Diesel vs. Hybrid

Discussion in 'Gen 2 Prius Fuel Economy' started by briloop, Aug 30, 2007.

  1. tripp

    tripp Which it's a 'ybrid, ain't it?

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    Madler,

    The Atkinson cycle does help somewhat, so the Prius does better than a typical 1.5L ICE. It may not approach a diesel, but it does pretty well. Driving between Denver and Omaha (and back) I got about 47.8 MPG ( 49.1 out/ 46.5 back) @ 75 mph. I'm not sure what a comparable diesel would have gotten.
     
  2. bwilson4web

    bwilson4web i3 and Prime

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    <div class='quotetop'>QUOTE(finman @ Aug 31 2007, 09:50 AM) [snapback]504877[/snapback]</div>
    [​IMG]

    Bob Wilson
     
  3. micheal

    micheal I feel pretty, oh so pretty.

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    <div class='quotetop'>QUOTE(madler @ Aug 31 2007, 11:52 AM) [snapback]504878[/snapback]</div>

    Sounds well and good, but why does the Prius rate 18% higher on the highway mpg than a Jetta TDI? This is from new EPA numbers for 2006 (couldn't find the TDI for 07 or 08 yet). Your argument in decreased efficiency and less hybrid improvement at higher speeds is true to some degree because the hybrid isn't as efficient on the highway. However, that doesn't mean it isn't more efficient than practically any other comparable vehicle (even a diesel). Perhaps this changes in favor of the diesels at extremely high speeds (like 90mph), but I think the point holds true even at typical interstate speeds (70-80mph).

    As far as your assertion of very limited improvement, I have seen several previous posts that cited very little power is needed to maintain highway speeds once one reaches it. I want to say 20hp or less (but don't quote me). Besides, there are a lot of features of say the Prius that allows for the reduced size, more fuel-efficient, Atkinson cycle ICE. The augment from the battery is no small benefit, since the majority of the time on the highway our time is spent just maintaining speed, thereby allowing for an engine that is designed to meet say our needs 80% of the time rather than an engine designed to meet our needs 20% of the time.

    BTW: It is getting dated now, but it is an apples to apples comparison of hybrids (Prius and HCH) to other frugal cars (Jetta TDI and Echo). HCH barely came out on ahead of the Prius with the TDI in 3rd. Includes both city and highway mileage. All in all, no benefit to the diesel above the hybrid and the Prius had better highway than the TDI (Doesn't say by how much). 3rd Page of Article
     
  4. patsparks

    patsparks An Aussie perspective

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    Because EPA figures do not include much travel at 100mph.
    Even with the 70mph speed limit on the UK motorways it isn't at all uncommon to be driving down the motorway at 80mph and have another car pass you like you're standing still.

    At the end of the day you are preaching to the converted, it's the European diesel driver you need to convince, or rather Toyota does.
    Can you blame Europeans for sticking with what they know? The benefit to risk ratio for a switch to hybrid is much worse for them than it was for a person who was already driving a petrol powered car.
    I think the big advantage is quiet engine and no stink on start up plus slightly better economy.
     
  5. Stivo

    Stivo New Member

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    I think some of you miss some important facts/ideas:
    1) The hybrid buzz in europe is way smaller than in america. Most cars here are hatchbacks or something in the size of a toyota yaris. They use much less gasoline than typical cars in the USA. Since the difference between a hybrid and a normal car isnt that big, hybrids get less attention. Check out toyota.ch to see this.
    2) The prius does worse than a diesel car at 170km/h (~105mph, the maximum possible speed for it). I have read about that a lot in german forums, so trust me on this one. But since this speed is only allowed on some german speedways, I usually think of this as irrelevant.
    3) There are just 4 hybrids for sale here: Prius, Lexus GS450h, Lexus RX400h (both Lexus of course very expensive) and the Honda Civic hybrid. You dont hear a lot about those, most people dont even know they exist.
    4) The time of the prius is coming here, later than in the USA for before mentioned reasons, but I keep seeing them on the streets more and more.

    Since switzerland does not have a single car brand I cant say anything about (the idea for the smart at least is from a swiss guy, the founder of swatch clocks) patriotic arguments to buy a car.
    For some impressions of cars and their gas usage, take a look at this site:
    http://www.spritmonitor.de/en/
    Keep in mind that this site is used mostly by german people.

