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# Diesel and ASTM-D341 formula for viscosity3

## Diesel and ASTM-D341 formula for viscosity

(OP)
I need to quantify the change in viscosity in diesel fuel with temperature.How can I calculate the change in viscosity using ASTM-D341 formula when the only diesel fuel data I can find  is  a viscosity range (2.2- 5.3 cSt) at one one temperature (40 Degrees C).

ASTM-D341 requires two viscosities at two different temperatures. Does anyone know another viscosity for diesel fuel at a different temperature so I can use the formula?

Replies continue below

### RE: Diesel and ASTM-D341 formula for viscosity

You may try using the ASTM viscosity/temperature chart and draw parallels to a line connecting 3 cS at 40 deg C with 1.4 cS at 100 deg C. The result would be only approximate, because 2-D diesels differ in their chemical composition. Of course, the best approach would be to measure two viscosities (at two temps.) and proceed from there.

### RE: Diesel and ASTM-D341 formula for viscosity

Unfortunately, diesel viscosity isn't a fixed value hence the range.  I do have some reference material on viscosities of diesel at the office but ......, if you can wait till Monday, I'll dig them out and post some values for you.

Most (but not all) hydrocarbon log viscosity versus temperature curves have similar slopes.  If you can find another fluid's curve, you can plot the range of diesel's visc using your upper and lower limits at 40C.

### RE: Diesel and ASTM-D341 formula for viscosity

You can download a spread sheet for ASTM D341 viscosity Vs Temperature calculations from www.ViscoAnalyser.com or from www.cheresources.com (you need to go to the newsletter to find it).

Calculating the viscosity at the desired temperature from only one known viscosity is a common problem, especially in the marine fuel oil market where frequently the viscosity is only quoted at the reference temperature (usually 40degC for diesel and now 50degC for HFO in the new ISO 8217 std.) Consequently approximations are used that assume a typical VI. Most of the fuel oil blending programs (available free from most Marine Fuel Oil Suppliers e.g. ExxonMobil Marine Fuels, Shell Marine Fuels, DNV PS etc) use such approximations. You could approach these companies for a free program or download a similar program from www.steamesteem.com

In the spreadsheet referenced above, a number of curves have been pre-plotted for different fuels using data taken from CIMAC which gives the viscosity at the reference temperature and typical viscosities at a second temperature. You will notice that the "A" and "B" values are shown from the ASTM D341 equation. However, diesel itself isn't plotted and you still need to fnd at least one typical set of viscosity data at two different temperatures and load this curve.

A simple approach for your particular diesel is to enter the known viscosity at one temperature and to approximate the viscosity at a second temperature and then to change this as often as necessary until what seem appropriate values for "A" & "B" are found.

### RE: Diesel and ASTM-D341 formula for viscosity

Sorry for the delay on this, I forgot <blush>

Your viscosity range (2.2 to 5.3 cSt at 40C) pretty much brackets the 'standard diesel 32.5 API' curve I have in an old Chevron reference manual (rescued during an office clean-out ).

At 210F, the viscosity of my diesel is 1.3 cSt.  At 0 F, it's 28 cSt and is liner on a log visc versus temp plot.

I'd plot my diesel on a ASTM D341 curve and then plot your two visc ranges and draw parallel lines to mine curve, that will give you the range of viscosities you can expect at other temperatures.

There's several different hydrocarbon cuts/products on this page and they all pretty much have the same slope.  Not 100% but pretty close and the diesel cuts are all essentially the same slope.

### RE: Diesel and ASTM-D341 formula for viscosity

'my curve', not 'mine curve'.  Sigh

### RE: Diesel and ASTM-D341 formula for viscosity

PS a little web seacrhing reveals that "diesel" can have viscosities in the range upto 24cst at 40degC.

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