Method for determining residual fuel and insolubles contamination in used marine engine lubricants using UV-visible spectroscopy and chemometrics

#The present invention relates to a method for determining residual fuel and insolubles contamination in used diesel engine lubricants using UV-visible spectroscopy and chemometrics.

#In recent years, diesel engines have been progressively replacing steam turbines in marine vessels, mainly as a result of the improved economics of the marine diesel. Marine diesel engines may generally be classified as slow-speed, medium-speed or high-speed engines, with the slow-speed variety being used for major, deep draft vessels. Slow-speed diesel engines are typically direct coupled, direct reversing, engines operating in the range of 90 to 250 rpm and usually run on residual fuels. These engines are of crosshead construction with a diaphragm and stuffing boxes separating the power cylinders from the crankcase to prevent combustion products from entering the crankcase and mixing with the crankcase oil. Medium-speed engines typically operate in the range of 250 to 1100 rpm and may operate on the four-stroke or two-stroke cycle. These engines are trunk piston design, and many operate on residual fuel as well. They may also operate on distillate fuel containing little or no residua. On deep-sea vessel these engines may be used for propulsion, ancillary applications or both. High-speed diesel engines are comparable to automotive trunk piston diesel engines and are normally employed in deep draft vessels only for special, ancillary applications. These engines generally require high quality distillate fuel oil for satisfactory operation.

#In low-speed marine crosshead diesel engines, the cylinders and crankcase are lubricated separately, with cylinder lubrication being provided on a once-through basis by means of injection devices that apply cylinder oil to lubricators positioned around the cylinder liner. The crankcase oil provides lubrication for the bearings, gearing, valve gear and other ancillary engine components and is typically an additive-type oil selected for good oxidation and thermal stability, water demulsability, corrosion protection and good antifoam performance. Alkaline additives may also be present to neutralize any strong acids entering the crankcase through piston rod glands and detergency and extreme pressure (EP) performance may also be provided by the use of suitable additives. Similar performance characteristics are appropriate for the crankcase oils in residual fuel burning, medium-speed trunk piston engines in which the crankcase oil may also be used, in certain types, for splash cylinder lubrication. Other types of medium speed engines may have separate force feed cylinder lubrication. In either case, oil that lubricates the cylinder drains into the sump.

#FIG. 1 shows the correlation of results obtained from the ultraviolet-visible spectroscopy method of the present invention to the Residual Fuel Detection (RFD) method of U.S. Pat. No. 5,169,785.

#FIG. 2 shows a comparison of results obtained for conventional base stock lubricants to that obtained for hydroprocessed base stock lubricants.

#FIG. 3 shows the correlation of results obtained from the ultraviolet-visible spectroscopy method of the present invention to ASTM D-893 for pentane insolubles.

#The content of unburned residual fuel and insolubles in used marine oils is estimated according to the present invention by ultraviolet-visible (UV-Vis) spectroscopy and chemometrics. When seeking to estimate residual fuel contaminants, a portion of the UV spectrum that is sensitive to aromatics is monitored, since the core of asphaltenes is rich with aromatic rings. The result is given as percent fuel contaminants or its equivalent based on the aromatic fuel components measured. It is important to note that knowledge of fuel characteristics is not necessary.

#The UV-Vis method of the present invention may also be used to estimate various types of insolubles, which are very important to engine builders in their diagnostic efforts. One chemometric model was developed for each insolubles type. The types include pentane insolubles, toluene insolubles, Soot Index and TGA soot. This new method estimates with reasonable accuracy all of these used oil properties from a single UV-Visible spectrum, which requires only a few minutes to acquire. This is in contrast to the time and labor-intensive ASTM test methods to which some of these correlate.

#The UV-Vis method of the present invention has been found to complement the RFD method of U.S. Pat. No. 5,169,785, described above, when seeking to estimate residual fuel contamination in used marine lubricating oil samples. U.S. Pat. No. 5,169,785 is hereby incorporated by reference for all that it discloses. Whereas the RFD method measures the quantity of vanadium in the form of vanadyl porphyrins, UV-Vis spectroscopy detects the aromatic character of the oil sample. From this information, the weight percent of unburned residual fuel contaminants is estimated. In essence, the two methods use two different “markers” of residual fuel. While both methods can be automated, a key advantage of the UV-Vis method is that it measures the amount of undesirable unburned fuel contaminants directly. A second advantage is that it can also estimate insolubles (pentane and/or heptane), without doing a time-consuming extraction, as well as estimate soot levels.