Lean premixed combustion,which allows for reducing the production of thermal NOx,is prone to combustion instabilities.There is an extensive research to develop a reduced physical model,which allows-without time-consum...Lean premixed combustion,which allows for reducing the production of thermal NOx,is prone to combustion instabilities.There is an extensive research to develop a reduced physical model,which allows-without time-consuming measurements-to calculate the resonance characteristics of a combustion system consisting of Helmholtz resonator type components (burner plenum,combustion chamber).For the formulation of this model numerical investigations by means of compressible Large Eddy Simulation (LES) were carried out.In these investigations the flow in the combustion chamber is isotherm,non-reacting and excited with a sinusoidal mass flow rate.Firstly a combustion chamber as a single resonator subsequently a coupled system of a burner plenum and a combustion chamber were investigated.In this paper the results of additional investigations of the single resonator are presented.The flow in the combustion chamber was investigated without excitation at the inlet.It was detected,that the mass flow rate at the outlet cross section is pulsating once the flow in the chamber is turbulent.The fast Fourier transform of the signal showed that the dominant mode is at the resonance frequency of the combustion chamber.This result sheds light on a very important source of self-excited combustion instabilities.Furthermore the LES can provide not only the damping ratio for the analytical model but the eigenfrequency of the resonator also.展开更多
Two simplified models for predicting minimum extinguishing concentration(MEC) of ultrafine water mist(UFM)(<10 m) were developed based on limiting oxygen concentration(LOC) and combustion limit temperature(CLT),res...Two simplified models for predicting minimum extinguishing concentration(MEC) of ultrafine water mist(UFM)(<10 m) were developed based on limiting oxygen concentration(LOC) and combustion limit temperature(CLT),respectively.Experiment was conducted using a modified cup burner which can reduce the surface adsorption of UFM.Two typical liquid fuels,n-heptane and ethanol,were used in the experiment.Tests using the same scenario were repeated 20 times or 10 times according to the variance of extinguishing time.The average and the standard deviations of extinguishing time were used to evaluate the fire extinguishing performance of UFM.Experimental results agree well with the model based on LOC,and disagree with the model based on CLT.The disagreements were explained by analyzing flow behavior of UFM.It was concluded that the primary mechanism of fire extinguishment with UFM was oxygen dilution.展开更多
文摘Lean premixed combustion,which allows for reducing the production of thermal NOx,is prone to combustion instabilities.There is an extensive research to develop a reduced physical model,which allows-without time-consuming measurements-to calculate the resonance characteristics of a combustion system consisting of Helmholtz resonator type components (burner plenum,combustion chamber).For the formulation of this model numerical investigations by means of compressible Large Eddy Simulation (LES) were carried out.In these investigations the flow in the combustion chamber is isotherm,non-reacting and excited with a sinusoidal mass flow rate.Firstly a combustion chamber as a single resonator subsequently a coupled system of a burner plenum and a combustion chamber were investigated.In this paper the results of additional investigations of the single resonator are presented.The flow in the combustion chamber was investigated without excitation at the inlet.It was detected,that the mass flow rate at the outlet cross section is pulsating once the flow in the chamber is turbulent.The fast Fourier transform of the signal showed that the dominant mode is at the resonance frequency of the combustion chamber.This result sheds light on a very important source of self-excited combustion instabilities.Furthermore the LES can provide not only the damping ratio for the analytical model but the eigenfrequency of the resonator also.
基金supported by the National Natural Science Foundation of China (Grant No. 51028401)Jiangsu Province-Supporting Science and Technology Program (Project No. BE2010677)the Research Grant Council of the Hong Kong Administrative Region,China (Project No.CityU118909)
文摘Two simplified models for predicting minimum extinguishing concentration(MEC) of ultrafine water mist(UFM)(<10 m) were developed based on limiting oxygen concentration(LOC) and combustion limit temperature(CLT),respectively.Experiment was conducted using a modified cup burner which can reduce the surface adsorption of UFM.Two typical liquid fuels,n-heptane and ethanol,were used in the experiment.Tests using the same scenario were repeated 20 times or 10 times according to the variance of extinguishing time.The average and the standard deviations of extinguishing time were used to evaluate the fire extinguishing performance of UFM.Experimental results agree well with the model based on LOC,and disagree with the model based on CLT.The disagreements were explained by analyzing flow behavior of UFM.It was concluded that the primary mechanism of fire extinguishment with UFM was oxygen dilution.
