Development of a water-cooled multi-hole calibration burner for optical measurements of flames with high pressures and temperatures

High temperature flames, which can be produced via oxygen-enriched combustion, potentially have improved the combustion characteristics over air-only combustion flames due to their substantially higher flame temperatures. These conditions necessitate the use of non-intrusive optical measuring methods to measure the temperature and the chemical species in the flame. To develop an optical measurement calibration burner that can be used at high pressure and temperature conditions, a new calibration burner which employed water-cooled multi-hole nozzle was developed in this study. Premixed CH₄/O₂/N₂ oxygen-enriched conditions were selected to investigate both the heat-resisting properties of the developed burner nozzle and the burner’s flame characteristics. OH-Planar Laser-Induced Fluorescence (OH-PLIF) measurements were conducted on the flames to observe the OH distributions. The flame temperature at 0.10 MPa was derived using a Boltzmann-plot for the OH fluorescence excitations. To verify the variation of molecular concentration with equivalence ratio for the experimental flames qualitatively, the experimentally acquired OH and CH chemiluminescence intensities were compared with the simulated partial pressure of OH* and CH*, respectively. Experimental results showed that the CH₄/O₂/N₂ flames were stabilized on the burner nozzle in a wide range of oxygen-enrichment ratio, from 0.40 to 1.0 at atmospheric pressure. At an oxygen-enrichment ratio of 0.45, the flames were also stabilized in pressure conditions up to 0.49 MPa, while the inner nozzle temperature was lower than 400 K. The OH-PLIF images showed that the OH was distributed almost uniformly along the axial direction of the burner, and demonstrated similar characteristics to that of a flat flame. The derived maximum flame temperature at atmospheric pressure was approximately 2650 K at an oxygen-enrichment ratio of 0.80. The variation of the OH and CH chemiluminescence intensities with change of equivalence ratios corresponded roughly with the simulated partial pressures of OH* and CH* at each pressure condition.