2011 X5 35i "greener" than 35d?

[Penguin]

As for diesel fuel being a "waste" product of the refining process, well, obviously not true but, as in many things, there is a historical grain of truth which explains how it got started many years ago.

There is an optimum breakdown of distillation products from a particular crude that will provide the easiest and most inexpensive set of output products. The ability to change the breakdown to a different mix of outputs has improved immensely over the years, and it is amazing what they can do to crude oil nowadays to get more of the lighter components, such as gasoline, while reducing heavier components. Cracking was the first of the technologies which allowed lighter fractions to be increased.

History of Gasoline

Many years ago before technologies were so advanced, there was a greater demand for the lighter/gasoline fractions and there tended to be an excess of the heavier fractions coming out of distillation processes due to a high demand for gasoline and lower demand for diesel (compared to the "normal" distillation breakdown of crude), e.g., many locomotives were still using coal, rather than diesel, even after WWII, and diesel truck usage was not as great vs. gasoline.

So while I was quite young in the 1950's, I recall that diesel fuel was dirt cheap in relation to gasoline, because there was a natural excess supply of diesel from refineries and, as in most supply and demand situations, the excess supply caused the low price.

So while diesel was never really a "waste product" of the refining process, it was sort of a component most refineries wanted to reduce and was considered an undesirable output of the process.

Since then, expanded diesel fuel applications have increased demand and refining processes have allowed refineries to increase to split of a barrel of crude to more gasoline output and less diesel fuel output.

Now, that's my understanding based on what I have read and my personal observations over the years, but I am quite open to any other opinions of how the concept of diesel fuel as a "waste byproduct" came about...

[JCL]

Penguin: Good links. The Cicero report is fairly up to date, with some effects of SCR still to be seen due to the different implementation timelines between the EU and NA. The DOE report is very dated. They aren't considering effects such as DI in gasoline engines, for example. And yes, I read the last link. Takes me back to my SAE days. One of the slides was particularly interesting, as it contained the following statements:

Emerging CO2 regulations are aggressive and will result in a paradigm shift. Fuel consumption technologies will no longer be based on the value proposition to the customer. They will be chosen based on mandate economics.

That seems a fairly sweeping statement given the current political climate and public acceptance of the climate change impacts of vehicle emissions.

With respect to the 'diesel fuel as waste' origin, I agree with your line of thinking. That does go back at least 40-50 years, however, as refinery outputs were greatly improved at least that far back. One other factor that came into play, other than the supply side changes, was the demand change due to variable fuel sources for the same application. Ships that ran on heavy fuel were configured to run on a variety of fuels, for example. The same thing happened with utility power generation, which used whatever fuel was most cost competitive (I was involved with diesel engines that were configured for heavy fuel, blended fuel, and diesel, but the same concept applies to multi-fuel thermal plants). As those markets were brought along, with their ability to purchase one of a variety of fuels, the refineries had more options in terms of being able to sell whatever they had that week.

[SkipSauls]

Thanks for all of the responses, and the ensuing discussion! I'm still not sure that there is a "clear" answer, no pun intended. Perhaps it is impossible or impractical, but it would be interesting to be able to accurately determine how truly "green" a vehicle is in real-world situations.

I will probably end up going with the 35d for the day-to-day economy, the better towing potential, and the eco-credit, which actually makes it less expensive than the 35i when similarly equipped. Perhaps in 3-5 years BMW will have a next-generation X5 that I'll want to replace it with. Something that weighs 500 lbs less and gets far better MPG from smaller, more efficient engines would be a nice start.

[JCL]

Originally Posted by SkipSauls

Perhaps in 3-5 years BMW will have a next-generation X5 that I'll want to replace it with. Something that weighs 500 lbs less and gets far better MPG from smaller, more efficient engines would be a nice start.

They will have a next generation X out next year, 900 lbs less, and that is a huge step forward. We likely won't get the 20d that Europe will, but it would make a lot of sense. BMW call it an X3. The new X3 is 0.5" shorter than the original E53 X5, but 0.5" wider and 1" lower than the E53.

