Research On Blowout Pattern Of Ramjet Combustor In Wide Range Engine Based On Characteristic Timescale

Scramjet is a type of ramjet engine.Compared to ordinary aviation engines,scramjet engines abandon rotating components such as compressors and blades,which leads to a quite simple structure and brings convenience to maintain.Scramjet has low self-weight and high adaptability to high-speed and wide speed flight.It is an ideal engine type that can be used for high-speed aircraft in China for a period in the future.For manpower transportation via aircraft,high speed and long flight distance are also required to reduce travel time to achieve faster deployment of combat power or observation to the target location;For weapons that can cause substantial strikes such as missiles,high flight speed is the key to achieve penetration and cause strike to time sensitive targets.The scramjet engine can precisely meet the above requirements and has broad application prospects.However,the scramjet engine needs to meet the following requirements before being widely used in production and daily life:(I)A wide working range and the ability to provide power for aircraft in various environments and flight speeds;(II)The ability to cruise at high altitude which enables the aircraft to maintain stable high-speed flight for a long time;(III)High reliability,able to maintain stable operation under harsh working conditions.In this regard,the prediction model of fuel jet trace under supersonic crossflow is proposed in this paper,and the characteristics and prediction method of lean fuel blowout of scramjet are studied,which provides a reference for design and optimization of scramjet from two aspects includig efficient operation and ability to cope with harsh conditions.The specific research content is as follows:(1)The spray and flameout test platform was built,and the spray experiments under a wide range of crossflow Mach numbers were finished.The whole process of transverse jet breaking and atomization was studied by taking shadowgraph pictures and recording the spray process;Chartacteristic of penetration height change was obtained by comparing height of spray under different injection and inflow conditions.By capturing the spray edge coordinates in the image and performing semi-empirical fitting,a lateral spray trace prediction model for supersonic crossflow flow in wide velocity domain was established.(2)Based on the images captured in the spray experiment,the Fast Fourier Transform and Proper Orthogonal Decomposition analysis of the whole spray region were carried out.Through the time domain and energy level distribution,the types of disturbances on the spray surface and their leading role in the overall disturbance were obtained.Finally,the laws of spray dynamic characteristics were summarized.(3)Blowout experiments under a wide range of crossflow Mach numbers(2,2.5,3)were conducted with different total temperature,total pressure,and fuel conditions.Data on the crossflow total temperature,total pressure,and fuel equivalence ratio were measured for lean blowout and near lean blowout states.The characteristic of lean blowout limit under different crossflow parameters was summarized,laying the foundation for thermal numerical simulation of combustor and derivation of lean blowout limit prediction method.(4)Based on lean blowout limit and near lean blowout conditions parameters obtained from experiments,thermal numerical simulation of combustor was conducted.The core region of combustion reaction was determined by static temperature and intermediate reaction product distribution,and relative flow timescale was measured.At the same time,Perfectly Stirred Reactor model(PSR)is used to decouple the chemical reaction inside the reactor from the flow characteristic.According to the reaction zone parameters,chemistry reaction time scale is calculated,and prediction method of lean blowout limit based on the Da number is finally obtained.