    Also, the prius is quite expensive. In switzerland we pay 38950 Swiss francs for the basic version, which comes down to: 32 393.5465 Dollars, in germany even 33 939.6911 Dollars. (but could be because of low swiss franc right now)
    The avensis, a very common model here, is cheaper than that and is roomier in the hatchback version.
     
  6. madler

    madler Member

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    <div class='quotetop'>QUOTE(micheal @ Aug 31 2007, 10:46 PM) [snapback]505320[/snapback]</div>
    Because the Prius has a smaller internal combustion motor, which is doing all the work at the relevant conditions. The Prius has a 76 hp ICE, the TDI is 100 hp. The bigger the engine, the more inefficient it is at a given lower power output.

    You apparently missed what I said in my post -- I was making a comparison between hypothetical vehicles of equal power and drag. Diesel ICEs are more efficient than gas ICEs, and the Prius is relying entirely on its ICE at constant speed on level ground.

    Also you have to be careful with mpg comparisons, since diesel fuel is denser than gasoline. It would be more fair to compare km per kg fuel or km per kg Carbon.

    Exactly. That is the main benefit of a hybrid. You have a smaller engine for the same overall performance experience. That's what I said in my post.

    Assuming you want to maintain the benefits of the very high energy density of hydrocarbon fuels, the ideal setup would be a hybrid diesel, with measures to reduce non-CO2, non-H2O emissions, including low-sulphur fuel. That would be a good bit more efficient (I'm guessing ~20%) than our gas hybrids.
     
  7. madler

    madler Member

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    <div class='quotetop'>QUOTE(tripp @ Aug 31 2007, 09:55 AM) [snapback]504968[/snapback]</div>
    Yes, that helps quite a bit. I've heard numbers like 10% over an Otto. Still short of a diesel.

    By the way, I saw an article where Toyota stated it would not pursue a diesel hybrid. They said that while the emissions would be lower, there would not be a market for it. The rationale was that the consumer wouldn't want to pay a premium for both the hybrid technology and the more expensive fuel.

    Of course, all of Toyota's competitors were saying the same thing about hybrids in the first place, that no one would want to pay that premium. Look who's laughing now.
     
  8. ken1784

    ken1784 SuperMID designer

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    Just FYI...
    Toyota European Hybrid Sales Accelerate Past 100,000 unit
    http://www.toyota-media.com/ems_corp_v1_gl...m318-613353.pdf
    "Toyota Motor Europe (TME) has announced that cumulative European sales of Toyota and Lexus hybrid vehicles have topped the 100,000 mark. Since hybrids were first launched in Europe in 2000, a total of 101,235 vehicles have been sold as of 31 July, 2007. This achievement highlights a rapid acceleration in the uptake of hybrid vehicles, with more than 50% of Toyota’s cumulative European sales achieved in the last 13 months."

    The world wide sales is 1 million, so the european sales is about 10% of all Toyota/Lexus hybrids.

    [email protected]
     
  9. gazz

    gazz Member

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    In the UK for the first time for a long time, diesel is more expensive than petrol, only about 2.5% but it eats into the diesel mpg advantage. If the demand for diesel keeps going up I wounder what will happen to the price.
     
  10. micheal

    micheal I feel pretty, oh so pretty.

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    <div class='quotetop'>QUOTE(madler @ Sep 1 2007, 01:40 PM) [snapback]505447[/snapback]</div>
    I have never read anything that says that diesel fuel is cleaner than gas inherently. Some things are better, some are worse (particulates and NOx). Plus, since hybrids like th Prius are something around 90% cleaner than a conventional gas vehicle, the TDIs are worse than hybrids in emissions. The EPA scores show an overall pollution score of 1 and 6.4 tons a year in greenhouse emissions for the TDI. This compares to an 8-9.5 pollution score (higher is better) and only 4.0 tons a year in greenhouse emissions for the Prius. The EPA site doesn't say if this is with ULSD or not, but if you have links to show that diesels are cleaner overall in emissions, than feel free to share.

