Simultaneous Monitoring of Chemiluminescence and Acoustic Pressure during Tulip Inversion

This study investigates the interaction between pressure waves and heat release during tulip flame formation in hydrogen–air premixed combustion. Experiments were carried out in a rectangular chamber (400 mm × 40 mm × 40 mm), with ignition initiated near one end. Two diagnostic techniques were used simultaneously to capture time-resolved data, and high-speed imaging was conducted separately to visualize flame behaviour over time.

The first method measured OH* chemiluminescence. Light emitted by the flame passed through a 310 nm bandpass filter and was detected by an APD440A2 photodetector. The signal, representing heat release behaviour, was recorded in real time using an oscilloscope.

The second method used a laser-based technique developed in our lab to detect thermoacoustic pressure fluctuations. A polarised laser beam passed through the combustion zone, where pressure gradients and vorticity caused deflection, measured using an analyser and photodetector. This method is described in detail by Joarder et al. (Phys. Fluids, 2025).

High-speed images helped correlate flame shape with pressure and heat release signals. Thermoacoustic signals from x = 200 mm and x = 220 mm showed a backwards-travelling pressure wave at ~3.55 ms. Chemiluminescence at x = 220 mm rose at ~3.2 ms and peaked at ~9.9 ms, indicating a clear phase lag between pressure and heat release.