Pulse and glide should be called Pulse & Pollute

[rfdesigner]

Originally Posted by Piwoslaw

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.

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

[rmay635703]

Originally Posted by abently

lol

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

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..

[Varn]

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.

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

Originally Posted by rfdesigner

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

[dcb]

Originally Posted by Varn

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. ..

(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.

[Varn]

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.

Originally Posted by dcb

(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.

[autoteach]

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).

[Hip001]

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.

[hackish]

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?

[UFO]

Originally Posted by hackish

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.

What to believe? ABA data or some "engineer"? I'm so confused.

Originally Posted by hackish

...
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.

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.

Originally Posted by hackish

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.

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.

Originally Posted by hackish

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?

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.

[orange4boy]

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:



That said some cars are better than others at cruise.