Well I did receive a reply from Optilube, but it was answer free. Apparently they consider their formula proprietary, and don't think water in fuel is an issue for modern diesels. I'll try again, but I'm not hopeful of getting useful information.

Researching diesel lubricity additives a little, these tend to be very proprietary monoacids or synthetic esters, can't find out very much about them. One fact though, is they are added in the 100 - 200 ppm range. That's half an ounce in 30 gallons. It should still make up a significant percentage of a 4 or 8 oz dose of additive though, but where it hides in the MSDS is not clear. They seem to be kind of nasty chemicals on their own.

 

I'm not sure why they link water in fuel with lubricity issues. They are really quite different.

Here's the problem with defining lubricity additives in diesel: Standard diesel fuel from the refinery contains substantial levels of sulfur. Hydroprocessing removes the sulfur, but also removes trace amounts of aromatic compounds and certain polar (charged) products that are responsible for key lubricity in the fuel. (Old highway diesel ran around 500 ppm sulfur. The EPA required in 2006 that this number be reduced to 15 ppm. Non-road diesel had to move down to 500 ppm and finally to ULSD.) The sulfur compounds were less of a problem directly but because the EPA was focused on removing nitrogen oxides, the available technologies for cleaning out nitrogen oxides were poisoned by the sulfur.

In a diesel engine with traditional high-sulfur highway diesel, eutectic nickel alloys were created on the surface of the steel in the engine to provide an extremely durable lubricating surface. This was an amazing approach to lubrication -- basically an inadvertent discovery of a unique phenomenon that gave diesel engines a durability that became legendary. Some of the trace polar compounds in the fuel are much more effective at this than others, and there are differences in diesel refining techniques that can affect how well the fuel responds to lubricity additives -- one refinery's products may respond quite differently from fuel refined at another.

Trying to reproduce this phenomenon and achieve the lubrication of traditional diesels with traditional diesel involves adding compounds equivalent to or better than the original ones that were removed. The originals were pretty caustic (old diesel pollution was enough to irritate anyone's lungs over time, and old diesel could burn your skin as well) and the current ones have to meet pollution standards of their own as well as provide lubrication. Generally they can't do what the old lubricants did, so they offer a relatively poor imitation of the original effect. Plus, they have to deal with diesel from different refineries; the original approach was pretty universal but after all the new pollution standards imposed on additives themselves, it comes down to tiny traces of active compounds in the additives and secondary lubrication provided by the cetane. This is why it's hard to compare fuel additives and hard to know exactly what's in them. I hope that makes it easier to understand why it isn't easy to understand diesel fuel additives.

 

They aren't linking Water In Fuel and lubricity, I am. I want a lubricity additive that does not increase the water coming through the system. Not sure how I get that. Most of the additives are a soup of "improvers" including cetane improvers and other things of unknown action. Optilube sells their XL product as a lubricity improver (and test support the claims) but there is other stuff in there that they won't say what it does and won't promise that it will not allow more water through. In particular it has polyethylene glycol ether, which many sources say is soluble in water and therefore possibly increases the solubility of water in diesel. I don't know, but neither will Optilube say.

We know Ford is paranoid of water in the fuel, so there is some reason to believe PM22 doesn't have this effect. It also has less lubricity improvement, according to 3rd party testing.

 

Actually, Optilube XL contains propylene glycol ester, a very different compound. PGE is insoluble in water and is used here as a surfactant and anti-foaming agent. It's present in very small amounts, consistent with use as a surfactant and anti-foaming agent, and not enough to carry enough water even if it were water soluble. So on that count you can rest easy. Here's the current MSDS sheet:

https://opti-lube.com/downloads/MSDS/DFI-XL-MSDS.pdf

However Optilube XL actually dilutes its level of cetane and other trace additives by addition of a large amount of naphtha. In comparison, Ford's PM22a contains only traces of naphtha and is primarily cetane fractions. I'd be interested to see the citations on studies that say Optilube outperforms PM22a because the only thing its contents might do is to increase ignition rate. And describing a "soup of 'improvers'" isn't quite accurate. Most of the listed ingredients have specific roles (such as propylene glycol ester as a surfactant and antifoaming agent).

When you look at PM22a, Ford simply describes it as the column distillate that happens to contain cetane. That's permissible and accurate, and reflects the reality of how such products are isolated (and for that matter, how diesel itself is produced).

