Abnormalities observed during the determination of the cold filter point of diesel after adding antifreeze agents

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This post was last edited by chicanpk on 2017-11-15 at 10:47. SH/T 0248-2006, \"Method for Determining the Cold Filter Plugging Point of Diesel and Domestic Heating Oil\", defines the cold filter plugging point as the highest temperature reached when the sample is cooled under specified conditions; at this temperature, the sample cannot flow through the filter, or it takes more than 60 seconds for 20 ml of the sample to flow through the filter, or the sample cannot completely flow back into the test cup. This value is expressed in \"°C\" as an integer multiple of 1°C. In one of these cases, the sample cannot flow back completely into the test cup. I have never understood why this happens – if it can go up, why can’t it flow back? However, since this situation is hardly ever encountered, no effort was made to analyze its reasons. Recently, cold filter point tests were conducted on various diesel fuels and different antifreeze additives, and it was observed that the samples did not flow back completely into the test cup. I would like to ask everyone for insights into the reasons behind this phenomenon. Below are some of the specific data from our tests. We selected 4 types of National V 0# diesel, purchased from Sinopec as well as 3 private gas stations. Among them, Sinopec and 2 private gas stations have a cold filter plugging point of -6°C for their diesel, while another private gas station has a cold filter plugging point of -1°C for its diesel; we denote this diesel as A. The blank cold filter plugging point for all diesel fuels was normal, with the time taken for 20 ml of the sample to pass through the filter being greater than 60 seconds. We selected various antifreeze agents (diesel low-temperature flow improvers) and conducted experimental analyses at the same proportions; it was found that the cold filter point of the diesel decreased significantly after adding these agents, with the reduction amount being around 10°C or even more. In the case of diesel sample A, when determining the cold filter plugging point, after adding all the antifreeze agents, the phenomenon occurred in which the sample could not flow back completely into the test cup (at this point, it took about 12 seconds for 20 ml of the sample to pass through the filter). Moreover, this phenomenon occurred at the same temperature range, namely from -1°C to -11°C. Our analysis should be related to the properties of that oil sample. Later, during the testing process, the tester conducted another measurement once the cold filtration point was reached, that is, when the sample could no longer flow back completely into the test cup. It was found that the sample could pass through the filter, and after filtration stopped, it could still flow back into the test cup smoothly; it was not until -15°C that the phenomenon occurred where it took more than 60 seconds for 20 ml of the sample to pass through the filter. However, in accordance with the standard specifications, we still determine its cold filter point to be -11°C. Since I had never encountered this phenomenon before, I wasn’t sure what to do. Could any teacher provide an analysis and explanation for this situation? Is it a normal phenomenon? Thank you!