what's the deal with sulfur, or lack of, in diesel fuel?

[1 FMF]

I read and hear a lot about today's diesel fuel being low in sulfur. And it comes across like it's a bad thing. What was the purpose of having sulfur in diesel fuel? Why is diesel fuel now low in sulfur?

and what are the different grades of diesel? I think the diesel for automotive use is #2 diesel? Is there a #1 or a #3, and what are the differences?

 

[Ken2]

Removing sulfur is a good idea for cleaner exhaust. Sulfur is well handled in the engine by oils with a suitable level of alkalinity (TBN) and sulfur does contain a goodly amount of BTUs, but is a significant contributor to air pollution.

Sulfur is a naturally occuring constituent in crude oil. If you hear about "sweet" crude, that's low sulfur and more valuable. "Sour" crude has high sulfur and needs more processing.

The organo-sulfur compounds in fuel have lubricating qualities as does some of the of the polar impurities also removed by the sulfur removal process. The removal of these compounds reduces the natural lubricity of diesel fuel. Refineries need to add lubricity additives back into the fuel, but there is not yet a standard to do so. Quality fuel suppliers do add lubricity additives to their fuel.

#2 diesel is the standard for most small diesel engines. I'm only aware of #1-D being used to blend with #2 in very cold weather, although there may be some engines that specify #1. I don't think that there's currently a #3. #4 is a heavy distillate fuel, or a blend of distillate and residual oil, for low- and medium-speed diesel engines in non-automotive applications involving predominantly constant speed and load (generators). This fuel probably needs to be heated and centrifuged. #6 fuel oil is very heavy, black, residual oil used in large boilers and medium and large diesel engines with heat (250°F) and centrifuging.

http://usapc.army.mil/miscellaneous/Lubricity.doc
http://www.chevron.com/prodserv/fuels/bulletin/diesel/
http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/PAGES/D975.htm?E+mystore


Ken

 

[MNgopher]

On Road diesel fuel in the US today contains much less sulfur than it used to many years ago. Current standards require the sulfur content be held to 500 ppb or less (could be ppm - cant remember of the top of my head). This was done mainly for emissions reasons. The sulfur contributes to sulfur dioxide emmissions, which is a major contributor to smog.

The old story was the low sulfur fuel was bad because it decreased the lubricating properties of the fuel. In reality, this is an old wives tale. The real story is that some refining processes to remove sulfur also removed other things that assisted with lubricity. This has been overcome with better refining processes and the use of lubricity enhancers.

New regulations will take affect in 2006-2007 that will lower the allowable sulfur in on road diesel fuel to 15 ppb. This will drastically reduce emissions and allow the use of convertors on diesel engines with a longer life. It should work fine in older applications with the corresponding reduction in emissions. The driving force here is to allow the use of other devices that will reduce emissions of diesel engine seven more in the future.

Diesel is commonly availible in three grades: No. 1, No. 2, and No. 4. No. 2 is what is the most common and is generally sold everywhere. It provides the best balance between lubricity, power, and energy. In colder weather though, the "junk" in diesel fuel starts to show up. Straight No. 2 starts to lose its ability to flow at temperatures of around +20 F. The waxes in the fuel start to congeal and turn into what can basically be called Jelly. This usually cannot make it through the fuel filter, although it can usually make it through the fuel lines. Fuel filter heaters can reduce this affect and get you to about -10 F.

In regions where cold weather is common, retailers sell "winter" diesel. This is usually a blend of No 1 and No 2. It is adjusted depending on forcasted temperatures. Additives may also be used to improve the charecteristics of No 2.

No.1 is essentially a lighter weight diesel that doesn't gel until much lower temperatures. It is similar to Kerosene. However, it generally costs more (has to be refined more than No. 2), and decreases fuel mileage because it has lower energy content. It will also start better than No 2 when cold.

You won't see No.4 sold basically anywhere. It is essentially a thicker, heavier, fuel.

Hope that helps!

 

[Bio-T]

It is hard to add anything to both of the responses already posted. One correction is that the allowable sulfur is measured in PPM. And it is correct that #1 is higher Cut of product at the Refinery. Hard to imagine that gasoline is still at 1000 PPM Sulfur Max.

 

[1 FMF]

thanks very much.

