Performance Analysis And Structure Optimization Design Of Multi-point Direct Combustion Chamber

With the development of civil aviation field,various countries have put forward higher requirements for the performance of the aero-engines.As the awareness of environmental protection is increasing gradually,reducing the nitrogen oxide emissions generated by the aero-engine combustion chambers has become an important consideration in the engine design process.Among the many new type low-pollution combustion chamber technologies,LDI combustion chamber technology has better development prospects.This article optimizes the head structure based on a typical 3×3 multi-point spray combustion chamber model,including three optimization methods: the center recessed swirler,the middle row recessed swirlers,and the changed size of swirlers.Then,through numerical simulation method,using the realizable k-? model as turbulence model,non-premixed PDF model and EDC model as combustion models,the characteristics under the cold flow field and the combustion flow field are calculated respectively,and the outlet temperature distribution and the nitrogen oxide emissions are analyzed.At the same time,the lean blow-out boundary is predicted respectively by using the numerical simulation method and the semi-empirical correlation method,and the prediction errors between these two methods are discussed detailedly.The calculation results in the cold state show that the lengths of recirculation zone for the typical multi-point combustor is among 30~40mm,while which for the center recessed combustor and the middle row recessed combustor are among 20~30mm.It suggests that the recess design of the head swirlers can reduce effectively the area of downstream recirculation zone and shorten the length of recirculation zone.For the design scheme of changing the swirlers size,because the central swirler chooses a model with small swirl number,and the circumambient swirlers choose the models with large swirl number,this leads to an increase in the area of downstream recirculation zone of the central swirler,which is extra 50 mm,and has an impact on the recirculation zone of the other circumambient swirlers.For the prediction of the lean blow-out boundary,this article uses two methods of numerical simulation and semi-empirical formula to make predictions,and analyzes the prediction results.The study found that the difference between the prediction results of these two methods is within 10%,and there is good consistency.At the same time,the fuel-air ratio of lean blow-out for the typical multi-point combustor and other three optimized combustors are respectively 0.0052,0.0048,0.0045 and 0.0039.It suggests that all three optimized models can widen the lean blow-out boundary.Among them,the effects of middle row recessed design and changed size design are better.Comparing the outlet temperature distribution of combustion chamber under appropriate combustion conditions,it is found that the outlet radial temperature distributions of each combustor satisfy the temperature distribution requirements of the turbine blade design.At the same time,the outlet temperature distribution of the middle row recessed design is more uniform,which is no high temperature concentrated area.By comparing the NOx emissions,it is found that near the proper combustion state,the NOx production peaks and gradually decreases towards lean and rich conditions.Within the range of normal operating conditions for combustion chamber,these three optimized models can reduce the nitrogen oxide emissions,and the effects of the center recessed design and middle row recessed design are more obvious.