The effect of non-axisymmetric fuel staging on flame structure in a multiple-nozzle model turbine combustor

Fuel staging is often used to suppress combustion instabilities in a gas turbine engine. This strategy is accomplished by applying differing flow rates of fuel to different nozzles of a multi-nozzle combustor. As such, the mixture composition and critical flame properties like flame speed and heat release may vary from nozzle to nozzle. In this experiment, five identical nozzles are arranged with a central nozzle surrounded symmetrically by four others; this is commonly referred to as a "four-around-one" configuration. The fuel is staged by adding more fuel through the middle and one outer nozzle, where staging through the middle nozzle will be referred to as axisymmetric staging, and staging through an outer nozzle is non-axisymmetric staging. This staging is analyzed through the use of tomographic image reconstruction. Images are taken in 5 degree increments over a 180 degree span around the flame for each staging condition. We compare three cases: one without staging, one with axisymmetric staging, and another with non-axisymmetric staging. Fuel staging can cause deviations in the flame structure where neighboring flames meet each other. Non-axisymmetric versus axisymmetric staging are found to result in different flame shapes and stabilization methods due to the difference in the number of flames that are interacting with the staged nozzle.