7 ms·

Are diesel vehicles actually more environmentally friendly? It sure doesn't seem that way driving behind one.

seren 11y ago
They emit less CO2 per kilometer but much more particulates (this is why they have a filter), which is worse health wise.
- happyscrappy 11y ago
  "Despite lower carbon dioxide emissions, diesel cars may promote more global warming than gasoline cars. Laws that favor the use of diesel, rather than gasoline, engines in cars may actually encourage global warming, according to a new study. Although diesel cars obtain 25 to 35 percent better mileage and emit less carbon dioxide than similar gasoline cars, they can emit 25 to 400 times more mass of particulate black carbon and associated organic matter ("soot") per kilometer [mile]. The warming due to soot may more than offset the cooling due to reduced carbon dioxide emissions over several decades, according to Mark Z. Jacobson, associate professor of civil and environmental engineering at Stanford University." http://news.stanford.edu/pr/02/jacobsonJGR1023.html http://news.stanford.edu/pr/02/jacobsonJGR1023.html
  - paulmd 11y ago
    That release is from 2002, which predates the introduction of Ultra-Low Sulfur Diesel in the US (Cali switched in '06, the rest of the US switched in '10). This drops the allowable particulate concentration from 500 ppm to 15 ppm, which as you would expect greatly reduces soot as well as emissions of all kind. The diesel we were running back then was garbage. It really had more in common with something like heating oil than the diesel the rest of the world uses, and is the reason why the US has a perception of diesel engines being dirty. It also created huge problems for porting small diesels over from Europe - they run at a much higher compression, but at those pressures the particulates in the fuel become abrasive and eat away the fuel injectors. Now we can use the same engine designs they are. It's win-win for everyone (except the oil companies I guess). Also, biodiesel reduces soot and other emissions even further. The only downside is that it has a higher gel point than fossil diesel. In southern states you can get away with running straight B100, in more northerly states you need to mix in 15% fossil diesel to get the gel point back down (B85 fuel).
    - happyscrappy 11y ago
      The 500ppm to 15 ppm is Sulfur not particulates and Europe is now trying to move away from diesel because of their air pollution problems. Paris wants to ban them altogether by 2020. Biodiesel does not have the same problems. http://www.telegraph.co.uk/news/earth/environment/11878435/Europe-must-now-come-clean-on-diesel.html http://www.telegraph.co.uk/news/earth/environment/11878435/E...
      - paulmd 11y ago
        The sulfur content of the diesel is the primary driver of particulate emissions. > The impact of diesel fuel sulfur reduction on directly-emitted and secondary atmospheric particulate is evaluated by experiment and analysis. Experimental evidence shows that fuel sulfur conversion rate to particulate sulfate is linear down to zero sulfur level. > Analysis shows that sulfur-derived particulate accounts for the vast majority of atmospheric particulate from diesel engines. Consequently, fuel sulfur reduction would have a far greater impact in reducing atmospheric particulate burden than any other diesel engine particulate control strategy. http://papers.sae.org/872139/ http://papers.sae.org/872139/ Sorry, this one's paywalled, but it's a finding that has been repeatedly reproduced in the literature. I completely agree about biodiesel. ULSD is a big step forward but biodiesel is even better in terms of emissions profile. It's also got a number of other things going for it - it can be run in conventional un-modified diesel engines that don't produce high-tech waste, and there's several factors that make its production more desirable than other biofuels.
        gnopgnip 11y ago
        Does biodiesel running in a properly tuned engine produce much NOX?
        paulmd 11y ago
