Experimental study on NO_x emission correlation of fuel staged combustion in a LPP combustor at high pressure based on NO-chemiluminescence

Experimental investigations on NOx emissions of a single-cup,Lean Premixed Prevaporized(LPP),module combustor were carried out at elevated inlet temperature and pressure up to810 K and 2.0 MPa,close to the real operating conditions of aero-engine combustors.This LPP combustor adopts centrally staged fuel injections which could produce separated stratified swirling spray flame.In the NOx emissions measurements,the ranges of dome equivalence ratio and fuel stage ratio were from 0.55 to 0.58 and 8%to 24%,respectively.The optical diagnosis on separated stratified swirling spray flame were carried out with fuel stage ratio changing from 15%to 30%.Therefore,NO*and OH*chemiluminescence images were obtained.The results show that NOx emissions increase with the increase of the fuel stage ratio.And from the chemiluminescence images,the main flame and pilot flame are found weakly coupled.The pilot flame plays a significant role in NOx emission production because of its higher adiabatic flame temperature.Based on the results of chemiluminescence optical tests,a new NOx emission prediction model is proposed based on the Lefebvre’s single flame model The estimate of local equivalence ratio of the pilot stage’s nonpremixed flame is modified considering the characteristics of spray combustion,and a"PLUS"emission prediction model suitable for separated stratified swirling spray flame is obtained.Compared to the experimental data,the"PLUS"model exhibits a good prediction in a range of±13%of deviation.

Experimental investigations of the spray structure and interactions between sectors of a double-swirl low-emission combustor

In this paper,the spray characteristics of a double-swirl low-emission combustor are analyzed by using Particle Imaging Velocimetry(PIV)and Planar Laser Induced Fluorescence(PLIF)technologies in an optical three-sector combustor test rig.Interactions between sectors and the influence of main stage swirl intensity on spray structure are explained.The results illustrate that the swirl intensity has great effect on the flow field and spray structure.The spray cone angle is bigger when the swirl number is 0.7,0.9 than that when the swirl number is 0.5.The fuel distribution zone is larger and the distribution is more uniform when the swirl number is 0.5.The fuel concentration in the center area of the center plane of side sector(Plane 5)is larger than that of the center plane of middle sector(Plane 1).The spray cone angle in Plane 5 is larger than that in Plane 1.The width of spray cone becomes larger with the increase of Fuel-Air Ratio(FAR),whereas the spray cone angle under different fuel-air ratios are absolutely the same.The results of the mechanism of spray organization in this study can be used to support the design of new low-emission combustor.

Dynamics of stratified swirl flame near lean blow out

This paper studies the flame dynamics near lean blowout(LBO)conditions in a stratified swirl burner.The novel BASIS burner is used and fueled with premixed methane/air mixture at atmospheric conditions.In the experiments,only the pilot flame works with four different equivalent ratios.It is found that as the flame changes from stable combustion to near LBO,the flame macrostructure changes from V-shape to M-shape.Meanwhile,a characteristic frequency of 405 Hz is found in the spectrum of heat release signal.The closer to LBO,the higher amplitude is found at the frequency peak.Post-processing of flame images illustrates that the 405 Hz comes from the circumferential movement of the flame.Large-eddy simulations(LESs)via OpenFOAM reproduce the flame dynamics near LBO,which agrees with the experimental results.LESs provide more insights into the flow fields,showing that the characteristic frequency of 405 Hz comes from the flame-vortex interaction.This study reveals the mechanism of flame and vortex interactions in a stratified swirl burner near LBO.The heat release signal is also found can be used as a candidate precursor for LBO.

Statistical characteristics of spray autoignition of transient kerosene jet in cross flow

To study statistical characteristics of the random spray autoignition,aviation kerosene was injected transiently into non-vitiated air crossflow in a flow reactor with optical accesses.The operating conditions were relevant to gas turbine combustor:the air crossflow pressure and temperature were in the range of 1.4-1.7 MPa and 830-947 K,respectively,and the jet-tocrossflow momentum flux ratios were 20,50 and 80.Statistical distributions of random ignition delay times with adequate convergence were estimated based on histograms.The dependences of the distributions on reactor pressure,temperature,and jet-to-crossflow momentum flux ratio were studied.The results show that the resulting distributions appear more concentrated with the increase of air temperature or jet-to-crossflow momentum flux ratio.And then the correlations for the mean and standard deviation of the ignition delay time sample data were developed based on the present results.Compared with the correlations of ignition delay time of homogeneous premixed gas-phase kerosene/air mixture reported in the literature,the results show a greater significance pressure dependence and lower temperature sensitivity of the ignition delay time of nonpremixed kerosene spray.