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Modern diesel engines and biofuels

Discussion in 'Diesels' started by Trollbait, Jul 24, 2011.

  1. Trollbait

    Trollbait It's a D&D thing

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    From another thread:
    What exactly are those obstacles for a modern diesel engine?

    Older diesels don't have a problem running bio-fuels. Manufacturers had limits stated for amounts of biodiesel, but that most surely CYA print. It is relatively easy, and likely the only source, to get homebrew fuel which may not meet accepted standards. They didn't want to pay for repairs caused by unknown adulterants in the fuel.

    There may be interaction issues between biodiesel and the motor oil formulated for diesel in mind back then. Which may still apply, if so.

    Biodiesel is already ultra low sulfur, so that isn't an issue.

    Are modern diesels so complex they can't adapt to different fuels? Is this fixable on current engines with some mechanical and programming changes, like FFV gas engines? Or would they need to be redesigned from the ground up?
     
    #1 Trollbait, Jul 24, 2011
  2. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

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    #2 ItsNotAboutTheMoney, Jul 24, 2011
  3. john1701a

    john1701a Prius Guru

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    Biodiesel actually increases NOx emissions.

    Biodiesel still has a gelling problem, even with additives.

    Ultra-Low Sulfur simply allowed diesel to clean-up emissions enough and keep cleansing equipment working enough to meet minimum eligibility for selling here. In other words, it earns a grade of just "D". That isn't the slightest bit competitive with the likes of Prius.
    .
     
    #3 john1701a, Jul 24, 2011
  4. wxman

    wxman Active Member

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    Actually, the Mercedes-Benz E350 BlueTec comes VERY close to hitting SULEV (http://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2011/daimler_pc_a0030403_3d0_u2_diesel.pdf - it just misses NMHC emissions requirement of 0.010 g/mile vs. 0.015 g/mile certified) and I would argue that it meets SULEV/Bin 2 "in spirit" since the regs allow 0.05 g/mile "running loss" evaporative VOC emissions and still be categorized SULEV/Bin 2 (diesel fuel is essentially non-volatile, thus evaporative VOC emissions are very low). The other diesel cars currently sold in the U.S. generally hit ULEV by a significant margin.

    As far as biodiesel is concerned, it generally reduces HC, CO and PM emissions significantly, which more than offsets the modest increase in NOx emissions. The "renewable diesel" biofuels have been shown to reduce emissions across the board.
     
    #4 wxman, Jul 24, 2011
  5. wjtracy

    wjtracy Senior Member

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    As noted by the other posters, "biodiesel" is an oxygenate made from vegetable oils and methanol and has certain fuel quality issues waxiness and compatibility, oxidation tendency, etc. There is a brute-force method to increase %veggie oil content which is to fully hydrogenate the veggie oil to convert it all the way to regular diesel (way more expensive). This is done in EU a little bit.

    If you recall Pres Obama's eco-speech a few months ago, he was talking about building 4-small bio refineries. The brute-force approach above is probably what he was talking about.
     
    #5 wjtracy, Jul 24, 2011
  6. El Dobro

    El Dobro A Member

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    The cleaning up of diesel exhaust is still a bit in its infancy. I'm sure improvements will keep coming along. In other countries, a fluid called Eolys is metered into the fuel tank at each fill up. It reacts with the fuel and allows the temp that the DPF cleanses at to be lowered. This also extends the life of the exhaust. So far, it's not used on this side of the pond.
     
    #6 El Dobro, Jul 24, 2011
  7. seftonm

    seftonm Member

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    The Popular Mechanics article is spot on. I had a chance to talk with an engineer for the Ford 6.7 PowerStroke and he said they did a lot of modeling and testing with biodiesel. The result is that they allow up to B20 even though they regenerate the DPF with post injection like most other manufacturers. B5 is the limit for many other manufacturers, while a few engines will take B20.
     
