CO2 (and other) emissions of biodiesel?

Discussion in 'Environmental Discussion' started by toronado455, Apr 22, 2014.

  1. toronado455

    toronado455 Member

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    How clean burning is biodiesel, such as that made from recycled cooking oil, as compared with gasoline and petroleum diesel? (I'm asking specifically about tailpipe emissions, not the overall environmental impact.)
     
  2. Emcguy

    Emcguy Member

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    A friend had biofuel in his old cruiser. If you stood behind it, it actually smelt like fish and chips when he reved it!
     
  3. GrumpyCabbie

    GrumpyCabbie Senior Member

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    You can run older diesel cars on such fuel and it is quite popular over here in the UK, often mixed with normal diesel. I know of many who run old VW diesel engines on it.

    But it shouldn't be used in the more modern common rail diesels or those with additional emission control, or so I've heard. You could be the guinea pig and try it out on your new diesel and see what happens, but if it all goes nasty, then you have an expensive bill.
     
  4. Easy Rider

    Easy Rider Active Member

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    Somewhat odd that you should single out CO2 in your question because..................
    Regardless of what fuel contributes the "C", there just has to be a certain amount of CO2 produced by the "burn" for a given amount of energy produced (along with a little CO). It's all of those "other" things coming out the tailpipe that are undesirable by-products.

    As it turns out, CO2 is undesirable too but it is not a "by-product".
     
  5. wxman

    wxman Active Member

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    Here is a graphic from EPA of conventional emissions from increasing blends of biodiesel (FAME) relative to emissions from petroleum diesel...


    [​IMG]


    These are engine-out emissions; tailpipe emissions from 2007-compliant (i.e., T2B5) diesels are vastly lower than previous generations, and biodiesel likely has little effect on tailpipe emissions of current diesels.
     
  6. Trollbait

    Trollbait It's a D&D thing

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    In general terms, it produces more NOx than petrodiesel, but it is naturally ultra low in sulfur. So no extra steps to get it to work with NOx emission controls. Then it is lower in other pollutants, like particulates, in comparison. So in an older, non-'clean' diesel it will increase NOx, but decrease everything else. Gasoline will likely be cleaner overall just because it has more emission controls than such diesels.

    In clean diesels, burning B100 isn't supported by the manufacturer. There are a few reasons for this. The first one is a suspicion on my part. The different physical properties between the fuels may require different fuel maps to make efficient use of the biodiesel. A gasoline car can likely run on a tank of E85, but a flex fuel one has a sensor to detect the ethanol, and the programing to efficiently use it.

    The main reason I have come across for the limits is because of the regeneration cycle for the DPF. These filters regenerated when clogged by spraying fuel on them to burn the dirt off. The cheap way to do this is to spray fuel into the cylinder during the exhaust stroke. This doesn't work the best with biodiesel. Its thicker, I believe, than diesel so more of it gets left in the cylinder. Where it can gunk up things and work its way into the crankcase oil. Which brings up a minor reason for the limits. Large percentage biodiesel blends may require different oil specs.

    The German auto makers use the spray in the cylinder method, and only allow B5. Ford and GM allow B25, and likely use to more ideal method for regenerating the DPF. Spraying the fuel directly into the exhaust before the DPF. Allowing a higher biodiesel percentage means less particulates, less DPF regenerating, and thus less fuel wasted there. The emission controls can handle the extra NOx.

    A CYA reason for the limit is that brewing biodiesel is a simple process that makes it something that could be done at home. Manufacturers apply a limit so they aren't responsible for problems caused by poorly made home biodiesel.
     
  7. miscrms

    miscrms Plug Envious Member

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    Note that there are likely differences between "virgin" biodiesel and biodiesel made from recycled oil. In general I would expect the virgin oil to produce a cleaner burning fuel, the recycled oil based fuel is likely going to have more "other stuff" in it that may contribute to extra emissions.

    Rob

    FYI here is a statement by the Union of Concerned Scientists on biodiesel. The gist seems to be that biodiesel from waste oil products can lead to a significant reduction in GHG emissions, but not so much with biodiesel from virgin stock. Their recommendation is if you already have a diesel vehicle its better to use biodiesel particularly if you can find sources that use recycled oil stock. If you are shopping for a new vehicle they recommend hybrids or electrics.
    Biodiesel Basics | Union of Concerned Scientists

    Rob

    I know you stated you wanted a tailpipe only discussion, but IMHO when it comes to bio fuels it doesn't really make sense to look at them that way. The tailpipe GHG emissions of biofuels are likely not significantly better or worse than their petroleum counterparts. Assuming the fuel burns with equal efficiency in a given engine, the amount of energy released is directly related to the carbon content of the fuel and consequently the GHG emissions associated with burning it.

    For biofuels to have a net negative effect on GHG emissions you have to take into account the amount of carbon absorbed out of the atmosphere during growth of the feedstock plants. But once you are taking that into account, you really have to look at the bigger picture of short term vs. long term effect on GHG emissions. Unfortunately these are very complex calculations, whose results depend a lot on the assumptions made. However, if you are cutting down (or worse burning) millions of acres of rainforest to create palm plantations (as people currently are) to meet the growing demand for cheap palm oil, its hard to see how that is a GHG win in the long term/bigger picture.

    [​IMG]

    While it seems like it should be possible to create biofuels that are essentially carbon neutral, I don't believe that anyone has yet demonstrated a model for large scale, cost effective production of biofuels that comes anywhere close in the long term. I believe this is the essence of the UCS position linked above.

    Rob
     
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  8. wxman

    wxman Active Member

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    Regarding GHG emissions of various fuels, CARB has a "look-up table" as part of its recently-adopted "Low Carbon Fuel Standard". In that table, biodiesel sourced from Midwest soybeans (i.e., virgin FAME biodiesel) has a carbon intensity (CI) of 83.25 gCO2e/MJ), including 62 gCO2e/MJ for "land use and other indirect effects", compared to 98.03 gCO2e/MJ for petroleum ULSD in California.

    FAME biodiesel from waste cooking oil has far lower CI (4.00 gCO2e/MJ for "BIOD007 - Conversion of corn oil, extracted from distillers grains prior to the drying process, to biodiesel"). That biodiesel (BIOD007) has the lowest CI of any fuel currently approved by CARB (next lowest is "landfill gas" (CNG) at 11.26 gCO2e/MJ).
     
  9. miscrms

    miscrms Plug Envious Member

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    Thats cool data wxman, do you have a link?
     
  10. wxman

    wxman Active Member

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  11. wjtracy

    wjtracy Senior Member

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    I take a shot at it:
    Re: Tailpipe CO2 (not talking about life cycle analysis) its up to 0-10% less CO2 than regular diesel oil.
    Basically biodiesel has approx. 10% oxygen so it has approx. 10% less energy content.
    Unlike ethanol in gasoline, however, the diesel engine seems to get about the same MPG on biodiesel as regular diesel. To the extent that MPG is equal, then you will approach 10% less CO2 out the tail pipe.

    As far as other emissions, that's s difficult question considering that new clean diesel vehicles in the US have strict emissions controls. We need to know what specific vehicle you are asking about.
     
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