Abstract

Lubricant ignition is a highly undesirable event in any mechanical system, and surprisingly minimal work has been conducted to investigate the auto-ignition properties of gas turbine lubricants. To this end, using a recently established spray injection scheme in a shock tube, two gas turbine lubricants (Mobil DTE 732 and Lubricant A from Cooper et al. 2020) were subjected to high-temperature, post-reflected-shock conditions, and OH* chemiluminescence was monitored at the sidewall location of the shock tube to measure ignition delay time (tign). An extended shock-tube driver and driver-gas tailoring were utilized to observe ignition between 1183 K and 1385 K at near-atmospheric pressures. A two-stage-ignition process was observed for all tests with Mobil DTE 732, and both first and second stage tign are compared. The secondary ignition was found to be more indicative of combustion and was used to compare tign values with lubricant A. Both lubricants exhibit three ignition regimes: a high-temperature, Arrhenius-like regime (>1275 K); an intermediate, negative-temperature-coefficient-like regime (1230-1275 K); and a low-temperature ignition regime (<1230 K). Lubricant A was found to be less reactive in the intermediate-temperature regime, but Mobil DTE 732 was less reactive in the low-temperature regime. As the low-temperature regime is more relevant to gas turbine conditions, Mobil DTE 732 is considered more desirable for system implementation.

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