Viscosity index calculator7/28/2023 ![]() Continuous drip samplers tend to be biased toward a lower apparent viscosity because they generally tend to collect more sample at lower viscosity.Ī number of bunker suppliers we have spoken with report that calculations based on the assumed viscosity of the fuel in the storage tanks can vary significantly due to stratification. Continuous viscosity measurement online revealed a significant viscosity variaton during blending which suggested that the required standard of 180 +ocst -10cst was not easily met. The same applies to the three samples taken during bunkering (begining middle and end) which are averaged. Then too you are basing your calculations on samples. These can give good results but by the time you get them, it is often too late. If you are blending fuel and measuring viscosity at 50degC i presume you are using the Hoffler falling ball viscometer and a hydrometer method. The spreadsheet is set up using the CIMAC fuels data. As is known from the problems that were highlighted in Singapore a year or so back, this is not always reliable nor is the sample taken for independent analysis as reliable as it should be because of the vulnerability of this systme to operator "error". On barges it is usual to use Hoffler falling ball viscometers and hydrometers, if they do not have online continuous vioscosity measuremnt. Fuel is blended in the refineries at 90 to 130degC referenced to 100deg C and measured using process capillaries backed by laboratory capillaries (ASTM D445)In terminals and on barges the blend temperature is usually between 30 and 60degC with 50degC as the reference temperature, something CIMAC is apparently going to codify (see the CIMAC web site and fuels working groups pages). Using calculations has too many unpredictable assumptions which can lead to widely varying results. There are now a number of very affordable solutions for this. PPS: the best way to blend fuels is to measure the viscosity of the blend and use this for feedback control. Kinematic viscosities appear to be loglog dependent on temperatures. Where w i = weight fractions of the components.Ĭoming back to your question, measure the viscosity at another temperature, and then extrapolate or intrapolate as needed to get the value at 100 oC. Ln visc blend = summation of (w i x ln visc i) with a 5-10% precision, There are charts for low and high viscosity ranges. One can also use the ASTM Standard Charts for Liquid Petroleum Products (D341) that give kinematic viscosities vs temperatures. The BP chart is helpful in making blends on a weight basis. The BP chart, for example, enables converting among various viscosities such as Redwwod I, Saybolt Universal and Saybolt Furol, all of them measured in seconds, to degrees Engler or to kin. You probably heard of paraffinic (high VI) and naphthenic (low VI) lubes. The VI or V/T dependence varies with chemical structure of the hydrocarbons. This is needed since the VI (viscosity index) of the fuels isn't known. ![]() In order to be able to find viscosities of fuels at various temperatures one needs to know two viscosities at two different temperatures.īy using charts such as the BP viscosity/temperature chart or the Refutas chart one can find the wanted value at other temps. ![]() There are various charts in the market to help you out. ![]()
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