2015 VW Golf TDI = 65 mpg!

We must be careful not to interchange the "energy footprint" of something with its "oil footprint".
I often read a similar meme on Peak Oil forums. It goes something like this:

"We will never be able to transition to EV's in time......do you know how much energy it takes to make an EV?"

Notice how they interchanged the words "oil" with "energy".
Yes, making an EV takes lots of energy.....mostly electricity, which can come from many sources, but not much from oil.

Same thing with diesel manufacturing.
Yes, U.S. refineries may be using more energy to make gasoline becomes the economics here work out that way.
But the energy used in re-arranging hydrocarbon molecules is mainly natural gas, of which the U.S. has an abundance.
The underlying "oil footprint" of diesel remains the same, however, because you need more barrels of oil to make an energy equivalent amount of diesel vs. gasoline.

Yes, some refineries are able to make equal amount of both, but that is only because they are set up to handle heavier crudes.

In order to put the "foreign-oil footprint" of diesel into context, we need only do a simple thought experiment:

What if a country -any country- decided it was going to reduce its oil consumption, and it was going to do so by going to an "all diesel" fleet. Would it work?
Of course not. This country would simply have a surplus of gasoline, which would have to be exported at a discount. The laws of trade and arbitrage for a commodity would hold. Diesel would NOT reduce a country's oil imports, except for a small region of the word for a short period of time.

That is why the "reduce foreign oil" argument is rarely used by diesel advocates.
With the exception of biodiesel, increasing diesel consumption does little to reduce oil imports

 

You're probably best checking fuely to see what the actual economy figures are due to this;

The tricks of the trade: How fuel economy figures for new cars are not as good as you think | Mail Online

 

I wasn't trying to switch terms. I was taking exception to having a diesel deflator based on the ratio of gasoline to diesel production amounts. A barrel of crude contains 25% to 35% gasoline. To meet US demand, we need to get 50%. So we make gasoline out of the other fractions.

Basing an anti-diesel argument point on this gasoline to diesel production ratio, when the high output of gasoline is only possible by converting diesel and other fractions into gasoline is misleading. If we take this to before the pump, then we should factor in the production costs(energy, emissions) for each gallon of fuel.

We once had oil in an abundance.

Not necessarily. Crude, diesel, and gasoline energy density are all about the same by mass. By volume, gasoline's energy density is less, but so is its physical density. For the same volume it got lighter. Because of the density differences in the products from the crude, there is something called processing gain. A 42 gallon barrel of crude can yield 44 to 48 gallons of products. Depends on the source crude, and what you want out of it.

If you want to negate the volumetric energy density advantage of diesel, just use MPGe. Doing so for the Jetta brings its combined number down to 30.5mpge, and the Cruze to 29.6mpge. Which is close to the gas models' mpg. Which makes sense when considering the fuels' energy densities being near the same.
Compare Side-by-Side

Further looking at that link, you can see the DD for fuel cost is also a faulty argument. Per 25 mile basis, it costs around $3 for all those cars. It's the penny wise, pound foolish reasoning that has people disliking premium gas. The price on the big sign is higher, but that doesn't account for the vehicles efficiency. It's a YMMV thing, but the cost per mile is about the same.

And the carbon DD is off. Partly for the same reason as the price one. It's more CO2 emitted per gallon of diesel, but the higher fuel economy yields a lower CO2 per mile, which is what emissions are measured in. It is also 13% more, not 30%. Which could come down lower when factoring in refining emissions.
How much carbon dioxide is produced by burning gasoline and diesel fuel? - FAQ - U.S. Energy Information Administration (EIA)

If we went all diesel, we would just convert the gasoline fraction of crude into diesel, or other economically valuable products. It still wouldn't help with oil imports for the same reason an all gasoline fleet doesn't. We just burn too much of it.

 

Does it truly need more barrels of oil to make diesel, or is it like that simply because that is what we decide to make?

 

As a hypothetical, if it were possible to convert a barrel of crude into 100% gasoline or diesel, we would get more gasoline in volume. Considering the energy density differences either would yield about the same amount of road miles in similar vehicles.

Which doesn't answer your question. It is simply what we decide to make is the quick answer. The fraction of straight gasoline, that which is seperated out by distillation, does not meet US needs. So we have to make more of it out of the other fractions. Depending on the crude, we might be able to meet current demand with the distilled fraction alone. Just have to remove the sulphur, and ensure it meets the right cetane number.

The heavier the crude we start with, the more energy we will have to put it in order to get what we want out.

 

A barrel of diesel has more energy than a barrel of gasoline, so yes if you were making 100% diesel it would take more oil. The discount on the other hand is that we waste less energy refining oil into diesel than refining gasoline. This gives the US refineries a surplus of diesel which is then exported at a profit compared to turning it into gasoline.

