Ultra-high-speed PLIF imaging for simultaneous visualization of multiple species in turbulent flames

Abstract

In order to obtain more detailed characteristics and information in highly turbulent flames, for a better understanding of the transient behavior of eddies in such flames, a measurement technique with sufficient temporal resolution is requested. However, the probing of species distributions relevant in combustion (e.g. OH, CHO) with ultra-high-speed laser diagnostics still remains a challenge. Nd:YAG clusters commercially available can generate only 4-8 pulses, although with high laser energy. Systems based on a diode-pumped solid-state Nd:YAG laser combined with a dye laser produce only about 100 μJ pulse energy at ultra-high repetition rates (≥50 kHz). Even more comprehensive information on the flame structure can be gained if simultaneous recording of multi-species is performed. In the present work, the development of the first ultra-high-speed diagnostic technique capable of simultaneous probing of hydroxyl radicals and formaldehyde distributions at a repetition rate of 50 kHz is outlined. This has been achieved by employing a burst laser pumped optical parametric oscillator system for the simultaneous detection of CHO excited at 355 nm and OH-radicals excited at 283 nm, where the interference of scattering laser light can be avoided. The applicability of the proposed technique was demonstrated in a highly turbulent jet flame. Moreover, the presented improvement in terms of the number of consecutive images recorded with ultra-high-speed planar laser induced fluorescence imaging is significant. Due to the high temporal resolution, the movement of CHO pocket enclosed by OH at the flame tip can be clearly captured. The transport velocity of the CHO pocket was calculated and found to be in good agreement with previous LDV results.

Single-shot time-gated fluorescence lifetime imaging using three-frame images

“…Monte-Carlo simulations were performed to evaluate the sensitivity of DIME for oxygen detection. The results indicated a high measurement sensitivity in the range 0.5 ~ 6mol/m 3 [22], showing that DIME has potential for quantitative diagnosis of complex flows. However, traditional RLD methods have a drawback: they are unable to offer robust estimations if the samples to be tested have a wide range of lifetimes.…”

“…Planar laser-induced fluorescence (PLIF) sensing technologies are widely used in many scientific fields, such as airflow, combustion, and plasma diagnostics [1] due to its ability to measure the concentration, temperature, pressure and velocity [2,3].…”

Compressed fluorescence lifetime imaging via combined TV-based and deep priors

“…Widefield fluorescence lifetime imaging (FLIM) is widely used in biomedical diagnostics and flow quantitative measurements, such as cancer diagnosis and treatment monitoring [1,2], identifying species concentration from reactive-flow systems [3], and understanding the transient evolutionary behavior of eddies in highly turbulent flames [4]. Most of these examples are non-repeatable transient events that demand a single-shot widefield measurement method.…”

Design of a novel high-performance ultrafast optical framing camera

“…As such, it is widely employed as an ultrafast imaging tool in remote sensing [8], detecting product surface defects [9], fluorescence imaging [10], inertial confined fusion [11,12] (ICF), and time of flight imaging [13]. Planar laser-induced fluorescence (PLIF) sensing technologies have been widely used in many scientific fields, such as airflow, combustion, and plasma diagnostics [14,15] due to its ability to measure the concentration, temperature, pressure and velocity [16,17]. A high spatial resolution and a high temporal resolution are required to guarantee high-precision in PLIF measurements.…”