Instantaneous flame front identification by Mie scattering vs. OH PLIF in low turbulence Bunsen flame

Abstract

Abstract: Simultaneous OH-PLIF and Mie scatter imaging were used to investigate turbulent premixed flame edge detection under a range of turbulence characteristics on a stabilised piloted Bunsen burner. A 527 nm wavelength laser beam is used to generate a Mie scattering sheet at 500 Hz, and a 283 nm wavelength laser sheet is created using 355 nm wavelength laser to pump an optical parametric oscillator to induce florescence from OH radicals at 5 Hz. A phase-locking technique is applied to synchronize and lock the two laser systems. The number density method has been used to detect flame edges in Mie scattering images, and three algorithms were applied to OH-PLIF images as a reference. A comparison of the methods and different parameter setting is made by using the metrics of location difference, flame surface density and curvature of flame edges. The processed data show that once a well-tuned window size is determined by applying the number density method, averaged spatial differences between Mie scattering images and OH-PLIF images are of the order of or smaller than the laminar flame thickness, demonstrating that under these conditions, high frequency Mie scatter measurements can be used as well as OH-PLIF images to define the flame edge at that spatial resolution. The positive result confirms that double-frame Mie scattering allows the measurement of high frequency conditional velocity distributions and flame properties simultaneously using solely Mie scattering, provided that the particle density is suitably designed to be around 16 px2 per particle. Graphic Abstract: