Filed under: Diesel, Hybrid, BMW
New BMW 7-series hybrid uses lithium, still won't match efficiency of diesel
When BMW launches a hybrid version of the new 7-series sedan next year it looks like it will probably use the same Two-Mode hybrid system going into the X6 crossover. That configuration mates the hybrid transmission with the twin-turbocharged 4.4L V-8 that also debuted this spring in the X6. If Britain's CAR magazine is right, this may also be the first of the Two-Mode hybrids to use a lithium ion battery. All the existing Two-Modes from GM and Chrysler are still using nickel metal hydride. One thing the hybrid system apparently won't be able to do is approach the mileage of the diesel engine in the 730d that will be available at the new luxury sedan's launch. According to Dr. Klaus Draeger, BMW board member responsible for R&D, the 7 series hybrid is targeted at fans of V8s who want a bit of green image rather than those that actually want the lowest fuel consumption. For those that want to save at the pump, the 6 cylinder diesel with its combined mileage rating of 32.6mpg (U.S.) is the way to go. The V8 hybrid is likely get closer to the 20mpg of the Lexus LS600h as well as being a lot more expensive.
[Source: CAR]
Reader Comments (Page 1 of 1)
Turbofrog 11:20AM (7/09/2008)
I wish I could have the heart to be surprised by news like this.
Why can't they offer a performance hybrid as well as an efficient hybrid with the diesel engine? It's not as if price is an issue with cars at this level.
Not like a luxury limousine could ever be a sustainable choice in the first place...
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meme 11:55AM (7/09/2008)
For God's sake, when will people stop comparing diesel mpgs with gasoline mpgs as though they should be equivalent? Diesel is 15% denser and releases 15% more CO2 when you burn it; you need to divide diesel mpgs by 1.15. The number to beat is really 34mpg. Do they beat that number? Who knows; they don't give the mpg of the hybrid.
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Sam Abuelsamid 2:20PM (7/09/2008)
Meme, when will you stop with your diesel disiniformation. Yes diesel fuel has a higher concentration of carbon. However, the diesel combustion cycle is about 30 percent more efficient than the Otto cycle. Fifteen percent of that 30 percent is about 4.5 percent. Take that off the 30 percent and you still have a net reduction in CO2 emissions with a diesel engine of over 25 percent compared to a gasoline engine of similar output.
It is true that burning 1 gallon of releases more carbon than 1 gallon of gasoline. However with diesels burning so much less fuel, the net benefit is still there and pretty comparable to most hybrid systems on an overall basis. Of course each has applications where it does better and the best choice for an individual depends on what type of driving they do.
scatter 12:55PM (7/09/2008)
"...the 7 series hybrid is targeted at fans of V8s who want a bit of green image..."
Well done BMW. 10 out of 10 for facillitating greenwashing. And these manufacturers have the gumption to whinge about the EU 130g/km limit? Their hubris beggars belief.
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CMiller 1:09PM (7/09/2008)
These will probably be released in a limited number just to test the battery. The X6 two mode is to supposed to be a limited production too. It seems that we will probably see the two mode paired with smaller engines and diesels later on, along with hybrid options in the 3 and 5 series.
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meme 3:36PM (7/09/2008)
"Meme, when will you stop with your diesel disiniformation."
Sam, it's not disinformation to point out the truth. Diesel *is* a denser fuel. Yes, diesel engines are more efficient. But this is *already reflected in their MPG*. What is *not* reflected in their MPG is the fact that that gallon contains more fuel. It is *disinformation* to present that gallon as being equivalent to a gallon of gasoline by doing a direct MPG to MPG comparison.
So long as people keep doing direct MPG to MPG comparisons without pointing this out, I'm going to keep pointing this out. It's distorting the relative benefits of different fuel-saving technologies, giving diesel an unfair advantage over hybrids, weight reduction, drag reduction, and essentially everything else.
