ULSD, Fuel Mileage, & Cetane Additives

[AndyH]

This isn't finished information. It's more of a call for experimenters and chemists.

My fuel economy has been somewhat erratic the last 18 months or so. I've attributed it to weather, switching from LSD to ULSD and back, biodiesel, sunspots, etc. Mileage hit 44 on the road one time. Most of the time it was 42 or so, and could drop to 36 with no warning.

One of the papers quoted showed differnces in performance when low 'natural cetane' fuel was treated with an over the counter cetane additive, and also when high natural cetane fuel was treated with additional additives. The charts seemed to say that in all cases, more cetane was better for high performance and/or high demand engines. But they also appeared to show that there was a performance drop when high natural cetane fuel was treated with an additive and used in lower-demand service.

I stuck with my normal driving routine and speeds and started playing with different cetane treats - none, single dose, and double dose. I ran three tanks in each condition. I'm using AMSOIL additives, so I was able to vary just the cetane treat rate while keeping the lubricity additive rate standardized.

It seems that, for my driving style in my un-chipped car, my fuel mileage can take hits up to 4mpg when I'm using either B20 or higher, or ULSD, and add any extra cetane.

I can still get a bit of a mileage boost running LSD when I add some cetane.

Since I've stuck with ULSD and no added cetane, my fuel mileage hasn't dropped below 40 and I'm seeing 44 much more frequently.

While I think the folks with chips and other performance mods may still benefit from some extra cetane, I suspect the stock vehicles might show a mileage increase with B20 or ULSD if they skip any cetane adds.

Thoughts? Chemists?

 

[mrGutWrench]

(snip) Thoughts? Chemists?

__. I'm not a chemist but I must have been doing something right -- my '02 averaged an overall 57 MPG for about 125K miles before it got totalled. I always ran a "fat" single dose of (mostly) Power Service (a little FPPS or the "other good stuff" that George recommends ... d@mn, the memory is about the worst part of getting old, but mostly PS).

__. I followed suggestions on this board and bumped my (stock) engine timing up. I don't really remember exactly what parameters but this was the instruction:
"You go to "login" type "12233" then push "do it" then push "adaptation" then type in channel "4" each 1 degree of advance is achieved by increasing the number by 100. Full advance is 5 degrees increase. My car runs best so far at 3 degrees. After you increase the number push "test" then push "save" It is that easy! "

__. Also, the kind VAG-Com users who worked on my car (including Matt [Car54] when he did my timing belt) made sure that the timing on the graph was right up at the top of the range.

__. Dunno is that made any difference but something worked for me. (Actually, I think everything worked for me. I have very easy driving conditions, I do mostly highway miles, the EGR was set to minimum, I'm almost always alone in the car, I can pick low-traffic times to drive, I kept tires up as hard as I could stand and went to "Plus 8" Michelins when the stock "Plus 4" Mic's wore out about 87K, ran a CAT filter, in addition to the additive. So, I don't know what each item contributed -- in fact, some items may even have had no contribution or even a negative, but I think the combo of additive plus advanced timing helped.)

 

[b4black]

Accurately measuring fuel economy is very difficult. The natural variation (noise) is much bigger than the changes you are trying to measure (signal).


In general, cetane has little effect on economy. ULSD and B20 has little impact on energy content and therefore fuel economy. Density (API Gravity) varies from fuel to fuel and is probably the most significant property to look at.


The only time an additive will help is if you have deposits on the injector tips causing mis-spray of the fuel. Then a detergent will help.

 

[AndyH]

Dunno, b4black. That's what I've been trying to nail-down with my cetane experimentation. I absolutely know it helps economy in the right situations.

Unfortunately, my close examples are diesel pickup owners with performance chips. Dodge/Cumins especially LOVE added cetane. I've seen consistent 1.5-2mpg boosts with these owners. But just when the programming is altered and they're pushing things harder than stock.

I suspect that's part of mrGutWrench's experience with cetane as well - the advanced timing.

