Fuel Oil Testing http://www.marinediesels.co.uk/members/Fuel_Oil/testing.
htm
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Fuel Oil
Fuel Oil Testing
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Stability and Compatibility
Before taking on bunkers it is advisable to take a sample from the suppliers tanks and test it for stability and compatibility.
If the fuel is unstable it is likely to stratify in the tanks and form asphaltenic sludges. If it is incompatible, then although it
may be stable on its own, when mixed with existing bunkers in the ships tanks, it may form sludges. This is why fuel
should be bunkered into empty tanks whenever possible.
A small sample of the fuel is heated to 50C to encourage instability. A sample
of the preheated mixture is placed on chromatographic paper and dried in a
small oven. The resultant spot is compared against reference samples. In the
case of a test for compatibility the two fuels are mixed in the same proportions
as would be found in the bunker tanks and the procedure repeated.
Water
The water test for fuel oil is similar to that for lubricating oil. A sample of the
fuel (5ml) is diluted with kerosene or toluene (20ml) and placed in the test
container. A satchet of a metal hydride is opened and placed upright in the
container without allowing the chemical to come in contact with the diluted
fuel. A lid containing a pressure gauge is screwed on carefully and the
container inverted and shaken for 2 minutes. The water in the fuel reacts with
the metal hydride producing hydrogen. The pressure in the container is
proportional to the water content and can be read from the scale.
If water is present then a further test should be made for salt water content.
This involves separating the water from the oil and testing for the presence of
sodium chloride using a go/no go indicator.
The latest equipment has a pressure transducer fitted in the base of the
container. After shaking, the container is placed on the test station module and
the water content read off a digital display. ( http://www.kittiwake.com )
Density
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Fuel Oil Testing http://www.marinediesels.co.uk/members/Fuel_Oil/testing.htm
A sample of the fuel is heated to 50C and a
hydrometer lowered into the oil. When a steady
condition has been reached, a reading is taken where
the meniscus touches the hydrometer stem and the
density corrected to that at 15C in vacuo.
Viscosity
Although the laboratory test for viscosity of fuel involves timing a quantity of fuel passing through an orifice, the on
board testing of viscosity usually involves rolling a ball down a tilted or inverted tube, which contains a sample of the
fuel. Improved accuracy is obtained by heating the sample (50C). The time the ball takes to roll down the tube is
measured and the result read directly from the instrument or from a conversion chart.
Calculated Carbon Aromacity Index (CCAI)
This is calculated from an empirical formula using the density and viscosity. Modern sophisticated test kit computers will
carry out the calculation for you. However the calculation is not difficult and can be carried out using a calculator with a
logarithmic function. The value, which should lie between the limits of 800 and 870 give a guide to the burnability of the
fuel and its ignition characteristics. The higher the number, the longer the ignition delay, and the hotter it will burn. This
number is used as a guide to setting the fuel quality lever on the fuel pumps.
The formula is CCAI = (density in kg/m3 @ 15C) - 81 - 141log[log(viscosity in cSt @ 50C + 0.85)]
For example: We have bunkered a fuel and measured its density at 15C as 989.9kg/m3, and its kinematic viscosity as
300cSt at 50C.
CCAI = 989.9 - 81 - 141log[log(300 + 0.85)]
= 908.9 - 141log[2.47835]
= 908.9 - (141 0.39416)
= 908.9 - 55.6
= 853.4
Pour Point
If required, an on board estimation of the fuel's pour
point can be made. It is not necessary to purchase
special equipment for this purpose. The following on
board method indicates if the fuel has a high or low pour
point.
A sample of 200ml of fuel oil is placed in beaker of 250ml and heated by immersing the beaker in a water bath of boiling
water. It may be necessary to hold the fuel oil beaker in the water while the fuel is heated to about 50C. The beaker is
then placed in a refrigerator and the temperature noted by means of either a digital or stem thermometer. At increments of
3C the beaker should be removed from the refrigerator and the contents tilted to see if they flow. This should be repeated
until no flow is observed.
Particulates
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Fuel Oil Testing http://www.marinediesels.co.uk/members/Fuel_Oil/testing.htm
A steel plate has a very shallow groove machined
into it which tapers in depth between 10 and 100
microns. A spot of fuel is placed at the top of the
plate and is then scraped down the length of the
plate in a single sweep with the supplied straight
edge. The particles can then be seen lying at the
position relative to their size on the plate.
Alternatively a spot of fuel is placed between two
clear perspex plates and rubbed together for
about 10 seconds. The amount the plates are
scratched is indicative of the abrasive solids
present.
Closed Flash Point
In the Pensky Martens apparatus approximately 75ml of sample is heated at
a slow constant rate with continual stirring. A small flame is then directed
through an opening at regular intervals with simultaneous interruption of the
stirring. The flash point is the lowest temperature at which application of the
test flame causes the vapour above the test portion to ignite. Alternatively an
automatic go/no go flash point tester can be used. Minimum flash point is
60C
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