Research On The Influence Of Nozzle Geometrical Deviations On The Atomization Characteristics Of Fuel Injectors

Fuel atomization is the process of injecting fuel into the combustion chamber and breaking liquid fuel into tiny droplets,and it is one of the most important working processes of aero-engine.The atomization performance of fuel atomizer directly affects the combustion efficiency,thrust and thrust-to-weight ratio,working stability and pollution emission.As the last flow channel before fuel injection,the nozzle orifice of the fuel atomizer has an important influence on the atomization performance.However,the influence rule of orifice deviation on the atomization performance is not clear,lead to the lack of theoretical basis for the tolerance design and error control.So that,in the process of production,there has a problem that either design precision is insufficient to deteriorate the atomization performance,or the design precision is too high to increase the manufacturing difficulty and reduces the production efficiency.Therefore,investigating the influence law of orifice deviations on the atomization performance of fuel atomizers to provide the theoretical basis and reference for the tolerance design and machining error control has become an important task to improve the quality and performance of an aircraft engine.The fuel atomizers commonly used in aeroengine are pressure-swirl atomizer,plain-orifice atomizer and effervescent atomizer.The common geometrical deviation can be classified as diameter deviation,conical deviation and inclined deviation.The main purpose of this research is to study the influence of three deviations on atomization performance of three kinds of fuel atomizer.The main research contents of this paper are:In the traditional SMD prediction model,the diameter of the nozzle is set as constant,so that the influence of orifice deviations on the SMD can not be analyzed.Aim at this problem,the influence of orifice deviation on the evolution of air-core with pressure is investigated,and the expression of equivalent diameter function containing orifice deviation was obtained by fitting.Then,the modified SMD prediction model is established by introduce the equivalent diameter into traditional SMD prediction model.Compared with the experimental results,the modified model reduced the prediction deviation from 21.3%to 8.5%.Further study the effects of orifice deviation on the SMD based on modified model,it can be found out that the 0⁵.0%diameter deviation,0².0°divergent conical deviation and0¹.0°inclined deviation will have little impact on the SMD,1.0°convergent conical deviation will increase about 12.5%of the SMD,so that the convergent conical deviation is needed more strict restriction.The influence law of orifice deviation on the cavitation state of plain-orifice atomizer is unclear.Aim at this problem,a prediction method of cavitation state for the nozzle with minor deviation is proposed.The critical pressure of cavitation inception and hydraulic flip is taken as the index parameter,through the finite element simulation study based on Fluent platform,the critical pressure models were established by studying the influence of orifice devitations on the critical pressure.Based on these models,the critical pressure of different cavitation states with different orifice deviations can be calculated.Based on this method,it can be obtained that the influence of±5.0%diameter deviation and 0².0°inclined deviation will caused about 2.0%of critical pressure variation,the impact of conical deviation is the most significant,1°of divergent deviation will reduce by 12.5%of the critical pressure,and the 1°of convergent deviation will increase by 114.2%.Therefore,the conical deviations need to be strictly controled in the manufacturing process for the plain-orifice atomizer.The index parameter used to analyze the influence of orifice deviation on the atomization characteristics of bubble nozzle effervescent atomizer is unclear.Aim at this problem,the quantitative influence relationship between the orifice deviation and the SMD?spray angle and critical gas-liquid flow ratio GLR_cri is investigated.It can be found that the atomization stability is the most sensitive to the orifice deviation.The experimental results showed that when the SMD average changed by3.8%,the corresponding spray angle changed by 14.5%,while the GLR_cri changed by 64.7%.Based on this phenomenon,an analytical method which using the GLR_criri as indicator parameter is proposed.It can be found that-10.0%⁺20.0%of diameter deviation and 1°divergent conical deviation has very small impact on the GLR_cri;2.0°convergent conical deviation will increase by 10%GLR_cri;2.0°inclined deviation will increase by 20.0%GLR_cri,so that the inclined deviation is the most sensitive deviation and it should be controlled more strictly.