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AutoDiesel said:
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If a typical centrifuge won't spin out the dissolved H2O then your fuel filter and pump aren't going to seperate it either.
As to your 1000 ppm variation statement. Your arithmetic seems to suggest that the measurement variation is at least an order of magnitude greater then the spec. itself. Even ASTM isn't that sloppy. That's equivalent to saying my ideal weight is 200 pounds plus or minus a 1000 pounds. Meaningless!!
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ASTM is checking for only free water. Up to 500ppm.
Since soy biodiesel can have water soluability up to 1500 ppm. theoritically you could still have up to 1500ppm soluable water
even after checking for and/or removing free water. The de-emulsifiing agent used while doing the centrifuge test will take some of that out so that is why I was generous and subtracted the 500 ppm from the 1500ppm limit and came up with 1000ppm difference.
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The centrifuge test is for measuring free water. If it gives you a reading of 300 ppm of free water, and your total water level is 1800 ppm, THAT IS NOT AN ERROR. It is a completely correct reading, as it is measuring free water. The problem is if somebody thinks it's measuring total water - it isn't. There is a reason ASTM regulates free water, rather than total water. Wanna guess what that reason is? I've already said it a couple times (once recently, many times in old threads).
Free water is what causes corrosion, and increased engine wear - not dissolved water.
Measuring free water does not mean you have a large margin of error - it just means you're measuring free water, rather than total water. That's not an "error" - that's a choice in what you're measuring. Free water is measured because it is what poses a problem - not dissolved water (incidentally, emulsified water is technically "free" water, as it is not dissolved. Centrifuge tests include emulsified water in the measurement, since it separates in a centrifuge).
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But in fact test by centrifuge are very inconsistent and inaccurate and rarely will show anything over 200 - 300 ppm water. Remember, even if you have removed 300ppm from a 1500ppm sample you still have 1200ppm left soluable.
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It rarely shows anything over 200-300 ppm because it requires very bad water contamination to get anything over 200-300 ppm. As for your last statement - so?
Most labs actually do a Karl-Fischer titration to measure the amount of total water (of course, some then incorrectly compare that to the ASTM standard, comparing total water to free water spec). The highest I've ever seen on a biodiesel test by Karl-Fischer titration was around 700 ppm of total water - around half of the saturation level (so even with that high of a water level, it would still need another 800 ppm before water would separate).
Incidentally, are you aware that the new European standard (EN 14214) has the same water specification as ASTM D 6751 - 500 ppm of FREE water?
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http://www.ec.gc.ca/transport/publications/biodiesel/biodiesel4.htm
The ASTM standard D-975 allows up to 500 ppm water in D-2. As the solubility of water in D-2 is only about 50 to 60 ppm, any water above this limit will separate out at the bottom of the tank or stay suspended as an emulsion. The solubility of water in SME is approximately 1500 ppm, while in B20 blend of SME in D-2 it is about 40 to. 60 ppm. Thus blending a water saturated biodiesel with D-2 can result in the separation of water phase providing a potential site for microbial growth (Van Gerpen et al., 1997).
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The saturation level in a B20 blend is NOT 40 to 60 ppm. THe saturation level would be between the saturation levels of the individual components, although not based on a linear combination. So, there is an increased risk of water separation with blending (but not nearly as great as that paper claims) - that's one reason I advocate using B100. /images/graemlins/laugh.gif
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As for you statement that a injection pump won't separate water, not true. With the temperature of the fuel and the pressures generated by the pump, and the injectors for that matter, it can.
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The pump heats up the fuel. What does the saturation level due when temperature increases? It goes up. If there is no free water in the pump in the fuel lines, the added temperature from the injection pump is going to RAISE the saturation levels, so no water would separate.
Why is it that all the people here who have had their injection pumps dismantled and inspected after a long time of using biodiesel had incredibly clean pumps? (I think it was Wally, who had either his own pump or the pump of a friend (who was using the fuel Wally makes) disassembled for inspection by a pump rebuilder, and the pump rebuilder said it was the shiniest pump he's ever seen)