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Development and Validation of an Experimental System for Investigating Oxygen Singlet Sigma State Effects on Premixed Methane-Air Flames

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Conference

2024 ASEE North Central Section Conference

Location

Kalamazoo, Michigan

Publication Date

March 22, 2024

Start Date

March 22, 2024

End Date

March 23, 2024

Page Count

11

DOI

10.18260/1-2--45611

Permanent URL

https://strategy.asee.org/45611

Download Count

24

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Paper Authors

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Ghazal Rajabikhorasani Western Michigan University

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Claudia M Fajardo Western Michigan University

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Abstract

Plasma-assisted combustion (PAC) provides the opportunity to improve energy conversion efficiency, enhance lean burn flame stability, reduce pollutant emissions, and foster the development of new combustion technologies. The plasma environment is characterized by the presence of charged particles, free radicals, and electrically excited species, among which the oxygen singlet sigma is found. Due to its distinctive capability to generate heat, active species, and modify transport processes, the high-energy plasma environment substantially modifies the fuel oxidation pathways. Because of the multi-timescale and non-equilibrium nature of plasmas, however, understanding the intricate connections between combustion chemistry, kinetics, and plasma physics remains the primary challenge in PAC research. An essential step toward achieving a comprehensive understanding is to disentangle the influence of distinct chemical species. Therefore, it is extremely important to design robust, reliable, and well-defined fundamental experiments to assess their impact on combustion. This paper describes the development of an experimental combustion system to investigate the effect of plasma species on methane-air combustion. The system consists of a six-way cross vacuum chamber with optical access windows. A vacuum pump maintains the chamber operating at pressures between 200 and 600 Torr through a pressure regulation system with 0.1 Torr resolution. The chamber houses a McKenna burner supplied with a premixed methane-air gas reactant stream. Mass-flow controllers precisely meter reactant flows, enabling the burner to operate at target equivalency ratios between 0.5 and 1.0. The burner operating temperature and exhaust gas temperature are controlled with a closed-loop cooling system consisting of a recirculating water chiller and a water-to-gas heat exchanger. Methane-air flame studies are conducted with a laser spectroscopy system developed to excite target chemical species and conduct concentration measurements. Oxygen excitation to the singlet sigma state (O2(b1Σ+g)) is achieved with a continuous-wave (CW), Titanium-Sapphire, narrowband ring laser operating at 765 nm. A frequency-doubled, Nd: YAG-pumped, dye laser, operating at 865 nm, generates coherent anti-Stokes Raman spectroscopy signals, facilitating measurements of OH concentration and temperature within the laminar methane-air flame. Precise positioning of optical components is achieved using a two-dimensional, computer-controlled railing system, which facilitates measurements of both temperature and species concentrations within the flame field with 5 μm spatial resolution. Calibration and validation of these subsystems have been carried out using simulation and reference experimental data to ensure accuracy and reliability. The experimental combustion system detailed in this paper provides a flexible and versatile platform to study the influence of distinct plasma species on methane-air combustion. The insights gained from these fundamental studies will contribute to the advancement of PAC technology, paving the way for real-world implementation in various combustion systems.

Rajabikhorasani, G., & Fajardo, C. M. (2024, March), Development and Validation of an Experimental System for Investigating Oxygen Singlet Sigma State Effects on Premixed Methane-Air Flames Paper presented at 2024 ASEE North Central Section Conference, Kalamazoo, Michigan. 10.18260/1-2--45611

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