That's what led to the experiment in the first place - I'd been assuming that the best I could do was raise cetane up to the 48/50 range, so had been single and sometimes double dosing each tank. 1-2 MPG is noise, absolutely, but somewhere between that and the spread between 36 and 44.5 there has to be real data.

Most of my fuel comes from the same pump. I have a ventectomy, and fill slowly until I have fuel at the last thread in the fill pipe each time.

I guess the only point is that I assumed cetane was always good, and that doesn't appear to be the case.

 

[wjdell]

The engine is quieter during the warm up period, thats all I see so far.

 

[Georgeseq]

Mr. B4Black, I have a number of companies I work with that would heartily disagree with your statement regarding no fuel consumption savings with additization other than cleaning injectors.
Companies with large off-highway I have worked with have worked with have validated 3% to 12% reduction in fuel consumption by using a cetane improving, demulsifying, lubricity enhancing, rust preventing diesel fuel additive. These reductions were tracked with a 6 month "without" additization and 6 to 8 months "with" addization.. These companies purchase in excess of 3 million gallons through 25 million gallons of #2 each year. With $2.50/gal diesel fuel and less than 2 cents/gallon treat costs, it is your basic no brainer..
Additionally, fuel filter life for the large off-highway diesels was doubled, tripled, eliminating costly, unplanned fuel filter changes brought about by high levels of asphaltine in current diesel fuels..

Mr. B4Black, would you care to share your data that indicates there are no performance/efficiency/fuel savings in using diesel fuel addization. Your statement is so absolute in this regard, you must have a lot of data to share.....
George Morrison, STLE CLS

 

[b4black]

I won't debate with an additive salesman. And I won't try to prove a negative.

There is no credible, non-biased data showing increased fuel economy due to cetane, lubricty, etc. Your experiment doesn't convince me. Did you even montior fuel density over these two six month periods?

 

[Georgeseq]

Well, then Mr. B4Black, that gives you license to make any statement you wish, with absolutely no valid data to back your statements... Most interesting position... And you will not try to prove a negative, yet most of your comments are most negative... I do not wish to get into a shouting match, and I do NOT porport that all diesel fuel additves provide proven economics, in fact just the opposite for most. However, there ARE diesel fuel additives which DO work, which have reams of data validation..
If you wish to do the Osterich routine and put your head squarely in the sand, that is just fine. But to make gross statements of condition, with no data to back up your flat statements is quite exasperating..
George Morrison, STLE, CLS

 

[b4black]

Well, then Mr. B4Black, that gives you license to make any statement you wish, with absolutely no valid data to back your statements... Most interesting position... And you will not try to prove a negative, yet most of your comments are most negative... I do not wish to get into a shouting match, ....

I don't know where all this is coming from, because I didn't say all that much in my first post. Usually peopel starting off with "Well, then Mr. B4Black.." are trying to start a debate.


It's not possible for me to show that all additives don't help fuel economy in all situations. So I go back to what I said before, I have never seen a credible, non-biased test showing increased fuel economy due to cetane, lubricty, etc.



During these times of high fuel costs, if someone (anyone) could substatiate real fuel economy improvements, it would be BIG news. Instead it a lot of snake oils and gadets. Acetone, tornados, combustion catalysts.....

 

[wjdell]

A good additive may not improve the mileage of a engine new or well tuned engine. But it will prevent a loss with age and miles do to deposits, often quoted as "power robbing deposits". These deposits would decrease your mileage in time. A good additive will help prevent this. So its not incorrect for them to say "saves fuel". There are many good additves, preventing deposits and premoting engine cleanliness are one. Dealing with water is two and is present to some degree everywhere. If additives deal with these two things, then they are worth the effort.

 

[mrGutWrench]

(snip) If additives deal with these two things, then they are worth the effort.

__. I'm never run without them. For these reasons and others.

 

[AndyH]

Not sure what's happening. I just got my best mileage ever in this old car - 45.51. No change to the driving cycle.