        I'll start right out by saying that NOx production is very sensitive to engine tuning, as VW has shown. If you run lean you increase your mileage, but you run hot which can increase your NOx output by two-digit factors. I scanned the literature real quick, and it's pretty mixed. I think stuff before the ULSD switchover pretty clearly favored the biodiesel, because No.1/No.2 were nasty. After the switchover, with a properly tuned engine, it seems to be pretty close with the ULSD having perhaps a slight edge. Without retuning the ULSD seems to be somewhat better. However all of this varies pretty broadly - some people found improved NOx levels just from switching biodiesel. I didn't find a good, modern paper that quantifies the increase, a few looked promising but were paywalled. http://umexpert.um.edu.my/file/publication/00003184_92278.pdf http://umexpert.um.edu.my/file/publication/00003184_92278.pd... I thought this was a good summary of the effects of biodiesel and tuning strategies on various engines. Like ethanol vs gasoline, biodiesel contains more oxygen than its fossil counterpart. It's also not as fully saturated. As such it just tends to run leaner and hotter, and that's why there's a change in average levels. There seems to be a huge variance in the data. Some possible explanations: every manufacturer tunes their engine a little differently, air conditions like humidity and altitude may play a part, and the composition of the biodiesel may not be constant (eg percentage of fossil mixed in, level of saturation in the feedstock, different additive mixtures, etc). I think manufacturers probably tune their engines primarily for fossil, and to improve mileage they tend to run them as lean as emissions standards will let them get away with. So they may be fairly sensitive to small changes. It would probably be best to add biodiesel to the emissions tests as well, to get them to pay some attention to tuning for it. Maybe there's a happy medium that will work acceptably with both. If not - flex-fuel ethanol vehicles are capable of automatically detecting the level of ethanol and adjusting their tuning to match, we should have something like that for biodiesel. Perhaps a property like acidity or density, levels of particulates, or presence of a taggant in the fuel. Anyway, hadn't looked at that stuff since before ULSD was out and didn't realize it had changed the picture a little bit. I don't mean to minimize the problem, acid rain sucks and we should absolutely do what we can to address it. But there's no zero-harm solution, if the increase can be mitigated or kept minor with proper tuning there are some compelling benefits to biodiesel over fossil diesel.
rjsw 11y ago
Part of the sales pitch is the better fuel economy of diesel cars. One problem in Europe is that sales of diesel cars have become so high that we are not making good use of all the distillation fractions of the oil.
LoSboccacc 11y ago
more a result of the co2 craze. then they discovered diesel contains helluvalot of particulate compared to standard fuels (ops!) and to reduce it you have to burn at higher temperatures (and now you have NOX) at which point it was too late, at least in Europe, where diesel is usually 10% cheaper to buy and overall 20% cheaper to run, so demand is high enough to keep it alive.
ipsin 11y ago
For about the last ten years, most of the diesel fuel in the US has been ULSD (Ultra-Low Sulfur), and in 2007 the EPA tightened emissions standards for new vehicles. If the VW vehicles made after 2009 met those emission goals, they would be much cleaner than the smoke-belching cars and trucks you may be thinking of. http://www3.epa.gov/cleandiesel/technologies/index.htm http://www3.epa.gov/cleandiesel/technologies/index.htm
- happyscrappy 11y ago
  I think part of the problem in the US is "off-road diesel" is taxed far less and therefore much cheaper encouraging people to use it on road, and it is terrible. By the way does anyone know of a good way to test for diesel particulates? I swear Boston commuter rails are leaking diesel fumes into the passenger cabins.
  - mfb 11y ago
    The device for measuring particulate concentration is called an aethalometer: https://en.wikipedia.org/wiki/Aethalometer https://en.wikipedia.org/wiki/Aethalometer
  - organsnyder 11y ago
    Is "off-road" diesel actually formulated any differently? My understanding is that it's taxed differently because it's only legal to use it in machines that aren't road-legal (farm & construction equipment, for instance), since much of fuel taxes goes toward road maintenance. I thought that the only real different is the presence/absence of a dye used to prove that you're using the correct type.
    - happyscrappy 11y ago
      Apparently they used to have higher sulfur but as of 12/2010 are all supposed to be Ultra Low Sulfur, although diesels will run on heating oil.
    - LordKano 11y ago
      As I understand it, it's legal to use it in other vehicles but only if those vehicles are used off of the public roadways. For example, if you have a large site and must move material internally to that site, you can use untaxed diesel while the vehicles are moving material on site.
Agustus 11y ago
