Active Control of Lean Blowout for Turbine Engine Combustors

A complete, active control system has been developed to permit turbine engine combustors to operate safely closer to the lean-blowout (LBO) limit, even in the presence of disturbances. The system uses OH chemiluminescence and a threshold-based identification strategy to detect LBO precursor events. These nonperiodic events occur more frequently as the LBO limit is approached. When LBO precursors are detected, fuel entering the combustor is redistributed between a main flow and a small pilot, so as to increase the equivalence ratio near the stabilization region of the combustor. This moves the effective LBO limit to leaner mixtures, thus increasing the safety margin. The event-based control system was demonstrated in an atmospheric pressure, methane-air, swirl-stabilized, dump combustor. The NOx emissions from the piloted combustor were found to be lower than those from the unpiloted combustor operating at the same safety margin and same nominal velocity field. The controller minimizes the NOx at constant total power by keeping the pilot fuel fraction at the lowest value needed to limit the number of precursor events to an acceptable level.