Hospitals, treatment plants and other similar facilities have vital assets that require uninterrupted power. Engine generators, also known as gen sets, integrate an engine and an electrical generator to provide electrical power where standard utility power is unstable or unavailable. Utilized for temporary power demands, gen sets are normally mounted on transportable skids or trailers (Figure 1).
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Figure 1. Typical Generator engine enclosure located adjacent to a customer site.
This article describes the problems and solutions available to owners who have incurred the operating costs of time-based oil changes in their respective gen sets.
Oil Change
Engine oils should be changed regularly so that their intended functions continue within the engine. Oil in Rotating Internal Combustion Engines (RICE) becomes gradually contaminated, and the degree of contamination can differ based on duty cycle, load factor, environment, age and the types of fuels used. It is critical to determine the type of contaminant in the oil so that immediate action can be taken to rectify the problem.
Routine Maintenance and Oil Condition
In routine maintenance of large engine generators, the main operating costs are material and labor expenditures related to changing the oil based on specific time intervals. Oil changes can be performed depending on operating hour intervals, irrespective of the fact that the generator was relatively idle or running at full load. So far, this task was non-negotiable, particularly when the gen set is still under the warranty period.
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Figure 2. Oil is contaminated by a number of contaminants from the combustion chamber.
The major oil contaminants include fuel, combustion by-products, acids, varnish, sludge, water, soot and coolants. Figure 2 shows how oil is contaminated by various contaminants from the combustion chamber.
Engine owners face a number of issues with scheduled oil changes. First and foremost, not all generators operate at the same load amount. As a result, an oil change may not be required for certain generators at the scheduled change interval. Unnecessary oil change not only increases the operating costs but also leads to unwarranted waste of labor and material.
Also, ongoing contamination issues cannot be solved with scheduled oil changes. Contamination of the lubricant can damage the engine, which may continue and increase over a period of time. Significant failures can also occur and lead to repair and downtime.
Oil Analysis
To overcome these issues, gen set service providers and owners carry out onsite or offsite oil analysis in order to ascertain both the lubricant and the condition of the equipment. This way, it is easier to determine whether oil change can be extended or revamped.
In fact, the benefits of condition-based oil changes have been acknowledged by the US EPA, who recently revised its regulations for stationary generators in backup/emergency mode to enable extended oil changes, in case condemnation limits are not surpassed (Table 1).
Table 1. US EPA NESHAP ZZZZ rule Amendment (Oct 2013) Condemnation limits for in-service oil
| PARAMETER |
CONDEMNING LIMITS |
| Total Base Number (CI RICE only) |
<30% of the TBN of the oil when new |
| Total Acid Number (SI RICE only) |
Increases by more than 3.0 mg of potassium hydroxide per gram from TAN of the oil when new |
| Viscosity |
Changed by more than 20% from the viscosity of the oil when new |
| % Water Content by Volume |
>0.5 |
Time-based oil changes can create waste due to pointless oil changes, while condition-based oil changes can be both practical and affordable. However, the latter practice is not very popular which can be attributed to two major reasons: investment in a dedicated lab is not always viable and prior technologies for onsite oil analysis are not adequate.
Therefore, in order to establish an effective condition based oil change practice, the tools employed to monitor oil conditions must be fast, portable, comprehensive, easy to use, and cost effective.
Oil Condition Monitoring Tools
The range of Spectro Scientific oil condition monitoring tools include a temperature-controlled kinematic viscometer, an infrared spectrometer and a portable fuel dilution meter. These tools present a complete set of in-service oil conditions including water contamination, fuel contamination, oil degradation, coolant contamination and viscosity.
All three tools are powered by battery and collectively utilize less than 1ml of oil. Table 2 shows the list of in-service oil parameters, which can be determined by means of the combination kits.
Table 2. Critical engine oil parameters
| GENERATOR ENGINE TYPE |
LUBRICANT PARAMETERS |
Diesel,
Gasoline,
Bio-diesel,
Propane,
Bio-gas,
Natural Gas |
Oxidation,
Nitration,
Sulfation,
Anti-wear additive,
TBN,
Water,
Glycol contamination,
Soot,
Fuel dilution,
Viscosity |
FluidScan
The FluidScan Q1000 (Figure 3) is a portable infrared spectrometer that is capable of measuring oil absorbance spectrum in the mid IR range, from 2.5mm to 12mm. This instrument has a patented flip top cell, which uses three drops of oil and takes only a minute to test.
Also, no solvents or chemicals are required to clean the cell. The FluidScan is extensively used in power generation plants, in laboratories as a titration alternative, in marine vessels, in fleet management for mining trucks and in industrial plants.
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Figure 3. FluidScan Q1000.
Portable Kinematic Viscometer
The Q3050 kinematic viscometer (Figure 4) is a portable, battery powered instrument specifically designed to measure the viscosity of oil at a controlled temperature of 40°C. Based on a preset viscosity index of a specified oil, the tool can extrapolate viscosity at 100°C.
Similar to the FluidScan, the split cell utilizes two drops of oil and takes 2 minutes to test. The result is 3% precision, which is sufficient to make informed decisions. The Q3050 is widely used in mining truck and marine vessel applications.
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Figure 4. Q3050 portable kinematic viscometer.
The Q6000 fuel dilution meter (Figure 5) uses the same Surface Acoustic Wave (SAW) sensing technique as the predecessor model, Q600, but is more compact and operated by battery. Measurements are based on a calibrated response of a SAW sensor to a fuel vapor in the sample bottle headspace, which is relative to the fuel content present in the engine oil sample.
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Figure 5. Q6000 fuel dilution meter.
Conclusion
Significant breakthroughs in oil analysis technologies have made oil condition monitoring tools easily available to maintenance professionals. A condition-based oil change practice can be easily implemented across numerous industries as it improves the reliability of the machine and also reduces operating and maintenance costs by eliminating disastrous failures. The fluid condition monitoring tools from Spectro Scientific make it possible to realize these cost benefits.
This information has been sourced, reviewed and adapted from materials provided by AMETEK Spectro Scientific.
For more information on this source, please visit AMETEK Spectro Scientific.