Yes, they are among one of the four items identified in improving fuel economy: Aluminum frames (carbon fiber is better but cost prohibitive at this time), diesel, streamlining (read shrink), and the other that I am currently blanking on. a. Diesel engines get 33% better fuel economy. [1] b. Have a lower total cost of ownership. [2] c. They are better than petrol gasoline on three out of five emission items, the one that is noticeable to the naked eye, particulates, is what causes concern. [3]The caveat is that petrol gas emits particulates at a smaller micron level, unnoticeable to the naked eye, and may actually be of greater concern to the general public. 1. http://www.carsdirect.com/car-buying/diesel-fuel-vs-unleaded-gasoline-understand-the-pros-and-cons http://www.carsdirect.com/car-buying/diesel-fuel-vs-unleaded... 2. http://www.dieselforum.org/files/dmfile/20130311_CD_UMTRITCOFinalReport_dd2017.pdf http://www.dieselforum.org/files/dmfile/20130311_CD_UMTRITCO... 3. https://uk.answers.yahoo.com/question/index?qid=20060926082929AA4DvqB https://uk.answers.yahoo.com/question/index?qid=200609260829...
- mhurron 11y ago
  Does all of this include Hybrid engines or just more traditional gasoline engines?
  - paulmd 11y ago
    The thing to remember is that hybrids and electrics tend to moderately trade off emissions for an increase in toxic waste from production. Neodymium for motors, tantalum for capacitors, lithium for batteries - all of those are bad news bears for the environment. Even stuff like copper isn't particularly awesome to produce. All other things being equal (mileage, emissions, etc), you should prefer the vehicle with a simple aluminum frame and engine over the high-tech wundercar because the impact of producing and disposing of it is lower. To the actual question - yeah, diesels running on biodiesel actually produce less GHG emissions than even hybrids. Ultra Low Sulfur Diesel is pretty close but just a bit above hybrids. The National Academy of Sciences published a study back in 2010 on the topic. The report itself is paywalled but there's a copy on the Arkansas state website. I snapped an image of the chart for ease of viewing. Note that ULSD was only introduced in the US in 2010 (2006 for Cali). The Euros have had it for quite a bit longer. So when you're reading studies, if it predates 2010 and it doesn't specifically say ULSD or Biodiesel then you should disregard it, because the new fuels are vastly cleaner and the playing field has shifted dramatically as a result. Biodiesel is often notated as something like B100, B85, or BD20 denoting the percentage of biodiesel in a mixture with fossil diesel. Pure B100 has a fairly high gel point and can cause problems starting in cold areas, so these mixtures include a fraction of ULSD to lower the gel point. http://imgur.com/FEOo1zB http://imgur.com/FEOo1zB http://1.usa.gov/1gO9jPL http://1.usa.gov/1gO9jPL
jhayward 11y ago
> Are diesel vehicles actually more environmentally friendly? Yes (legal) diesel passenger vehicles and light trucks sold in the US since [edit: 2007] are significantly cleaner in all respects than their gasoline equivalents, although that difference goes away soon as the gas regulations catch up. It's very unlikely you could detect whether the vehicle in front of you is gas or diesel just by looking at it or smelling the exhaust. That said, there are a lot of pre-2005s out there, showing smoke and smelling bad. Also the heavy trucks are just now getting the emissions requirements that lighter vehicles have had for the last 10 years. I have a 2012 heavy-duty diesel pickup. Except for the logo on it and maybe the sound of the engine, you'd never know it was diesel.
- sliverstorm 11y ago
  The sound of the engine is usually the giveaway to me. Clatterclatterclatter... I sometimes have to roll up my window when I am at a stoplight next to a heavy-duty diesel.
  - ubercore 11y ago
    Our now-maligned cheater TDI really doesn't sound any different than other 4 cylinder engines of its size and power. The exhaust does smell different, I prefer it to gasoline exhaust (don't _like_ it, but find it less offensive).
  - jhayward 11y ago
    Even the sound of the newer engines is reduced. Common-rail fuel injection reduces injector noise, which is most of that rattle you hear. The emissions equipment muffles the exhaust a bit. Even valve noise is reduced because they need to control things to finer tolerances. But a big diesel will always sound a bit beefy I think. The smaller 4-cylinders shouldn't be discernable from gas at all.
    - sbalea 11y ago
      My 2.0L turbo diesel engine (on non-VW variety) sounds very different than its 2.0L gas sibling. And I definitely like it :)

