The role of cool-flame fluctuations in high-pressure spray flames, studied using high-speed optical diagnostics and Large-Eddy Simulations

Journal Article · Sat Nov 12 00:00:00 EST 2022 · Proceedings of the Combustion Institute

DOI:https://doi.org/10.1016/j.proci.2022.07.242· OSTI ID:1994026

Tagliante, Fabien  ^[1]; Nguyen, Tuan M.  ^[1]; Dhanji, Meghna P.  ^[1]; Sim, Hyung Sub  ^[2]; Pickett, Lyle M.  ^[1]; Manin, Julien ^[1]; Kukkadapu, Goutham  ^[3]; Whitesides, Russell  ^[3]; Wan, Kevin ^[1]

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1. Sandia National Lab. (SNL-CA), Livermore, CA (United States). Combustion Research Facility
2. Sejong University, Seoul (Korea, Republic of)
3. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Here this work investigates the low- and high-temperature ignition and combustion processes, applied to the Engine Combustion Network Spray A flame, combining advanced optical diagnostics and large-eddy simulations (LES). Simultaneous high-speed (50 kHz) formaldehyde (CH₂0) planar laser-induced fluorescence (PLIF) and line-of-sight OH* chemiluminescence imaging were used to measure the low- and high-temperature flame, during ignition as well as during quasi-steady combustion. While tracking the cool flame at the laser sheet plane, the present experimental setup allows detection of distinct ignition spots and dynamic fluctuations of the lift-off length over time, which overcomes limitations for flame tracking when using schlieren imaging. After significant development to improve LES prediction of the low-and high-temperature flame position, both during the ignition processes and quasi-steady combustion, the simulations were analyzed to gain understanding of the mixture variance and how this variance affects formation/consumption of CH₂0. Analysis of the high-temperature ignition period shows that a key improvement in the LES is the ability to predict heterogeneous ignition sites, not only in the head of the jet, but in shear layers at the jet edge close to the position where flame lift-off eventually stabilizes. The LES analysis also shows concentrated pockets of CH₂0, in the center of jet and at 20 mm downstream of the injector (in regions where the equivalence ratio is greater than 6), that are of similar length scale and frequency as the experiment (approximately 5–6 kHz). The periodic oscillation of CH₂0 match the frequency of pressure waves generated during auto-ignition and reflected within the constant-volume vessel throughout injection. The ability of LES to capture the periodic appearance and destruction of CH₂0 is particularly important because these structures travel downstream and become rich premixed flames that affect soot production.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Office of Sustainable Transportation. Vehicle Technologies Office (VTO); USDOE National Nuclear Security Administration (NNSA); National Research Foundation of Korea (NRF); USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• Grant/Contract Number: AC52-07NA27344; NA000352; NRF-2022R1F1A1071759
• OSTI ID: 1994026
• Alternate ID(s): OSTI ID: 2000579
• Report Number(s): LLNL-JRNL-830842; 1047467
• Journal Information: Proceedings of the Combustion Institute, Vol. 39, Issue 4; ISSN 1540-7489
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
diesel spray combustion
cool-flame
large-eddy simulation
high-speed formaldehyde PLIF
OH* chemiluminescence