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Sam Abuelsamid 3:50PM (7/09/2008)
Unfortunately the way you word it implies that a diesel engine of equivalent performance emits more carbon dioxide than a spark ignition engine and that is simply not true. Another factor that you neglect to mention is that diesel is one of the first fractions to come off when refining crude oil. It takes more energy to refine gasoline than diesel swinging the well to wheel energy balance even more in favor of diesel
meme 4:30PM (7/09/2008)
I don't see how more clear I could have been than saying that diesel mpgs and gasoline mpgs are not equivalent. Do you have a suggested wording? And will you agree to not directly equate diesel mpgs with gasoline mpgs without mentioning this difference in fuel density?
"It takes more energy to refine gasoline than diesel swinging the well to wheel energy balance even more in favor of diesel"
That depends on the crude source and worldwide demand. Back during the 80s, for example, diesel demand was low enough that Iraq was actually reinjecting their heavier fractions back into their wells for pressure (it's now causing problems now in terms of production from those wells). If you have a heavier crude, yes, you need more cracking to produce gasoline. On the other hand, diesel generally needs more desulfurization, which also takes energy. And either way, the diesel *contains* more petroleum than the gasoline. The energy content in fuel far outweighs the energy used to refine it.
Diesel mpgs are simply not equivalent to gasoline mpgs, and you need to either point that out or not mention it at all.
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ale 5:10PM (7/09/2008)
However, while that may be true, when Joe somebody walks up to a diesel pump and gets fuel, over the course of the entire year he is saving money on his fuel purchases even when diesel is a buck more or about 25% more.
Whether diesel mpg does equate or not, the economies in the amount of money saved win out (whether or not fuel is really saved, i dont care) If over a three year period that diesel is saving me money, i could care less if diesel mpg is different, which i still dont see, but im not gonna contest. Still, just goes to show diesel ingenuity at its finest
Bill 11:22PM (7/09/2008)
Mpg is what counts, since we all buy fuel by volume.
You seem to be arguing that diesel should be artificially penalized simply because it contains more carbon.
As Sam pointed out, more carbon does not necessarily mean more CO2 emissions, because the diesel cycle itself is much more efficient than the Otto cycle.
You'd have to measure actual CO2 emissions on the gasoline vs. the diesel models of each vehicle - I doubt the difference would be as high as 15%.
Diesel here in the U.S. does carry a price penalty of 15-20% over regular unleaded.
Part of the reason is record demand from Europe, part is the cost of de-sulfurization - no one knows how either will change over time.
It should not surprise anyone here, however, that taking the cheap way out with a "mild" hybrid gains much less mpg than using a turbodiesel.
montoym 7:04PM (7/10/2008)
Quote from ale - "However, while that may be true, when Joe somebody walks up to a diesel pump and gets fuel, over the course of the entire year he is saving money on his fuel purchases even when diesel is a buck more or about 25% more" -
Exactly.
Personally, I could care less about the CO2 emissions of my car. Without going into a big Global Warming debate, I just simply don't belive that man-made CO2 is going to ruin our planet. For one, CO2 is proven to be a very, very mild greenhouse gas, with water vapor being significantly more potent and far more abundant. Secondly, in the history of the World, CO2 levels have been many times higher than current levels and during those times, the temp of the Earth has been both much higher and much lower than where we are today. There is no evidence proving that CO2 drives the temperature of Earth IMO.
So, beyond that point, what matters to me and 95% of consumers out there(especially those not artificially forced to consider CO2 output due to gov't rules), is how much they spend to drive their cars. In this case, diesel wins virtually every time. In most automotive applications, diesel engines achieve 30% or higher mpg's than a comparable gas model. For instance, the '09 Jetta TDI achieves 34mpg combined from the EPA(which is well-known to be low-balling it significantly) and yet it still is almost 42% better than the 2.5L model which achieves 24mpg combined from the EPA. So, even with 20% higher fuel cost(almost exactly 20% difference from RUG to Diesel in my area from gasbuddy.com), there is still a significant savings due to the greater mileage.
