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Old 09-16-2010, 09:33 PM   #1 (permalink)
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Pulse and glide should be called Pulse & Pollute

I've always felt that pulse and glide was a bad idea. A few weeks ago I managed to borrow a 5 gas analyzer and tried to see if I could determine the difference in emissions comparing a few different methods of saving fuel.

Unfortunately I haven't had the time to properly compile the data but from what I've seen it appears that shutting the engine off on my 1993 honda civic VX and then restarting it after only a 20 second coast produced approx 4-6x the pollution as running it for the same 20 seconds. Also, accelerating back up to the 100kph cruise speed caused significantly more pollution. The car has a factory 3 way cat installed and is well maintained. Since I only had access to the analyzer for an afternoon there were a lot of tests I wanted to do but wasn't able to.

One thing I regret is that I wasn't able to accurately measure fuel flow. I wanted to borrow an accurate aircraft fuel flow meter but was not able to. I was hoping to see if I could determine how the scheme managed to save fuel.

I may get another chance to use the unit in November. I'd offer to meet up and test with any other hypermilers around Ottawa but you'd need to have a bung installed in the exhaust system after the cats. I'm also interested to compare the results in November as I suspect the restart pollution is being caused by the cat temps dropping.

-Michael

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Old 09-16-2010, 09:47 PM   #2 (permalink)
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which gases were higher, and by how much for each?
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Old 09-16-2010, 09:47 PM   #3 (permalink)
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...hm-m-m-m, I'd prefer to see the "...numbers..." before I condemn EOC, but I cannot dispute what you've seen.

...look forward to seeing your results being posted.
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Old 09-16-2010, 10:10 PM   #4 (permalink)
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The VX looses lean burn when you shut the engine off. It takes something like 30 seconds for lean burn to reengage.

That is my understanding.

For that reason, EOC P&G in a VX is not really a practical strategy, and I use pulse and glide with the engine idling. With an idle fuel consumption of .125 GPH you are getting 8 times the speedometer reading in mileage during the glide phase.

Another option for those who can benefit from EOC glides is to bump start the engine and avoid the fuel enrichment that comes with using the starter for restarts.

I would find it hard to believe that that strategy, when used to perfection, and mileage can be doubled, compared to normal operation, would result in higher overall emissions.

The C02 readings for my VX are very close to much more modern hybrids, without hypermiling techniques.

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Mech
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Old 09-16-2010, 10:25 PM   #5 (permalink)
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...what does the 'rule-of-thumb' say?

"...if idling for more than 30 seconds, it's more economical to shut the engine off and restart than to continue idling."
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Old 09-16-2010, 10:51 PM   #6 (permalink)
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We're talking about different pollutants here. If you allow your cat to get too cold, you're going to see a sharp rise in NOx and HC emissions as the cat doesn't function when it's cold. However, automakers were able to squeeze engine stop/start systems past the EPA, and some were able to achieve a SULEV rating while doing so. Whether this is an artifact of the EPA's testing methodology not representative of the actual NOx and HC emissions of hybrids, I'm not sure. It's at least an indication that engine-off is inoffensive enough that the EPA condones it.

Some cars run rich after a key start, others run rich even after a bump start. Some do not. Running rich creates lots of HC pollution, and CO2 as well.

The one pollutant all of us can measure is CO2. The ScanGauge will give you a pretty close estimate of how much you're emitting. P&G has been shown to reduce your CO2 emissions substantially.



Factoid: You can reduce your NOx emissions by cruising down the highway in 4th gear instead of 5th.

Reality: The resulting increase in CO2 emissions have* a greater GWP than the NOx you'd emit, even in lean burn.

*I haven't done the math, but if you have a three-gas analyzer and an mpg gauge, you can. I did do the math for the SULEV CVT Insight without lean burn versus the LEV MT Insight with LB, and the MT has the lower GWP despite higher NOx emissions.
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Old 09-16-2010, 11:27 PM   #7 (permalink)
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How do you define "pulse & glide"?

Can it also be coasting (while not in gear) with the engine still running? Is that included in the concept of P&G?

If not, should coasting always be strictly differentiated? I didn't think that any sharp distinction was made in discussions of it here
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Old 09-17-2010, 02:23 PM   #8 (permalink)
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I figured that if the engineers that designed my car to be shut off every time I stopped they would have designed it to do that.

Triple or quadruple the amount of starts that the starter has to make It can't possibly last as long. Ever price a new starter or ring gear? That is a lot of gas. Consider the emissions that are created to make and install the replacement.
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Old 09-17-2010, 03:54 PM   #9 (permalink)
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a couple observations from my own experience,

I don't key off, have kill switch.

engine doesn't rev up on start (neutered idle control)

90% of time I bump start anyway

my starter cost $60 to rebuild after 120k miles.

am polluting zero at long stops and when coasting.

not really sure the sensationalized title is all that accurate. You have to have controls and reflect what people are actually doing to have a reasonable test.
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Old 09-17-2010, 04:41 PM   #10 (permalink)
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Quote:
Originally Posted by RobertSmalls View Post
We're talking about different pollutants here. If you allow your cat to get too cold, you're going to see a sharp rise in NOx and HC emissions as the cat doesn't function when it's cold. However, automakers were able to squeeze engine stop/start systems past the EPA, and some were able to achieve a SULEV rating while doing so. Whether this is an artifact of the EPA's testing methodology not representative of the actual NOx and HC emissions of hybrids, I'm not sure. It's at least an indication that engine-off is inoffensive enough that the EPA condones it.
Stop&Start systems are getting popular in Europe (I recently read that up to 70% of new cars will have it within the next few years), since it helps in the European fuel consumption test cycle, and helps to squeeze into the next-highest EURO emissions class. New cars have thermal insulation on their cats, which is a good idea for anyone who EOC's or drives efficiently enough to keeps temperatures low.

Thyme: I always understand that plain P&G is with the engine on, unless otherwise implied. But many members see it the other way around. This thread is about engine off P&G, I believe.

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