    The smaller engine allows for better overall performance in terms of mpg and 0-60 times. This is based on typical US highway speeds according to the EPA estimates (18% better). (the 0-60 times are also in favor of the Prius over the Jetta TDI). The US does not have roads where one can drive 100mph legally and I don' t know of anyone that has done it for more than a short amount of time. I haven't seen comparative tests at this speed so I don't know how it will pan out. The reviews that do highway and interstate comparisons (probably speeds from 65-75mph) show the Prius coming out ahead (as mentioned in the article I linked earlier).

    None of this is to say that diesels are horrible or bad. Improving fuel economy is a goal that all cars should try to do and just one technology won't do the trick. I have heard that a diesel hybrid would be hard because diesels would have a hard time with the constant stopping and starting (at least in the city). If that isn't true then I agree that a diesel hybrid would be a great solution. Diesel fuel can be hard to find and more expensive in some areas, so that could be a knock against it.
     
  11. silver-machine

    silver-machine New Member

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    well Ihave both a 2007 Prius and a toyota diesel ( avensis estate 2004) both do about 80 miles a day, partly on motorways.... and the mpg figures for each are pretty comparable, I get about 56 from the avensis and 58mpg from the prius. The avensis is a size larger. however.
    Cost wise in the UK Diesel and petrol cost about the same, and both vehicles cost about 7.8 pence in fuel per mile.
    Both cars are perfectly ok at high speeds, although the diesel mpg is a bit better if you are cruising at 80, and as it is a larger car I would prefer it for a long motorway journey, but Id prefer the prius for a cross country jouney.

    I think the reason for the lack of hybrids in europe is that they are pretty fully priced and cost more than other models. the tax break and current emphasis on CO2 emissions in the UK mean that hybrids are more attractive on this side of the channel.

    ( oh and Ive never heard of anyone not buying a toyota because its a paki car, but those who are ignorant enough to be racist are ignorant enough hang prjudices on anything)
     
  12. Jonnycat26

    Jonnycat26 New Member

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    <div class='quotetop'>QUOTE(micheal @ Sep 1 2007, 01:46 AM) [snapback]505320[/snapback]</div>
    I suspect the weight of the Jetta may have something to do with it. And I know that's a taboo subject... but the Jetta TDI gets good mileage in spite of it's weight... whereas the Prius is as lightweight as possible to help with it's mileage.
     
  13. madler

    madler Member

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    <div class='quotetop'>QUOTE(micheal @ Sep 2 2007, 12:32 PM) [snapback]505960[/snapback]</div>
    Those are apples and oranges if the objective is to figure whether a diesel hybrid would be a good idea or not. The question is how the engine technologies compare at the same power output.

    "Clean" has many dimensions. We'll start with CO2. Diesels are at least 20% more efficient (per mass carbon) than gas engines at the same power. So a comparable system will produce 20% less CO2.

    For other emissions, diesels are much, much worse than gas engines, for particulates and NOx. That is, if you don't do anything about them. The particulates are soot from the sulfur -- we've all seen the black smoke come out of the Mercedes or Volvo diesel in front of is, and the NOx is a result of the higher temperature combustion. (The higher efficiency is also a direct result of higher temperature combustion.)

    The first thing to do is to use only ultra-low sulfur diesel fuel (97% sulfur reduction). It is available now nationwide, and by law it will be the only diesel available in the US by Dec 2010. That greatly reduces the soot, and allows for a particulate filter to burn up the remaining soot (90% of it) before being emitted.

    There are urea (yes, urea) injection systems and standard catalytic converters for reducing or managing the NOx emission to meet US standards and even California standards.

    These are all showing up just now in 2007 models of diesel cars (e.g. Mercedes), being referred to as "clean diesel". Volkswagen is coming out with one in 2008 -- the 2008 Jetta clean diesel will be good for all 50 states, meeting the strict ULEV2 standards . These is a premium of about $1000 for these engines with emission mitigations over comparable gas engines, but are marketable due to the higher efficiency of the diesel engines (even with all the emission stuff hanging off them).

    I suspect that gas engines with NOx mitigation can still do better than the cleanest of clean diesels on NOx, (this depends of course on how much you're willing to spend on the mitigations). So there is a little pick-your-poison here. Do you care more about the CO2 or the NOx?

