Hypermiling a diesel

[meelis11]

Hi,
is there any differences in hypermiling techniques when driving diesel car? I made search and did not find such topic.

Maybe some tips are in petrol only, some for diesel only? Would like to know. Lets discuss these differences here.

Q1) Does pulse and glide (in neutral) make same % difference compared to steady speed drive than in petrol car. I think it probably does not give same amount of difference beacause diesel does not have throttling losses.

If I am lucky, I have new car tomorrow evening...diesel
Audi A4 Avant 1.9TDI 81kw, 1997

Meelis

[Vekke]

On diesel you have to make the Push with full throttle (97%). RPMs should start the push at torgue peak or rigth before it. On a 1.9 TDI that is about 1800rpm. Use the shortest gear that meets the RPM reguirement. Usually 4:th gear.

If you want to get low figures on your TDI I would recommend to buy 175/80R14 tires to front and 60/40 lowering spring kit.

On petrol gas position is about 70%.

[Diesel_Dave]

I P&G with my diesel and see probably a ~25% benefit vs steady speed. Granted, I also have a 3+ ton truck so it's not exactly the same as a passenger car.

You're right that diesels don't have throttling losses, most there is still a sharp dropoff in BSFC at light loads. That's due mainly to factors other than throttling, such as heat transfer and the theromdynamic effects of lower temperatures and pressures which reduce efficiency. So the concept of running higher loads as a means to higher efficiency is still valid with a diesel.

Secondly, one advantage that a diesel has when P&G is that since you don't have throttling losses, your "glides" are relatively more fuel efficient than a throttled engine when you're coasting in neutral (idling). That being said, idle FE can vary significantly from vehicle to vehicle.

Here's an old thread on the topic:
http://ecomodder.com/forum/showthrea...esel-9664.html

[tinduck]

Originally Posted by Vekke

RPMs should start the push at torgue peak or rigth before it. On a 1.9 TDI that is about 1800rpm.

Hi there,

that does not work for me (2.0 L TDI in VW T5 Van); I use much less fuel when accelerating if I do this from around 1200 RPM (as soon as the engine can deliver enough torque to accelerate).

Generally spoken, I have the impression that I use less fuel if I avoid full boost pressure, which comes around 1700 RPM. Since my setup does 1400 RPM at 56 mph (90 km/h) which is my preferred cruising speed, I am usually well below that. Upshifting early (<1600 RPM) does the rest.

BUT: I usually do not P&G, so things may be different when doing this.

so long,

tinduck

[meelis11]

So driving techniques are almoust same in gasoline and diesel cars, but probaby nut behind the wheel in gas car can make bigger difference (in FE %) compared to "normal driver"?

[ConnClark]

Pulse and glide is a waste of fuel for me. If you just cruise in your in between your peak torque and the half way point to peak power rpm you'll be just fine. For my car my peak torque is about 50mph at 2300rpm and my peak power is around 100 mph at 4250 rpm. At 70mph my rpm is 3000 which hits right dead center of my upgraded turbo's compressor map.

The main reason other than safety why I don't pulse and glide is it will plug my DPF.

[Vekke]

Its trickier to get as effiecient burn in a petrol because gas position is different, and you may have to tweak it during acceleration (correct if I am wrong). In a diesel simple pedal to the medal attitude brings best fuel efficiency if certain facts are met. So in a diesel you dont have to adjust the nut so much...

What I wrote applies almost all turbo diesels, but some in some cars the torgue peak is higher. Steady throttle and highest gear if drived steady speed is also a efficient choice but still the accelerations to target speed/posted speed limit should be:

1. Done at torgue peak or close to it
2. Using shortest gear possible so without revving it over 2500 rpm or 3000 rpm. This depends on the car. On my lupo 3L the electromanual gearbox in eco mode car computer uses gears so that it starts the acceration at 2000 rpm and shifts bigger gear in 3000 rpm. On my lupo almost nothing happens under 2000 rpm. I believe that engineers protect in my lupo the gearbox in lower rpm range. You can hear and feel when engine reaches 2000 RPM. Noise changes from baaam to BAAAAAAM if you know what I mean .

On the lupo if I am doing P&G the speed drops to 74 km/h the engine will put the third gear in because in fourth the RPMs drop under 2000 RPM where nothing happens. At 83 it already changes to fourth. So in that speed range manual would be better because it also takes fuel at least in the lupo to change gears.

Effect of the driving technigue can easily be tested on short test route. It does not have to be long 6 miles or so. Your 09 VW will show quite accurate readings with different driving technigues. Keep the test speed close to 50 MPH so aero does not play so big role.
1. First steady throttle like you drive at the moment from 0-50 and keep it there
2. Second trip that with rapid acceleration to target speed and steady speed
3. third rapid acceleration and to target speed +7 MPH coast so that you lose 16 MPH and again a push.

My estimation of the results are
1. Is worse
2. is 4% better
3. is 15% better

BR:Vesa

[rmay635703]

Originally Posted by Vekke

On diesel you have to make the Push with full throttle (97%). .

The above is only applicable to TURBO diesels, naturally aspirated like mine smoke up a storm and waste fuel near WOT, best at about 75% ish

Cheers
Ryan

[Mustang Dave]

Yes, black smoke is wasted fuel. I try to accelerate quickly with "Big Red", but I try to minimize the smoke. Unless someone is "drafting" me.

[Diesel_Dave]

Originally Posted by ConnClark

Pulse and glide is a waste of fuel for me. If you just cruise in your in between your peak torque and the half way point to peak power rpm you'll be just fine. For my car my peak torque is about 50mph at 2300rpm and my peak power is around 100 mph at 4250 rpm. At 70mph my rpm is 3000 which hits right dead center of my upgraded turbo's compressor map.

The main reason other than safety why I don't pulse and glide is it will plug my DPF.

How did you manage to get a DPF on a '85 vehicle?