Experimental study on NOemission 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.