How do you Pulse & Glide your diesel vehicle ?

[JacobAziza]

Now I could certainly be wrong, but I think that given that even the best diesel is only 40% efficient (60% of fuel goes to waste heat) that any vehicle, regardless of gearing or aerodynamics or turbo or whatever, would potentially benefit from P&G, so long as the glides were at least twice as long as the pulses, because then for 2/3 of the trip, that 60% loss is eliminated.

In other words, because ICEs are SO inefficient, just having the engine turn actually takes more fuel than actually moving the car. Therefor the greatest potential reduction in fuel comes from it not turning at all.

Someone please explain to me differently if I am missing something.

[roflwaffle]

The specifics depend on, well, the specifics. For instance a TDI has it's best fuel consumption at 90% of it's peak torque at it's torque peak, but other turbocharged or NA diesels don't have the same characteristic. Even the new 2.5L TDIs doesn't behave in the same way, although they're closer to the older TDI than the older TC'ed/NA diesels were.

[roflwaffle]

Originally Posted by JacobAziza

In other words, because ICEs are SO inefficient, just having the engine turn actually takes more fuel than actually moving the car. Therefor the greatest potential reduction in fuel comes from it not turning at all.

Someone please explain to me differently if I am missing something.

You just need one more thing. It's because ICEs are so inefficient at part load that P&G works. They're fairly inefficient even at their most efficient, but at part load their efficiency is worse. It's more efficient to operate an engine periodically at peak load than it is to operate it constantly at part load, all things being equal.

[ConnClark]

Originally Posted by Arragonis

I meant the point. I agree for NA diesels maybe P&G is not useful (albeit depending on weight vs torque) vs turbos. For TDs I think P&G has all sorts of possibilities...

Well according to this BSFC chart for my turbocharged engine the peak efficiency for all different loads falls right around the rpm of peak tourque

[Arragonis]

Originally Posted by ConnClark

Well according to this BSFC chart for my turbocharged engine the peak efficiency for all different loads falls right around the rpm of peak tourque

Maybe we need to some ABA testing of P&G vs lugging on the same route. I've started P&G more since the new year and the average has gone up so far. I need to check when I finally get to fill up, I haven't this year yet.

[Piwoslaw]

Isn't it that a turbodiesel (compared to NA) has more torque at a lower rpm, just where hypermilers need it? Well, almost where they need it, I can feel my engine really kickin' it above 2200rpm, but I try to stay below 2000. Anything that will shift torque to lower rpm is welcome (Modding the variable geometry turbo? Remapping the ECU? New, cooler intake? Adding a resistor here or there?).

[Arragonis]

2200 ? That seems high. Mine is puffing away at 1800 onwards. Is the variable part of the turbo working OK ? Sometimes they can stick especially with little use and long times standing without use.

Plug in remappers are quite good for CR HDis. I think Euromodder was looking at one for his V50.

[euromodder]

Originally Posted by Arragonis

2200 ? That seems high. Mine is puffing away at 1800 onwards.

That's a VW engine
They don't mind really low rpm.
Even the 1.4 and 1.2L TDi will put up a good fight at low rpm.

With the smaller PSA engines like Piwoslaw and mine, the horses are only ponies in the lower regions.
From low rpm, they pick up more reluctantly than their VW counterparts.

In 4th, 1800 rpm is the lower limit for me (2000rpm in 5th).
It'll do lower rpm, but at a price.

Plug in remappers are quite good for CR HDis. I think Euromodder was looking at one for his V50.

After the 140.000km service, as the all too frequent DPF regenerations will need to be looked at.

I don't want them to blame it on the remapping, nor do I want the dealer to overwrite the new mapping in an attempt to remedy the DPF issue.

[ecoxantia]

I tried P+G on my regular commute, brisk acceleration followed by engine-on glide.

The results, according to the on-board fuel computer were not encouraging - 70mpg (imperial) for P+G vs at least 75mpg for a "light foot " approach.

This isn't a very objective test, since the P+G was one whole commute and I don't have a direct comparison. I'll try some more and report back!

Simon

[Arragonis]

Originally Posted by euromodder

After the 140.000km service, as the all too frequent DPF regenerations will need to be looked at.

I don't want them to blame it on the remapping, nor do I want the dealer to overwrite the new mapping in an attempt to remedy the DPF issue.

What about ones you remove before a service, if I was going for a C1 HDi (on my list) then I would probably add a removeable plug in box.

Originally Posted by ecoxantia

I tried P+G on my regular commute, brisk acceleration followed by engine-on glide.

The results, according to the on-board fuel computer were not encouraging - 70mpg (imperial) for P+G vs at least 75mpg for a "light foot " approach.

Yeah, thats something I was going to mention - the on board is only slightly higher and sometimes lower than before, the SG2 is always higher. I suppose the proof will be in a few tanks time.