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Strategies to keep cats from melting

IamCDNJosh

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I think we all have been using smart phones for nearly 15 years now. Batteries have not gotten better in that time. With my experience of having to replace an expensive phone every 1-2 years because the battery won't hold it's charge for a complete 8 hour day with mild use and the manufacture choose to not make a known failure point easily replaceable... I'm not all too excited about going through the same thing but with a 40k$ car.
Batteries with solid state cathodes are now being tested by auto manufacturers theoretically able to do 1000's of charging cycles with limited degradation. Early Tesla Model 3's are starting to hit 100k miles, showing about 6% degradation on the battery.

I disagree with EVs being a more enjoyable drive. I've been in a few, and even ridden in one around a track and they have no soul at all. Quiet, way too refined, all the joy is sucked out of the experience. What's the point? Boring. And mass adoption will never happen, the infrastructure doesn't exist nor can the electrical grid handle it, especially considering they don't want to use fossil fuel or nuclear for power generation.
Cool story.
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K4fxd

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Cool story.
If you want plug in electric cars you need electrical generation capacity. Along with places to plug them in. We are reducing capacity and increasing demand. Not a smart thing to do.
 

SpeedLu

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Cool story.
Be as dismissive of my statement as you like, doesn't change the reality that EVs face an impossible climb to mass adoption. Try to be more open-minded if you're going to engage in discussion in a public forum. 🙂
 

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SpeedLu

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engineermike

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I did a test this morning to see if I could avoid COT altogether at WOT. I had a good starting point because I'm able to run 22-23+ deg timing at WOT at 9-10 psi boost, which helps with the EGT. I commanded .75 lambda just after the shift, ramping down to .73 just before the next shift. This successfully kept the EGT low enough to prevent it from triggering COT. I verified using the mid-bed thermocouple that the actual temp stayed in the safe range. This was for pulls from 45-135, but the temp was flatlined so I think it would avoid COT for a full quarter mile pass if needed. I'll share the log if anyone is interested.
 

engineermike

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Another interesting note is that the above method resulted in a 0.3 second reduction in 60-130 time…maybe I’m onto something.
 

GregO

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I commanded .75 lambda just after the shift, ramping down to .73 just before the next shift.
So 11.03 ~ 10.73 AFR ?
What were the lambda settings before your changes ?

Interestingly enough, CVT speed run engines achieve maximum WOT power at mid 11’s AFR with upper 1000° to mid 1100° F EGT’s (depending on probe placement) in the WOT time range of 8 to 10 seconds.
This is with fuel devoid of any oxygenates.
 
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slime_bullet

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I log with HPScanner. They are called O2 Voltage B1S2 and B2S2. The voltage doesn't matter as much as the switching. With new cats the voltage drifts very slowly over time. With aged cats, the voltage will toggle high to low (I think 0.450v is the mid-point) back and forth slowly, like 5-30 second swings. With failed cats, the voltage will swing very rapidly. The pic below shows a new cat (gray) and an aged but still functioning cat (white). The timespan is 30 seconds.

1615249420334.png
Mike, I'm going to guess if you have high
I log with HPScanner. They are called O2 Voltage B1S2 and B2S2. The voltage doesn't matter as much as the switching. With new cats the voltage drifts very slowly over time. With aged cats, the voltage will toggle high to low (I think 0.450v is the mid-point) back and forth slowly, like 5-30 second swings. With failed cats, the voltage will swing very rapidly. The pic below shows a new cat (gray) and an aged but still functioning cat (white). The timespan is 30 seconds.

1615249420334.png
Mike, I'm going to guess that if you have high flow cats that this logic can be thrown out the door?

20220706_205750.jpg


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Mspider

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Be as dismissive of my statement as you like, doesn't change the reality that EVs face an impossible climb to mass adoption. Try to be more open-minded if you're going to engage in discussion in a public forum. 🙂
Anything is possible with a long enough time horizon though. Which is why I kind of get frustrated when people use the word "never". Got look at history and you will learn that we today are doing a lot of things people said would never happen.

Just sayin
 

engineermike

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I've been doing some thinking and figuring and I might have stumbled onto something. I knew the temps we are seeing in the cat aren't hot enough to melt the ceramic substrate. And, the temps I've been measuring aren't hot enough to appreciably degrade the catalyst wash-coat. But I've inspected 2 "failed" stock cats and the failure wasn't melting or wash-coat phase change - it was cracks in the monolithic block allowing exhaust to bypass the catalyst. I've seen a pic or two of the monolithic block breaking into smaller pieces and clogging the muffler. So my hypothesis is that the peak cat temp can be controlled using lambda pretty easily, but the heat-up rate at WOT causes differential thermal expansion (the center heating up faster than the edges) and that stress causes the cracks. If this is true, then we are actually failing stock cats by heating them up too quickly, like, doing a burnout or dyno-pull after a cool-down period. I could see that happening quite easily.

So it gets even better...I did some looking around and it turns out that the Hellcat actually has a programmed max cat temp just like we do. But the Hellcat also has a max heat-up rate. If the temp rate of change is too high, it will go into COT and enrich it and slow down the rate of change.

Most Ford tunes I've seen run lambda at .83 - 87 at low/mid rpm (stock coyote is .85) then add fuel at high rpm. This is true for Whipple and Roush as well. I went ahead and changed mine to .79 at low rpm, as I believe this will slow down the temp rate of change.
 
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Torinate

Torinate

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Wow that's really interesting.

So taking this into consideration, it's no so much max temp, but how it's getting there so quick. Hellcat engineers seem have figured it out. Is there anything like that on the GT500 tune?

So limiting the large change of heat cycle may be the key to keeping them alive.

Great info Mike.,
 

engineermike

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I don’t see anything about a heat-up rate limit in any ford tune.
 

MCS

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@Torinate let me know if you find the solution man, I'll be looking at this next year myself. We're almost on week three (Monday) of waiting for my Roush Phase 2 kit so we'll need this next year I'm sure :)
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