The gulf coast refineries are very good at looking at the price of petroleum products and deciding what will be most profitable to make. That is gasoline right now, so they spend more money changing other parts of oil into gasoline.

 

The OP never came back and explained what gallons or MPG testing his (unknown) sources used.

 

I have a source if you want numbers
2015 Volkswagen Golf First Drive – Review – Car and Driver

The only way you get over 60 mpg is european combined cycle in imperial gallons.

 

Of course YOU have sources and can cite what gallons and testing cycles were used, you are not a troll.

 

And of course you have sources and can cite how a midsize diesel car can possibly get anywhere close to 60mpg in the city (which it would need to do in order to have combined of 60) without any sort of hybrid drivetrain, regen capture or start/stop??
Oh, and said midsize sedan is reasonably priced, so no large use of aluminum or carbon fiber.

Good luck trying to make such a car. Of course the 60mpg is nowhere close to real-world USA mpg, combined.
I'm sure you knew this, or you are trolling?
I'm sure you have links/sources/sites that can tell us just how such a car would get phenomenal city mpg with no exotic lightweight materials or hybridization whatsoever?
Please share.

 

In fact, the OP hasn't even been back to view the replies to his pot stirring.

 

Hello Mr Scorpion:

I did post a factual reply that showed that the Prius got fairly unbelievable numbers under both the Japanese and to a lesser extent European testing cycles. In that post I linked to the relevant Wikipedia article. I have offered no data about any diesel in this thread, so I am at a loss how to document nothing.

Should I ever say anything positive about any diesel smaller than 1000 kilowatts, I will try to find some facts off your list.

The diesel hybrid I am most familiar with:



Komatsu no longer sells the 685E, here are the spec for the similar 730E which can also use trolly assist.

http://www.komatsu.com/ce/products/pdfs/KAC_730E.pdf

 

I googled the information in the OP
2015 Volkswagen Golf TDI First Drive Review | TFLCar.com: Automotive News, Views and ReviewsThe Fast Lane Car: Auto News, Views, and Reviews
I don't think he was being trollish, he just believed the link that said

It seems like a pretty common thing for ignorant sites to quote european numbers, even those in imperial gallons as epa mileage. We had a link with toyota hybrids doing the same thing. Its prettly clear this car is not magic. If you like a stick shift and a vw, its going to be the most efficient thing out there. If you like vw and variable transmissions, the jetta hybrid is going to be much better. I don't really like vw cars. Some audi's are OK IMHO, but some people really like vw's and sticks. The golf diesel should be able to beat that honda cr-z

 

I knew you weren't switching terms; but I am still having a hard time understanding how the use of natural gas and electricity at refineries plays into gasoline vs. diesel? I suppose it has to do with one's motivation for going diesel? For cost savings, it obviously doesn't matter - only the price does. For someone concerned with CO2 emissions, you are correct that you have to look at the entire well-to-wheels lifecycle, especially upstream emissions.

I guess I approach it a little differently. My main reason for driving a hybrid is to use less foreign oil. Therefore, I would want U.S. refineries to be refining the MOST optimal mix of diesel vs. gasoline (in a way that yields the most 'miles per barrel') regardless of how much natural gas or electricity was needed to do so. I realize that U.S. refineries are in the business of making money, so they will refine based on price of inputs vs. outputs, and not on whether the oil they use is foreign or domestic. But if a country wanted to reduce it's foreign oil consumption, it would make sense to sacrifice relatively cheaper, domestic, abundant resources (electricity, NG) in order to minimize consumption of a costlier, foreign, increasingly scarce resource (oil).

Yes...not sure what it has to do with NG use today. We have lots of NG now, so it makes sense to displace expensive and dirty foreign oil with NG in the short-to-medium term. Long term is renewables and maybe nukes.

The numbers you came up with are exactly what one would get if they used my formula:

Diesel MPG / DD, where DD = 1.3 (I realize this is wrong for CO2 as you point out, more below)

6-speed 2.0 L Jetta TDI: 34 mpg combined
6- speed 2.0 L Jetta: 26 combined

34 / 1.3 = 26.15 mpg, right on the money

Not sure how DD for fuel cost is faulty. Cost-per-mile is cost-per-mile. This is the most straight-forward calculation.
Yes, the cost difference between the sedans. per 25 miles, is marginal.
Now, tell that to someone who drives 25,000 miles a year.
They would have to take this 'marginal' difference and multiply x 1000.......every year

