Ignition of Aged Lubricants in a Shock Tube

Abstract

Lubricants experience harsh conditions which result in degradation of the oil. To imitate similar conditions, Mobil DTE 732, a common gas turbine lubricating oil, was subjected to high temperatures for an extended period of time, until thermal degradation occurred, indicated through the creation of coke. Samples were taken throughout this process, with the sample that was tested having been exposed for 78 h. Utilizing an endwall injector system, the samples were ignited behind reflected shock waves in the high-pressure shock tube (HPST) at Texas A&M University. The injector system utilizes the incident wave to increase the temperature of the lubricant past its vaporization temperature, thereby vaporizing the fuel prior to the arrival of the reflected shock. Using this system, the base Mobil DTE 732 and the 78-h sample produced from the coking test were tested at 1.06–1.58 atm and between 1171 and 1373 K. The ignition delay times (IDTs) of the samples were recorded utilizing pressure rise and hydroxyl chemiluminescence located in the sidewall of the shock tube. Upon the analysis of the results, there were negligible changes in the ignition behavior of the fuel, based on ignition delay time. However, changes in the combustion behavior were experienced, such as an absence of two-stage ignition and lower viscosity for the post-coke sample.