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Discussion Starter #1
On another site someone was saying that if you use biodiesel in concentrations over B20 you would get polymerization if you use high pressure common rail injection.

From what I can tell, the high pressure causes the biodiesel to become 'stringy'. The person who brought this up said that these strings would clog the injectors. I'm thinking that if this even happens, it would clog the filter, not the injectors.

I don't know much about this but I doubt it would happen as low as B20. I would think if this happens it would probably be at much higher concentrations.

Does any know at what concentrations polymerization can start to happen in our trucks?

If you get polymerization will it get caught by the filter or can it get to the injectors?
 

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In the Bosch HPCR injection system the filter is before the injection pump. This portion of the fuel system is slighty pressurized in the Dodges due to a lift pump, it's under vacuum in the GMs and "sucked" from the fuel tank all the way to the injection pump. The Bosch CP3 injection pump is two stages in a common housing. A gear-type first stage provides the vacuum fuel draw and pumps up the fuel to 100 psig or so to feed the three high pressure plungers that pressurize the common injection rails. If polymerization is occuring because of pressure, it will occur in the pump and rails - which feed the injectors, not in the filter. Since the rails and injectors run between 10 and 30,000 psig, I can't see these strings "clogging" the injectors!
 

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I don't know if the information is correct but I can tell you the high pressure occurs AFTER the filter. The injection pump pressurizes the fuel then it goes to the injectors. Also, I haven't heard any of the guys running Dmaxs and BIO having any problems.
 

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Discussion Starter #4

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Great info and link, Mark My Word - thank you.
 

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The biggest problem with Biodiesel is off spec fuel...I believe the problem is rampant.

The only truck I heard that could not run the pure B100 was the ford. It seems with just a little diesel 5-10% things clear up.
 

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The biggest problem with Biodiesel is off spec fuel...I believe the problem is rampant.

The only truck I heard that could not run the pure B100 was the ford. It seems with just a little diesel 5-10% things clear up.
Yes, the quality issue is the thing that makes me a little nervous about using it. Hopefully its just because its new and with time the quality will get better. I wish there was an easy way to tell the quality.

The ironic thing is, I'm not really sure how confident I am in the quality of the dino diesel we get either!
 

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I didn't read that thread, but I wouldn't be overly concerned by this. Polymerization is usually considered to be catalyzed more by heat and oxygen exposure than by pressure. I would have to do more reading to come to a definite conclusion, but of all the potential pitfalls of using biodiesel, I think this ranks relatively low. Clean, dry, spec. fuel should be just fine at any mix percentage.
 

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This kind of tells the thread in a "nutshell":

Mike Briggs, administrator wrote:

On the issue of polymerization/oxidation - the iodine number is related to how readily an oil (or biodiesel) will polymerize - but again, it only does so under conditions the fuel shouldn't be in anyway (ie water contamination, etc.). Biodiesel doesn't directly polymerize itself - it first has to be oxidized to form peroxides, which THEN polymerize. So, without the potential for oxidation, you won't get polymerization. Another potential issue - if there are substantial levels of glycerin remaining in the fuel (which ASTM quality biodiesel shouldn't have), you can get acrolein formation from the glycerin, with the acrolein itself polymerizing in combustion chambers. See http://www.deh.gov.au/atmosphere/biodiesel/submissions/pubs/logical.pdf
for more on this (this is the comments from a VERY highly regarded chemist when Australia started forming its standardization for biodiesel). You can search for "polymerize" to see the parts where he deals with this specifically.

So, ultimately the issue of polymerization should come down to fuel quality. Excess glycerin can lead to acrolein formation and polymerization. Excess water or other poor storage issues can lead to oxidation/polymerization of the biodiesel itself. Injection Pressure by itself shouldn't be an issue - but of course I could be wrong.

The simplest "solution" for biodiesel would be to not remove the vitamin E during processing, as it is a natural antioxidant (this is removed in some distillation processes. Some biodiesel plants currently remove it, some don't). Keeping it in there prevents oxidation, so polymerization cannot occur (although if you have excess glycerin, you can get acrolein formation and polymerization of that). That is likely why the Navy found their biodiesel to be so stable in their tests (considerably more stable than the diesel fuel) - the brand they were using is one that keeps the vitamin E in.
 

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Mark,

Usually it is wise to stick with B20 from the pump. First look at the fuel in a clear glass/container. It should be crystal clear. If cloudy then most likely it is wet and contains too much water.

Even clear fuel can contain too much water...which only a fuel test will tell you..in PPM.

You can also stick in the Fridge and see and what temps the fuel gets cloudy. That should give you an idea of the range in which you can use the fuel.

If you find a supplier you can ask for test results etc. I tested the fuel from my Biodiesel supplier(B20 from the pump).

Water by itself is not so much a problem when it is dissolved...cloudy fuel...but when it get cold that water could fall out and be free.

If it occurs in your rail...start up...bad news for the injectors.

Water...or lack of it..like Habanero mentions is the key to good biodiesel.

Cold weather is the other issue. Depending on what the bio is made from...Cold weather could cause some components of the fuel to fall out.

This could cause filter plugging. A spec..I thought...is Cold filter Plugging performance....is dependent on what type of oil is in the Biodiesel...soy..canola...or worse recycled which contains animal fats.
 