Yes, you are correct. I got my numbers crossed.
When I said "30% more carbon", I actually meant to say that a diesel car will typically get "30% more miles per gallon of fuel than a gasoline car."
We can see that in the Jetta, gasoline vs. diesel.
The gas Jetta gets 26 mpg.........if we take this times 1.3, or 30% more, we get 33.8 (right on the money, TDI is rated 34)

But you are right, a gallon of diesel only has 13% more carbon than a gallon of gasoline, so when it is burned it only produces 13% more co2.
The 13% disadvantage of diesel in terms of carbon footprint is overcome by the 30% more efficiency (and the greater BTUs in 1 gallon diesel vs. gasoline) in diesel engines, resulting in a lower per-mile co2 level as compared to conventional gasoline version of the same car. The per-mile emissions advantage of diesels would be much smaller (or non-existent) when compared to a hybrid car.


Now, the funny thing is my numbers will still work for per-mile co2.

13% more carbon = 1.13 more carbon
30% more miles = 1.30 more miles

1.13 divided by 1.30 is
1.13/1.30 = 0.86923077, or about 87%

Jetta gasoline, CO2 per mile: 344 g/mile
Jetta diesel, CO2 per mile: 297 g/mile

297/344 = 0.863372, right on the money

Agreed 101%

 

Oil Refineries choose the optimal mix for profits. This creates more gasoline and less diesel at US refineries than would be optimal for energy content. Some of the oil is cracked to shorter hydrocarbons for gasoline, during the process some of its energy is lost.

Two things have raised the price of diesel. First Ultra low sulfur is now required for cars, but not ships. To remove the sulfur some of the oil is used or natural gas, which adds to the cost and lowers well to pump efficiency. The other change is that demand in Europe is high, so diesel exports even after the cost of transportation creates demand on US diesel production increasing the spread between gasoline and diesel wholesale prices.

Now its difficult to buy E0, most gasoline is E10, getting 93% of its energy from the oil. Summer and winter blends are also different in oil content.

Here is the average crack from 42 gallons of crude oil.
Refining Crude Oil - Energy Explained, Your Guide To Understanding Energy - Energy Information Administration



Because of the way dpf is cleaned in vw diesels, biofuels need to be only a small part of the mix. Biodiesel may be much more efficient than corn based ethanol, but to get there you need an older diesel, or a dpf that is not cleaned by squirting unburnt fuel out of the engine as vw does.

From the oil chart, you see other products. One of these is petroleum coke, which is a decent raw material in many processes, and can be burnt in power plants, but poor for liquid fuels. Gulf refineries export a great deal of this to foreign countries. More hybrids and plug-ins will reduce gasoline demand and push refineries to a more optimal energy crack of the oil.

 

This is a YMMV issue, and it's up to the individual to research what will work best for them. For example, the Jetta TDI costs less to go 25 miles than the 1.8L petrol. The Cruze diesel costs more than the Eco model. But is using the EPA assumed mix of 55:45 city:highway. If the person's miles are mostly highway, then the Cruze diesel will do better than the Eco and the Jetta. In actual results, it might even do better than a Prius for a person. It is just a 4% difference in their highway fuel economy.

The DD is faulty because it is just looking at the price and ignoring the value. At $3.58 a gallon, you are getting 324.27 btus per cent with regular gas. With diesel at $3.94, it is 328.64 btus/cent. Yeah, the diesel costs more, but you are getting a little more energy for your money. Then the car goes further per gallon. Whole milk costs more, and has more calories than skim. You wouldn't use the price difference to somehow claim a person actually consumed less calories from that whole milk. This DD feeds on people's sticker shock over diesel, but anyone that can calculate a price per distance will just see it as anti-diesel FUD.

The details make things messy. Crude is not created equal. One of the contributors to the US exporting more diesel is that we have refineries processing the Canadian tar sands and the real heavy, possibly as bad as tar sands, crude from Venezuela. Making those into gasoline will get expensive. So the oil companies make more diesel out of them, sell it to Europe, and buy gasoline from places processing more light crude. It's cheaper, and actually more energy efficient this way.

Choosing between diesel or gas alone isn't how you get off foreign oil. The one reduces a person's over all consumption of oil needs to be chosen. Hybrids can do this well, but they work for everyone do to real or imagined reasons. So diesels can be another option. I know that the Jetta and Cruze examples show that the cost per mile and energy efficiency are about the same between the diesel and gas models, but the gas models were equipped with the most efficient gas engine. The 2.0L diesels aren't the smallest available overseas, and in the Cruze's case, are the most powerful engine choice. For those that care, it is generally easier to beat EPA in a diesel to help counter balance that.

I'd like to see more sensible diesel options. It is conceivable that a 4 cylinder diesel can replace a 6 or possibly 8 cylinder gas engine in a truck. Sounds like the Ram 1500 is getting a diesel next year. So it will be interesting what exactly we get.