We don't have premium fuel down here. All the fuel has been ULSD from Valero. The only additive I'm using is AMSOIL's 2007-compliant Diesel Concentrate. This product does not contain cetane or cold-flow additives.

I'm about 6500 miles into a CJ-4 oil evaluation. This oil came down in viscosity during the first 5000 miles. I thought the mileage increase might be related to the thinner oil. But it's very close to the 5W-40 Euro (AFL) I ran previously. (The 505.01 products appear to thin some at 5000 miles then thicken in the last 1/2 of the interval.) So I don't think the oil is a factor.

The car does take a couple more cranks to start when the temp gets into the mid and low 30s compared to the much easier starting with the cetane additive.

 

[OkiTdi]

Cetane Mileage Reference

See the abstract below from a University of Michigan study of cetane and fuel economy. The bottom line is that cetane improvers do improve mileage, but the reason is because they are very energy dense materials. Cetane additives are typically nitro compounds (hexyl, isopropyl, etc. nitrates). That's nitro as in TNT--trinitrotoluene. So you get a lot of energy out of a small volume, and it's that energy that's making the mileage look higher.

The real question one should ask in this case isn't miles per gallon, but miles per dollar, i.e., miles travelled divided by cost of the diesel plus the cost of the additive. I doubt that one will see any improvement on this basis since the cetane improvers are more expensive than diesel fuel.

One anecdotal piece of information. I don't formulate fuels and lubes, but I work with guys who do (I've worked in energy/fuels R&D for 30+ years--PhD in chemistry). None of the formulators I know use any addititives (fuels or lubes) in their personal vehicles. Why? They'll usually tell you that while an additive improves a specific fuel or lube property, it will usually degrade other properties, often driving the fuel or lube out of spec.

OkiTDI

[FONT=Arial, Helvetica, sans-serif]Fuel Economy and Power Benefits of Cetane-Improved Fuels in Heavy-Duty Diesel Engines[/FONT]
[FONT=Arial, Helvetica, sans-serif]Journal & Paper No:[/FONT][FONT=Arial, Helvetica, sans-serif]SAE 972900[/FONT]
[FONT=Arial, Helvetica, sans-serif]Authors:[/FONT][FONT=Arial, Helvetica, sans-serif]Dennis N. Assanis, University of Michigan
Gary J. Green, Mobil Technology Co.
Timothy J. Henly, Ethyl Petroleum Additives, Inc.
Michael E. Starr, Southwest Research Institute

[/FONT][FONT=Arial, Helvetica, sans-serif]Abstract:[/FONT][FONT=Arial, Helvetica, sans-serif]A program to explore the effects of natural and additive-derived cetane on various aspects of diesel performance and combustion has been carried out. Procedures have been developed to measure diesel engine fuel consumption and power to a high degree of precision. These methods have been used to measure fuel consumption and power in three heavy-duty, direct-injection diesel engines. The fuel matrix consisted of three commercial fuels of cetane number (CN) of 40-42, the same fuels raised to CN 48-50 with a cetane improver additive, and three commercial fuels of base CN 47-50. The engines came from three different U.S. manufacturers and were of three different model years and emissions configurations. Both fuel economy and power were found to be significantly higher for the cetane-improved fuels than for the naturally high cetane fuels. These performance advantages derive mainly from the higher volumetric heat content inherent to the cetane-improved fuels. A preliminary study on a fourth engine, which was outfitted with in-cylinder pressure transducers, was performed. The pressure data were utilized to derive heat-release profiles in order to investigate the effects of natural and additive-derived cetane on combustion. There was no apparent difference in heat-release behavior between a naturally high cetane fuel an raised to the same cetane number with cetane improver.[/FONT]

 

[b4black]

I don't think that it is so much that the cetane improver is energy dense. I think what is happening is the that the base fuel of the cetane improved deisel is more dense that the naturally high cetane diesel.

Typcially the higher the natural cetane, the lower the density. This is one reason truckers don't necessarily want higher cetane fuels. They don't need the cetane and it will hurt their fuel economy. Plus, no matter how you improve the cetane, it will cost money.

