How do you eco-drive a diesel ?

Discussion in 'Diesel powered automobiles' started by groar, Nov 1, 2008.

  1. groar

    groar X-Frenchy: very

    Lately a lot of papers are talking about lower consumption and lower emissions (at least about CO2) of diesel. In eco-driving forums it seams that more and more people would like to have a diesel.

    As half French people, I have diesel cars. If I have rather good percentage over EPA for the megane, I have difficulties with the scenic (see my signature). Of course the facts the scenic is heavier (2844 lbs vs 2491), has a bigger Cd (0.33 vs 0.31) and a bigger Frontal Area (25.3 sq.ft. vs 21.4) doesn't help, but Combined EPA ratings is better for the scenic (39.8 mpg(US) vs 35.1).

    On both cars I added a front grill block and it helps to have the engine hot quicker :) I'm also using DFCO and/or NICE-On coasting, keeping a lower steady speed and having moderate accelerations. I have iMPG display only in the scenic. I can have 2.3 l/100 at a steady 70 km/h (100 MPG at 43 MPH), but it's difficult to achieve and any move of the right feet or change in road inclination will dramatically make the consumption greater and/or the speed lower.

    I'm wondering if there is some advices more toward to diesel than gasoline. After a quick search I didn't found any advice on how to eco-drive a diesel except to shift up at 2000 rpm instead of 2500 for a gasoline, but I'm already doing it...

    What are the eco-driving and eco-modding tips that are working for your diesel ?

    Thanks in advance,

  2. Chuck

    Chuck just the messenger

    The principals in Beating the EPA - The Why’s and How to Hypermile also apply to diesels. The main difference I'm aware of is they idel much more efficiently so FASing might be done less....say you are going a long distance down a gentle hill - I can glide very well on my Insight and sometimes forget the FAS.

    seftonm does very well with his TDI - hope he adds something to this thread.
  3. xcel

    xcel PZEV, there's nothing like it :) Staff Member

  4. seftonm

    seftonm Veteran Staff Member

    Hi Denis, you are off to a good start with your grill block, and I hear the dCi's can be quite good on fuel.

    The first step is to get your tires inflated to the maximum sidewall pressure. Try to use the highest gear you can. Keeping rpm's down helps a lot in my car. Once you have an understanding of the basic and intermediate techniques, pulse & glide is probably the first advanced technique you should look at. It is the technique that gave me the biggest improvement in my car. The fuel consumption difference between pulse & glide and constant speed in my car is quite large, and I think your car will be similar. If you are concerned about the turbo cool down time, pulse & glide with NICE-on instead of a FAS will still give some great results because of a diesel's low idle fuel consumption. I know of many people with diesels who do the FAS and don't have problems, but none of them have a dCi.

    For my car, the two modifications that made the biggest improvement were a coolant heater and a grill block. Both help the engine warm up much faster, which helps to lower fuel consumption during the warm-up phase. That is especially important during our Winnipeg winters but may not be as important in Toulouse.

    I have a feeling your car is capable of some excellent fuel consumption figures, and you will soon start to see what it can do :) If you have any more questions, do not hesitate to ask.
  5. groar

    groar X-Frenchy: very

    Thanks for the replies. I will read these docs again.

    With the scenic, a 2001 dCi (turbo diesel common-rail), I'm currently at EPA +33% in the morning when I have light traffic. In the evening with medium traffic I have "only" EPA +10%. With some short trips during week-ends, I have a current tank at EPA +20%.

    With the megane, a 1997 turbo diesel, my best tank is EPA +50% and I don't have any iMPG display in it...

    Whatever I'm doing, I can't do better then the EPA +33% during my morning commutes with the scenic. On the highway my best is Highway-EPA +10%, but to do that I have to drive at 10-15MPH under the speed limit. At steady Highway speed limit the Highway-EPA is simply unachievable...

    Now my best tank with the megane was done this summer with hotter temperatures (20-30°C vs 5-10°C now) and lower traffic (25 minutes vs 35-55 minutes now). Against traffic, I avoid heavy traffic and stop the engine when I'm idle more than 15 seconds.

    I have a big hill to climb. Thanks to the iMPG display I'm now accelerating quickly at the beginning and keeping a steady speed of 70 km/h to have a 7 l/100 consumption. Before I was accelerating more slowly and had a consumption over 10-12 l/100 during all the hill.

