2.2. Laser diagnosticsThe flow fiel

2.2. Laser diagnostics
The flow field was studied using a conventional fibre-coupled 2D LDV system (Dantec) in the for- ward scattering mode. The off-axis detection angles were either 10° or 80° to monitor axial and radial or axial and tangential velocity compo- nents. The probe volume length varied corre- spondingly from 2500 to 200lm. The probe volume diameter remained constant (240 lm) for both configurations. Notice, that the measured PDFs of the axial velocity component were unaf- fected by the extended probe volume. Combustion air and fuel were seeded with MgO particles approximately 1 lm in diameter. Measurement uncertainties for mean and fluctuations were esti- mated to be

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2.2. Laser diagnosticsThe flow field was studied using a conventional fibre-coupled 2D LDV system (Dantec) in the for- ward scattering mode. The off-axis detection angles were either 10° or 80° to monitor axial and radial or axial and tangential velocity compo- nents. The probe volume length varied corre- spondingly from 2500 to 200lm. The probe volume diameter remained constant (240 lm) for both configurations. Notice, that the measured PDFs of the axial velocity component were unaf- fected by the extended probe volume. Combustion air and fuel were seeded with MgO particles approximately 1 lm in diameter. Measurement uncertainties for mean and fluctuations were esti- mated to be <5% and <11%.To measure time-series, the system was operat- ed in 1D (axial velocity component) to maximize data rates. An enhanced fuzzy-slotting technique [7] was applied to calculate the correlation func- tion from 106 random samples taken at each mea- surement location. Velocity bias was accounted for by using transit time weighting. Optical hard and software were tested at an isothermal jet [7]. Corresponding power spectral densities (PSD) obtained from a fast Fourier-transformation (FFT) were in excellent agreement with data from the literature [36]. This proved the capability of the instrumentation.LDV measurements were restricted for reactive conditions to the 2 bar case as at higher pressures a rapid contamination of the inner quartz window prohibited reliable flow field measurements.The flame structure was studied by OH planar LIF. Although critically regarded as a flame front marker due to its slow decay in post-flame gases [37], peak OH concentration, and steep OH-gradi- ents at the primary flame front correlate reason- ably well with heat release. Here, a narrow-band
tuneable KrF excimer laser (Lambda Physik) was used to excite OH at the temperature-insensi- tive P1(8) line in the A2R+