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.
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... :thumbup:

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.

CO2 gets recycled by the plants NO and CO does not. Think about that.

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.

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.

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.

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.

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

maybe they need to come up with a better cat....

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.

With advances in battery tech, electrically preheating the cat may become an option in future hybrids.

Then again, advances in batt tech mean we'll be using the ICE less and less anyway as the proportion of electric propulsion increases vs ICE propulsion.

Welp, based on FireEngineer's statement, and this paper, I'm pretty sure the Camry hybrid's glide window is smaller because of emissions. If y'all check Figure 3, you can see that catalyst efficiency drops significantly as a *function of temperature. Now, in terms of a hybrid, the catalyst on a stopped car would definitely not cool as quickly as one on a moving car, so I'm assuming that's anecdotally not a problem, and maybe it isn't much of a problem in warmer climates. But if the catalyst temperature drops below ~250C, efficiency drops rapidly, and when the engine turns on again it must dump another rich excursion through in order to light off the cat again, which I'm guess will significantly increase HC emissions on an SULEV vehicle, which requires ~99.5% HC conversion rate. If that rate drops below ~100% for, say, 5 times on a ten mile trip, instead of the usual once assocaited with startup, it could drop the vehicle down to LEV status. If anyone here is actually concerned about emissions as well as fuel economy, which some posters claim to, I think getting a pyrometer down there to make sure everything doesn't cool off too much would be a good idea. :p

*This is also why my truck runs so rich from the factory. The richer mixture from the carb required to make sure emissions don't go too lean and kill the cat are good for ~3mpg across the board.

Their are a whole bunch of tradeoffs, here, if you look close enough.

For example, do the emissions you do not emit, while the engine is off, save more than the increased emissions, if any, which are put out when the car is turned back on?

If the engine is at "normal" temperature, which for arguments sake is a minimum temperature where the catalytic converter will function, how long can the engine be turned off, with no air flow through the catalytic converter, since the engine is off, before the catalytic converter gets cool enough to not function.

If you've just climbed a grade, the catalytic converter will be at a significantly higher temperature than the minimum required for it to function. How much engine off coasting, down the other side of the hill, is possible, before the catalytic converter gets to a low enough temperature where it begins to not function properly.

If you really want to monitor this, maybe you could get a remote sense thermometer and put it next to the cat, so that you could monitor how hot the cat gets under normal, level driving, so you could have a baseline to monitor the temperature, so you only coast as long as the cat is hot enough to function when you restart.

If you discover the catalytic converter is getting cool, to easily, maybe you could have a muffler shop build a steel blanket to put around the catalytic converter to keep it from cooling down so fast?

If someone has the way or means to measure or monitor this some way, that would be great. In the meantime, I doubt that anyone doing EOC to cut their fuel costs, should be discouraged in any way from the very positive contributions they are making.:)

No, not discouraged. But at the same time, depending on outside temps, etc... they shouldn't think that their actions will keep everything hunky dory. The majority of HC emissions happen when the car is started and the cat has to be lit off w/ a colder engine. If I do an EOC, and drop the cat's temp to below ~250C, it has to be lit off again, which means another rich excursion, and another HC spike. The thing is, as long as the cat's operating correctly, HC emissions are virtually nil (Figure 3 last post). If it's required to light off again, that's going to be something more than nil. So, no matter what, if the cat's operating temp drops enough, we're going to see a spike compared to a properly operating cat, because it should allow nearly no HC emissions. ;)

*sigh*

Does anyone read any of my posts? Or do y'all just ignore me? :confused:

Nope. I think you may be misinterpreting the Camry glide issue.

The car will go ICE off with no difficulty when the accelerator is released, once warmed up, just like the Prius.

So the Camry's glide "problem" isn't getting the ICE to stop running - it's getting the car to coast while also avoiding either regen or EV assist (which has little to do with cat temps).

omgwtfbyobbq when they test the emission on a hybrid how is that test done? Don't they take this into account when they certify it?

It's not about the ICE stopping, it's about how long the driver can travel at some ~speed w/ the engine off and the cat cooling down. If the car's in regen mode, it's going to slow down faster than if it were coasting, vera? And the same goes for EV assist mode except it'll accelerate faster. The whole point imo is that is the driver is accelerating or decelerating at a rate faster than a coast, Toyota is minimizing the amount of time the ICE is off and the cat is cooling. Unlike w/ the Prius, where they disabled the EV button, but drivers were still able to get it to coast for relatively long periods of time, which can cool down the cat more than if over the same period of time the car was decelerating or accelerating more. By doing those two things, exaggerating acceleration and deceleration if you will, the amount of time the ICE is off and the cat is cooling is a relatively certain quantity.

zpiloto, I wouldn't think so. I'm not sure exactly how the emissions test is done, it may be the same as the economy test, but I doubt they have a situation where they P&G from 35-45mph.

Well I would have to agree with the question raised by the original post. There is no doubt that I have abused the EOC thing once I saw what it could do to my mileage. It is also quite apparent to me that my car is still in a rich mode at the end of many of my burns in the morning:( . Often the engine runs less that 1/3 of the time and the burns are about 10 seconds long.

Hypermiling is new to me and I am still amazed at how far I can move my car on a small amount of gas :) .

I know I have to be polluting more. I was just trying to not think about it. The pyrometer is a very valid idea. Maybe an asbestos wrap or something like that is in order.

Maybe there is an inexpensive analyzer that could tell us when the cat is burning. My nose can certainly smell unburned hydrocarbons but if I ran a hose to the tailpipe it might look like I was trying to do something much worse than get better mileage :eek: .

It would be nice to know how quickly the cat cools down. I dont know where you could get a sensor that would measure those kind of temps.
I think directing more airflow above the car, and waiting several minutes after COOLANT reaches operating temp would be safer for emissions. I don't EOC in the wintertime, because it is so cold out (N. Vermont). I only do it when temps are over 50 deg F...kind of similar to my dads hybrid civic's autostop...except i am more careful, because i know the cat cools off faster when the car is moving.
It would be nice to have a metal fairing around the cat to deflect airflow...that you could remove during the summer.

Like everything it is a balencing act...there are sometimes unforseen consequences from trying something different. I think in cities emissions (hc, nox, so2, co) are more of an issue because they affect people directly and sometimes severely due to the density of traffic. In the countryside, co2 might be a more major concern (though emissions still have a negative effect in the country: nox and so2 cause acid rain). in the countryside it would make more sense to run a diesel vehicle or other carbon efficient engine with higher emissions...or maybe to EOC a bit more than in town.

Here's some interesting info on CATs I don't know when you would EOC with the engine is not at idle but:
And more interesting reading.https://vehicle.me.berkeley.edu/Publi...eti_Avec06.pdf

I believe that info about damaging your cat is fairly dated (note leaded fuel reference) and mostly applied to older cars with mechanical fuel pumps and carburetors.

Here's a EGT probe/pyrometer, which seems to be pretty good. Imo, this combined with some time with a local smog guy would be the best bet for figuring out the relationship between how cool you get pre-cat and how well the cat operates/how high HC emissions when the engine is started back up, so you can figure exactly what temperatures are best for EOCs/MPG/HCs.