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Old 05-14-2007, 10:59 AM   #1
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FE driving, good for mpg but bad for emissions?

After reading some more, uh, fanboy'ish, material regarding emissions, I got to thinking about them given the driving style of some high mpg drivers here. Because, in order for a three way cat to function properly, it has to be at operating temperature, which is why there's a rich excursion when it may be cooling down, or on startup, etc. Now, it would be great is all those people doing engine off coasting, and claiming their cars have low emissions levels, were to take a couple smog tests. One with a totally cold car, and one w/ a warmed up version, and see what HC, CO, NOx, etc.. emissions are. Since it would provide us w/ enough info to determine how clean certain types of fuel efficient driving are.

Aside from that, based on anecdotal evidence, I think that this is a big enough concern for manufacturers to get involved. Especially since people pulsing and gliding and hypermiling in a Prius may end up running into the same situation. And maybe even going from PZEV to LEV.
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Originally Posted by MetroMPG
Trying to achieve "deadband" consistently (no energy flow to or from the battery) - ie. pure gliding - was very difficult. It would take quite a bit of practice to become sensitive enough to use the pedal to get that state on command.
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Originally Posted by FireEngineer
The Camry hybrid is VERY difficult to get into a glide compared to my Prius. Seems to be a common "fault".

Wayne
Imo, by making it hard to put into a glide, Toyota has insured that the driver, short of keying off, if they can do that, can't drive in a way that would make the cat cycle a whole bunch of times, which probably increase HC/CO/NOx emissions by a significant amount. It's speculation, but I wouldn't be surprised if the EPA saw a few people doing this and told Toyota to make it harder for them...
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 05-14-2007, 02:11 PM   #2
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I've thought about this - my car has no CAT at all, and my new driving style (avoiding engine enrichment) prevents a lot of HC emissions (because at 10:1 ratio (full throttle or anywhere in the turbo boost zone), a third of the hydrocarbons going in come out unburnt!

I think, these days, global warming has to be the highest concern. And CO2 is the main problem here. Unburnt hydrocarbons make up a tiny proportion of the emissions compared to the CO2 (unless you are on full throttle), and each unit of unburnt hydrocarbons is worth two units of CO2 for global warming potential (info from looking at alternative refrigerants in air-con). So, although more NO, CO, etc, causes more smog, CO2 is what is going to make the world turn into a big desert, and make everyone die in the end. So I still do engine-off-coasting etc

My view may of course be wrong - what does everyone else think? (The main point is that CO2 emissions will always surpass, hundreds to thousands of times, the other emissions.
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Old 05-14-2007, 02:27 PM   #3
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CO2 gets recycled by the plants NO and CO does not. Think about that.
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Old 05-14-2007, 03:17 PM   #4
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I though about this and it would be interesting to see how much emissions there would be in a 10 mile trip were the engine is off for 5-6 miles of it. As far as the Prius you can't go into stealth mode until the engine is warmed up. So the CAT would have reached temp and during the Pluse and Glides you are using the engine for the pluse so it should keep it above the light off temp.

When they do the EPA testing is not that just measuring CO2 to come up with a MPG figure. If it was a problem wouldn't it show up during the testing ? Also since the average hybrid driver can not beat EPA that would mean that the majority of drivers are not letting the CAT cool down.

Interesting idea and I like to hear more comment from those in the know who have driven the camry if that's what they think but it could just be a considence.
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Old 05-14-2007, 07:30 PM   #5
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It is not difficult to get the Camry Hybrid's engine to shut OFF. Just like the Prius, it will run after a cold start until some predetermined temp is reached.

The challenge is achieving a glide where the engine is off, AND there is also neither EV assist or regen occuring.
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Old 05-14-2007, 07:34 PM   #6
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I've often thought about the emissions question. For those occasions where I do take my car on a trip across town & back, it's common that it doesn't reach peak operating temps.

On those trips, I use less than half as much fuel when hypermiling than I would if I just drive the car to ensure it gets hot.

So I think the question Landspeed raises is valid - are some emissions "worse" than others?

Obviously governments of different jurisdictions think so.
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Old 05-14-2007, 07:43 PM   #7
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Our experience with the Escape Hybrid allowed ICE-off propulsion and sitting for a couple of minutes or more. I doubt that after a motor and cat are warmed up that such long off-times are being approached by anybody here except on extended grades.

In short, it's probably not an issue.
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Old 05-15-2007, 06:11 AM   #8
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With the Prius if the cat ever gets cold enough the ICE will start and run, you cannot truly glide until the engine has brought the cat back up to temp. Saying that, in the summer it takes a LOT of pulse and glide to cool the cat. In cooler months just a good ICE off glide down a long enough hill can cool the cat down.

The cat cooling off/not lighting up is the primary reason that the EV button has been left off the North American models, emissions rule over MPG.

Wayne
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Old 05-15-2007, 06:41 AM   #9
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maybe they need to come up with a better cat....
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Old 05-15-2007, 07:42 AM   #10
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My car gets to peak operating temp very quickly (less than a mile) I don't start EOC'ing until after that, so the cat should be warmed up.
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