seren 11y ago

They emit less CO2 per kilometer but much more particulates (this is why they have a filter), which is worse health wise.

happyscrappy 11y ago
"Despite lower carbon dioxide emissions, diesel cars may promote more global warming than gasoline cars. Laws that favor the use of diesel, rather than gasoline, engines in cars may actually encourage global warming, according to a new study. Although diesel cars obtain 25 to 35 percent better mileage and emit less carbon dioxide than similar gasoline cars, they can emit 25 to 400 times more mass of particulate black carbon and associated organic matter ("soot") per kilometer [mile]. The warming due to soot may more than offset the cooling due to reduced carbon dioxide emissions over several decades, according to Mark Z. Jacobson, associate professor of civil and environmental engineering at Stanford University." http://news.stanford.edu/pr/02/jacobsonJGR1023.html http://news.stanford.edu/pr/02/jacobsonJGR1023.html
- paulmd 11y ago
  That release is from 2002, which predates the introduction of Ultra-Low Sulfur Diesel in the US (Cali switched in '06, the rest of the US switched in '10). This drops the allowable particulate concentration from 500 ppm to 15 ppm, which as you would expect greatly reduces soot as well as emissions of all kind. The diesel we were running back then was garbage. It really had more in common with something like heating oil than the diesel the rest of the world uses, and is the reason why the US has a perception of diesel engines being dirty. It also created huge problems for porting small diesels over from Europe - they run at a much higher compression, but at those pressures the particulates in the fuel become abrasive and eat away the fuel injectors. Now we can use the same engine designs they are. It's win-win for everyone (except the oil companies I guess). Also, biodiesel reduces soot and other emissions even further. The only downside is that it has a higher gel point than fossil diesel. In southern states you can get away with running straight B100, in more northerly states you need to mix in 15% fossil diesel to get the gel point back down (B85 fuel).
  - happyscrappy 11y ago
    The 500ppm to 15 ppm is Sulfur not particulates and Europe is now trying to move away from diesel because of their air pollution problems. Paris wants to ban them altogether by 2020. Biodiesel does not have the same problems. http://www.telegraph.co.uk/news/earth/environment/11878435/Europe-must-now-come-clean-on-diesel.html http://www.telegraph.co.uk/news/earth/environment/11878435/E...
    - paulmd 11y ago
      The sulfur content of the diesel is the primary driver of particulate emissions. > The impact of diesel fuel sulfur reduction on directly-emitted and secondary atmospheric particulate is evaluated by experiment and analysis. Experimental evidence shows that fuel sulfur conversion rate to particulate sulfate is linear down to zero sulfur level. > Analysis shows that sulfur-derived particulate accounts for the vast majority of atmospheric particulate from diesel engines. Consequently, fuel sulfur reduction would have a far greater impact in reducing atmospheric particulate burden than any other diesel engine particulate control strategy. http://papers.sae.org/872139/ http://papers.sae.org/872139/ Sorry, this one's paywalled, but it's a finding that has been repeatedly reproduced in the literature. I completely agree about biodiesel. ULSD is a big step forward but biodiesel is even better in terms of emissions profile. It's also got a number of other things going for it - it can be run in conventional un-modified diesel engines that don't produce high-tech waste, and there's several factors that make its production more desirable than other biofuels.
      - gnopgnip 11y ago
        Does biodiesel running in a properly tuned engine produce much NOX?
        paulmd 11y ago
        I'll start right out by saying that NOx production is very sensitive to engine tuning, as VW has shown. If you run lean you increase your mileage, but you run hot which can increase your NOx output by two-digit factors. I scanned the literature real quick, and it's pretty mixed. I think stuff before the ULSD switchover pretty clearly favored the biodiesel, because No.1/No.2 were nasty. After the switchover, with a properly tuned engine, it seems to be pretty close with the ULSD having perhaps a slight edge. Without retuning the ULSD seems to be somewhat better. However all of this varies pretty broadly - some people found improved NOx levels just from switching biodiesel. I didn't find a good, modern paper that quantifies the increase, a few looked promising but were paywalled. http://umexpert.um.edu.my/file/publication/00003184_92278.pdf http://umexpert.um.edu.my/file/publication/00003184_92278.pd... I thought this was a good summary of the effects of biodiesel and tuning strategies on various engines. Like ethanol vs gasoline, biodiesel contains more oxygen than its fossil counterpart. It's also not as fully saturated. As such it just tends to run leaner and hotter, and that's why there's a change in average levels. There seems to be a huge variance in the data. Some possible explanations: every manufacturer tunes their engine a little differently, air conditions like humidity and altitude may play a part, and the composition of the biodiesel may not be constant (eg percentage of fossil mixed in, level of saturation in the feedstock, different additive mixtures, etc). I think manufacturers probably tune their engines primarily for fossil, and to improve mileage they tend to run them as lean as emissions standards will let them get away with. So they may be fairly sensitive to small changes. It would probably be best to add biodiesel to the emissions tests as well, to get them to pay some attention to tuning for it. Maybe there's a happy medium that will work acceptably with both. If not - flex-fuel ethanol vehicles are capable of automatically detecting the level of ethanol and adjusting their tuning to match, we should have something like that for biodiesel. Perhaps a property like acidity or density, levels of particulates, or presence of a taggant in the fuel. Anyway, hadn't looked at that stuff since before ULSD was out and didn't realize it had changed the picture a little bit. I don't mean to minimize the problem, acid rain sucks and we should absolutely do what we can to address it. But there's no zero-harm solution, if the increase can be mitigated or kept minor with proper tuning there are some compelling benefits to biodiesel over fossil diesel.

