To what extent does diesel fuel quality affect MPG? - PeachParts Mercedes-Benz Forum

shertex · #1 07-16-2014, 08:31 AM

I know that there are a whole host of factors that bear upon fuel economy. Does anyone know the degree to which fuel quality affects fuel economy? When I see wide swings in MPG, I never really have a sense how much is due to my driving habits and how much might be due to the fuel.

Anyone have a guess as to how to quantify this? I'm sure studies have been done....

vstech · #2 07-16-2014, 08:56 AM

I know cetane ratings affect mpg, as do winter/summer grades.

shertex · #3 07-16-2014, 09:13 AM

I think I have a sense of how winter vs. summer affects mpg. But let's say we're only talking about summer fuel. How wide a variation might one see?

Dan Stokes · #4 07-16-2014, 09:35 AM

This is an excellent question and I'm afraid I don't have much to add to the knowledge base on here. We used a specific test fuel (bought from Howell Hydrocarbons) that had a consistent formulation - this keeps test-to-test variability to a minimum. However, I don't recall that we did any fuel comparisons regarding FE or emissions.

I'll check in with my SIL and see if she has any insight - I know they've done some on-road measurements of Diesels with a SEMTEC (this is a self-contained mobile emissions measurement system) and they may have tried different fuels.

Dan

Diesel911 · #5 07-16-2014, 10:05 AM

I don't believe the Customer really knows what comes out of the Pump. Refineries make Fuel from the varied sources of Crude Oil of which the compisition of varies widely.

Except for Government use I think no one really checks if what comes out of the Pump at your local startion meets the spcecs on the Tag on the Pump.

This is not a comment from me but from another Member who was/is a Big Rig Truckdriver:
"I have done extensive record keeping about what improves the mileage on my N14 Cummins, as I am a long-haul truck driver. During the $4.50 plus days, I was going crazy trying everything to increase my mileage above 5.5 mpg. The only thing that consistently worked, was to use an upper cylinder lubricant in the correct amounts. I used a gallon of Lucas, or 1/2 gallon of 2-stroke oil for approximately 300 gals. They were the only products that consistently raised my fuel mileage and quieted the engine down. However, since 2-stroke oil doesn't have an injector cleaner, I had to put that in, either as a dedicated cleaner, or switch to the actual Lucas (or USA Lube) at least once every six fillups. ATF made no difference on my fuel mileage or quieting down the engine, but worked as an injector cleaner, in the right amounts. Unfortunately, the ultra low sulfur diesel does not perform as well on our older MBZ or heavy-duty truck engines, necessitating a regular dose of upper cylinder lubricant. However, I have noticed that Bio-diesel does quiet things down, if at least B11, but didn't make a difference in mileage, and maybe a bit less power."

I have read that some People believe that Chevron Diesel has in general a Higher Cetane rating than others. However, it is difficult to see how that claim can be supported with out testing it.
Subjectively if your Engine nails less after a cold start then with other Fuel you can suspect that the Cetane Rate might be higher.

But, Cetane can also be decieveing. 100% Biodiesel has a higher Cetane Rating than Diesel Fuel but delivers lower milage because the Fuel inself has less Energy in it.

You will get less milage from any blend of Biodiesel mixed with Diesel Fuel and it sometimes comes from the Pump like that. Read the Sticker on the Pump to get some idea what you are getting.

tjts1 · #6 07-16-2014, 11:53 AM

I noticed the 300d idles a bit louder on Nevada diesel vs California diesel. Probably the diffence between 55+ cetane in CA and 48 cetane in NV but there was no fuel economy difference.

Jeremy5848 · #7 07-16-2014, 12:49 PM

With only occasional exceptions (traveling out of town) both our '95 E300 and '96 E300 normally-aspirated diesels have used B20 biodiesel pumped from the same pump at the same station since 2009 (2012 for the '95 car). AFAIK, here in coastal California there is no difference summer or winter in the diesel blend. Our driving is mostly around-town. Any difference should be due to the driver's right foot, the state of tune of the engine, and the quality of the fuel.

The fuel economy for both of my cars stays in the 27–28 mpg range year-'round. For example, the '96, driven by my wife, has gotten so far this year, 27.2, 27.8, 26.9, 27.6, 26.2, 27.2, and 26.7 mpg (2648 miles driven, 97.681 gallons consumed, 27.1 mpg average). This is all around-town driving; highway driving nets 30 to 32 mpg in both cars.

Jeremy

Dan Stokes · #8 07-16-2014, 03:34 PM

The SIL didn't have any info to add, at least up to this point. She's traveling for work right now but my bro can't remember them using any pump Diesel in their testing (he was along for most of this testing).

Dan

JimFreeh · #9 07-17-2014, 07:48 AM

Quote:

Originally Posted by tjts1

I noticed the 300d idles a bit louder on Nevada diesel vs California diesel. Probably the diffence between 55+ cetane in CA and 48 cetane in NV but there was no fuel economy difference.

Pretty high cetane numbers. Here at the east coast, 40 cetane is the norm. You can find 45 cetane accasionally at Hess and Chevron diesel outlets, though.

Jim

vstech · #10 07-17-2014, 08:09 AM

I wonder why the cetane varies so widely between the coasts... 40 is most round me as well.

t walgamuth · #11 07-17-2014, 10:03 AM

I've never been able to notice much difference in fuel for economy or power. None in fact.

Diesel911 · #12 07-17-2014, 10:49 AM

If I put Power Service with the Cetane Booster in the Tank of My Volvo when I accelerate hard there is less smoke. Less smoke would imply that the Fuel is burring better.

I actually don't pay attention to mileage unless there is some really obvious difference so I cannot comment on mileage.

