Analysis Of Flow Dynamics And Composition Structures Of Non-premixed Impinging Jet Flame

The flame-wall interaction is widely present in industrial combustion devices,internal combustion engines,solid heating processes,tunnels and building fires,which affects the flame propagation and flow characteristics to a certain extent.Fully grasping the combustion and propagation characteristics of near-wall flames has important theoretical significance for the study of heat transfer,fluid mechanics and combustion,and has important practical significance for reducing the casualties and property losses in fire accidents,and improving the performance and service life of combustion devices.In order to cope with the increasingly serious energy crisis and environmental problems,and reduce the casualties and losses in fire accidents,it is of great significance to explore the combustion and propagation characteristics of impact flames,and reduce the emission of pollutants during the combustion process.A study on the flow and combustion characteristics of non-premixed impinging jet flames in the near wall region is carried out using experiment and numerical simulation.In this paper,a non-premixed combustion system is used to conduct experimental studies on the impinging jet flame,and the combustion characteristics at different conditions are compared.Using the PIV optical measurement system,based on the cross-correlation measurement method,the velocity distribution in the flow field is measured,and the temperature distribution on the wall is measured using a high-temperature thermocouple.According to the experimental measurement conditions,a large eddy simulation study is carried out,which uses turbulent kinetic energy transport sub-grid model combined with the detailed GRI-Mech 3.0 chemical reaction mechanism.The dynamic characteristics,flame instability and pollutant emissions of non-premixed impinging jet flames driven by momentum are carried out.It is found that the generation of vortices is caused by shear instability,which is attributed to velocity gradient at the mixing interface of fuel and air.There are also vortex shedding,merging and fusion of isolated vortex islands during its development and propagation.The turbulence intensity decreases at the front edge of vortex,while it increases at the back edge of vortex.Besides,the compositional structure of nonpremixed impinging flame is related to the motion of vortex structure,which may lead to flame instability.The flow dynamics of impinging jet diffusion flames is affected by the coupling effects of Kelvin-Helmholtz instability,convection instability,RayleighTaylor instability and head-on collision instability.Both the increase of coflow velocity and the decrease of coflow temperature can enhance the hydrodynamic instability.In addition,the increase of coflow velocity may promote CO production,especially in the low mean mixture fraction region(0.07-0.26).The distribution of CO is more uniform and dispersed in large coflow velocity case,which is related with a stronger convection and diffusion process.Besides,the decrease distribution of local emission indexes of CO and NO is also shown in the case of high coflow moisture content,which can weaken the production of CO,thermal NO and prompt NO,and accelerate the consumption of NO.Moreover,CO reduction occurs mainly in the high CO concentration region,while NO reduction is observed in the whole flow field.