How do you Pulse & Glide your diesel vehicle ?

[Piwoslaw]

I think it may have to do with speed. The gains from pulsing and gliding dwindle at highway speeds, hence steady driving in high gear is better.

Slower speeds are a different story, when the pulse is shorter, and the glide so much longer.

[JacobAziza]

Originally Posted by Piwoslaw

I think it may have to do with speed. The gains from pulsing and gliding dwindle at highway speeds, hence steady driving in high gear is better.

Slower speeds are a different story, when the pulse is shorter, and the glide so much longer.

It seems to work well for me even on the highway...

then again, many would argue that I drive at less than "highway speeds" when on the highway

[Piwoslaw]

Originally Posted by JacobAziza

It seems to work well for me even on the highway...

then again, many would argue that I drive at less than "highway speeds" when on the highway

The break even point depends on many things - the car's aero, the engine's efficiency, the transmission's gearing, whether you are pulsing with engine on or off, etc.

Maybe the rule of thumb should be to not drive faster than the break even speed?

[Arragonis]

Originally Posted by Piwoslaw

Maybe the rule of thumb should be to not drive faster than the break even speed?

Determining that seems tricky though if I'm getting great averages on instruments but then only average averages at the pump.

Its hard to trust the insttruments.

[COcyclist]

Originally Posted by euromodder

I haven't seen any positive results from it either, I'm afraid. So I no longer use P&G on long stretches of road.

I do however try to coast as often as possible - i.e. getting up to or keeping sufficient speed so I can coast to certain points where speed needs to be reduced anyway like turns, speedbumps, PSL reductions,... at an appropriate speed.

I will coast in neutral-engine on, on grades at are steep enough that I don't lose speed (and not too steep that I use what little engine braking there is on a diesel) and at posted speed reductions at the edge of towns. The pulse and glide works for a gas or petrol vehicle because that engine is less efficient at part throttle and light load. Our diesels don't have a throttle plate so the is much less restriction to the air pumping through the diesel engine. They can be very efficient at part throttle and light load as in highway driving.

[Arragonis]

COCyclist - I'm pretty much doing what you do (I think if I understand it correctly) but I'm getting nowhere near the figures you are. OK my engine has more hp but the Fabia is lighter than the Golf and I have the 6sp.

I think I'm hitting a plateau and I think (maybe wishfully) that it is the environment. In terms of time the first 1/2 of my journey is queuing traffic. I engine off when I can but its sometimes crawling so not much chance to (loads of beeping because I choose not to sniff the behind of the person in front of me all the time).

Then the second half is 4-lane (2 each side) bypass and I sit on the left (slow) side with the trucks sometimes, although I sometimes go on the right. The difference between a 'good' and a 'fast' run is maybe 45 vs 50 average MPG on the computer. The journey back is in reverse and I can carry up to 65 before the traffic starts and then if I get a good run maybe 55 by the time I get home.

But my tank to tank average is only just nudging 50-51 Imp.

[COcyclist]

Aragonis, it sounds like I have a couple of "environmental" advantages that help my tank to tank averages. I live in a sparsely populated part of the Western U.S. so almost all my driving in this car is highway. Stop and go traffic kills your mileage. Also, I live at 6,300 feet above sea level. The thinner air let's my car slip through with less air resistance. On some of my trips I drive for extended periods at over 8,000 feet elevation and the ScanGuage shows great mileage figures for that part of the trip. I do wish I had a six speed though, perhaps I could do even better.

[JacobAziza]

Originally Posted by COcyclist

The pulse and glide works for a gas or petrol vehicle because that engine is less efficient at part throttle and light load. Our diesels don't have a throttle plate so the is much less restriction to the air pumping through the diesel engine.

I thought that was all pulse and glide was about too at first. I have since been schooled better (by the good folks here on ecomodder)

Pumping losses are part of the equation, but not all of it.

Another part is just that all ICE engines are terribly inefficient, at any speed.
The maximum efficiency of a diesel is something like 40%, and that's before accessory and drivetrain losses.

If your glides are 3 times as long as your pulses (they are for me), but it takes less than 3 times as much fuel to accelerate as to hold steady, then you come out ahead just due to the fact that the engine is off for more time than it is on. It works because the engine uses more fuel just to turn itself than it does to actually move the vehicle.

Of course, if it took more than 3 times as much fuel to accelerate as to hold steady, then you'd be better off not using P&G.

[Arragonis]

Originally Posted by COcyclist

Aragonis, it sounds like I have a couple of "environmental" advantages that help my tank to tank averages. I live in a sparsely populated part of the Western U.S. so almost all my driving in this car is highway. Stop and go traffic kills your mileage. Also, I live at 6,300 feet above sea level. The thinner air let's my car slip through with less air resistance. On some of my trips I drive for extended periods at over 8,000 feet elevation and the ScanGuage shows great mileage figures for that part of the trip. I do wish I had a six speed though, perhaps I could do even better.

It gets worse CO, I'm @ sea level. More or less.

[COcyclist]

Originally Posted by JacobAziza

Another part is just that all ICE engines are terribly inefficient, at any speed.
The maximum efficiency of a diesel is something like 40%, and that's before accessory and drivetrain losses.

If your glides are 3 times as long as your pulses (they are for me), but it takes less than 3 times as much fuel to accelerate as to hold steady, then you come out ahead just due to the fact that the engine is off for more time than it is on. It works because the engine uses more fuel just to turn itself than it does to actually move the vehicle.

Jacob, I totally agree that an engine that is not running uses less fuel than even a diesel engine that is idling during coasting. I do believe it is possible to get some remarkable mileage numbers out of a TDI through pulse and E-Off Coasting. Although my area is rural I still on drive on two lane roads with limited passing zones. I have just not found it practical in my situation to glide with the engine off due to concerns for the key ignition, turbo and clutch. However it may work well for some.