Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Would a diesel-electric hybrid be better mpg than gas-electric hybrid

  1. May 12, 2007 #1
    Given the earlier thread, why not combine diesel with electric motors?
     
  2. jcsd
  3. May 13, 2007 #2

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    We can kill three birds with one stone. :biggrin:

    http://www.msnbc.msn.com/id/10788292/

    Note that trains have been running diesel over electric for decades.
     
  4. Mar 13, 2010 #3
    I would almost assure that. Though from everything ive read, a detached diesel motor/generator would be more efficent than a parallel drive design, as a detached generator would let the diesel run at peak efficiency constantly rather than constantly changing rpm and efficiency
     
  5. Mar 15, 2010 #4
    This is called a series hybrid and is the type of hybrid that most hybrid auto manufacturers are now focusing on.

    While a diesel based hybrid may get better fuel economy than a gasoline engine, it doesn't necessarily make it better. Diesel engines generate a lot of pollution, which is why they are not very common in the US for commercial vehicles. Gasoline is a much more cleaner burning fuel which is why its most commonly used. Future series hybrid electric/gas cars will probably use stratified ignition engines, or something close to it, to try and take advantage of the benefits the diesel cycle offers, but still using the clean burning fuel, gasoline.
     
  6. Mar 15, 2010 #5

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Ultra-low-sulfur fuels now required in the US contain 15 ppm sulfur, compared to ~500 ppm in the older fuels. Particulate traps used in late-model diesels further reduce emissions. Diesels are very common in commercial, but not private vehicles, primarily because diesels could not meet emission standards. They do now.

    Assuming Exxon et al manage to produce biodiesel from algae [$600 million recently invested by Exxon alone], diesel CO2 emissions would be reduced to near zero. Also, biodiesel contains no sulfur.
     
    Last edited: Mar 15, 2010
  7. Mar 15, 2010 #6

    brewnog

    User Avatar
    Science Advisor
    Gold Member

    Sorry, this is cobblers. Do you have anything to back up the claim that Diesel engines "generate a lot of pollution"? Have you actually even compared a modern gasoline engine with its Diesel counterpart, in terms of brake specific NOx/CO/HC/PM/CO2 emissions, or do you just think "old lorries make smoke, so all Diesel engines must be terrible"?
     
  8. Mar 15, 2010 #7
    No it isn't. Yes I do. Yes, and no I don't. A simple google search reveals lots of info about how gasoline is cleaner than diesel....

    http://www.hybridcenter.org/hybrid-watchdog-hybrid-vs-diesel.html


    http://www.grinningplanet.com/2005/04-12/diesel-vs-gasoline-article.htm

    http://www.cicero.uio.no/fulltext/index_e.aspx?id=6871

    The text book right in front of me, (An Introduction to Combustion, by: S.R. Turns) also supports my claim. While the sulfur content in diesel has decreased, it hasn't changed the fundamental ways diesel engines operate. Unless flame temperatures can be lowered, fuel can be better atomized, or diesel production be made more efficient, I don't see how diesel could ever be cleaner than gasoline. If I'm missing something or don't know of some technological breakthrough that has made this possible please enlighten me.
     
  9. Mar 15, 2010 #8
    Biodiesel is still far from reality. Even so, diesel engines whether biodiesel or not, still generate pollutants. Yes there is less CO2, but theres also plenty of CO, NOx, HC, etc. But if biodiesel creates less of the pollutants than gasoline, I don't know, I've heard mixed information. Do you have any info on this?

    EDIT: Some good info about biodiesel,
    http://www.ucsusa.org/clean_vehicle...html#Biodiesel_versus_gasoline_in_cars_and_li

    [​IMG]
     
    Last edited: Mar 15, 2010
  10. Mar 15, 2010 #9
    Driving a modern, small displacement diesel can be fun. I assume they'd make a fine hybrid animal given their advantages in torque and economy.

    Of course, pollution is in they eye of the beholder. Europe loves diesel cars and things there are clean, especially Germany.

    Yes, diesels pollute an order of magnitude more than gasoline. But if you consider the 'problem' of automotive gasoline pollution equivalent to the 'problem' of time dilation at highway speeds (as I do), you should have no moral hangups with a diesel.
     
  11. Mar 16, 2010 #10

    brewnog

    User Avatar
    Science Advisor
    Gold Member

    Topher925, are you really standing by your link which holds the Tier 2 on-road regulation as being consistent with a modern on-road (Tier 4b, Stage V etc) Diesel engine?
     
  12. Mar 16, 2010 #11
    As already pointed out, trains have been utilizing diesel/electric power for a very long time.

    They also have jet turbine/electric systems. Which may not be as practical in a family sedan :wink:
     
  13. Mar 16, 2010 #12

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Not true. Biodiesel is in common use now. What is not sustainable is the source - that typically being soy and canola, cotton, and a few other crops. That is why algae-derived fuels are the key. Algae can produce five to ten times the yield per acre-year, or more, compared to any other fuel crop.

    Not less CO2; I said virtually no CO2. In principle, biodiesel emits no new CO2 - only that absorded from the atmosphere by the fuel source [crop]. It is carbon neutral. No other fuel option can make the same claim, less perhaps ethanol, which has other serious drawbacks and is completely unsustainable. The best option for a sustainable source of ethanol may be...algae.