I would mention, since it hasn't come up in this thread, that cetane (including PM22a and similar cetane enhancers) are highly flammable. Bear that in mind when storing cetane enhancer in the truck.

 

Read that MSDS again. It is 'ether', not 'ester'. I am not knowledgeable enough to know what is different between the two, but I can read . Do you see anything in the Optilube XL MSDS that looks worrisome from the point of view of water?

I have asked more pointed questions of Optilube, but have received no reply yet.

Here is one cite (though not a direct comparison to PM22) and coming from the manufacturer, but from a real lab. The other is the often cited test done on the other forum, which compares Optilube XPD to many others (but not PM22).

 

Sorry, the "ester" was an autocorrect function at work. You can actually have both an ester and an ether of propylene glycol and they are for all intents and purposes the same. What I was focusing on was that this is propylene glycol rather than polyethylene glycol.

There's a big difference between polyethylene glycol and and propylene glycol. Your worries about water being introduced via polyethylene glycol weren't really an issue and with propylene glycol, are completely a non-issue.

That first report, from Opti-Lube, is comparing different Opti-Lube fuel additives on the basic HFRR test that fuel lubricity is tested by. It's actually linked to the Opti-Lube XPD webpage as a test conducted by Opti-Lube. It isn't the only test and not sufficient by itself, but the HFRR is straightforward and most fuel labs are set up to do it. You can take your own fuel and additive combination and have a similar test run for about $25.

On the second test, the 2% REG sample is basically enriched biodiesel. No surprise it has high lubricity because that's a characteristic of biodiesel. However, it also tends to grow contaminants faster and it solubilizes contaminants in the tank and fuel lines, so unless you're on it all the time, your engine actually runs rough and has clogs. Use it all the time without exception and it works better, but there's an energy cost and you have to treat it like religion.

XPD is a catch-all additive mix. It is anti-gelling at low temperatures, it increases your cetane count moderately (only by 3 points, when you may need to get from a common level around 40 to above 50), and it generally helps resolve odd contamination issues in diesel. For example, it's not uncommon for diesel to be contaminated with some gasoline, especially at consumer gas stations. It includes cleaners that help clear gunk from your injectors, with the risk that it can also clear a lot of junk from farther back in your fuel system and dump it all in your injectors. In short, it's a mixed bag and may help you, may hurt you, but it certainly doesn't provide an adequate boost in cetane, reflecting the fact that cetane alone isn't how your diesel block gets lubricated.

Hope that's clearer.

 

Just to clarify for everyone jumping in to read this thread, cetane and lubricity are two completely different and independent things. The cetane rating of a fuel does not give any indication of it's lubricity, and vice versa. They are two different measurements of fuel quality.

Lubricity is self explanatory. Most people without a degree in chemistry can probably get lost in the various types of lubricating enhancement products out there. I won't attempt to touch on that part, because quite frankly my knowledge is next to none.

Cetane is a measure of the ignition delay. Simply put, the higher the cetane number, the less time between Start Of Injection (SOI) to Start Of Combustion (SOC), with all other things being equal. It's the opposite of octane rating in gasoline, where the higher numbers mean a longer ignition delay. In both cases (cetane and octane), neither are an indicator of the overall burn rate (how long it takes to burn the fuel after ignition).

Now my own thoughts on the matter...

Ideally, the additive that ultimately should be the only thing to ever go in the 6.7L, and what Ford recommends, are products that boost cetane, and improve lubricity. Any other products that do anything else other than enhance those two fuel quality indicators, Ford strongly recommends not to use. Ford claims their PM22 does both, and PM23 does the same along with anti-gel agents. Although as we've seen in this thread, getting an exact chemical makeup of some products, and their effectiveness, is extremely hard to come by, and even hard to decipher for the average person like me. My head spins reading some of that.

In the end, most fuel across the country is sufficient enough. Ford does not require additives, which I view as only further validating my thoughts. I personally don't use additives unless it's anti-gel, and even then I'll probably go through half a bottle for the entire winter (Denver doesn't stay cold long enough to use anti-gel all the time).