The X1 will be even smaller and lighter when it arrives.

Good luck with the 35d

[SkipSauls]

The website (Fuel Economy) has been updated to reflect the slightly lower 35i MPG rating, resulting in the 35d now being the "greener" of the two by a small amount.

I ordered my 35d on October 18th and it looks like it will be here in a bit more than a week from now, which is nice. I was still considering a 35i up to the last minute, but after weighing all of the pros and cons of each, the 35d made the most sense. The "greeness" of it didn't really matter in the end, although it's certainly not a bad thing.

[admranger]

I didn't look at all the links, but I wonder if they account for the 10% ethanol that is in many gasolines now (and decreases the btu content per unit mass of the gasoline)?

I am not sure I'd buy a diesel X5 unless I was going to routinely travel long distance or, better yet, tow something. I love diesels, don't get me wrong, but with the advances in the twin turbo gas motors, it's getting tough to justify any "savings" by using them. The VW Jetta TDI's perhaps being the outlier due to their small displacement and ridiculous fuel economy numbers.

Are the much better 4.0d numbers mostly due to the 8-speed trans or some other features? These are intriguing numbers.

Now, for a really interesting argument, go into the true "green-ness" of a hybrid, especially considering battery manufacture and recycle.

Also, I over discussions of "green-ness" and any sport activity/utility vehicle.

[AzNMpower32]

I wouldn't be surprised if the 35i is slightly cleaner than the 35d, as the 35i is new technology and the relevant 35d drivetrain debuted back in 2006 in the 535d (the M57 itself came out in 1998, the one sold in the X5 debuted in 9/06).

For comparison purposes, the xDrive40d is cleaner than the xDrive35i with lower fuel consumption and CO² emissions.

[XXX555]

Originally Posted by AzNMpower32

I wouldn't be surprised if the 35i is slightly cleaner than the 35d, as the 35i is new technology and the relevant 35d drivetrain debuted back in 2006 in the 535d (the M57 itself came out in 1998, the one sold in the X5 debuted in 9/06).

For comparison purposes, the xDrive40d is cleaner than the xDrive35i with lower fuel consumption and CO² emissions.

I need to disagree on both of your points:

Better mileage with the 35d and better/lower CO2 output so greener in that sense. How does the newer tech tranny make it greener?

With 425ftlbs of torque (v. 300ftlbs for the 35i) and reviews of the newer 8 spd tranny 'hunting' for the right gear, I don't miss the new technology or lower mpg/higher CO2 in the 35i either. The six speed with all that torque is perfect. 40d will have the 8 spd to make manufacturor easier/efficent.

[JCL]

Originally Posted by XXX555

Better mileage with the 35d and better/lower CO2 output so greener in that sense.

I can understand your focus on fuel efficiency at the pump vs barrels of crude, since you pay at the pump. It isn't the measure that was used to start this thread, but that's fine.

What I don't get is why you focus on CO2 output and don't consider NOx output when comparing gasoline models to diesel models. There are lots of published CO2 figures since that is the primary regulated emission in Europe. However, in North America, the effects of NOx are considered and regulated to such an extent that they are the reason you have a urea injection system onboard your 35d.

[XXX555]

Originally Posted by JCL

I can understand your focus on fuel efficiency at the pump vs barrels of crude, since you pay at the pump. It isn't the measure that was used to start this thread, but that's fine.

What I don't get is why you focus on CO2 output and don't consider NOx output when comparing gasoline models to diesel models. There are lots of published CO2 figures since that is the primary regulated emission in Europe. However, in North America, the effects of NOx are considered and regulated to such an extent that they are the reason you have a urea injection system onboard your 35d.

I understand your points and appreciate them. However, I was purely responding to the post presuming that the 35d was less green due to the lack of an 8 spd tranny/'old technology'. I know/knew that the 35d has better mpg and co2 numbers and used that in my response. Can also add better NOx numbers to my response.