Study On Low Emission Combustion Chamber Design And Premixed Combustion Characteristics

With the pollution increasing in the world,the issue of gas turbine pollutant has been paid more and more attention,which is forcing the design goals of gas turbines combustor from the previous simple pursuit of high efficiency into the current high-performance and low-pollution.Because the premixed combustion mode can greatly reduce the flame temperature,scholars have investigated much about the lean premixed combustion chamber design research.China's low-NO_x emissions combustion technology research started later than foreign countrues and the gap of basic research and engineering development is obvious.The main way to achieve low pollution emission is to use premixed and graded combustion method to control fuel and air mixing,to optimize the flow field structure to achieve a reasonable distribution of temperature,to reduce the residence time of high temperature combustion product,thus to meet the requirements of low pollution emissions.However,the lean premixed combustion system may produce combustion instability such as flashback and blowoff,so the fuel and air premixing devices should be designed to meet the engineering requirements.It is of great practical value to design and operate the combustion chamber of low-emission gas turbine.Therefore,this paper has carried out the following works:(1)Different turbulence models(RANS and LES)and turbulent combustion models(FPV,PaSR and transport PDF)were verified by comparing with the experimental results,and the CPU time cost and calculation accuracy were analyzed.The simulation and experiment of the lean premixed flame were carried out to investigate the applicability of the turbulence combustion model and the chemical reaction mechanism.(2)The combustion mode of swirl combustion chamber and its influence on combustion field and emission characteristics were analyzed by experiment and LES simulation.The shape of the flow path(Quarl)will directly affect the mixing characteristics of air and fuel,which can convert the diffusion flame into partial premixed flame and reduce the flame temperature and NO_x emission.(3)The combustion characteristics of low swirl combustion chamber are analyzed by experiment and calculation.The velocity field distribution and flame stability mechanism of low-swirl flow are analyzed emphatically.Low swirl combustion,compared to conventional high-swirl combustion,will greatly reduce the high temperature gas residence time in the combustor,maintaining very low NO_x emissions while CO emissions basically unchanged.(4)The flashback and blow-off process of Siemens SGT-800 lean premixed swirl combustion chamber under normal temperature and pressure were studied by means of experimental method(high speed camera and PLIF),which provides guidance for the design and operation of lean premixed combustion.(5)The design scheme and calculation formula of the traditional combustor are verified,and the empirical formula of the combustion chamber size was modified,the design method of the low swirl pilot and the lean premixed combustion chamber is developed.The effects of momentum ratios and fuel jet positions on the mixing charactistics were studied and the multi – holes effusion cooling technique was studied.