Characteristic Research For Micro-miniature Lean Premixed Swirl Combustor

Lean premixed combustion is one of the most promising low-pollution combustion technologies for gas turbines,which can effectively reduce pollutant emissions,but it can also cause the problems of combustion instability and insufficient cooling of the wall surface of combustor.To solve the problems,this paper designs a micro-miniature lean premixed swirl combustor,which adopts annular jets in mixing tube and cooling microchannels embedded in walls,and then the combustion characteristics of the combustor are studied with experimental and numerical methods.First of all,a micro-miniature lean premixed swirl combustor was designed.It contains changeable mixing tube structures,enabling the use and study of mixing tubes with and without annular jet,and it has a central vertebral body and convergent exit to suppress flashback.Fluent software is used to conduct numerical simulation study on the cold and hot flow field of combustor to explore the influence of inlet flow rate,equivalent ratio and air temperature on the flow field structure.The results show that the flow field of the combustor contains obvious central backflow zones and angular backflow zones which are separated by the shear layer.With the increase of the intake flow rate,the axial velocities of the cold flow field and the hot flow field of combustor increase,the pre-mixing degree of air and methane on the outlet section of mixing tube increases,the combustion intensity increases,and the flow field temperature increases.With the increase of equivalent ratio,the velocity of the cold flow field is basically unchanged,the velocity of the hot flow field increases and the pre-mixing degree of air and methane on outlet section of mixing tube increases,and the temperature of the flow field increases.With the increase of air temperature,the velocity of both cold and hot flow field increases,the pre-mixing degree of air and methane decreases,and the combustion intensity increases making the flow field temperature rise.Then,the swirl combustor were machined and an experimental system based on the swirl combustor was established,which is made up by the section of combustion,cooling and measurement.The effects of the inlet condition and annular jets in mixing tube on the the combustion characteristics were studied.The results show that the increase of intake flow rate,equivalent ratio and air temperature are beneficial to the increase of combustion efficiency and reduction of CO emission,while the amplitude of pressure oscillation fluctuates.The increase in inlet flow rate and equivalent ratio can change the shape of the flame.Increase of annular jet frequency and duration time can improve the premixing uniformity of methane and air,reduce the CO emissions,increase NO.emissions and combustion efficiency,but with the increase of jet flow rate,CO emissions decrease at the beginning and increase later,NOx emissions increase at first and then decreases,the combustion efficiency also decreases after initial increasing,certain values of jet flow rate would help to curb the oscillation of combustion pressure.In the end,effects of cooling of microchannels embedded in combustor wall on the characteristics of lean premixed combustion were studied.Heat transfer of microchannels can be coupled with combustion flame.The cooling of microchannels reduces wall temperature efficiently,but it also causes the flame to contain sparks or even yellow fire,reduce the combustion completion,increase CO emissions,reduce NOx emissions,and reduce combustion efficiency.