Experimental Study Of Flow Characteristics Of The Low-Calorific Lean Premixed Nozzle On Micro Gas Turbine

At present,people are facing the fossil energy depletion,pollution and other problems of energy and environment crisis.Biogas as a renewable energy has received the widespread attention throughout the world.Distributed energy supply(DES)systems are able to adapt to the dispersion and small-scale application of the biogas.Micro gas turbine(MGT)is widely used in DES as power machinery,and it possesses the advantages of compact structure,low emissions,high output power and good adaptation to different fuel.The performance of combustor and nozzle are important to ensure that the MGT can work normally when it is fed by biogas.This thesis mainly focuses on flow characteristics of the lean premixed nozzles and combustor of a 60 kW MGT,providing references to the application of biogas and modification of MGT.The models of the original premixed nozzle(OPN)and 2 types of new enhanced premixed nozzles(EPN1 and EPN2)are designed and a singlenozzle combustor test bench is built according to the real structure of nozzle and combustor of the 60 kW MGT.According to the operating parameters and similarity criteria,experimental comditions are acquired aiming to find out the relation of the air excess ratio in the nozzles and the parameters of air and fuel,such as air mass flow,air temperature,fuel mass flow,pressure difference in and out of the nozzle.The results show that the air excess ratio in EPN1 and EPN2 is 0.5 higher than OPN.The air excess ratio will increase when the total air mass flow though the nozzle increases.The change of air temperature will not effectively affect the air excess ratio in the nozzle.The air excess ratio will decrease when the fuel mass flow increases.The pressure difference in and out of the nozzle is the main factor to affect the air excess ratio.Then the flow structures and characteristics in the three types of nozzles and combustor are acquired by PIV experiment.The results show that the flow structures of combustor will not be effectively affected by the structures of nozzles.The average velocity at the outlet of EPN1 and EPN2 is approximately 10% higher than OPN.Stable swirl motions can be observed at the outlet of EPN1 and EPN2,which will benefit the premixedness of fuel-air.The turbulent kinetic energy of EPN1 is 50.9% lower at the outlet than the OPN,which will benefit the stability of flow.Finally,the snap-shot POD is applied to analyze the data from PIV,to investigate the coherent structures of the flow in nozzles.The results show that the turbulence energy will more concentrated in the first 10 modes in EPNs,with the value of 70.1% and 62.3%,compared with 47.2% of OPN.The two types of new nozzles possess similar POD structures of the first two modes,indicating that the two new nozzles possess similar characteristics.The experiments in this thesis show that the EPNs can better adapt to the low-calorific biogas by providing better air excess ratio,stable swirl motions at the outlet and low turbulent kinetic energy.