I posted this on the Frybrid forum and thought it was worth reposting here.
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I always reccomend getting the best quality wvo one can. But even with a great supplier you never know for sure if some water has been inadvertantly introduced to a batch you are filtering. It is much better to assume that water is in the wvo than to not. Why?

Tthree main reasons:
1. If prefiltered wvo containing water is introduced to a heated tank the water present will tend to settle out. This conentrates the supended water near the bottom of the tank so wvo being sent to the engine will tend to contain a higher percentage of suspended water than the wvo originally poured into the tank.

2.A portion of this concentrated suspended water (micro-droplets) will settle all the way to the bottom of the heated tank and form free water. This will encourage microbial growth. The problems associaated with microbial growth in fuel tanks are well documented..and not only a headach to remedy..but expensive as well.

3. Water blok filter elements designed for diesel fuel are not designed to absorb or block passing micro-droplets of water suspended in vegoil. They are designed to absorb free water (large usnsuspendable drops of water) in diesel fuel. I have found that there is evidence they do absorb some free water in vegoil...but none that they do so with suspended micro-droplets of water.

This presents two questions:
1. Is it worth dewatering simply to prevent any water that MIGHT be present from reaching the heated fuel tank?

and
2. Is it worth risking damage to your Injection Pump if suspended water micro-droplets make it past your on board filter element?

Which I suppose begs the question:
Do suspended micro-droplets of water passing through an IP do any damage?

Every Diesel/IP tech I have posed this questions to stated without hesitation.. YES. Not being one to simply take the opionion of experts as fact I researched how this damage might occurr.

What I found was that two mechanisims involving suspended water can cause damage to IPs:

1. Water tends to absorb acidic compounds in vegoil especially wvo..concentrating them. This acidic water can "etch" the mirror like surfaces of the internal parts in an IP greatly accellerating wear since the slightly roughend surfaces create more friction.

and
2. As the micro-droplets pass through the IP they are subjected (along with the fuel they are suspended in) to suddenly and dramatic changes in pressure. This has little effect on the fuel but causes the entrained water micro-droplets to "explode" with an amazing amount of force (considering how small they are). If the micro-explosion happens in close proximity to a metal surface it will cause very small amounts of the metal to be essentially "blasted off" that surface. In the highly polished and very close tolerance clearances of an IPs "guts" BOTH the removeal of this material from these surfaces and the abrasive damage it does as it exits the IP can dramatically shorten the life of an IP.

And IPs are very expensive to replace.
Having to replace an IP every 100,000 miles is unacceptable to me since I know that properly cared for they can last 2-4 times that long. And the prospect of having to replace an IP every 50,000 miles simply because I got a couple of tankfulls of "wet oil" every now and then makes me very..very careful about the quality of wvo I introduce into my fuel tank.

Considering the consequences of taking the risk that ALL my wvo will be water free I feel it is unacceptably risky to do so. And dewatering is SO simple that I cannot imagine that anyone else would KNOWINGLY take that risk either. The fact that some folks don't dewater and have not had problems YET does not indicate it is not higly risky. Except for a slug of free water passing through an IP the damage is not dramatic...is is insidious and slow. It does not announce itself with a BANG..but rather happens over a period of tens of thousands of miles and announces itself with very slowly deteriorating IP performance.

By the time it is noticed..it is too late to do anything about it.

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Another poster added this regarding the mechanism of "cavitation" in IPs. Used here with his permission.

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Cavitation is a very fascinating phenomena. It is caused by the fact that
water boils at different temperatures depending on the pressure.

Damage caused from cavitation is not due to water 'exploding' into steam but rather occurs when the steam cavity collapses back to liquid. The surrounding fluid rushes in to fill the void with a remarkable amount of force. This implosion is much like the effect of shaped explosive charges.