rjsw 11y ago

Part of the sales pitch is the better fuel economy of diesel cars. One problem in Europe is that sales of diesel cars have become so high that we are not making good use of all the distillation fractions of the oil.

LoSboccacc 11y ago

more a result of the co2 craze. then they discovered diesel contains helluvalot of particulate compared to standard fuels (ops!) and to reduce it you have to burn at higher temperatures (and now you have NOX) at which point it was too late, at least in Europe, where diesel is usually 10% cheaper to buy and overall 20% cheaper to run, so demand is high enough to keep it alive.

ipsin 11y ago

For about the last ten years, most of the diesel fuel in the US has been ULSD (Ultra-Low Sulfur), and in 2007 the EPA tightened emissions standards for new vehicles. If the VW vehicles made after 2009 met those emission goals, they would be much cleaner than the smoke-belching cars and trucks you may be thinking of. http://www3.epa.gov/cleandiesel/technologies/index.htm http://www3.epa.gov/cleandiesel/technologies/index.htm

happyscrappy 11y ago
I think part of the problem in the US is "off-road diesel" is taxed far less and therefore much cheaper encouraging people to use it on road, and it is terrible. By the way does anyone know of a good way to test for diesel particulates? I swear Boston commuter rails are leaking diesel fumes into the passenger cabins.
- mfb 11y ago
  The device for measuring particulate concentration is called an aethalometer: https://en.wikipedia.org/wiki/Aethalometer https://en.wikipedia.org/wiki/Aethalometer
- organsnyder 11y ago
  Is "off-road" diesel actually formulated any differently? My understanding is that it's taxed differently because it's only legal to use it in machines that aren't road-legal (farm & construction equipment, for instance), since much of fuel taxes goes toward road maintenance. I thought that the only real different is the presence/absence of a dye used to prove that you're using the correct type.
  - happyscrappy 11y ago
    Apparently they used to have higher sulfur but as of 12/2010 are all supposed to be Ultra Low Sulfur, although diesels will run on heating oil.
  - LordKano 11y ago
    As I understand it, it's legal to use it in other vehicles but only if those vehicles are used off of the public roadways. For example, if you have a large site and must move material internally to that site, you can use untaxed diesel while the vehicles are moving material on site.

