Measurement of Dynamic Flame Response in a Lean Premixed Single-Can Combustor

Combustion oscillations are a serious technical challenge for stationary gas turbine manufacturers. In order to address this issue, the development cycle for a gas turbine combustor typically involves an extensive test program. In many cases, the dynamic stability observed in sub-scale test rigs differs from the commercial engines. If encountered late in the development cycle, these rig-to-engine variations can impact an entire engine program. This paper discusses an experimental approach to measure time-scales (i.e., fuel-transport time and flame response time) that play a critical role in combustion oscillations. If these time-scales can be measured throughout the development cycle, the rig-to-engine variations in combustor performance may be improved. The results described in this paper are collected from a nominal 1MW_th single-can combustor rig operating on natural gas. The inlet-air temperature and pressure are 589K (600°F) and 760 kPa (7.5 atm), respectively. The measured time-scales are significantly larger than the bulk fuel-transport time calculated from simple estimates. In order to explain these discrepancies, a simple flame model is presented to show how the flame structure can influence these time-scales. This model is also used to illustrate how these critical time-scales can change as a function of operating condition.