High-speed CH2O PLIF imaging in turbulent flames using a pulse-burst laser system

Quasi-continuous burst-mode laser for high-speed planar imaging

“…The typical signal-to-noise ratios (SNRs) for the current PLIF signals relative to spatial noise in the background are 47:1 at 10 kHz and 40:1 at 20 kHz without pixel binning. This is similar to the SNR reported elsewhere for 1 ms duration, 10 kHz burst-mode CH 2 O-PLIF images collected with 5 × 5 pixel binning and a similar field of view [17].…”

“…The extended record length allows imaging of the complete detachment and reattachment of the flame layer in the stabilization region for both sets of images. By comparison, other burst-mode PLIF systems have demonstrated only 1 ms of record length [7,17], equal to the time separating any two images in the 10 kHz sequence presented in Fig. 4.…”

100 kHz thousand-frame burst-mode planar imaging in turbulent flames

“…Third-harmonic generation of up to 30% is achieved with a type-I LBO crystal after the beam passes through a half-waveplate for 532 nm and a full waveplate for 1064 nm. At these fluences, there is no evidence of harmonic-conversion degradation during the burst, with the conversion efficiency being similar to prior work [4,5,8]. The resulting ultraviolet pulse train of 15 mJ∕pulse at 355 nm is unprecedented for burst durations of nearly 1000 pulses, allowing for extended time records of formaldehyde (CH 2 O) PLIF at 100 kHz with high signal-to-noise ratio (SNR).…”

“…The limitations of continuously pulsed DPSS laser systems have been addressed, in part, by advancements in burst-mode laser technology. For example, the ∼10-100 times higher pulse energies of burst-mode lasers can be used to access a wider range of combustion parameters of interest at higher frame rates, including OH, CH, NO, CH 2 O, soot, fuel-tracer concentrations, mixture fraction, and velocity [4][5][6][7][8][9][10][11][12]. However, a key challenge for burst-mode laser systems has been the short burst duration (up to 200 frames) and, therefore, limited temporal dynamic range (TDR) [4].…”

All-diode-pumped quasi-continuous burst-mode laser for extended high-speed planar imaging

“…This technology has been demonstrated for high-speed measurements of temperature [13]; mixture fraction [14]; PLIF of OH [10,15], NO [12,16,17], CH [18][19][20], and CH 2 O [21,22]; and Raman line imaging of O 2 , N 2 , CH 4 , and H 2 [23], with measurements ranging from 1 kHz to 1 MHz. One approach to burst-mode operation is to utilize multiple oscillator-amplifier chains in a parallel configuration, allowing up to eight high-energy pulses in a time-correlated sequence [15].…”