Investigation On The Organization Strategy Of Fuel/air In A Trapped Vortex Combustor

The trapped vortex combustor(TVC)has been studied and developed for more than twenty years since it was proposed.However,there are still some obstacles for it being used in practice,eapecially for some underlying mechanisms are not well enough understood to date.Take the organization strategy of fuel/air for an example,little effort has been made so far to conduct systematic investigations on this issue in TVCs,especially for those who fed by liquid fuel.Under these conditions,the objective of this study is to get insights into the organization strategy of fuel/air in a TVC fed by liquid fuel(kerosene).Compared to the existing literature,the main contribution of the present work is to not only provide a more comprehensive understanding of the organization strategy of fuel/air in a TVC,but also provide some valuable design concepts to TVC designers,especially to those who are interested in improving combustion performance of the TVC fed by liquid fuel.Firstly,experimental and numerical studies have been carried out on the flow field,fuel distribution characteristics and combustion performance of the cavity.Results indicate that,(1)the dome structure has a great influence on the entrainment of the mainstream into cavity,which induces different flow flieds in the cavity.A smaller main vortex will be formed near the bottom wall of the cavity with high turbulence intensity as great amount of mainstream air is entrained into the cavity.Under this condition,unsatisfactory ignition and LBO performance will be acquired by the TVC.However,excellent combustion efficiency will be achieved.A larger main vortex and a smaller second vortex will be formed in the cavity with lower turbulence intensity as little of mainstream air is entrained into the cavity.In addition,outstanding ignition and LBO performance will be achieved by the TVC.Furthermore,lower combustion efficiency will be obtained.(2)It also found that the distribution of the droplet in the cavity depends greatly upon the fueling atomizer.A circular fuel pattern with great many of fuel being directly injected onto the bottom wall of cavity could be observed in the cavity as it is fueled by pressure-swirl atomizer.Under this condition,the ignition performance,LBO limits and combustion efficiency of the TVC are unsatisfactory.However,a narrow fan fuel pattern with excellent ignition and LBO performance and higher combustion efficienfy will be achieved by the TVC as the cavity is fueled by the novel atomizer.Secondly,experimental and numerical studies have been carried out on the flow field,fuel/air mixing characteristics and combustion performance of the mainstream.Results indicate that,(1)the dome structure has a great influence on the flow structure of mainstream for the restriction of the strut.A convergent mainstream flow and larger recirculation zones behind the strut could be found as the strut is shorter.And higher combustion efficiency of mainstream is achieved by the TVC at low fuel to air ratio regiem.However,lower combustion efficiency of mainstream is acquired at high fuel to air ratio regiem.A divergent mainstream flow and smaller recirculation zones behind the strut could be found as the strut is longer.Besides,lower combustion efficiency of mainstream is achieved at low fuel to air ratio regiem in divergent flow.However,higher combustion efficiency of mainstream is obtained by the TVC at high fuel to air ratio regiem.As anticipated,moderate recirculation zones and combustion efficiency is obtained by the TVC as the strut length is of a moderate value.(2)The fuel distribution and mixing characteristics of fuel/air in the mainstream depend highly on the number of the hole setted on the mainstream fueling setup.A dispersed fuel distribution with deep penetration and lower combustion efficiency could be obtained by the mainstream as the number of the hole is 2 or 3.A uniform fuel distribution with proper penetration could be observed in the mainstream as the number of the hole is 4.Under this condition,highest combustion efficiency is achieved by the mainstream.As 5 holes are setted on the mainstream fueling setup,a concentrated fuel distribution with shallow penetration could be acquired by the mainstream.Additionally,lowest combustion efficiency is obtained by the mainstream.The effect of the cooperation between cavity and mainstream on the combustion performance has been carried out as an ongoing investigation of the former studies.Results indicate that,(1)the TVC fueled by the novel hybrid-atomizer and mainstream fueling setup exhibits excellent advantages both in combustion efficiency and OTDF as compared with that fueled by pressure-swirl atomizer and mainstream fueling setup.(2)The combustion efficiency increases with the cavity fuel to mainstream fuel ratio increases as the total fuel to air ratio kept as a constant.Finally,based on the above studies,the organization strategy of fuel/air for the TVC has been summarized and identified by the improved combustor.The results indicate that the combustion efficiency above 98.82 % is achieved by the improved TVC as the fuel to air ratio varying from 0.01 to 0.015.Besides,combustion efficiency above 99 % is obtained by the improved TVC as the fuel to air ratio varying from 0.037 to 0.040.Besides,the OTDF is lower than 0.20 as the fuel to air ratio beyonds 0.03.Furthermore,a lean blowout fuel to air ratio of0.00283 is achieved by the improved TVC.The above results indicate that the performance requirements of the combustor with high temperature rise could be fairly met by the the improved TVC designed by the proposed strategy.