Ian L. Critchley

Active Control of Combustion Dynamics for Lean Premixed Gas Fired Systems

The present paper describes an active control system consisting of a fast-acting actuator valve, coupled with a control algorithm capable of adaptive phase and amplitude control for pressure oscillation suppression. Experiments were conducted using two separate combustion test rigs: a small, lean premixed, tubular combustor (75 kW) and a larger premixed annular DLE system (4 MW). Active control of pressure oscillations at frequencies of approximately 90 Hz and 300 Hz was demonstrated on the 75 kW rig. Up to 90% reduction in single-frequency dynamic pressure amplitude and 70% reduction in peak-mean was achieved. Simultaneous suppression of these two distinct modes was also demonstrated. The system was also demonstrated on a full-scale 4 MW combustion rig, with peak-mean dynamic pressure reductions between 33–45%. Instability reductions were achieved by pulsing fuel supplied to either a diffusion or a premixed flame. The response of the flame was notably better for the premixed case. For the premixed flame, combustor pressure pulses were realizable up to a frequency of about 400Hz, while the diffusion flame could only induce combustor pressure pulses up to approximately 50Hz. Adaptive frequency, phase and amplitude logic were developed, allowing automatic selection of the optimal values of these parameters to maximize suppression efficacy to suit the particular operating condition.Copyright

Diode-Laser-Based Sensor Measurements of Nitric Oxide and Carbon Monoxide in Combustion Exhaust Streams

All-solid-state continuous-wave (cw) laser systems for ultraviolet (UV) absorption measurements of the nitric oxide (NO) molecule and mid-infrared (IR) absorption measurements of carbon monoxide (CO) were developed and demonstrated. For the NO sensor, 250 nW of tunable cw UV radiation at 226.8 nm is produced by sum-frequency-mixing in a beta-barium borate crystal. For the CO sensor, 2μW of tunable cw IR radiation at 4.5 μm is produced by difference-frequency mixing in a periodically-poled lithium niobate crystal. A tunable external-cavity diode laser (ECDL) provides one of the fundamental beams for both processes so that the wavelength of the generated UV/IR can be tuned over NO/CO absorption lines to produce a fully resolved absorption spectrum. The sensors were used for measurements in the exhaust stream of an operating auxiliary power unit (APU) gas turbine engine and a well-stirred reactor (WSR). During these tests, NO was measured in the exhaust at levels below 10 ppm. For measurements at levels above 20 ppm, the NO emission levels obtained using the new sensor agreed with the results of probe sampling chemiluminescent analyzer results to within 10%. A detection limit of 0.8 ppm of per meter path length at 1000 K is estimated for the NO sensor. Measurements with the CO sensor demonstrated an agreement with extractive probe sampling to within 15%. The estimated detection limit of the CO sensor is a few ppm per meter path length at 1000 K.Copyright