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

which gases were higher, and by how much for each?

...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.

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.

regards
Mech

...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."

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.

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 :confused:

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.

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.

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.

I want to see the raw data.

Personally i think if you are causing the pollutants to increase by killing then re starting the engine the answer is simple - don't turn off the engine!!

by drop from 2750rpm under load to an idle of 800rpm unloaded will still VASTLY reduce fuel used and gassed produced.

I thought p&g was engine on or off
EOC was engine off coasting.

but consulting the glossary, they are both engine off, i.e. CODFISH

http://ecomodder.com/forum/showthrea...e-ii-3505.html

hackish -

I have worried about the same thing. On the chance that your data confirms your hypothesis, that is one reason I converted my non-heated 02 sensor to a heated version :

http://ecomodder.com/forum/showthrea...2-a-10921.html

But like everyone else says, the VX lean-burn mode is a special case, and we need to see the data. A comma-delimited output in the "code" editing wrapper would help a lot for independent analysis.

CarloSW2

I was under the impression that P&G would even apply to automatic transmissions, i.e. when you take your foot off the gas and coast (whether in drive or in neutral). Actually the practice is more like accelerate and coast but it fits under the broader idea of pulse and glide, just not to the same degree.

If that's the case, then we would need a separate term for coasting. Maybe we should scrap the term P&G and substitute differentiating terms of engine-on coasting vs. engine-off coasting. :confused:

Personally, I don't see any substantial FE achieved by shutting the engine off for very brief periods. More numerous restarts do shorten starter life, simply from increased use & wear but that doesn't seem to be of concern those whose only criterion is hypermiling, not economy of total $$$ in operating costs. Situations like shutting the engine off at a long red light are the exception; they probably save whatever fuel would have been expended during extended idling. But that strategy does not involve coasting. ;)

for purposes of this discussion, what's the diff between eoc and dfco? aside from clutch-in/neutral vs in gear?

so about 1/3 of a tank for me is spent with the injectors off either DFCO or EOffC/pulse and EOff glide.

in 8 months I have not burned 120 gallons by hypermiling including above techniques. without them my gasses by ppm may be worse, but so much worse that they are not covered by not burning 120 gallons?

you can buy a lot of starter rebuilds for 120 gallons in gas :)

400 and something dollars worth according to the fuel log, however I have been driving this civic like this for the last 8 months with who knows how many miles on the current starter and it has yet to give any indication that the starter is in poor shape.

I have been EOCing and P+Ging a lot lately with my better batteries. My starter started to stop working so I was worried about a rebuild but it turned out to be that the solenoid was worn off one on side of the contact plate. After 300,000 K I'm not surprised. Brushes were fine and windings perfect. I spaced out the plate with a washer to expose unworn material and now it's good for another 300,000. I love my Toyotas.

What about the Prius and the like? It has a lot of "eoc" time but still qualifies as an ULEV (or whatever) and no insulated cat. Perhaps the issue with your VX is software related.

I have heard that insulating the cat is a very bad idea. They can overheat and melt down. Perhaps shielding it from the airstream is enough but not too much. Another advantage of belly pans?

My glides are usually a 1/4 mile or much more so I doubt I'm worse off although I will look at a shield for the cat soon. Must be better than just the stock one which would be designed for worst case scenario over-heat.

I have long since believed that the volume of pollution is far more important than the quality of it. Even when pollution is 100% clean it is still CO2 & CO.
If you get dramatically better FE it simply is not possible to be emitting the same volume of pollution. Each gallon of gas converts into a specific amount of pollution regardless of its cleanliness.

Also studies are showing that sulphur may help with global cooling, maybe sulphur in diesel wasn't a bad idea especially in rural areas where the effect is a little fertalizer and not smog.

I would still like to see this data you speak of... even "pre-compiled"

this reminds me of the new DPF's on trucks. To get rid of the particulate they trap it and then burn it at a high temperature with more diesel. This ends up netting less PPM of the bad stuff, but more Millions of all the stuff, as MPG suffers.

lol

Data is indisputable, so do that when you can and I'm sure we will crunch the numbers for you.

:)

where does one find a portable 3 gas analyzer for cheap?

t's not too bad, something like ~.3+mpg for a ~20mpg diesel pickup truck.

well, there are many people claiming a 3mpg gain with a dpf delete.

Do that have documentation? The only thing I could think of to explain that would be a wonky DPF system or if the engine was a real NOx queen.

Edit- It looks like all the DPF kits come w/ something that flashes the ECU, which is probably where any mileage gains are coming from.

Diesel particulate filters are almost mandatory on European diesels (hard to pass new emissions standards without one), but I'm not sure how eco-friendly they are on a global scale. Yes, they reduce particulate matter almost to zero, but they need to be burned out every now and then. When initially testing emissions and fuel economy for a new model, the car is new and the DPF is not clogged. I wonder how those tests would go during a burnout?

For PSA diesel engines (Peugeot/Citroën, but also certain Fords, Volvos, Subarus) there is a fuel additive called Eolys, which is about 5% cerium and 80%-90% hydrocarbons. When the ECU initiates burnout, fuel is added to raise exhaust temperatures, and the Eolys fluid is injected into the fuel going to the engine, lowering the temperature at which PM starts to burn (from 550°C to 450°C). The cerium does not burn, but stays in the filter (I believe it binds whatever is left over after burning the PM). After a while, this cerium residue starts to clog the DPF and it should be replaced after 120k km.

VW also has a DPF technology with a urea-based fluid.

So, at its best, a PF diesel is very clean. But if it is driven efficiently (=low exhaust temperatures), then it will be burned out quite often (=more fuel+additive) and will need a replacement filter sooner (=extra resources, not to mention costs). EO(ff)C-ing a diesel with a PF may lower the already low temperatures even further, but then new, hi-tech turbodiesels shouldn't be cycled on and off too often. If you go racing on the Autobahn every now and then, then you're OK, but for everyday driving your ECU is going to start adding fuel (and fuel additives) every so often.


Another question: If we are concerned about catalyst cooling, then should we be DFCOing? When engine braking, air is pumped through the engine, then through the cat, cooling it from the inside. Yes, compressing it inside the cylinders raises its temperature somewhat, but upon exiting it is still much cooler than during normal combustion, and so also cooler than the cat.

Perhaps CO and hydrocarbons might be doable affordably, plenty of inexpensive home CO and combustible gas monitors in the market. NOx is a little harder to come by. But yah, the CO2 isn't a welcome pollutant either, plus everything it took to get the extra fuel in your tank that P&G saves.

The 'stop/start' systems are pretty smart.

What's happened is that, I think Bosch, has developed a system where the starter motor and alternator has been combined, AND (important bit) they have done away with the field coil and gone permanent magnet which gets you from 65% efficiency up to 90%. Then they put in a fast charge/discharge battery system and a computer and suddenly your 'alternator' is producing power at 90% efficiency when you break, storing excess so when you accelerate again you don't load the engine at all.

Once you've done all that then you can get electric air-con electric power steering etc. all driven off 'breaking energy'.. and meaning the engine efficiency at low power is substantially better.

An example is the Volvo S40 1.6Drive start/stop which has 84mpg exurb vs the non-stop/start which is 74mpg.

Derek

Yes the data is indisputable, MS Windows new version does feel faster, looks better and feels more responsive. I'm a PC and this assembly of meaningless data was made by me..

Motorcycles have used permanent magnet alternators for some time. The trouble with them is that they have to shunt excess energy to ground. Not as efficient way of making power as one would think.

The nice feature of an energized rotor is that you cut down the rotor current to a level that the system needs. Basically if you don't need energy you are just freewheeling the alternator. I cringe at a 90 dollar battery replacement every 4-5 years. Now I have a 500 dollar battery? Dang.

As far as purchasing a new car for better mileage, what is the economy in spending 20,000-40,000 dollars to save 4-800 dollars a year. Something like a 2% return on your investment.:eek:

Go for it become a beta tester. Once it is 3-4 years old and fixed, I might buy a used one.

(Motorcycle) PM generators are efficient,
1. no field charge, ever
2. no fan needed
3. excess current is not "shunted to ground", that would only make the engine do extra work.

Newer units *should* be utilizing switching(pwm) to ensure only enough energy is tapped from the alternator to maintain battery voltage. Older units probably used linear regulation which makes more heat, which may be the source of the confusion. If the regulator designers are really geeky they would add synchronous rectification, which has far less loss than plain old bridge rectification. But we are not talking about a huge amount of current on your typical motorcycle and it adds significantly to the cost vs a simple pwm scheme and a handful of diodes.

I have never had a bike with pwm only shunted current, touching one convinced me that newer designs were not available. Thanks for the info. A google search brought me up to date.

Still I don't buy the economics of a new vehicle.

Powersports charging systems are disappointing at best. If it isn't the R/R going bad every 15-30k miles, its the stator, and if it isn't either, water got in the wires or connectors and melted them like cheese pizza. The only ones that show a higher level of reliability are those that use an automotive style alternator or they put the RR in direct airflow (and that still leaves the stator up for grabs).

Just a casual reply to the title.....
If gas was not so expensive, I'd be more concerned about the pollution. Bottom line is I'm trying to get the most mileage out of a tank of fuel. I only turn it off at stop lights so I'd be very surprised if it pollutes more than leaving it running.

Sorry I haven't had much time to follow up on this. I purchased a 5 gas analyzer and while testing it out caught a chunk of snow and that destroyed the probe. Haven't been able to justify another $1600 for a new probe.

No doubt people are aware of carmakers pushing to move cats closer and closer to the manifolds. In fact many engines were redesigned to put the intake at the front so there would be enough space for a cat immediately after the head.

I managed to spend a couple of hours (and beer) discussing some of the eco-modder topics with one of a certain carmaker's engineers. One thing that was explained to me is that the GDI engines are the future since they're practically the only things that will pass all the more stringent emissions regulations coming down the pipe. These things can be programmed to essentially spit burning mixture out the exhaust on startup just to light the cat off quicker and meet the cold start requirements.

With hybrid cars like the Prius they have extra insulation and cat temp calculations are part of the engine control strategy just to ensure the average pollution is as low as possible. This explains why they can shut off and turn back on and still keep low emissions.

Finally I ran the pulse and glide idea by the engineer and he flatly said it is entirely false. Obviously people on here have managed to record gains with their pulse and glide thing but his description of the physics involved make sense. I'll try to describe it the best I can.

ICEs have different fuel requirements per unit of work. This is measured as brake specific fuel consumption BSFC. Generally, the higher the energy output the worse the BSFC is (within the operating range of the engine - I'm not talking WOT at 800rpm). To improve upon this carmakers even added extras like EGR to reduce pumping losses and many have switched over to electric power steering and such just to reduce fuel consumption. I might add that the losses of power steering are proportional to engine speed and on the highway then proportional to your vehicle speed.

Now, pulse and glide you accel to some speed, shut the engine off and coast down to some other speed then resume. The problem is that nearly all engines are designed to have the best BSFC at cruise, not accelration. In fact, EGR normally turns off during acceleration.

Since v=d/t the pulse/glide person is going to be travelling at some average speed. For some time they consume 0 fuel and for some time they consume an above average amount of fuel accelerating. The amount of work is the same whether you go fast or slow but BSFC, the engine's energy output and the losses (pumping, air resistance etc) are different.

At this point I got a bit lost in the calculus but since air resistance is exponential by the speed it turns out the friction from air resistance is greater when you are pulsing than the amount you save when your glide falls below the average speed.

Now, you've got more friction losses than someone cruising constantly at the average speed. The engine has to output a little more total energy than the average speed case. At higher outputs the engine is less efficient. At the end of the day more power out under less efficient conditions - P&G cannot possibly work.

I wonder why those who do it are recording gains or if anyone has ever done an objective test by figuring out their average speed with P&G and compared it to driving the same average speed. Or is it just some vehicles that did better while most do not? Maybe something older that doesn't have features like DBW and EGR?

The complicated engineering answer seems to say P&G cannot work. I've always questioned it myself. Can anyone describe how it possibly could work? Maybe it's a component of an overall driving style that as a whole provides gains?

What to believe? ABA data or some "engineer"? I'm so confused.
Nearly all engines are most efficient at their torque peak, under a heavy load. Lighter loads have more throttling losses and are also at a higher BSFC.

The efficiency is great enough under acceleration to offset the difference in aerodynamic losses, and if you use hills properly, that can mostly be negated. And aerodynamic mods make P&G that much more effective.

The fact remains that it works, and very well. Plug some real live numbers into it, not that easy, and you will be able to verify it does. Better yet, try it doing yourself and then experience will teach you.

The reason its seems to be counter intuitive to you is that you think BSFC is lowest at low load. The truth is it's the opposite. BSFC is lowest at full load. Just study a BSFC chart. I'll link to the Prius because it's a very efficient engine to begin with:

http://hiwaay.net/~bzwilson/prius/pri_power_700.jpg

That said some cars are better than others at cruise.