I'm sorry I didn't take the time to read this whole thread; I have two questions though, if someone can be bothered to help me catch up here:
1) A while ago I dug up 2-5 minutes as light-off time, and 25 minutes as cool-off time. (refs below). To me that infers that a engine-on duty cycle much larger than 20% with EOC cycles much less than 25 minutes will tend to light the cat or keep it lit. So I find the OP's results surprising. (Has this already been pointed out?) Yes, both of those figures are crude, real world results depend especially on load, also cat size, also the cat follows an S-shaped Wiebe function, so significant increases in emissions may occur significantly before the cat cools below light-off, but even without doing the math I expected fairly low emissions at 50% duty cycle, which is more typical (for my driving).
2) Has anyone done anything to reproduce the OP's temperature measurement? (Wondering if the OP's car is unique in this regard, or if the sensor is in a biased location.)
Sorry again for my laziness.
References:
1. 25 minutes cool-off time: see Fig 2 and Table 2 on p3:
http://www.nrel.gov/vehiclesandfuels..._emissions.pdf
2. Light-off time:
Bottom of page:
NSLS Everyday Science | Catalytic Converters
Paragraph 1 on p1, Fig 3.2, 3.3, 3.4 on pp 27-29:
http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf