I tried reading through the sticky and searching but came up empty. Sorry if this has been asked before.
The way I understand it, the diglycerides and trigylcerides are not soluable in methanol which is why they precipitate out in the 3/27 test.
So my question is, can't you just keep adding methanol? Isn't 27ml just a lower limit?
You should be able to just keep adding more and more methanol and any diglycerides/triglycerides will remain insoluble right?
The test is one part biodiesel to nine parts methanol. The original test had more than 27ml.
There was some earlier discussion about using different ratios like 2:9 or 1:5 as an attempt to make the test more sensitive. ie, it passed 3/27 so I tried 6/27 and it still passed. I was never convinced that was a valid application.
The way I like to make it more sensitive is to increase the test volumes from 3:27 to 50:450.
Another reference is this article from the original CBT.
Thank you for the information.
I was thinking an interesting variation of the test would be to keep adding biodiesel until you ended up with a precipitate. In other words, saturate the methanol solution. Then figure out the ratio based on how much biodiesel you added to the methanol.
But I'm not sure that would tell you anything. If you were underconverted, you would have precipitate as soon as you hit the 1/9 ratio. Adding more bio would only increase the precipitate.
Like you are saying, the increase in sensitivity comes with the total amount of biodiesel tested. The methanol is just along for the ride. The increase in sensitivity is not because your test is more accurately approaching the 1/9 ratio. The increase in sensitivity is solely due to the increase in the amount of bio tested and therefore the ease with which you can detect a small precipitate.
I like using the 3/27 ratio but add a twist on temperature, chill the test in a fridge for 15-20 minutes then check. Look for any white fallout, little cloudy is ok. Was told this trick by someone who tests fuel every day. The stock 3/27 ratio and 68F temp is good for home brew but might not equal an ASTM passing grade.
3 samples I've sent to a lab after using this variant all passed...
Altering concentrations shouldn't affect anything. It is either soluble or insoluble. Non-converted oils don't precipitate, they just don't dissolve. Increasing biodiesel to methanol ratio would make non-converted oils more visible.
If you have access to a centrifuge a light spin will tell you pretty quick if you have conversion.
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