Agustus 11y ago

Yes, they are among one of the four items identified in improving fuel economy: Aluminum frames (carbon fiber is better but cost prohibitive at this time), diesel, streamlining (read shrink), and the other that I am currently blanking on. a. Diesel engines get 33% better fuel economy. [1] b. Have a lower total cost of ownership. [2] c. They are better than petrol gasoline on three out of five emission items, the one that is noticeable to the naked eye, particulates, is what causes concern. [3]The caveat is that petrol gas emits particulates at a smaller micron level, unnoticeable to the naked eye, and may actually be of greater concern to the general public. 1. http://www.carsdirect.com/car-buying/diesel-fuel-vs-unleaded-gasoline-understand-the-pros-and-cons http://www.carsdirect.com/car-buying/diesel-fuel-vs-unleaded... 2. http://www.dieselforum.org/files/dmfile/20130311_CD_UMTRITCOFinalReport_dd2017.pdf http://www.dieselforum.org/files/dmfile/20130311_CD_UMTRITCO... 3. https://uk.answers.yahoo.com/question/index?qid=20060926082929AA4DvqB https://uk.answers.yahoo.com/question/index?qid=200609260829...

mhurron 11y ago
Does all of this include Hybrid engines or just more traditional gasoline engines?
- paulmd 11y ago
  The thing to remember is that hybrids and electrics tend to moderately trade off emissions for an increase in toxic waste from production. Neodymium for motors, tantalum for capacitors, lithium for batteries - all of those are bad news bears for the environment. Even stuff like copper isn't particularly awesome to produce. All other things being equal (mileage, emissions, etc), you should prefer the vehicle with a simple aluminum frame and engine over the high-tech wundercar because the impact of producing and disposing of it is lower. To the actual question - yeah, diesels running on biodiesel actually produce less GHG emissions than even hybrids. Ultra Low Sulfur Diesel is pretty close but just a bit above hybrids. The National Academy of Sciences published a study back in 2010 on the topic. The report itself is paywalled but there's a copy on the Arkansas state website. I snapped an image of the chart for ease of viewing. Note that ULSD was only introduced in the US in 2010 (2006 for Cali). The Euros have had it for quite a bit longer. So when you're reading studies, if it predates 2010 and it doesn't specifically say ULSD or Biodiesel then you should disregard it, because the new fuels are vastly cleaner and the playing field has shifted dramatically as a result. Biodiesel is often notated as something like B100, B85, or BD20 denoting the percentage of biodiesel in a mixture with fossil diesel. Pure B100 has a fairly high gel point and can cause problems starting in cold areas, so these mixtures include a fraction of ULSD to lower the gel point. http://imgur.com/FEOo1zB http://imgur.com/FEOo1zB http://1.usa.gov/1gO9jPL http://1.usa.gov/1gO9jPL

jhayward 11y ago

> Are diesel vehicles actually more environmentally friendly? Yes (legal) diesel passenger vehicles and light trucks sold in the US since [edit: 2007] are significantly cleaner in all respects than their gasoline equivalents, although that difference goes away soon as the gas regulations catch up. It's very unlikely you could detect whether the vehicle in front of you is gas or diesel just by looking at it or smelling the exhaust. That said, there are a lot of pre-2005s out there, showing smoke and smelling bad. Also the heavy trucks are just now getting the emissions requirements that lighter vehicles have had for the last 10 years. I have a 2012 heavy-duty diesel pickup. Except for the logo on it and maybe the sound of the engine, you'd never know it was diesel.

sliverstorm 11y ago
The sound of the engine is usually the giveaway to me. Clatterclatterclatter... I sometimes have to roll up my window when I am at a stoplight next to a heavy-duty diesel.
- ubercore 11y ago
  Our now-maligned cheater TDI really doesn't sound any different than other 4 cylinder engines of its size and power. The exhaust does smell different, I prefer it to gasoline exhaust (don't _like_ it, but find it less offensive).
- jhayward 11y ago
  Even the sound of the newer engines is reduced. Common-rail fuel injection reduces injector noise, which is most of that rattle you hear. The emissions equipment muffles the exhaust a bit. Even valve noise is reduced because they need to control things to finer tolerances. But a big diesel will always sound a bit beefy I think. The smaller 4-cylinders shouldn't be discernable from gas at all.
  - sbalea 11y ago
    My 2.0L turbo diesel engine (on non-VW variety) sounds very different than its 2.0L gas sibling. And I definitely like it :)