Theoretic And Experimental Studies On Lean Direct Injection Combustor

As environmental protection and emission standards become increasingly strict, many low-pollution combustion plans at home and abroad have been drawn up and low-emission gas turbine combustor have been developed. Studies have shown that Lean direct injection (LDI) combustor can effectively reduce pollutant emissions and is difficult to induce auto-ignition and flashback, which is considered to be the most promising for the next generation of ultra-low pollution combustion chamber.In recent years, studies on LDI combustor have been carried out a lot in Europe and United States, although it is still in the development and testing phases. In China, some researches have been conducted, but it started late, and most of research models of LDI injector and injector arrays have been investigated by other countries. Moreover, most of research methods were numerical simulation. The study on LDI in China is still in the stage of exploration.In this paper, a LDI injector called dual-swirl burner with venturi premixer was proposed based on theoretical analysis. Some technical difficulties and scientific problems about the LDI injector development were studied by theoretic analysis and experiment. Combining the numerical simulation with experiment, some key parameters related to the structural design of LDI combustor, such aspect ratio Ra and confinement ratio Rc, were also investigated. A new annular combustor employed multipoint injection LDI technology was proposed after the studies on LDI injector and structural design of LDI combustor, and an improvement scheme using LDI technology was applied to1MW gas turbine combustor for NOx reduction. Moreover, the three-head test parts of both the LDI model combustor and the original combustor were designed, and flame characteristics, the quality of outlet temperature field, total pressure loss, combustion efficiency and pollutant emissions were studied contrastively.The main contents and conclusions of this dissertation are as follows:(1) For the atomization characteristics measurement of atomizer of single element LDI injector, the spray experiment system was established and the data acquisition method was proposed. Flow rates were measured by the volumetric method. The spray boundary and cone angle were tracked by the active contour model (ACM). The results showed the ACM method eliminates the arbitrary factors inherent in the threshold method, especially subjective factors included in the direct measuring method, which increases the accuracy of the spray cone angle test. (2) In consideration of the design of the swirler structures of single element LDI injector, the effects of the swirler structures, including swirler stage number, swirl direction of dual-stage swirler and shrinking angle β of mixing section, on combustor performance (total pressure loss, combustion efficiency and pollutant emissions) were studied experimentally. The results showed that, swirler structures have great influences on the performance of combustor. The total pressure loss of dual-stage co-swirl combustor is greater than that of the single-stage swirl combustor with the same swirl number. The total pressure loss of dual-stage counter-swirl combustor is slightly lower than that of the dual-stage co-swirl combustor. At different lean fuel-air ratios, compared with the single-stage swirl combustor and dual-stage co-swirl combustor, the dual-stage counter-swirl combustor has higher combustion efficiency and lower pollutant emissions. Combustor total pressure loss increases with increasing the shrinking angle β. Combustion efficiency and pollutant emissions are also affected by the shrinking angle β. The optimal3selection should weigh the total pressure loss, the combustion efficiency, and the level of pollutant emissions.(3) In consideration of the structural design of LDI combustor, key parameters, Ra and Rc. were investigated by both experiment and numerical simulation. The results showed that, Ra and Rc significantly affect the flow and combustion characteristics of the single element LDI combustor. With Ra increasing, color of the combustion flame becomes blue gradually, and both flame temperature and pollutant emissions generally exhibit a declining trend. At Ra>2.5, the whole flame is almost a blue one. and both the combustion temperature and pollutant emissions reach a very low value. Moreover, the effects of aspect ratio on the flame structure, appearance, temperature and the level of pollutant emissions are very small in this case. As Rc increases, the combustion temperature and pollutant emissions first decease and then increase in general, and the exhaust temperature first increases and then decreases. There is an optimal confinement ratio, at which the whole flame is blue and the pollutant emissions become the lowest.In addition, the effects of Rc on flow field of dual-stage counter-swirl combustor were investigated based on Reynolds Stress Equation Model (RSM) after validation of reliability and effectiveness of the model. In the researches, the influence factor n was defined to analyze the influence of Rc on the structure of recirculation zone. The results showed that, the confinement characteristics of combustor are related to its structure. The confinement characteristics of the dual-stage counter-swirl combustor flow are different from those of single-stage swirl combustor. The flow characteristics of the dual-stage counter-swirl combustor at different Rc can be classified into three categories. Additionally, the confinement characteristics of the dual-staae counter-swirl combustor combustion were also further analyzed based on its flow confinement characteristics.Furthermore, large eddy simulation (LES) was employed in optimization of LDI combustor structure. The results showed that, for the LDI combustor with the given structural parameters, LES can obtain the instantaneous flow characteristics of the combustor in detail. The work can provide guidance on optimization of LDI combustor design in future.(4) For the combustion characteristics of the three-head test parts of the LDI model combustor, the flame characteristics, quality of outlet temperature field, total pressure loss, combustion efficiency and pollutant emissions were studied, combined with the three-head test parts of the original combustor. The results showed that, it is close to a blue-violet turbulent premixed flame for the LDI model combustor but a yellow diffusion flame for the original combustor. Moreover, the performance on the quality of outlet temperature field, total pressure loss, combustion efficiency and pollutant emissions in LDI model combustor are superior to those of the original combustor.