Systematic measurements of OH chemiluminescence for fuel-lean, high-pressure, premixed, laminar flames

Systematic measurements are reported of OH chemiluminescence from a premixed laminar flame at pressures and equivalence ratios ranging from 0.5 to 2.5 MPa and 0.66 to 0.86, respectively. The objective was to obtain non-existent experimental data and to determine the viability of using OH chemiluminescence as an active-control parameter for high-pressure, premixed flames. The signal from the first electronically excited state of OH to ground (at 305.4 nm) was detected through a band-pass filter with a photo-multiplier tube. For constant mass flow rate, OH emission decreased significantly with increasing pressure. Emission also monotonically increased with the equivalence ratio. A linear relationship was observed between increasing mass flow and increasing chemiluminescence. These trends support the conclusion that suitable resolution and dynamic range exist for a high-pressure flame to be adequately controlled to minimize both NOx and CO emissions. Results are presented for a simple, active-control system using OH chemiluminescence measurements to demonstrate flame stabilization for equivalence ratio disturbances at fixed, elevated pressures. Finally, only qualitative agreement was observed between the measurements and numerical predictions of OH chemiluminescence using an adiabatic, freely propagating premixed flame. Although more work is required on the chemical-kinetic mechanism of OH chemiluminescence, the modeling effort supports the use of OH chemiluminescence for active-feedback-control applications.