60319 - Combustion and Oxidation of Lube Oils at Gas Turbine Conditions: Experimental Methods 

Because of the high temperatures involved, undesirable ignition events can happen during gas turbine operation, often necessitating expensive down time and repairs. The ignition events are often linked to the lubricant, a flammable mixture of large hydrocarbons with a very low vapor pressure. To understand better the fundamental role of the lubricant in such ignition events, increased understanding of the fundamental thermal and oxidation characteristics of such oils is needed. To this end, a suite of different tests has been set up and demonstrated at the TEES Turbomachinery Laboratory at Texas A&M University to study various aspects of lubrication oil breakdown and oxidation at elevated temperatures, mostly those related to their coking and ignition behaviors. Four types of tests been implemented: thermal cook-off under controlled heating; ignition delay time measurements using a shock tube; hot-plate ignition; autoignition temperature determination; and a high-temperature coking experiment. Such tests can be used both for fundamental understanding of how lube oils burn and for comparing the reactivity of various types and grades of oil. Additional comparisons such as the effects of aging, oxidation, and thermal degradation can also be made. Each technique is briefly described in this paper as they pertain to gas turbine lube oils, and sample results are presented for a common lubrication oil, Mobil DTE 732. Comparisons are made to heavy fuels which have been characterized more often, such as kerosene-based jet and diesel fuels, when possible.