 

[mojo]

Just a little clarification is needed in talking about sulfur levels and available testing procedures for determining the lubricity of diesel fuels. As someone else point out, currently off-road diesel is permitted to have up to 0.50% or 5000 ppm (parts per million) sulfur. Likewise on-road diesel is limited to only 0.05% or 50 ppm sulfur. In 2006, the levels for on-road diesel will be lowered to 0.015% or 15 ppm sulfur. These limits are defined by the ASTM D 975 standard specification for diesel fuel oils.

Refining to lower the level of sulfur as someone else pointed out removes these organo-sulfur compounds that have primarly provided the necessary protection against wear problems that can occur in those fuel lubricated rotary fuel injection pumps that are found in many light duty diesel engines. These "lubricity sensitive fuel pumps" are manufactured by four companies, Stanadyne, Bosch, Denso and Delphi.

There have been two laboratory tests that have been on the books for several years that can measure the level of lubricity in diesel fuels. One is referred to Scuffing Load Wear Test (ASTM D 6078) where as the other is the High Frequency Reciprocating Rig (ASTM D 6079). The problem with either of these two procedures not being incorporated into the diesel fuel standard D 975 has been debated in numerous ASTM meetings where attempts have been made by many of the equipment manufacturers to have these techniques adopted. In my opinion, the oil producers historically have wanted any fuel specification to have as few limits as possible and have viewed this lubricity requirement as yet an additional burden. It is odd however, that the Engine Manufacturers Association (EMA) have since published their FQP-1A Guidelines on Premium Disel Fuel which includes a requirement for lubricity using the ASTM D 6078 procedure. Further there has been a World-Wide Fuel Charter document that has been issued for both gasoline and diesel fuel and this charter includes a lubricity test for all four categories of diesel fuel that are listed.

Maybe in time, ASTM will get its act together and incorporate a lubricity requirement in ASTM D 975. It certainly better come before consumers have to start using the ultra low sulfur diesel in 2006.

 

[Bio-T]

The current EPA limit of OTR diesel fuel is 500 PPM, not 50 PPM. When the new limits take effect of 15 PPM an alternative is Biodiesel. A mix of 20% Bio and 80% diesel fuel would be desireable but even as low as 2% Bio will make a difference. If this option is not available, the aftermarket additive companies will be busy selling their products.

 

[mojo]

Vetteman, thanks for correcting my mistake. However, the fact that the industry standard D975 is supposed to provide a fuel that addresses all the requierments of engines does not mean you can continue to add other ingredients to correct this lubricity problem. I find it hard to understand how the Europeans in as early as April 1999 issued their EN 590 Diesel Fuel Standard which by the way, included a lubricity requirement using an ISO method. Granted we all know that Biodiesel in the 2 - 5% range is an effective lubricity enhancer, but why does a consumer have to generate cocktail mixtures to correct a deficiency. Operating engines with low lubricity fuels over a period of time is like loading up your arteries with high fat foods. You are OK until a heart attack comes along. The fact that OEMs feel the need for lubricity control is evident in the EMA, the World-Wide Fuel Charter, and other standards should open the door.

 

[Bio-T]

Mojo,

I couldn't agree with you more. I was just looking for a way out with older engines as I am to old to look at new vehicles.

 

[MNgopher]

Thanks also for correcting the ppb vs ppm question. I couldn't remember at the time I posted, so thats why I said it could be ppm, which it is!

 

[sprintman]

Oz is going from max 500ppm to 50ppm sulphur. BP already have a diesel here that meets the spec.

 

[MolaKule]

"No.1 is essentially a lighter weight diesel that doesn't gel until much lower temperatures. It is similar to Kerosene. However, it generally costs more (has to be refined more than No. 2), and decreases fuel mileage because it has lower energy content. It will also start better than No 2 when cold."

Some diesel oil additives use a jet fuel additive that prevents gelling and increases combustion temps slightly.

 

[mojo]

MoleKule,I have been involved with jet fuels for some time and did not know of any additives per se that reduce gelling and increase combustion temperatures. The Air Force is currently working on some material that can reduce the freezing point of commercial jet fuel (i.e., Jet A) which is -40 C to that of Jet A1 (or JP8) which is -47 C. But that is still in the development phase. Can you elaborate?