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I've debated the acrolein issue before as well and I really don't even see that as being a problem. There is hardly any polymerization that occurs inside the combustion chamber, and even if there is, who cares? Particularly with the cupped design of DI pistons, any polymers that do happen to form are combusted right along with the rest of the fuel. The time scale involved is just too short-combustion is a much faster process than polymerization. Now if you start getting spray on the sides of the combustion chamber from a faulty or partially-plugged injector, you might begin to have some issues with build-up on the rings. But in the case of the common-rail system in our trucks, you are going to have other drivability issues from a bad injector before enough time goes by to build up anything on the rings.

As to the Vitamin E, yes it is a natural anti-oxidant as are all the tocopherols and tocotrienols present in many vegetable oils. But, they all occur in greatest concentration in the solids and "gums" of the oil. So, if refiners are leaving it in, chances are the cloud point of the product is going to be much higher. Added to this, antioxidants are a high-value coproduct of the oil. If refiners can become more efficient at separating and purifying these products, the whole process becomes more cost-effective. That can do nothing but help the industry as a whole.

When I was at Ok. State we were working on projects profiling the antioxidant components in wheat germ and peanut oils, so I have a little experience in this area.
 

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Habanero - I think the concern is with polymerization occuring as the fuel is compressed to 23,000 PSI in the fuel rails....not in the chamber.

I have never heard of this being an actual problem in a vehicle....but rather a concern on paper.

On another forum someone asked about running B100 in a 6L Ferd. No one was responding, so I repeated the basic line that I had read at thedieselstop....being that a little diesel will ward off the polymerization. Girl Mark (we all know her, right?) stepped in and said that that was only a rumor, and there is nothing that she knew of that made it true.

I still do not understand the whole thing.....crude oil is used to make polymers too, so it seems like the same caveats would apply there?

I recall reading that it had to do somehow with FFA's in the oil, but I am not sure.

MT
 

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Habanero - I think the concern is with polymerization occuring as the fuel is compressed to 23,000 PSI in the fuel rails....not in the chamber...MT
From Idle_Chatter's post above that I was referring to:

Mike Briggs, administrator wrote:

On the issue of polymerization/oxidation - the iodine number is related to how readily an oil (or biodiesel) will polymerize - but again, it only does so under conditions the fuel shouldn't be in anyway (ie water contamination, etc.). Biodiesel doesn't directly polymerize itself - it first has to be oxidized to form peroxides, which THEN polymerize. So, without the potential for oxidation, you won't get polymerization. Another potential issue - if there are substantial levels of glycerin remaining in the fuel (which ASTM quality biodiesel shouldn't have), you can get acrolein formation from the glycerin, with the acrolein itself polymerizing in combustion chambers. See
http://www.deh.gov.au/atmosphere/bio...bs/logical.pdf
for more on this (this is the comments from a VERY highly regarded chemist when Australia started forming its standardization for biodiesel). You can search for "polymerize" to see the parts where he deals with this specifically.
 

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Thanks for the clarification.....I had not looked at the link yet.

So if the acrolein is at least partially responsible for the polymerization, wouldnt one assume that those running WVO (full of acrolein, Ive heard?) would have an issue with this?

And is it possible for polymerization to occur as the fuel is compressed pre ignition?
 

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Thanks for the clarification.....I had not looked at the link yet.

So if the acrolein is at least partially responsible for the polymerization, wouldnt one assume that those running WVO (full of acrolein, Ive heard?) would have an issue with this?

And is it possible for polymerization to occur as the fuel is compressed pre ignition?
WVO, for the most part, has no acrolein in it in and of itself. There could be tiny amounts produced through the frying process, particularly in abused (overheated) oil. Generally when you hear of acrolein in fried foods, it is that which is produced from the starches in the food being fried, not the oil itself.

There are mechanisms by which the triglyceride molecule can break down into acrolein. But it has always been my contention that the oxidation (i.e. combustion) reaction has a faster rate of reaction than the polymerization reaction. So kinetically, the combustion reaction is going to be favored. This becomes even more true when you are considering this is a diesel engine, which by design runs with excess oxygen.

Now if you have situations in which you are not getting complete combustion, such as under heavy load where you observe particulate formation, you may have conditions that would permit some acrolein formation. I haven't to this point seen any research on this topic, although it may be out there. But as far as engine damage is concerned, these conditions that may lead to the production of acrolein (i.e. heavy load, high fueling, oxygen-starved) also produce a lot of heat inside the combustion chamber. This would serve to prevent deposition on the cylinder walls and piston anyway.

Is it possible for polymerization to occur as the fuel is being compressed? It is possible, as you have an oxygen rich, hot environment. But depending on injection timing, most of the compression is already done. So again based on kinetics, I think oxidation is going to win the race. Even if there was some polymerization occuring, any polymers formed within the fuel envelope are going to be oxidized right along with all the other carbon-based molecules.
 

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Thanks for the explanation.....you know your ochem well!
 

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has anyone in this forum converted a common rail diesel engine ...well i have got 25000 miles so far so good 90%wvo 10%kero..call me crazy ...good day
 

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Youve got your Dmax running on that blend?
 

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has anyone in this forum converted a common rail diesel engine ...well i have got 25000 miles so far so good 90%wvo 10%kero..call me crazy ...good day
Where do you live? What are the daily temps.?
 
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