An Optical Method for Heat Flux Measurements in Stagnation Point Laminar Methane/Air Flames using Thermographic Phosphor Thin Films and the Effect of Hydrogen Addition

This study is a novel optical approach that employs light-induced phosphorescence from thermographic phosphor thin films. The heat fluxes and wall temperatures of almost one-dimensional flat premixed flames that primarily strike upward against a horizontally oriented, water-cooled, circular flat plate are examined using this method. To evaluate the heat flow rate from the flame, chromium-doped alumina (Cr: Al2O3) ruby was applied to both sides of the plate's core, which is an alumina ceramic substrate. The substrate was excited on both sides by a green light-emitting diode (LED) array, and temperature measurements were taken on either side. When the fuel–air mixture flows at lower velocities (0.05–0.5 m/s), a matrix-style flat burner enclosed in a water-cooled jacket produces a laminar, one-dimensional flame. Nozzle burner is better suited for higher fuel-air mixture velocities (0.6-1.2 m/s). A hollow, water-streamed disk with an outside diameter of 200 mm and a thickness of 30 mm comprises the heat receiver. A brass ring encircles the ceramic plate on the flame side, while the top is sealed with a translucent acrylic glass cover. The acrylic glass maintains exceptional transparency across the phosphorescence and excitation wavelength ranges and remains dimensionally stable at temperatures relevant to the experiment (up to about 120 °C on the water-cooled, pressurized side). On the heated side of the ceramic plate, the temperature remained relatively low (under 500 K) due to the direct contact between the plate’s backside and pressurized cooling water at approximately 3 bar.The receiver disk features 12 mm diameter cooling-water channels located on its opposing faces. The ceramic plate, which is made of aluminium oxide (Al2O3), is 80 mm in diameter and 6 mm thick. Ruby is used as a phosphor on both sides of the plate. A green light-emitting diode (LED) array with a peak wavelength of 525 nm and an average output power of 2.4 W was used to light the plates. The signal of phosphorescence from each side of the plate was detected with the aid of two photomultiplier (PM) tubes. Before being transferred to a PC, the signal was averaged over 128 pulses using a digital oscilloscope. A rapid pulse generator provided the driving signal for the green LED. Data concerning the heat flux rate were derived from these investigations. The findings of the model were compared with those of the experiments.