    Note that only the limit of your graph shows the results for pure biodiesel.

    Biodiesel is notoriously low in emissions, less NOX emission, which are a bit higher than petrodiesel. Beyond that, the emissions from any particular biodiesel fuel depends on the source of the fuel. Oils low in saturated fats, like oils from algae, produce the cleanest fuels. Being high in saturated fats, soy produces a relatively unclean biodiesel, which is what most studies would have used.

    There are two factors to consider regarding the energy content of petrodiesel. First is the amount of energy contained in a gallon of fuel. While this tracks approximately 1:1 with the amount of crude required, we transport ~25% less fuel to the market for a given amount of energy. Beyond the reduced distribution energy costs, diesel engines are more efficient than IC engines.
     
    Last edited: Mar 16, 2010
  14. Mar 16, 2010 #13

    mheslep

    User Avatar
    Gold Member

    Topher, after citing this:

    one can see your first blanket answer to the OP's query about gasoline versus diesel pollutants in this engineering forum was incorrect on a per km distance for CO2 and CO. It is known that Bio-diesel burns cleaner than petrol diesel. Brownog also drew your intention to the new Tier 2 bin 5 EPA standards, which reduce particulates to nearly nothing.
     
  15. Mar 16, 2010 #14

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    This thread really got way off on a tangent...

    In response to the OP's question- yes, diesel hybrids (parallel or series) will tend to get better mileage than a gasoline one. This is due to the fact that turbo-diesel engines are generally more efficient than a gasoline engine because of their high compression ratio and turbocharging. Additionally, Diesel has approximately 10% more stored energy per volume than gasoline, adding to a diesel vehicle's MPG rating (but not overall energy efficiency).

    The reason they aren't widely available is mainly cost. A turbodiesel engine is more expensive than a naturally aspirated gasoline one, which can make a big difference when you're putting a lot of expensive hybrid equipment on a vehicle as well.
     
  16. Mar 17, 2010 #15
    No. I'm not familiar with the politics, but only the science of how thermal engines work.

    I did not know this. Where is it being used?

    Yes, but keep in mind that NOx emissions are one of the most harmful emissions created. The idea behind a closed CO2 cycle is appealing but you can't ignore the other harmful products that are generated as well.

    I'm sorry, I don't understand your logic??? I never stated that diesels produced more CO2 or CO, I merely stated that diesels produce more pollution than their gasoline counterparts, which according to my sources they do. I have seen no information that suggests otherwise.
     
  17. Mar 17, 2010 #16

    mheslep

    User Avatar
    Gold Member

    Meaning what, that neither CO2 nor CO are pollution? In post 3 you made the blanket statement
    [my highlights]Without attaching a qualification that assertion is incorrect. The truth is the pollution profile, diesel vs gasoline, is mixed for unit of energy delivered. Also, this considers only the gasses at the point where they are exhausted directly from the cylinder. Post processing in the most recent engines might change the mix decidedly in favor of diesel, I dunno.

    Look, I could point to those same sources and naively make the reverse statement because I happened to focus only on CO2 and CO in favor of diesel.
     
  18. Mar 20, 2010 #17

    brewnog

    User Avatar
    Science Advisor
    Gold Member

    My post wasn't about the politics, it was about the technology which is now being used to ensure that NOx and PM emissions of Diesel vehicles are now a tiny fraction of what they were a few years ago; and in some cases can be cleaner than the air being drawn into the engine. Saying Diesel engines are "more polluting than gasoline" is just misguided if you're comparing a smokey old truck with a Euro V (or equivalent) petrol. I could just as easily claim that Diesel is "cleaner" because the CO emission limits now are half for Diesel what they are for gasoline. The thing is, if you only look at selected pollutants, it's easy to claim that either is somehow inherently "less polluting" than the other. Look at the bigger picture.
     
  19. Mar 25, 2010 #18

    Ranger Mike

    User Avatar
    Science Advisor

    well said Brewnog....I share your views on the diesel

    btw ..you are invited to my Earth Day celebration next month..( bring your old engine oil and tires for our bon fire)
     
  20. Mar 25, 2010 #19

    mheslep

    User Avatar
    Gold Member

    Well said, as are the CO2 emissions, the benzene emissions, etc (lower, not necessarily half)
     
  21. Mar 25, 2010 #20

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Modern diesel engines are pretty much as clean as gasoline.
    They produce less CO2 and you get more miles/gallon, PM are about the same as gasoline although there is a concern that the mix of particle sizes produced by diesels is more harmful.

    A plus of diesel for hybrids is that you can make very efficent small diesels - the original european version of the smart car had a 800cc diesel. Diesels are also simpler and you can turn them off and restart them with less loss of efficency than a gasoline engine.

    The big problem is acceptance in the US, it's hard to get fuel because nobody has diesels and nobody buys diesels because you can't get fuel. Also opinions take a long time to change.

    Another factor is the way pollution is calculated, in the Eu it's generally g/km so the easiest way to reach the level is to increase the number of km/litre by building smaller engines. In the US it was always pollutant concentration so the easiest way to meet the target was to build bigger engines. This is changing though.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Would a diesel-electric hybrid be better mpg than gas-electric hybrid
Loading...