Benzman53 · #13 07-17-2014, 03:08 PM

Quality of diesel fuel in any given area of refined product distribution is mainly driven by crude feedstock and refinery operations. Low cetane diesel is comprised of more aromatics whereas higher cetane diesel has a higher parafinicity index. And now in laymans terms, high aromatics are due to limited processing of certain crudes (all crudes are not the same). Early diesel production was a straight cut off the crude stills with very little additional processing. Except for third world countries, this is pretty much in the rear view mirror due to our environmental regulations. Low sulfur requirements require additional processing to remove sulfur; the predominant process is hydrotreating. This does a good job of sulfur removal and also yields a higher quality diesel due to saturation of the hydrocarbon molecules with hydrogen. This converts some aromatics to paraffin compounds. Paraffins are higher cetane components. The fuel economy game is not solely driven by cetane (though it helps by assisting ignition). The amount of energy in each diesel gallon can vary from refinery to refinery based on their processes and blending of other components into the diesel "pool". Diesel fuel has components in the 430 to 650F boiling range. As the percent of "heavies" (550 to 650F) increases, so will you fuel's energy content. Conversly, if the fuel has a high percentage of "lights" (under 500F), the energy content will be less and result in reduced MPG. Moral to this story is to find the best fuel in your area and stick with it. In my location our diesel fuel comes from either Phillips 66 or Valero. Being retired from P66, I am very familiar with the processes in that plant and they yield an excellent diesel with an average (yes it can vary a bit) cetane rating of 46. Valero also produces good diesel, every bit the equivalent of the P66. Amarillo, TX is referred to as the World's Largest Truckstop no doubt due to the quality of fuel available. Directly east into Oklahoma the diesel is lousy and out west in New Mexico it's not much better.

vstech · #14 07-17-2014, 03:14 PM

Quote:

Originally Posted by Benzman53

Quality of diesel fuel in any given area of refined product distribution is mainly driven by crude feedstock and refinery operations. Low cetane diesel is comprised of more aromatics whereas higher cetane diesel has a higher parafinicity index. And now in laymans terms, high aromatics are due to limited processing of certain crudes (all crudes are not the same). Early diesel production was a straight cut off the crude stills with very little additional processing. Except for third world countries, this is pretty much in the rear view mirror due to our environmental regulations. Low sulfur requirements require additional processing to remove sulfur; the predominant process is hydrotreating. This does a good job of sulfur removal and also yields a higher quality diesel due to saturation of the hydrocarbon molecules with hydrogen. This converts some aromatics to paraffin compounds. Paraffins are higher cetane components. The fuel economy game is not solely driven by cetane (though it helps by assisting ignition). The amount of energy in each diesel gallon can vary from refinery to refinery based on their processes and blending of other components into the diesel "pool". Diesel fuel has components in the 430 to 650F boiling range. As the percent of "heavies" (550 to 650F) increases, so will you fuel's energy content. Conversly, if the fuel has a high percentage of "lights" (under 500F), the energy content will be less and result in reduced MPG. Moral to this story is to find the best fuel in your area and stick with it. In my location our diesel fuel comes from either Phillips 66 or Valero. Being retired from P66, I am very familiar with the processes in that plant and they yield an excellent diesel with an average (yes it can vary a bit) cetane rating of 46. Valero also produces good diesel, every bit the equivalent of the P66. Amarillo, TX is referred to as the World's Largest Truckstop no doubt due to the quality of fuel available. Directly east into Oklahoma the diesel is lousy and out west in New Mexico it's not much better.

nice info, thanks!

Dan Stokes · #15 07-17-2014, 04:40 PM

Quote:

Originally Posted by Benzman53

Quality of diesel fuel in any given area of refined product distribution is mainly driven by crude feedstock and refinery operations. Low cetane diesel is comprised of more aromatics whereas higher cetane diesel has a higher parafinicity index. And now in laymans terms, high aromatics are due to limited processing of certain crudes (all crudes are not the same). Early diesel production was a straight cut off the crude stills with very little additional processing. Except for third world countries, this is pretty much in the rear view mirror due to our environmental regulations. Low sulfur requirements require additional processing to remove sulfur; the predominant process is hydrotreating. This does a good job of sulfur removal and also yields a higher quality diesel due to saturation of the hydrocarbon molecules with hydrogen. This converts some aromatics to paraffin compounds. Paraffins are higher cetane components. The fuel economy game is not solely driven by cetane (though it helps by assisting ignition). The amount of energy in each diesel gallon can vary from refinery to refinery based on their processes and blending of other components into the diesel "pool". Diesel fuel has components in the 430 to 650F boiling range. As the percent of "heavies" (550 to 650F) increases, so will you fuel's energy content. Conversly, if the fuel has a high percentage of "lights" (under 500F), the energy content will be less and result in reduced MPG. Moral to this story is to find the best fuel in your area and stick with it. In my location our diesel fuel comes from either Phillips 66 or Valero. Being retired from P66, I am very familiar with the processes in that plant and they yield an excellent diesel with an average (yes it can vary a bit) cetane rating of 46. Valero also produces good diesel, every bit the equivalent of the P66. Amarillo, TX is referred to as the World's Largest Truckstop no doubt due to the quality of fuel available. Directly east into Oklahoma the diesel is lousy and out west in New Mexico it's not much better.

I agree - thanks a lot! As I said in other posts, my expertiese is in Diesel dyno testing and if I didn't happen to be involved in a fuels program I wouldn't have much info on this - and I wasn't.

What's the relationship between paraffins and clouding (if there IS any relationship)? Seems like you would want lots of paraffins to get more power/FE (greater energy density) but I'm sure there's a practical limit.

Dan