It would have been interesting to know the impact of the the cetane improved fuel versus it's base fuel (whicch will have the same density for the most part).

 

[03_01_TDI]

andy, did you take into account that even though you used the same pump. The actual fuel may be from a different refinery, supplier, and/or even oil field region. Which would greatly effect cetane and other factors without your knowing.

 

[TwoSlick]

If the cetane of the fuel is too low during cold weather, then the engine will be running inefficiently during the warmup phase, ie the fuel will ignite too late on the compression stroke to generate maximum Hp and torque. In this case a cetane boost can help maintain normal engine performance and improve fuel efficiency in relation to an engine that isn't running well and is knocking.

This isn't rocket science....

TS

 

[OkiTdi]

It would have been interesting to know the impact of the the cetane improved fuel versus it's base fuel (which will have the same density for the most part).

If you read carefully, you'll see that the study did this. The unadditized high cetane fuel did not have higher fuel economy. The fuel that was additized to get higher cetane was the fuel that had the higher fuel economy.

OkiTDI

 

[Sappington]

__. I'm not a chemist but I must have been doing something right -- my '02 averaged an overall 57 MPG for about 125K miles before it got totalled.

Oh man, sorry to hear about that, Bruce! Was everyone okay? Congrats on your Wagon though - they're great vehicles.

The only additive I use is Power Service Anti-gel in the winter. For all of the benefits that you guys are talking about, it seems like Biodiesel would be a cheaper option. It raises your cetane and cleans your lines. It's a little less energy dense, so you lose a little bit of power and fuel economy I suppose, but the cost is much more favorable per gallon than, say, Power Service. If you're only concerned about mpg, though, then it may not be the way to go.

It makes me wonder, though, how much of the cetane boost from Biodiesel will balance out the drop in energy density when it comes to mpg.

 

[AndyH]

I spent about 2 hours searching and can't find the paper that caught my eye last summer. It's linked to the forum somewhere...

In one section of the test, they compared performance of different natural cetane base fuels with and without additional cetane additives. Results were listed for light, moderate, and heavy service.

The chart that I remember showed that adding a cetane additive to a high natural cetane fuel actually caused lower performance for light and moderate use, and increased performance in heavy/hard use.

This is what got me thinking about my additive use, as most of my driving is light to moderate.

I found that consistent use of single and double doses of a 100% octylnitrate cetane additive seemed to reduce fuel economy for my light/moderate driving.

My mileage seems to have improved since I stopped using any cetane additive.

Placebo/Nocebo comment: I expected fuel mileage to decrease when I stopped using the cetane addtive with ULSD fuel. My results appear to be opposite my expectations.

Other comparsions: I have a number of customers with diesel pickup trucks - Dodge, Ford, and GM. Most have a performance chip of some type. The Dodge Cummins daily driver (no load) picks up 2 mpg with a cetane additive as the only additive. This seems to be pretty consistent with stock and chipped Dodge/Cummins trucks. The Ford and GM trucks don't seem to respond as dramatically. We couldn't see a difference in performance or mileage with the stock Ford trucks.

The best fuel economy I achieved prior to this winter, was last May's trip from San Antonio to Duluth, MN. Two aboard, cruise control set to 65, no A/C, Kuhmo's at 44PSI, LSD fuel from Missouri, steady-state interstate cruising. 44.2 mpg.

My local driving is broken into multiple trips with cold starts, has stop lights, speeds varying from 35 to 90 (normally 70-75), and varying loads -- I came back from Dallas last tank with a 1600 pound load for 300 of the tank's 1050 miles. 45.5. I'm already 650 miles into this tank and it took more than 400 miles for the fuel gauge to hit '18'. Today's load was only 1200 pounds. This tank will perform close to last tank if it keeps up this way. Normally I only get 320-340 miles on the extra fuel until the fuel gauge starts to click down.

I don't know what's happening, but I like it!