| Laser ablation plasma-assisted combustion is a new technique which can not only increase the flame blow out limit, enhance the stabilization of combustion, but also can decrease the need of laser power. It has important meaning for the application of laser induced plasma-assisted combustion. Aimed to solve the problems of high frequency laser ablation plasma-assisted combustion, such as the lack of parametric data, the unknown mechanism, the disserta tion will carry out the research on the characteristics and the mechanism of kHz frequency laser ablation plasma-assisted combustion.Firstly, the dissertation introduces the research progresses of laser induced plasma assisted combustion, analyzing its shortcomings in the mechanism and practical applications, and presents the main research contents of this paper. Then it gives the method of the laser induced plasma assisted combustion involving the temperature and the flow characteristics basing on the tec hnologies of molecular emission spectral matching and schlieren. Secondly, using the emission spectra of CH molecule, the methane air premixed plane flame temperature in three-dimensional under 2.24 mm height of Mc Kenna standard burner is obtained. It verifies the spatial uniformity of the standard burner.Finally, using frequency 1kHz, 532 nm Nd: YAG laser ablation plasma of tantalum target, the blow out limit, the structure, the propagation velocity and the temperature of the methane air premixed flame are studied. Also confirming the leading mechanism of laser ablated plasma assisted combustion. By using the laser ablation plasma of the average power 5.5W, the methane air premixed gas with the equivalent ratio of 0.7-1.2 and the flow velocity of 4m/s achieves a stable combustion. It expands the equivalence ratio range of stabilization combustion and increases the blow out limit by 30%-340% compared with the non-plasma combustion. And then the influences of flow velocity, equivalence ratio, the average laser power on the flame structure of plasma assisted combustion are got through the approaches of chemiluminescence and schlieren. The higher the laser power and the more close to the appropriate ratio, the larger volume of the flame kernel and the more stable combustion. With the increase of laser power, the height of the flame stabilization is reduced. When the laser power is increased from 3.48 W to 6.38 W, it can decrease the height of stable flame which the equivalent ratio is 1and the flow velocity is 4m/s by 0.52 mm. It has significant meanings for the miniaturization of the burner. Next, the flame velocity of plasma assisted combustion is obtained based on the time-space evolution characteristics of the flame kernel. The research shows that because of the laser ablation plasma, it greatly improves the flame velocity of the methane air premixed gas. When the average laser power is 4.52 W and the equivalent ratio of premixed methane-air gas is 0.8-1.3 with the speed of 4m/s, the flame velocity increases by 28.2%-240% compared with the non-plasma combustion. The increase of the flame velocity can improve the flame stabilization and blow out limit. At last, this paper analyses the mechanism of laser ablation plasma assisted combustion, according to both the temperature characteristics by comparing the air, methane-air premixed gas and the methane-nitrogen gas and the influence of average laser power on the time-space evolution properties of temperature on flame kernel assisted by laser ablation plasma. The results indicate that the thermal effect(the macroscopic rise of temperature) of laser ablation plasma is limited, and the main physical mechanism is that the active particles produced by laser ablation plasma promoted the combustion process of chemical reaction. |
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