    #7 seftonm, Jul 25, 2011
  8. Trollbait

    Trollbait It's a D&D thing

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    I know of the gelling properties. It is a surmountable issue, even if it means mixing in fossil fuels at this point. Unlike the hygroscopic properties of ethanol. But this a concern for both old and modern diesels.

    Its pollution profile is different, but worse is a matter of opinion. NOx is bad, but particulates are the usual demonized portion in diesel, which are lower from biodiesel. Is it different enough to require retuning the emission system.

    The PM article makes it sound like the issue is just the injection location of fuel for the DPF. Which has a known fix, and manufacturers are working towards DPFs that don't need regeneration to save fuel.
     
    #8 Trollbait, Jul 25, 2011
  9. wjtracy

    wjtracy Senior Member

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    This article (may not be authoritative) tends to contradict your opening statement OP, TrollB.

    Rudolf Diesel designed diesel at first to run on 100% peanut oil.
    But vegetable oil is not the same as Biodiesel.
    Biodiesel is modified veggie oil. This article says B100 has certain solvent properties (re: paint, plastics, etc) that was bad in old diesels. Newer diesels have been designed to better handle the biodiesel.

    Biodiesel

    Also US DOE link:
    B100

    B100 or other high-level biodiesel blends can be used in some engines built since 1994 with biodiesel-compatible material for parts such as hoses and gaskets. However, as biodiesel blend levels increase significantly beyond B20, a number of concerns come into play. Users must be aware of lower energy content per gallon and potential issues with impact on engine warranties, low-temperature gelling, solvency/cleaning effect if regular diesel was previously used, and microbial contamination. To avoid engine operational problems, pure biodiesel (B100) must meet the requirements of ASTM D6751-09, Standard Specification for Biodiesel Fuel (B100) Blend Stock for Distillate Fuels (summary of requirements).
     
    #9 wjtracy, Jul 25, 2011
  10. El Dobro

    El Dobro A Member

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    #10 El Dobro, Jul 25, 2011
  11. Trollbait

    Trollbait It's a D&D thing

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    Forgot about the early solvency issues. Biodiesel will break down the rubber fuel lines in older (going on 20yrs) diesels, but by 1994 most makers were using compatible materials. While I'm sure there are some PITA examples, replacing the fuel lines is pretty straight forward. Biodiesel is no where near as nasty as gasoline in terms of spills and skin contact.

    It isn't an immediate reaction, and some biodiesel converts choose to wait for leaks before replacing lines. If gaskets are involved, it could be a hassle and expensive, but I've only seen discussions involving fuel lines.

    Bacterial contamination is likely a problem with biodiesel that has sat for awhile. I don't know the comparison between the two, but it also happens to petrodiesel.

    The main concern when converting to biodiesel applies to all engines. Fuel tanks used for petrodiesel will build up gunk over time. Not problem while still using regular diesel. Biodiesel, though, has better cleaning properties, and that gunk will come loose and clog the filter. If you are switching to biodiesel, better keep some spare fuel filters on hand.
     
    #11 Trollbait, Jul 25, 2011
  12. MapOfTazifosho

    MapOfTazifosho Junior Member

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    I've been running B20 in my car for several months now...the engine runs smoother, quieter, smokes significantly less, smells less bad and returns the same fuel economy.

    I've replaced the fuel lines, pre-filter and primary fuel filter. As much as I love diesel and biodiesel, I'm going to order a 2012 Prius...not sure if I will keep my old MB...
     
    #12 MapOfTazifosho, Sep 29, 2011
  13. bestcarquote

    bestcarquote New Member

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    Most of the manufactures decided to inject fuel into the cylinders just after the cylinder fires and the exhaust valve opens. At this point, the fuel vaporizes and the vapors move down the exhaust to the DPF and clean it. Because biodiesel is denser than conventional diesel fuel (it has a longer hydrocarbon chain) and has a higher distillation temperature and boiling point, it does not vaporize as easily. Some of the fuel ends up adhering to the cylinder wall and runs past the rings, diluting engine oil.


    Thanks
     
    #13 bestcarquote, Nov 29, 2011
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