    With the scenic I'm using both NICE-ON Coasting and DFCO. I'm first using NICE-ON Coasting to lower MPG without loosing too much speed, then using DFCO to have a null consumption and loose more speed. With the megane I was using only NICE-ON Coasting so I was not saving as much fuel. Both cars have same tires with a 51 PSI sidewall. While megane is inflated at 46, scenic is inflated at 51 currently. But the comfort in the scenic lowered a lot from 46 to 51 so I may go back to 46. During my few city driving, I feel the coasting lasting forever :)

    About grill blocks on both cars, I closed the lower one except the sixth toward the turbo.

    I'm just wondering if there could be diesel specific tips, noticeably on these common rail diesels. These high pressure diesel have a better consumption, but seams to be more difficult to eco-drive.

  6. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Groar:

    ___Eco-Drive is good for maybe 20 or so % and you are far beyond that already. Hypermiling a diesel is as easy as learning to DWL while watching an iFCD on any drive. It is just like an Insight, HCH-I or -II. Find that point where your have maximized your FE and keep it there using all the techniques you have available to you. Stay the hell out of the turbo, and 2,000 RPM? You are throwing it away that far up the tach in a reasonably performing diesel.

    ___Good Luck

  7. npauli

    npauli Well-Known Member

    I'm new to HM in general, and diesel in particular, but I'll state here the little bit I've learned so far from my gigantic diesel truck. Mine's a common rail diesel too.

    1) Keep those RPMS's low, low, low. I ran a couple tanks trying to keep RPM's at peak torque or below (1800 rpm for me) because I've read that best BSFC happens around peak torque and part load. Then as an experiment, I started shifting sooner, keeping RPMS as low as possible but above 1100 rpm where my driveline has a nasty resonance. The low-rpm technique gained a good 1mpg or so (5% for me). Seems like you don't want to spin the engine & parasitics any faster than necessary, and this effect trumps whatever causes lowest BSFC near peak torque when you're running with pretty low loads. I also get a big difference in FE on the highway depending on speed, but this is a combination of engine speed and wind resistance. The wind part will be less important for you, but still significant.
    2) a warm diesel is a happy diesel. I ran some quickie hand calculations to estimate how much energy goes into taking my engine & fluids from room temp to operating temp. It was about the energy content of .1 gal of diesel. In practice, I've seen the fuel gage go down much slower when I can combine trips and do all my running around town while the engine's warm. I've started using a coolant heater, oil pan heater, and partial grill block because of this, but don't yet know how much it's helping.

    I'd also recommend that you keep in mind that turbos don't like rapid temperature swings. Until somebody shows me some thermal-mechanical fatigue simulations showing that my turbo should have infinite life no matter how many times I shut it off hot, I'm going to be too scared to try stuff like FAS.
  8. groar

    groar X-Frenchy: very

    What I wasn't understanding is why I can save 33% in the megane without FCD, while I can save only 20% in the scenic with FCD...

    After 3 tanks in the scenic, it seams I'm improving myself, noticeably as the temperature is dropping. Thanks to the onboard computer I can say that when the ICE is cold it consumes 5.2L/100 (10% saving from the 5.9L/100 rating), while when it's hot it consumes only 3.5L/100 (40% saving).

    At 70km/h I can find the sweet spot at 2.3L/100, and at 80km/h it's at 3.0L/100. Now these hot spots are so volatiles that any change in road level or a truck overtaking me and the consumption increases by 10-20% and/or the speed decreases by 5-10% !!!

    3 possibilities I imagine :
    • the heavier weight and greater Cd and FA of the scenic make it more sensible to road conditions.
    • as I drive nearer from scenic's sweet spots (as I drive by looking at the FCD), the gas waste is smaller and doesn't permit to absorb the changes in road conditions without generating a speed change.
    • the high grade diesel (cetane 55 instead of 51) has less impact in scenic's more complex common rail turbo diesel engine than in megane's simpler turbo diesel engine.

    As my wife and I are swapping our cars regularly, from tomorrow I get the megane back :) Since I'm eco-driving, I prefer the megane which is lighter, while my wife prefers the scenic which is higher.

  9. seftonm

    seftonm Veteran Staff Member

    Lol, high grade diesel at cetane 55? Just another thing for me to be jealous of Europeans for. Diesel in North America usually has cetane in the low 40's.
  10. groar

    groar X-Frenchy: very

    Depending on the norm used, the octane is rated at 46 (ISO 4264) or at 51 (ISO 5165).

    The high grade diesel is in fact standard diesel to which are added several additives. The added procetane increases the cetane index.


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