And even lower in a hybrid diesel. No one car is going to work for everyone. Which is why choice is go. Diesels can improve an individual's fuel use. Just like hybrids. Both have pros and cons, and both can be misused.

 

Acchh........you are making my head hurt.

The DD is NOT FUD..........your failure to understand it and accuse it of being FUD............is FUD!!

Take a good look at how I derived it. It is 101%, absolutely mathematically, correct.
(While the formula is valid, the "garbage in, garbage-out" rule still applies. )

I am trying to give an accurate picture of what a mpg for a diesel car REALLY MEANS when you factor in (i.e., 'discount') the disadvantages that diesel fuel has in several regards.
This is an ACTUAL NUMBER, not something I can just make up because I want to make diesels look bad.

You mentioned BTU's, but you are forgetting this is already factored into the mpg (the numerator)!
That is one of the reasons diesels go further on a gallon, because of its higher energy content.

So to recap, here's a simple example (using gas prices in my area):

$3.50 regular gasoline
$4.00 diesel

Let's say I am on PC and I see an advertisement for a 2014 Golf TDI. It says it'll be able to do 65 mpg on the highway.
I think, "Wow, that's pretty good....right now I do mostly highway driving in a 2010 Prius that gets 50 mpg."
Well, I know that diesel fuel is more expensive.
The question is, how will this new Golf compare to my Prius after factoring in the price difference?
Well, one way is to just calculate the cost per mile. The other way is MPGe and that's essentially my formula


Take TDI mpg claim, divide by DD, this is MPGe

MPG/DD = MPGe

what is the DD in this case? It is always "1+Percent worse that Diesel is than Gasoline"

So, that works out to "How much more than gasoline", or $4.00 / $3.50 = 14.29% more cost

So, DD is 1.1429

Taking the 65 mpg highway claim of the 2014 Golf TDI, we get:

65 mpg / 1.1429 = 56.87 mpg

What does this mean? This is the mpg your Prius would have to get on the highway in order to be as cheap (per-mile) as the Golf TDI.

So, if you're getting less than 56.9 mpg on the highway in your Prius, then the 2014 Golf TDI is cheaper.

Is this the only criterion for making the Golf better? No, of course not. You also have to look at city and combined mpg, among other factors.

The formula is simply a metric, a point of comparison.

Btw, if you wanted to look at city mpg, you just use MPGe = cityMPG/DD,
and for combined MPGe = combinedMPG/DD

We can validate:

$4.00 / 65 mpg = $.0615 per mile for Golf TDI (highway)
$3.50 / 57 mpg = $.0614 per mile for 2010 Prius (highway)

So, 57 mpg is the relevant number in this case, and something every Prius driver can relate to.

As you progressively get less than 57 mpg, your cost-per-mile (highway) goes up vis-vis 2014 Golf TDI.
As you progressively get more than 57 mpg, your cost-per-mile (highway) goes down vis-vis 2014 Golf TDI.

So, I think it would be safe to say that the 2014 Golf TDI will have a lower cost to operate on the highway, but of course that could change rapidly if diesel gets more expensive. We don't have the highway #'s for the Gen IV, but upper 50's highway should not be out of reach.

So, we should have a pretty competitive battle between these two for "king of the highway" in cost-per-mile.
Of course, the Prius will DOMINATE the city.

 

... and Highway miles is the Big Factor here. As been mentioned already on this post, Diesels in general are bred for highway long distance. Once we get in stop & go city traffic, then it becomes a liability. I've heard many a tales of TDI engines clogging up from heavy city commutes. Does the inherent design prevent any solution to this?


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It absolutely is. Every $ spent has an opportunity cost.
Every dollar spent on TDI/Bluetec is one less dollar spent on, and driving cost and technology curves on, hybrid and EV tech.
At the individual level, sure it doesn't matter much - and some heavy highway drivers come out ahead.
But at the national level, yes it does matter.
We simply get more "foreign-oil-independence bang" for our buck with Hybrid/EV than we do with diesel, especially as there has not been large-scale biodiesel production, but there HAS been Leaf, Volt, Tesla, and rapid deployment of public charging stations.

Agreed. And what I am trying to do is give some of those pros and cons a numerical value, so it is easier to compare the two!

 

Diesel Engines themselves are perfectly fine with city driving. The turbo diesel runs well with very lean mixtures keeping the engine efficient with highly variable speeds.

The turbos do get hotter in a city cycle, and need to cool down, but this can be done in an automated fashion. The big problems have to do with the newer pollution control devices, primarily the dpf (diesel particulate filter). I don't see any technical challenges here, they just need to get the technology of the filters and cleaning them right.