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Theoretical and Experimental Study on Premixed CH4/O2 Combustion by Laser-Induced Excitation of Oxygen Molecules

Author: ShaoQiang
Tutor: YuXin
School: Harbin Institute of Technology
Course: Physical Electronics
Keywords: combustion by laser-induced excitation oxygen molecule of excited state H2/O2 reaction CH4/O2 reaction ignition delay time
CLC: TN249
Type: Master's thesis
Year: 2009
Downloads: 13
Quote: 1
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Abstract


With the advancement in aerospace technology, the development of large thrust rockets and supersonic combustion needs fuel combustion reaction rate of a higher demand. Therefore, how to effectively improve the combustion reaction rate and reduce the ignition temperature has become a hot subject of research. As the laser’s characteristics of directionality, monochromaticity and high-energy, the application of combustion technology by laser-induced excitation provides us a new method to enhance the rate of chemical reactions. Up to now generally three mechanisms by which laser radiation can affect the combustion processes have been investigated. These are laser-induced thermal ignition, laser induced photochemical ignition, and laser induced spark ignition. In recent years, a new method of the excitation of vibrational or electronic states of reacting molecules is brought up in order to reduce the active energy and increase the rate of chemical reaction. In this paper, the theoretical and experimental research is proceeded to investigate the mechanism of laminar premixed combustion by laser-induced excitation of oxygen molecules. Besides, theoretical and experimental research is also proceeded to investigate the mechanism of combustion by laser-induced plasma.Based on the theory of energy transitions and X3Σg--b1Σg+、X3Σg--a1?g triplet forbidden transition which is refer to laser-induced combustion and the theory of chemical reaction dynamics and combustion, we establish a laminar premixed combustion model of laser excitation of vibrational or electronic states of oxygen molecules, and calculate the active energy containing a1?g , b1Σg+ excited oxygen.Using the calculation software of chemical reaction dynamics CHEMKIN, we simulate H2/O2 and CH4/O4 premixed combustion processes at excitation of b1Σg+ and a1?g states of oxygen molecules by laser radiation with wavelengths 762nm and 1268nm, demonstrating that under the laser radiation ignition delay time is significantly reduced. In condition of temperature T=900K、pressure P=1atm、aorption length l=103cm, the H2/O2 reation delay time is 0.05326s without laser and 0.0184s by laser radiation of 762nm, 10kW/cm2, which is reduced 65%; In condition of temperature T=1000K、pressure P=1atm、aorption length l=103cm, the CH4/O2 reation delay time is 0.23443s without laser and 0.02861s by laser radiation of 762nm, 10kW/cm2, which is reduced 87%. Moreover, we analyze the influences of laser power density, temperature, pressure and other conditions on combustion reactions.We design and build combustion reaction experiment platform for the study of flame propagation characteristics and the measurement of flame propagation speed. Using this platform, a laminar premixed combustion experiment of the excited oxygen molecules activated by 762nm laser is made. We measure the flame propagation velocity with and without laser excitation in bunsen burner method. The flame propagation velocity is 152.91mm/s without laser excitation, 166.33mm/s by 761nm laser excitation, 162.06mm/s by 761.5nm laser excitation, 158.35mm/s by 762nm laser excitation, which are increased 8.77%, 5.98%, 3.55% separately.Femtosecond laser is used to activate molecular oxygen for laminar premixed combustion experimental study. We measure the change of flame propagation velocity in bunsen burner method and find that the velocity increased apparently. The flame propagation velocity is 157.15mm/s without laser excitation, 176.71mm/s excited by laser radiation focused on nozzle, 172.02mm/s focused below nozzle, 188.57mm/s aside nozzle, 184.19mm/s on the top of flame front, which are increased 12.4%, 9.46%, 19.99%, 17.21% respectively. The fluorescence spectra of oxygen molecules shows that the generation of O, O+, O2+ leads to the increase of flame propagation speed.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Laser technology, the maser > Laser applications
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