| Along with the increasing requirements of natural gas engine's power performance and emission quality,it is crucial to research natural gas engine gas injection system flow characteristics deeply for improving natural gas engine fuel supply conditions and optimizing gas distribution control features.Knowing the flow characteristics of natural gas engine injection system,on one hand,it could optimize every delay during injection process and lower fuel diffusion with control system to reduce emission,on the other hand,it could contribute to the mixing of natural and air,enhance natural gas engine fuel efficiency.Two angles of time and space were proposed to analyze the flow characteristics of gas injection system in this paper.It provided effective theoretical basis to optimize the engine fuel supply that using the numerical method for different conditions of gas injection system to research the flow state.Firstly,the mathematical-physical model,which was applied in the analysis of gas injection system partical expansion flow state,was established based on the method of RANS in this paper.Then,verified the model by the partical expansion flow schlieren images of Sandia laboratory.The results showed this model could capture the near field shock wave structure of the jet exit during partical expansion time and flow state parameters.So the model could be utilized to study flow characteristics deeply in gas injection system.Secondly,simulating the gas injection system 3D transient flow process in ANSYS Fluent software,three phases named late rising period,stabile period,the end of the injection were defined through referring to the result of injection pressure ratio 11.This paper analyzed the effects of flow oscillatio in the stable period,and characteristical frequency and the length of nozzle were inversely proportional.Also,the paper analyzed that pneumatic delay in system was due to pressure wave transmission,and it had effect on fuel supply system control process.However,put gas delay in the system is due to the nozzle after gas injection valve closed natural deflated,and nozzle is mainly manifested as the function of the accumulator cavity during that time.Besides,according to gas injection process on different injection pressure ratio and nozzle structure,this paper showed the relationship between injection pressure ratio and nozzle structure and mass flow rate characteristic parameters for loweringlatency and improving stability of mass flow rate.Finally,based on ANSYS Fluent,gas injection system with outfield was simulated.Discussing gas jet stream near field structure during stable period which aer velocity distribution and density distribution,and the effect of injection quality spatial distribution,they showed that Mach disk structure had an weaken effect on gas jets penetration in central axial direction in partical expansion jets,and the turbulent kinetic energy increase caused by it would promote the development of the jet on the radial.According to Ouellette formula,this paper deduced injection quality and penetration secondary had direct ratio relationship,and the relationship was verified by simulation results. |
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