So while many people sweat over which additives to use, how much, how often, etc.... I personally think that the vast majority of it is a waste of time. At least for me. I've thrown in some PM22 in the new truck, and never noticed a difference. My old 7.3L I tried out several different additives, and again never noticed any changes whatsoever. Some people may have different experiences altogether. I'm sure there might be some areas where fuel quality is such that lubricity and cetane boosts would take on a noticeable difference. In most cases, however, I believe there is a such thing as a placebo effect. It's not uncommon for people to think they hear changes in the sound of their motor or feel a power difference in the seat of their pants when using an additive.

I'm also adamantly against oil additives. They are one of two things - 1) snake oil, or 2) change the properties of oil enough to make a difference in one area of the motor, but could cause problems elsewhere in terms of proper lubrication. Best example is the good old 6.0L injector stiction problem. Lots of people swear by this or that oil additive to clear up stiction. Problem is that it's only masking a physical problem with the injectors, and causing the oil to act differently everywhere else that it touches. This means something is not getting properly lubricated elsewhere in the motor.

Anyway, enough of me being on the soapbox.... Obviously I'm not a big fan of the additive industry. Few products are worthwhile, and most of the rest are best at separating your money from your wallet.

 

I'd agree on oil additives. Fuel additives, however, are a way to correct deficiencies in regional fuel supplies. This description of the cetane number is good but can use a couple clarifications. First, cetane is simply a very explosive component of the refinery fractions that become Number 2 diesel, or ULSD today. By combusting very readily, it allows your engine timing to be very accurate and it also burns more completely, and both phenomena reduce wear in your engine. But what people are actually talking about all the time is cetane number, which is simply a measure of how explosive your diesel fuel is. The faster it burns, the higher the cetane number, or vice versa. At this point, when one is talking about cetane number, it isn't about a certain level of cetane in the fuel but rather just a measure of explosiveness, compared to pure cetane (which no one would want to use in an engine). A product like PM22a is called a cetane enhancer, as if it contains large amounts of cetane, but it actually is a cetane number enhancer, and provides compounds that increase the explosiveness of the fuel. That addresses the point in the previous post.

Now a cetane enhancer tends to have a variety of ingredients. There are some that have anti-gel compounds, detergents, and other ingredients added to be more versatile. Some of those additives are only seasonally required, or only required in certain situations, or not really required at all. But there is a significant portion of a cetane enhancer that is simply a fraction of very flammable compounds coming off a refinery column. Sulfur isn't included, which makes the EPA happy, but that fraction will contain various cyclic benzenes, hexanes, naphtha, and so on. It's a hodgepodge but it's very flammable and helps with ignition. But that same fraction also carries minute amounts of polar organic compounds that bond to the the steels in your engine and, despite their small concentration, do a superb job of improving lubricity. Those compounds bond to the steel and in turn attract other compounds that protect the surface of the steel from abrasion. That fraction can vary, depending on the refinery and what the additive company wants to see in it. This is why cetane number enhancers can vary quite a bit. It's a fraction that evaporates rapidly and burns off very fast, and often is simply allowed to burn off because there isn't as much demand for it. But when added to diesel fuel, it restores not only combustible compounds but also some compounds that contribute to lubricity. There are other ways to add lubricity, in particular by isolating the compounds that stick to the steel and directly improve lubricity, but it doesn't take a lot of them to do the job, and a cetane enhancer improves combustion, reduces wear by improving combustion, and can provide agents that affect lubricity of the fuel.

 

Ah, propylene vs. polyethylene - maybe I can't read after all!

I gathered early in your contribution that cetane and cetane number are two different things and that you were referring to cetane as an organic compound rather than a test number. The difference I had not completely appreciated before, and your last post clears that up further. Thank you. I also wondered what the relationship of some of these ingredients to lubricity was.

Many of the soups (which I still think they are) have ethylhexyl nitrate as the cetane number improver and it seems to be generally accepted as such. But most of them also contain "petroleum distillates" or a pseudonym, it sounds like this may actually be some of the restored cetane ingredients you are talking about. And contained there is also some of the recovered lubricity.

The other common ingredients are ethylhexenol and trimethylbenzene. Are these oxygenators or cleaning agents?

Do any of the additive ingredients have any significant effect on particulate byproducts, that would lead one to suppose they would reduce buildup in the DPF?

 

Ethylhexyl nitrate enhances cetane number by improving the explosiveness of the diesel in very small quantities (you want the quantities to be small, because the tradeoff when you get explosiveness is that they don't give you too much power -- they dilute the mileage per gallon of the fuel). Now the "petroleum distillates" or "naphtha" are just terms for the collection of flammable compounds that are isolated as a certain fraction at the refinery, the fraction that also contains the cetane enhancers one wants to use. They help a bit with cetane number, but not as effectively. However, they contain mixed up in them some of the trace compounds that improve lubricity.