    If I can meet strict emission standards for NOx, then I care more about minimizing CO2 than reducing the NOx below those standards.

    The same is true of gas engines. I remember ads for something saying that the worst possible thing you could do to your car engine was to start it, which had some truth to it. But Toyota figured out that if you spin up the engine to 1000 rpm before squirting any fuel in, the problems are avoided. There may be other start-up problems unique to diesels that I'm not aware of. But that's what engineers are for. Ford and Peugot are both working on diesel hybrids for around 2010.

    Side comment: this all makes sense only if your diesel comes from oil. If you're using diesel from coal or diesel from crops (biofuels), then you're making more CO2 to generate the fuel and so you'd be at a net loss compared to the gasoline. (In the future there may be a way to make biofuels that doesn't take more energy in than you get out, but that's certainly not the case for biofuels today.)
     
  14. patsparks

    patsparks An Aussie perspective

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    <div class='quotetop'>QUOTE(silver-machine @ Sep 3 2007, 05:33 AM) [snapback]505978[/snapback]</div>
    I hate the predudice of my friend. It is one thing I try to drive out of them but they wont change. I see far less of them than I once did. Please don't hold this against me as it isn't my opinion at all just what I was told by one person.
     
  15. coloradospringsprius

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    <div class='quotetop'>QUOTE(Jonnycat26 @ Sep 2 2007, 04:10 PM) [snapback]505982[/snapback]</div>
    Not much. Jetta TDI: 3,020 pounds. Prius: 2,890 pounds. Less than the weight of one average-sized passenger.

    And btw, "it's" = "it is." (Sorry, I can't help myself! ;-)
     
  16. madler

    madler Member

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    <div class='quotetop'>QUOTE(Jonnycat26 @ Sep 2 2007, 01:10 PM) [snapback]505982[/snapback]</div>
    I don't know how exactly the EPA computes highway mileage, but at constant speed on level ground the weight is not a factor at all. The weight comes into play in getting the vehicle up to that speed in the first place, or in climbing hills. However at constant speed on level ground, all you need to fight is drag and friction. A maglev train on the moon would require no motive power at all to maintain speed on level ground.
     
  17. RobH

    RobH Senior Member

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    <div class='quotetop'>QUOTE(madler @ Sep 2 2007, 04:14 PM) [snapback]506047[/snapback]</div>
    Biodiesel is usually described as being carbon neutral. The CO2 released on burning was originally captured from the air in growing the plants. Biodiesel burns cleaner, and doesn't smell bad.

    What am I missing?
     
  18. Jonnycat26

    Jonnycat26 New Member

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    <div class='quotetop'>QUOTE(coloradospringsprius @ Sep 2 2007, 08:00 PM) [snapback]506066[/snapback]</div>
    Okay, so the Jetta weighs more... add that and the fact that the Jetta has wider tires (better handling, better stopping, worse mileage). As I said, the Jetta is not built for economy... unlike the Prius.
     
  19. madler

    madler Member

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    <div class='quotetop'>QUOTE(RobH @ Sep 2 2007, 07:50 PM) [snapback]506122[/snapback]</div>
    The fossil energy required to grow the crops, as well as the energy to process the crops to make the fuel. This includes the production of fertilizer and pesticides, farm machinery, pumping water, grinding, and transportation. Soybeans require 27 percent more fossil energy than the biodiesel produced, and sunflowers require 118 percent more fossil energy than the biodiesel produced. So you'd be far better off taking the diesel that would be used for farming and transporting the crops and instead burning it directly in the diesel vehicles that the biodiesel was destined for.

    There are similar losses for the production of ethanol from corn, switchgrass, or wood.

    On the other hand, corn prices have risen 70% since the administration called for ethanol production from corn, even though it is a net energy loser. Energy loser, but big time money maker for the corn guys. They sure knew whose ear to bend in the White House. Almost as good as the hydrogen story the administration made up. I can't wait to hear the next one.
     
  20. IsrAmeriPrius

    IsrAmeriPrius Progressive Member

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    <div class='quotetop'>QUOTE(Jonnycat26 @ Sep 2 2007, 09:07 PM) [snapback]506149[/snapback]</div>
    You left out Volkswagen's stellar reputation for reliability.
     
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