Next time you are boiling a pot of water on the stove, observe the bottom of the pot (inside of course.) As boiling is approached, you will see bubbles forming. If you watch closely, you can see that many of these bubbles form and then vanish. This is accompanied with a sort of rustling sound. You are hearing the collapsing bubbles, or the imploding cavities. As the water begins to boil, the bubbles, instead of collapsing, grow and rise, leaving the surface as steam. WARNING - boiling water is hot - don't stick your face in or near the water as you can be severely burned.

Reducing pressure or increasing temperature are the two ways of boiling water. Water droplets react to their local conditions, not the fluid average. You can expect conditions to be highly turbulent in an injection pump with all manner of shock waves dancing through the liquid. A shockwave includes a low pressure portion, which can be low enough to boil any suspended water droplet resulting in a cavity of steam, especially at elevated temperatures in the IP. (Plus we are heating the VO, making matters worst.) If the cavity of steam is against a pump surface when it collapses, the force of the implosion can and will erode the surface by blasting small bits off. This is not good.

(As an aside, wet sleave diesel engines can have erosion problems. The cylinder liner pushed into the block has coolant directly on the outside. The forces from compression and ignition can be enough to cause shock waves in the coolant, resulting in cavitation and erosion on the outside of the cylinder liner. Google 'cavitation diesel' to learn more)

The moral of all of this is if you do not wish to make your IP mechanic rich, put the effort in and get the water out of your veg oil.

Oh yeah, fuel tends not to do this because it has a much higher boiling temperature and lower vapour pressure. This approximately means that the conditions are not extreme enough for the fuel to cavitate. Modern super-high pressure diesel injection systems may need to be designed to prevent fuel cavitation. The same Google search suggested above will get hits related injector modelling and technology relating to fuel cavitation.

Corrections and clarifications of the above description are encouraged.

And remember, listen to Dana and dewater your vegetable oil!

Excellent description of cavitation (a subject I know something about). By extension, possibly the same cautions would apply to other volatile fuel components as well as to water. I'm thinking of petrol, methanol, white spirit etc. which some folk add as fuel improvers.
Aeolus

quote:

Originally posted by David L. Teal:
Excellent description of cavitation (a subject I know something about). By extension, possibly the same cautions would apply to other volatile fuel components as well as to water. I'm thinking of petrol, methanol, white spirit etc. which some folk add as fuel improvers.
Aeolus

I would imagine, by inference, that the relative damage possible would be related -inversely proportional - to the liquid's boiling point.
In this case, one would imagine that petrol would have a greater propensity for cavitation than water.

Have I missed something?

Tony,

I though that too. But aparrently it is not that simple. When I asked a diesel tech he admitted he did not know exactly why water acted this way and fuel did not.

When I asked a local physics instructor the reason he asked what my background in physics was. I said college level...25 years ago...and he "explained" it had to do with the "special" properties of water compare to other liquids. When I asked him to elaborate he said "you don't have the background to understand it fully".

Which either meant I don't have the background or he didn't know the answer. I am still curious. Anyone know a phyicist?

More from the Frybrid forum:

quote:

I have never worked as a fry cook so my logic is missing that real world experience. I would think that any water, or ice, introduced into oil above 212 degrees would turn to vapor and dispel into the air. I could be wrong.

Hi Greg,

It would make perfect sense that if oil containing water were heated to above the boiling point of water all the entrained water would boil off. And of course it would make dewatering soooo much simpler. Unfortunatley there are two kinds of water which can be in wvo.

Free water is large droplets than cannot b euspended by the high viscosity of the oil and fall to the bottom. When you heat wvo with free water on the bottom you notice that althogh the top of the oil reaches 212° F the water is still sitting on the bottom of the the oil unphased (physics geek pun) that it should logically be boiling off into the atmosphere. If you have taken the time to set up a pan with multiple temp probes at different levels (why would anybody do this?) you will notice that although the top is well over 212°F the oil (and water) on the bottom is still cooler than that. Eventually you would also notice the temperatue rising in the probes lower in the pan and right after you noticed that the temp near the bottom of the pan was rising to 212°F ther ewoudl be a muffled "BUMP" sound followed by lots of pain.

This was some of the water reaching 212°F and instantly turning to steam. Teh sudden increase in volume of the water then instantly displaces very ot oil causing it to leave the pan and deposit itself all over you. OW...OW..OW...OW..OW. If ther is enough oil on top of the water it will "absorb" the small explosion and the steam will condense before it can escape the oil. it will now mostly be in the form of suspended water.

This is the second form of water in wvo and it acts a little differently. It will stay suspended nearly indefinately in unfiltered wvo. It seems to have an affinity for the particulates suspended in the wvo and until these are reomoved will not an to settle out and form freee water. If however the particulates are removed it will begin to slowly move under the force of gravity toward the bottom of the oil. At first this will just cause the concentration of suspended water "micordroplets" to get higher near the bottom and lower near the top of the oil. Little by little the droplets will join up with each other as the concentration increases and these larger micordroplets will fall faster and faster and joint together faster and faster as they do. Eventually they becoem large enough to fall out completely and they will be sitting on the bottom of the oil.

Where if you try to boil them out they will go back for the most part into suspension. If you add enough heat they will form smaller and smaller microdroplets and as the circulation of hot oil brings them to the surface they will escape to the atmosphere. The amount of energy it takes to accomplish this is incredible though.

quote:

Is there a way to test a batch of fuel for water content ?

Free water can often be seen withthe naked eye sitting on the bottom of a container of oil. Large midrodroplets of suspended water will make popping, crackling, sounds when heated in a shallow pan, and even small microdroplets of suspended water can be seen turning to steam in a shallow pan as the oil is heated. These will appear as very small bubbles that form as the oil is heated.

quote:

Is there an additive that absorbs the water so it can burn similar to gas de-icer products ?

Not that I am aware of.

OK, I'm not sure why suspended water is a problem. Dana, you mention it may cavitate, but cavitation happens under loss of pressure, not pressurization. If the water makes it to the IJP in liquid form, compressing it will only keep it liquid. Your contact that hinted at the split nature of water was being a bit snooty -- there's no real secret. The strangeness of water occurs when it freezes, it expands rather than contracting further. That's why full bottles explode when frozen.

Sorry to question the premise of this thread, but I don't buy steam explosions being a problem in high pressure, below boiling point enviroments. Perhaps once injected into the relatively low pressure cylinder, and extreme temperature, steam can harm injector tips, but IP damage??

quote:

Reducing pressure or increasing temperature are the two ways of boiling water. Water droplets react to their local conditions, not the fluid average. You can expect conditions to be highly turbulent in an injection pump with all manner of shock waves dancing through the liquid. A shockwave includes a low pressure portion, which can be low enough to boil any suspended water droplet resulting in a cavity of steam, especially at elevated temperatures in the IP. (Plus we are heating the VO, making matters worst.) If the cavity of steam is against a pump surface when it collapses, the force of the implosion can and will erode the surface by blasting small bits off. This is not good.

Well you can reject the premise if you want...but talk to a IP tech and they will regale you with the dangers of water cavitating inside a pump. It is far from theoretical to them sicne they see hundreds of pumps every year that are toasted by it happening.

Maybe this will help. There are places in the internals of an IP which are subjected to pulses of high vacuum. Pressure is not a constant state in an IP. While it may produce high pressure fuel pulses on the injector side..but in order to do so it creates similar pulses of high vacuum on the "filter side" of the internals. Theses low pressure pulses are what create the conditions under which cavitaion can easily ocurr.

Hey...look at the antifreeze in a wet sleeve type diesel engine. Although it is under what we might consider a constant state of pressure desinged to prevent water from boiling at temperatures higher than 212°F at temperature much lower than that cavitation occurs on the outer (coolant) side of the cylider wall. Even though the coolant is under pressure the High Pressure pulses (shock waves) it is subjected to created by the explosions inside the compression chamber also create corresponding pulses of low pressure which when localized against the sleeve create cavitation. In some engines this is often enough over time to actually blast pinhoels all the way through the liner. The NON PS Ford (IH) 7.3L diesel is famous for this.

Pressure everywhere..but pulses of high "negative" pressure as well.

I could see issues arising along the friction surfaces in the plunger. Obviously large amounts of water will not adequately lubricate the surface, and acids could also be a problem there. But I'm also starting to see the point that there could be some chaotic action at the boundary where the fuel is compressed.

Water in a diesel fuel system is simply a matter of friction and the first parts to suffer are injector nozzles with the IP usually surviving much longer as long as it gets lubrication B4 too long.

About 100 ml of suspect fuel (water or non spec fuel) is enough to destroy injector nozzles.

quote:

Originally posted by 666:
Water in a diesel fuel system is simply a matter of friction

666,
Could you provide something to support this?
It is so contrary to everything I have learned on this subject I can't believe it is accurrate.


I believe the rest of your stament to be correct but it seems you are saying that cavitation is not a factor in IP damage. Is this what you meant?

i would be careful of advice from the injector pump rebuilders. they control the information in that industry . they make it to be rocket science. until someone learns something, everything seems like rocket science, then its easy. all the pump rebuilders i have met say that biodiesel and wvo will destroy pumps and should never be used. sounds similar to the mechanics that told us that 10% ethanol in our gas will destroy a gas engine. we know it to be false, and we i know that my pump has run on wvo for 6 weeks now, saving me $300 so far. if a rebuild costs me $400 and 4 hours to remove and replace, then i have only a few more weeks to go and i'll break even. put everything in perspective and take it easy. perhaps i'll get a spare pump and switch it regularly, but until that happens i'll keep running along. i've seen more water in fuel station diesel than in a 5 gallon can of hot filled oil and no one seems concerned about that. filtres take out the droplets, is there really a concern about the water in suspension. most pumps ive seen that need rebuilding are caused by leaking seals, running on normal pump diesel. the vw dealer will not sell any internal parts in the pumps, futher making the pump rebuilding industry into the rocket science it wants to be billed as. keep driving.

Isn't the other way to do it dissolving the water in solution by using ethanol? Water in solution should cause none of these problems... being chemiccally bound in the mix, unless the vaccum created in the IP boils it out....

Water in the mix in fact adds to the power and efficiency of the in chamber burn? or so I've read here.

This is what I have been doing, adding 1 to 2% ethanol.... rather than expend energy heating the oil..

This makes much more sense to me as you say except for the energy expended to acquire to ethanol (possibly a little pricey)
However,more efficient overall because it will pick up and dissolve other impurities at least enough to carry them through the fuel filter media and create a more combustible mixture in the cylinders(lower flash point).

But woudl this prevent the suspended water from causing cavitation as it passed through the IP?

I agree that suspended water passing through an IP is more desirable than free water doing so. But only because the smaller the microd droplets the smaller the micro "explosions/implosions" which erode the IP internals. So while alcohols might disperse free water and therefor lessent teh chance of major cavitation episodes..would it lessen the efect of suspended water cavitation?


I have not been able to find any evidence that this is so. I would certainly like to since it would simplify on the road dewatering immensly. But until I DO find some verifiable evidence that supports this I will continue to advise that removeing suspended and free water before wvo is placed in a fuel tank is the safest procedure.

Dana you refer above to suspended water resulting from the addition of alcohol to wet veg oil. This is missing the point. The idea is to add sufficient alcohol to completely dissolve the suspended particles of water not to just make them smaller.

This question of cavitation is interesting. Perhaps the answer to whether adding alcohol will be beneficial can be deduced.

Here are some facts:

Many people use unwashed biodiesel which contains about 2 to 3% methanol and report no problems. Some people have experimented with 10% ethanol in veg oil and report no problems. Methanol and ethanol have lower boiling points than water and should cavitate more easily.

It appears therefore that something which is dissolved in oil at a modest concentration does not cause cavitation in the IP. If an alcohol is added to the veg oil, sufficient to cause the small amount of water present to dissolve, one would think the water would no longer be able to cause cavitation.

For this purpose dry isopropanol is more effective than ethanol as it is a better cosolvent and less is required.

Dana there is a difference between suspended water and dissolved water... suspended water would be in the form of microdroplets of probably millions or more of molecules in size. Remember how big Avagadro's damn number was?

A visible drop, which is all it takes to ruin an IP as i undestand it, contains billions of molecules of water.

By contrast, dissolved water has molecules of water distributed equally throughout the whole liquid associated with one or more ethnaol molecules which are able to associate with the oil molecules so well that they can take the water molecule along for the ride, so to speak. It may take a number of ethanol molecules to associate and dissolve a molecule of water; having to surround it and shield it from the oil.

Suspensions are usually visable, ie cloudy oil, but very fine microdrops in suspension might exist in WVO invisibly... I do not know. Solutions on the other hand are commonly as clear as the parent solvent but can take on the colour of the dissolved substance eg copper sulphate in water is blue.

In this case I believe a solution of ethanol and water in oil should show clear coloured oil the same as waterless WVO of the same type. Again an assumption on my part not properly tested.

Of course when you spoke of suspended water you may have meant dissolved water... I don't know and I hope I haven't baffled everybody with too much science...

But to further this thread we may need to distingush between suspended/free water, visble free water and dissolved invisable water...

Neutral's post was not on when I drafted this...

When I went through injector rebuild class in school, I do not recall every hearing about "cavitation" of water as a possible cause of damage in the injectors or highpressure side of the IP. Liquid water was discussed (along with dirt particles), because it allowed metal-to-metal contact between precision parts, leading to wear and galling. One cc of liquid water ingested into an IP will ruin it almost instantly.
Rotary IP's operate under pressure, once past the vane pump built into the first (low pressure) stage. Obviously common rail pumps won't have the problem, either. That leaves unit injectors (old Jimmy diesels), and in-line pumps without low pressure pumps (VW Rabbit?) to worry about. I don't believe that normal engine operating "shock waves" can cause cavitation in micro-droplets of water - that's a technology pretty close to what I do in my day job, and I'd expect to see a lot of broken hardware if it were the case. I don't, so that's why I think "cavitation" is more of an urban myth. I'm open to the argument though.
But back to the subject, water in fuel oil is always bad, unless in too small a quantity, and so dispersed, that it cannot interrupt the lubricating film between important moving parts. That's why dissolved water is less harmful than liquid droplets. Dana started this with a good description of the dangers and causes.
Cheers,
JohnO

This message has been edited. Last edited by: johno,

quote:

Dana there is a difference between suspended water and dissolved water... suspended water would be in the form of microdroplets of probably millions or more of molecules in size.

Thanks for clearing that up. I did not realize that alcohols could further disperse mocrodroplets of water into possibly harmless "solutions" of alcohol encased water molecues and wvo. I learn something new every day.

I've read that you're not supposed to ever use an alcohols in a diesel fuel system. You're supposed to let the water fall out in the water seperator. The alcohol interfers with that process. (or at least I've been told) So is the alcohol added as a "margin of safety"? Somewhere else I've read about using methyl hydroxide? (or something like that, I've got to go back and look) How true is this?

quote:

Originally posted by knkreb:
I've read that you're not supposed to ever use an alcohols in a diesel fuel system. You're supposed to let the water fall out in the water seperator. The alcohol interfers with that process. (or at least I've been told) So is the alcohol added as a "margin of safety"? Somewhere else I've read about using methyl hydroxide? (or something like that, I've got to go back and look) How true is this?

It sounds like, in this case, water separators do not work for SVO use because the water is not free, as it gets in diesel fuel. It seems to me using alcohol would be a measure of safety when using SVO. And what's wrong with a touch of alcohol in the SVO -- it's a common additive in many diesel fuel treatments. "Isoheet" for one, says it's safe for diesel engines, why not just use some of that mixed into your SVO?