BYDAVIDDOYLE- CTC ANALYTICALSERVICES
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Color Inexpensive Relatively ineffective.
Blotter Inexpensive Semi-quantitative - Test results can be subjective. Hard to distinguish soot levels above 4 percent. Also indicates dispersancy performances left in an oil.
Blotter/Lantos Solvent Extraction Inexpensive Semi-quantitative - Test results can be subjective. Also indicates dispersancy performances left in an oil.
Blotter Photometer High Equipment Cost Semi-quantitative - Effective up to 4 percent with higher precision. Also indicates dispersancy performances left in an oil.
Blotter/Reflectance Meter Moderate Equipment Cost Semi-quantitative - Effective up to 4 percent with less subjectivity than visual blotter.
Infracal Infrared Soot Meter Relatively Expensive Quantitative - Very accurate up to 12 percent. Easy to use.
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Insolubles, Pentane/Toluene Relatively Expensive Quantitatively accurate - Test results included all insoluble material, not just soot.
FTIR (Infrared) Inexpensive Quantitatively accurate - Susceptible to instrument interferences.
Soot Meter Inexpensive Quantitatively accurate - Very reliable and accurate up to 12 percent.
Total Gravimetric Analysis Expensive Highly accurate - Most definitive method, accurate at any concentration.
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More attention is being paid to soot levels in used diesel engine oil over the past few years due to changes in engine designs to meet exhaust emission standards, which have led to increased soot formation during combustion. Soot levels are expected to continue to increase in diesel engines made after October 2002 with the introduction of cooled EGR systems in engine design.
drain interval, contaminants such as water, fuel coolant, or excessive soot buildup.
The biggest drawbacks to using the blotter test as a field test screening method is that soot values above 4 percent are really not distinguishable. Therefore, the test is not effective above this concentration of soot in the oil. Also, interpretation of the test results can be subjective between individuals performing the test.
Consistency in application of the method can also be a factor in test result interpretation.
As stated previously, there are variations on the blotter method.
Some variations are concerned primarily with sample size, heating, drying time and choice of blotter paper. These are all variations on a basically manual, low cost application. With these types of variations, consistency to applying the method is the key. Anyone using the blotter test to screen for soot level in their engine oils should retain the blotter samples in a binder logged with all relevant information, such as date, time on the oil, engine information, and any laboratory information on the same sample which would include soot but should also include information regarding contaminants such as water, fuel and glycol.
More technical variations on the blotter test that can still be applied to the field may include the investment in some basic equipment. A more technical application can give a higher level of precision for the test results, but with additional expense in material or equipment.
An enhancement to the basic blotter test is referred to as the Lantos Method and is outlined in the July-August 2002 issue of Practicing Oil Analysis magazine. The method uses chromatography grade blotter paper that is cut into rectangular strips. A sample of homogenized used engine oil is deposited 20 mm from the end of the test strip and allowed to dry at room temperature (Figures 3 and 4). After drying, the clean 20 mm portion of the blotter test strip is bent at a right angle and placed on a support rack.
The rack containing the strip is then placed in a tray containing solvent so that the test strip is supported above the solvent with the bent right angle portion of the strip submerged in the solvent. Two solvents are alternately used which are heptane and toluene. This is a variation on a laboratory method that uses solvent extraction to monitor oil degradation material and contaminants. The test strip soaks up the solvent and soluble material in the oil is extracted from the oil spot and spreads across the remaining portion of the test strip. Solvent extraction by the heptane and then toluene can be performed on the same test strip or on two separate test strips. The insoluble material left behind after heptane and toluene extraction will contain free carbon and indicate general levels of soot in the oil.
This method will also indicate oxidation and resinous material due to oil degradation by displaying products that are insoluble in heptane but soluble in toluene. Interpretation of test results can be subjective and consistency in application of the method is important. Finished blotter test strips can be logged with previous test strips for interpretation along with pertinent sample information. The Lantos Method using solvent extracted blotter can be an effective FFiigguurree 11
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screening tool for soot that is complemented with actual laboratory analysis.
Another enhancement to the blotter test is to incorporate the use of a photometer to measure light absorption of the blotter spot. The photometer can measure the intensity of the light absorbed by the oil spot and correlate the measurement to soot concentration. This application is detailed in the September-October 2002 issue of Practicing Oil Analysis magazine. This method references the heating of an oil sample to 240°C for five minutes in order to stress any oil with a marginal service life. After the sample cools 2 mls of oil are dropped onto blotter paper and allowed to wick in an oven at 80°C for an hour. The Practicing Oil Analysis article references the use of a VPH 5G CCD Photometer by ISL, which can optically measure the light absorbance of the insoluble material on the blotter spot. Test results can then determine dipersancy performance and general soot levels as well as lubricant degradation in a used oil sample. The use of a photometer to determine soot measurement with the oil blotter eliminates individual subjectivity in the test result interpretation. This method is still limited to soot levels only up 4 percent but is an effective screening tool, which allows for higher precision. ISL supplies the VHP 5G photometer at a cost of around $24,000 from Petroleum Analyzer Co.
The cost of the VPH 5G photometer may not be practical for field analysis when compared to the cost of a standard laboratory analysis, but a simple reflectance meter could still be incorporated into the theory of the photometer in order to screen field samples for relative soot levels at a much lower cost. Basically, the percent light reflectance of a blotter sample that is registered by the meter correlates in the same manner as the light absorbed by the photometer. The information obtained in this manner would be much less detailed than with the VPH 5G but would still allow the operator to make a more consistent and less subjective evaluation of the blotter test for soot screening.
As previously mentioned, logging and retaining blotter tests, along with relevant information, will greatly enhance the interpretation of the results for soot levels. This would also include any laboratory test results available on the same oil sample.
A more precise and convenient field method that is different from the variations on the blotter method for soot determination, but also more expensive, uses a portable Infracal soot meter. The soot meter is based on infrared technology and can accurately determine soot levels in used engine oil up to 12 percent. This field instrumentation correlates well to laboratory soot determinations and is easy to use. The instrument uses some simple calibration and quality assurance techniques and the actual analysis takes less than a minute. As with the blotter methods, having a homogeneous sample is important. Test results are displayed on an LED readout. The instrument can also incorporate a remote plug for doing soot determination via the lubrication system using a sensor installed in an engine. The portable Infracal soot meter for field application cost between $1,000 and $1,500 and can be obtained through Wilkes Enterprises or Koehler Instrument Co.
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LLaannttooss MMeetthhoodd -- BBllootttteerr TTeesstt Toluene Insolubles
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3.0 % Soot 5.0 % Soot 7.0 % Soot