Additionally, yes it does cost more to buy the diesel engine, but with the fuel savings, that will be erased in a few years of normal driving, even more quickly once diesel prices drop back down to their historic levels closer to gasoline. Plus, a diesel is built to last much longer as well, due to the stronger block and internals and the lower revs that diesels have. Not to mention the higher resale value down the road if you choose to sell it, Used TDI VW's are selling at a premium right now.
I'm seriously looking closely at a diesel vehicle as my next car purchase. Even better if they can offer something like the VW Twin Drive concept to achieve even better mileage http://www.autobloggreen.com/2008/06/26/vw-plans-first-electric-car-by-2010-now-testing-golf-twin-drive/.
With a car like that, I'd never have to use diesel fuel during my work commute and when I did use the diesel engine, I'd be getting 50mpg hwy with it. I'd buy one tomorrow if they were available.
ale 5:11PM (7/09/2008)
However, while that may be true, when Joe somebody walks up to a diesel pump and gets fuel, over the course of the entire year he is saving money on his fuel purchases even when diesel is a buck more or about 25% more.
Whether diesel mpg does equate or not, the economies in the amount of money saved win out (whether or not fuel is really saved, i dont care) If over a three year period that diesel is saving me money, i could care less if diesel mpg is different, which i still dont see, but im not gonna contest. Still, just goes to show diesel ingenuity at its finest
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Joseph 7:57PM (7/09/2008)
Just because the hybrid gets lower mpg than the diesel, does not mean it is less efficient. As I understand it, most of the mpg gains from a diesel, is from the higher energy density of diesel. Because of this, a diesel that gets 32mpg is not more efficient than a gas car that gets 31mpg.
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wxman 11:59PM (7/09/2008)
According to documentation of UC-Davis' "Lifecycle Emissions Model" (LEM), ultra low sulfur diesel (ULSD) fuel with 5 ppm sulfur by weight requires an average of 0.0812 BTU per BTU of product while reformulated gasoline requires an average of 0.170 BTU per BTU of product.
http://www.its.ucdavis.edu/publications/2003/UCD-ITS-RR-03-17-MAIN.pdf
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Cary 11:47PM (7/10/2008)
Oh shit! Can I say shit? If so, oh shit son. WXMAN for the Mother F-N Win.
To douchebag Meme: Factor Grams of CO2 per mile. You would be fun to watch on "Are you smarter than a 5th grader" or in the UK "Are you smarter than a 10 year old." The re-runs of your crash and burn loss to a 10 year old would be replayed on variety comedy shows for decades to come.
meme 1:27AM (7/10/2008)
"As Sam pointed out, more carbon does not necessarily mean more CO2 emissions, because the diesel cycle itself is much more efficient than the Otto cycle."
The efficiency is already accounted for in both the gasoline and diesel efficiency numbers. What's *not* accounted for is the difference in carbon per gallon. The efficiency issue is a red herring here, since both mpg numbers *already account for it*. There's one piece missing on this puzzle, and that's the energy content per gallon.
wxman: Great reference! Factoring in refinery energy costs, then, we get that there's still a 6% bias toward diesel remaining in mpg figures from an energy consumption standard. From a petroleum consumption standard, however, the number will higher, as only part of the refinery's energy comes from petroleum.
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Bill 1:27PM (7/10/2008)
But on a per-mile basis, again, you need to measure the CO2 emissions.
Though as another poster said, I doubt U.S. consumers care about CO2 vs. MPG.
CMiller 11:40AM (7/10/2008)
Meme,
It seems readiing all your posts your argueing something that isn't completely worth argueing. What are the overall difference in efficiency, a few percent? All I know is I can get more power, better few economy, and fewer emissions from the same size diesel engine as i can from a gas engine. With all of these diesel filters being developed it seems that diesel will soon be cleaner, (if it already isn't in certain applications), than a gas engine.
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CMiller 11:42AM (7/10/2008)
Wow, it seems I can't type today :(. I meant to say fuel economy and not few economy.
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