| The utilization of renewable energy is one of possible ways to reach carbon emission net-zero targets.However,the intermittent nature inherent in renewable energy will pose a great threat to the security and stability of energy supplements.Natural gas is a transition option in achieving net-zero targets and an important balancing measure in the future energy system.Micro gas turbines fueled by natural gas will have broad application prospects with the implementation of multi-energy complementary ideas.Rapid response to changes in energy demand is one of the features of future energy systems.Therefore,micro-gas turbines must have better part-load operation capability.Modern commercial micro-gas turbines all use lean premixed combustion technology,which may suffer pollutant emissions increase and poor flame stability under part-load operating conditions.The fuel staging idea widely adopted in heavy-duty gas turbines is referenced in this paper.This paper considers the influence of premixing characteristics differences caused by circumferential fuel staging on combustor exhaust characteristics and flame dynamic characteristics.The purpose is to demonstrate the feasibility of improving the micro-gas turbine combustor part-load operating performance by simple circumferential fuel staging.The selection of a proper ignition equivalence ratio is important to ensure an excellent quick start-up capability for micro-gas turbines.The variation of flame shape under various ignition fuel ratios and equivalence ratios is analyzed based on flame visible radiation.When the ignition fuel is 10%,the minimum ignition equivalence ratio is 0.082 and the suitable value is around 0.493 based on the flame shape and dynamic characteristics.The combustion efficiency will drop if the ignition equivalence is too small.The flame will be too long or shake violently if the equivalence ratio is too big.The suitable equivalence ratio window is widened with the increase of the ignition fuel ratio.Then,the temperature distribution characteristics and outlet characteristics of the prototype combustor are studied under 50% to 100% heat load ratio conditions by using CFD.The temperature distribution characteristics in the fluid formed by swirlers are greatly impacted by the fule staging scheme.However,the temperature characteristics in the main reaction zone are mainly related to the heat load ratio.The influence area of the pilot flame will gradually expand as the heat load ratio decrease.When the heat load ratio is constant,OTDF,the combustion efficiency,and NO emission will be affected by the fuel staging,but the total pressure recovery coefficient results are almost unaffected.OTDF and NO emissions can be reduced up to 9.5% and 8.7%,respectively,by selecting a proper fuel staging scheme.After then,the flame dynamic characteristics are studied based on OH*chemiluminescence images.The accuracy of the CFD method used in Chapter 4 is further verified by comparing the experiment and the CFD results.The effect of circumferential fuel staging on flame dynamics is studied by analyzing the dynamic characteristics of heat release rate.The heat release rate temporal distribution uniformity is significantly affected by fuel staging,but the flame frequency shows an excellent linear correlation with the turbulent frequency.When the heat load ratio is constant,the frequency results differ by a maximum of 4%.Finally,the feasibility of the combination of circumferential fuel staging with exhaust gas recirculation(EGR)is studied experimentally.In the field of MGT,EGR is a feasible solution to improve the part-load performance and fuel flexibility.The changing of heat release rate spatial distribution caused by EGR may have a substantial impact on flame frequency characteristics.Therefore,the influence of EGR on heat release rate is investigated experimentally under various heat load ratios(50% to 100%)and EGR ratios(0 to 20%).The result shows that EGR can improve the spatiotemporal characteristics of heat release rate and reduce the influence of fuel staging.But the flame frequency still correlates well with turbulent frequency.It is feasible to combine circumferential fuel staging with EGR to improve the part-load operation capability of the combustor without changing the control logic of fuel staging. |
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