 (permalink)
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Cyborg ECU
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Quote:
Originally Posted by Piotrsko
Doesn't the cat have overtemp isses when too much air is introduced?
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That is the kind of thing I cannot find clear answers for online. I see contradictory things... some say lean burn makes the catalyst cooler.
__________________
See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.
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