A number of these compounds have the side benefit of reducing particulate byproducts. They do this simply by combusting the fuel more fully, leaving less behind.

 

Keep in mind that cetane, when referring to diesel fuel, is a number and not a component or compound. It's one of several measurements of diesel fuel quality. Just like octane is not a component of gasoline, it's simply a measurement of the resistance to ignition in gasoline.

Other measurements of fuel quality are lubricity, energy content, density, water content and contaminates, and other factors.

Now there is a compound known as cetane, or also N-hexadecane.

Again keep in mind that cetane is only a measurement of ignition delay when referring to diesel fuel. It does not have anything to do with how "complete" a fuel burns, because it does not measure burn rate. The chemical compound of cetane, N-hexadecane, has a completely different burn rate than diesel fuel, completely different energy content, hence the two are not measured. What is measured is the SOI to SOC. Pure cetane rates at 100, and diesel fuel is compared to that rating scale of 0-100.

Getting closer. Not really how "explosive", because that would indicate energy content more than cetane. But yes how quickly it will begin to combust after it's been injected.

Again, cetane does not measure the overall burn rate, or the energy content of the fuel. It only measures the time between injection and combustion. It's a very strict measurement. There are several methods for measuring the cetane index of diesel fuel, and every single test only measures the time between SOI to SOC. No cetane test measures how long the fuel continues to burn, or how complete it burns, or how much energy it has, etc.

The rest of that is on point.

Hopefully everyone understands how cetane is measured in diesel fuel. Improving cetane doesn't mean the overall quality of the fuel is increased. It only reduces the delay in combustion. Everything else would require different additives to change lubricity, or change the energy content, or affect the water, or treat other contaminates. Many of those other qualities of diesel fuel will greatly change how it burns once combustion has started, how complete it will burn, and how much power it will deliver overall.

 

So, in the typical diesel additive, the lubricity improvement is in the "naptha" or "petroleum distillates" component? Or one of the other common ingredients mentioned above?

 

All your edits of my comments about cetane versus cetane number are points I made in my posts. Could you take a look and see if there's a reason why you singled those points out when they'd already been covered? Thanks.

 

I thought I explained it completely. But that's ok I'll try again. After all it's a forum and sometimes what's in our heads doesn't translate well across the keyboard. I think you understand the concepts well and I wasn't trying to push that to the wayside, it's just the terminology gets a bit mixed up for others coming into this thread and trying to make heads or tails of everything. I was just attempting to sort out the differences so there wouldn't be as much confusion.

For example, you discussed cetane and how "complete" the fuel burns. You also mentioned how fast it burns, and you also mentioned how explosive diesel fuel is with higher cetane numbers. Cetane has nothing to do with that, as I outlined and explained how/why in that post.

Cetane, with regard to diesel fuel, is only a number. The higher the number, the shorter the delay between Start Of Injection (SOI) and Start Of Combustion (SOC). Anything that happens after the diesel fuel has begun to combust, including how much of the fuel burns, how much it explodes (energy content), how quickly or how fast it burns.... none of that is part of the cetane rating.

Where cetane ratings come in only happens from the point of SOI to SOC. That is the only thing it measures. Key word when thinking about combustion and cetane, is the word "start". Testing diesel fuel for cetane ratings only measures when the combustion reaches a certain starting point, as dictated by the individual test (there's several version and they have different measurement standards).

Explosiveness happens after the start, think "energy content" or BTU's. What also takes place after SOC is "completion" of the burn and how quickly or how fast the fuel burns up.

Is that a bit more clear?

 

The way I am understanding it is that "cetane" as commonly discussed on this board and in casual diesel conversation is the test number assigned to a particular fuel. But there is also "cetane" as in the organic compound or mixture of organic compounds, which is being removed in the fuel refining process. The removal of this fraction both reduces the cetane test number, and reduces the lubricity of the fuel. So while cetane - the number - may not affect anything but the delay between SOI and SOC, cetane - the chemical - may do several other things. We probably need a convention like referring to them as Cetane Number and Cetane Compound, as "cetane" by itself is ambiguous.