Improper combustion, cylinders off-balance, blowby, dispersancy of lubricant and other important parameters can be detected economically at an early stage using a variation of the classical blotter test with simple and inexpensive equipment.
This simple, semiquantitative, low-cost test was devised to provide information on the state and operating condition of internal combustion engines, as well as on the performance of the lubricant by combining the principle of method ASTM D893 “Insolubles in Used Lubricating Oils” with selective solvent extraction applied to a used oil spot deposited on a paper strip (chromatographic separation). Low-skilled personnel can perform multiple tests simultaneously, and technicians can easily create a permanent record of results, in an engine photo album to monitor and verify its status throughout its lifetime.
For this new approach to an old procedure, laboratory facilities are not required - tests can be carried out onboard or in the repair shop. However, there are safety hazards involved with handling gasoline or petroleum spirits and no open flames can be present during testing.
Easy to Use
The steps to perform this procedure are fairly easy. The reproducibility of the test results depends upon the quality of the solvents and the filter paper. The number of samples that can be tested simultaneously is practically unlimited and should be adjusted to requirements of the test parameters. Test results are normally available within 24 hours. This test contributes to cleaner engines, reduction of wear and downtime, less fuel consumption, longer lubricant life and less pollution. Anomalies are detected at an early stage.
Procedure
First, collect the necessary equipment and materials (see sidebar). Then, for each chromatogram (or strip of filter paper on which a drop of used oil is deposited and processed), perform the following procedures:
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Deposit 10 ml of thoroughly homogenized used crankcase oil approximately 20 mm from one of the extremes of a filter paper strip (Figure 1) and dry the strip at room temperature.
- After drying, bend the strips of filter paper at right angle just above the dried spot (Figure 1).
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Position strips that are simultaneously eluted on the stainless steel grid inside the photographic tray (Figure 2), making sure that the bent tip is pointing downward (Figure 3).
Figure 3. Place Chromotograms in a Steel Rack in a Photogragphic Tray and Fill with n-heptane Until Level Where Solvent Touches Paper
- Cover the bottom of the tray with n-heptane to a level where the solvent reaches the bent tips of the paper strips without moistening the grid, and cover the tray with the glass plate.
- Permit the solvent to rise by capillarity until it has reached the end of each strip, then remove the strip from the tray and allow them to dry at room temperature. At this point, n-heptane solubles covering an ample zone at the farthest edge of each strip may be visually observed.
- Recover remnant n-heptane in the tray for future use and replace it with toluene; or alternatively, a second tray may be used for elution with toluene.
- Place the strips, previously extracted with n-heptane, into the tray containing toluene solvent for elution.
- Remove the strips from the toluene before the solvent reaches the previously extracted n-heptane solubles. The strips must be continuously monitored during this stage - it is mandatory that the toluene not reach the previously extracted n-heptane solubles.
- Extract the strips from the toluene-containing tray and dry them at room temperature.
- Repeat the toluene elution process to assure total extraction of toluene solubles.
- Recover the remnant toluene for future use.
- Inspect the strip for diagnosis and recommended actions.
- Maintain a record of the strips for trending and analysis purposes.
Inspecting the Strip
Three distinct zones can be observed on each chromatogram (Figure 4):
- Circular zone where the original oil drop was deposited (free carbon);
- Line across the strip halfway between extremes of said strip (insoluble resins and/or oxidized matter);
- Farthest end of the strip corresponding to n-heptane solubles (unaltered oil).
Inspect the strip to observe the following:
Free Carbon
Free carbon is the portion of the used oil that cannot be eluted either with n-heptane or with toluene. Its components are carbonized lube oil and lubricant additives, incompletely burned fuel, small wear particles and insoluble external contaminants (dust, silica crystals, cat fines, etc.). Evaluation of free carbon is based on intensity, shape and position on different zones of the paper strip. It reflects mode of combustion, injection timing, diesel knock, dispersancy of the lubricant, etc.
Cylinders with identical modes of combustion produce identical carbon patterns. Carbon patterns for cylinders off-balance differ significantly from aforementioned patterns. Factors that influence the pattern of free carbon are:
- Fuel quality,
- Fuel conditioning,
- Brands and types of engines,
- Operating conditions,
- Mechanical condition of the motor and of injection system,
- Service hours since last overhaul,
- Quality of maintenance work,
- Lubricant brand,
- Service hours of lubricant,
- Amount of lubricant supplemented,
- Operating conditions and/or
- Specific fuel and lube oil consumption.
It is suggested that a pattern be established for each engine considered normal. When an improvement is observed, the reason for the improvement should be investigated. Reasons for the improvement may include: injector overhaul, valve repair, major repair, oil replacement and fuel filter replacement. The new, improved pattern should replace the former standard. Wherever possible, patterns from two identical engines, operating under similar conditions should be compared and the better pattern should be approved as standard.
Insoluble Resins or Oxidized Matter
Matter insoluble in n-heptane, soluble in toluene is the portion of the used oil, which can be extracted from the remaining spot with the solvent toluene, after elution with n-heptane. Insoluble resins or oxidized matter consist mainly of oxidized and polymerized hydrocarbons, resulting from oxidation of the lubricant, exposure of the oil to high temperature, contamination with combustion products and/or combination of these factors. They are usually the result of worn, stuck or broken piston rings, worn liners and blowby.
The insoluble resins are chemically unstable and tend to increase in molecular weight when exposed to hot surfaces such as piston skirts, underside of piston crowns, valve stems and guides, etc., causing gums and lacquer deposits on these surfaces. Due to their insulating and adhering nature, the gums can cause piston rings and valves to stick, combustion chambers to loose hermeticity, poor heat dissipation during operation and thermal fatigue.
The intensity and color of the lines is indicative of the mechanical state of liners and/or piston rings, stuck piston rings as well as the presence of lacquer deposits on piston skirts and piston crown undersides. Service hours, specific lube oil consumption and type of fuel (distillate, residual, gas, dual fuel) must be considered when interpreting results.
Unmodified Oil
Most of the n-heptane solubles consist of the components of the original oil, which have suffered insignificant, or no chemical modification due to heat, contamination or exposure to combustion gases.
The traditional blotter spot method is a powerful technique in and of itself. However, when combined with solvent extraction per the Lantos method, its usefulness is increased many times. If the desire to assure engine reliability and make smart maintenance decisions isn’t enough motivation, tightening emissions laws, and their anticipated affect on engine lubricant health should make you want to look carefully at the Lantos method for solvent extracted blotter spot analysis. With proper care in handling solvents, this method can be used onsite to provide quick, reliable results.
Equipment
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Photographic tray
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Size depending on number of tests to be carried out simultaneously
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Surface required per chromatogram: approximately 120 x 30 mm
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Glass plate cover for above tray
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Stainless steel grid consisting of parallel rods
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Diameter of rods: approximately 1 mm
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Distance between rods: approximately 20 mm
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Supported to remain parallel to the bottom of the tray approximately 10 mm from the bottom
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Sized to fit inside the tray
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Microdispenser
Materials and Reagents
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Filter paper strips: Dimensions 100 mm x 20 mm
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Whatman Nº 1 and Nº 2, or equivalent
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n-heptane - analytical grade
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Toluene - analytical grade
