In choosing the lubricating oil for a gas turbine system, properties such as viscosity, viscosity index, corrosion prevention, and thermal stability are chosen to optimize turbine longevity and efficiency. Another property that needs to be considered is the oil’s reactivity, as the oil’s ability to resist combustion during turbine operation is highly desirable. Although loosely described by flammability limits, an oil’s reactivity needs to be well defined. Lubricating oils also differ widely in their composition due to differing additives such as anti-oxidants, detergents, and rust inhibitors. These additives not only change the base oil composition but also affect the oil’s reactivity. As manufacturers are reluctant to advertise the relative amounts of additives and overall composition of their product, predicting an oil’s reactivity based on its chemical composition is not possible. In evaluating a method to define reactivity, the extremely low vapor pressure of these oils makes conventional vaporization by heating impractical due to the high temperatures and fuel cracking as well as issues with preferential vaporization. Due to these issues, another method to evaluate reactivity of lubricating oils is required.

To this end, a new experiment has been design and tested to evaluate the reactivity of lubricating oils using an existing shock tube facility at Texas A&M University equipped with an automotive fuel injector. This experiment disperses a pre-measured amount of oil into a region of high-temperature air to study auto-ignition. To ensure proper dispersal, a laser extinction diagnostic is used to measure the oil particles behind the reflected shock as they are dispersed and vaporized. A sidewall CH\* chemiluminescence diagnostic measuring light emitted during combustion at around 431.5 nm is used to determine ignition delay time. Pressure is also measured at the sidewall and endwall positions for test repeatability and exothermicity of the experiments. The experiment has been validated by conducting experiments with ethanol and comparing the results to previous heated shock-tube experiments conducted in the same facility. Using this method, various 32 and 46 weight oils identified as widely used in the gas turbine industry from Shell, Chevron, and Mobil were tested. A detailed comparison of the results from this investigation as well as a discussion of the implications thereof will be presented in the paper.


Auto-Ignition of Gas Turbine Lubricating Oils in a Shock Tube Using Spray Injection

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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