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Obormot

timing advance for E85 and ethanol

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There are many instances of that rusty.  The wife's Honda Insight runs in lean burn mode and has a catalytic converter which stores NOx for a period.  You will often see instantaneous fuel efficiency surge to 75mpg on flat, level road @ 70mph.  But when the computer detects the catalyst is 'full' of NOx, the car drops out of lean burn (ie goes into 'rich burn') to put extra heat into the catalyst to reduce the NOx into N2 and O2.  As a result, you see a substantial drop in MPG during this lean burn phase.  Additionally, the auto trans version doesn't have the lean burn mode, was rated at ~54 mpg instead of ~68 for the manual.  But the auto trans version has the better "SULEV" rating while the manual gets only the "SLEV" rating.

 

As far as the advance issue, I think we're talking the same thing, just different terms.  Olav says 'hotter exhaust' with more retard and I mentioned 'hotter combustion' with more advance.  These are essentially one in the same.  For a given quantity of fuel, you can either burn it in the combustion chamber under optimal timing, or in the exhaust pipe (with retarded timing).  If you start the combustion late, the gas is still on fire when it leaves the chamber, so of course this heats up the cat tremendously and burns up all the HC emissions, just like the table shows.  The trouble is, if you look at either my test or the honda test overall fuel consumption rises very rapidly with retarded timing.

 

NOx dropped with either retarded timing or richened mixture - either one will substantially cool the combustion event.  It rose with a lean mix or advanced timing - both notorious for hotter combustion.

 

CO2 was fairly stable - you're either burning the fuel in the combustion chamber or the catalyst, either way you get the same CO2 out.  The lowest CO2 was with the rich mix, which also happened to spike up the HC's.  This is simply a sign of inefficient combustion - unburned fuel was present, so products of combustion were lower.

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