Research On Theory And Method Of Purification Of Large Diesel Engine Exhaust Based On Two-phase Flow

The purification of large diesel engine exhaust particulate matters is researched with the combination of theoretical analysis,mathematical modeling,simulation calculation,simulation experiment and bench experiment in this thesis.The purification theory and method of wavy surface water film adsorbing diesel exhaust particles based on the two-phase flow theory are proposed.Kinematics and dynamics models of exhaust gas in straight and bent pipe devices are established,and the efficiency of separation and capture of particulate matter is analyzed in this thesis.At the same time,the sedimentation model of particulate matter in the pipeline is established.The influence of different structural parameters(pipe diameter,pitch,spiral angle)on exhaust resistance and particulate collection efficiency is analyzed through the ANSYS simulation.On this basis,innovative theories and methods for the purification of particulate matter by wave-shaped adsorption plate unit group with lower exhaust resistance and higher collection efficiency are proposed.In this thesis,the collision-separation model of droplets and particles is established,the theory of water film adsorption is studied and the model for adsorption of particulate matter on a horizontal water film and a vertical water film is established respectively.And the formation mechanism of the water film on the surface of wave-adsorption plate is researched.The water film is formed with micropores on the plate to make water seep out,as a result,the formation and motion model of isotonic water film is established.The experimental platform for simulation and bench experiments is built to validate the feasibility and effectiveness of the theories and methods of diesel exhaust particulate purification proposed in this thesis.The main content of this thesis is as follows.Firstly,the dynamic model of exhaust particles in straight and elbow pipes is established,and the influencing factors of particulate matter in the sedimentation process are obtained through theoretical calculations.On this basis,and the effect of straight and elbow pipes on the settling of exhaust particles is compared through simulation analysis and bench experiment.Besides,the influence of elbow pipe structure parameters on the capture efficiency of particulate matter and exhaust resistance is researched through simulation analysis and experiments.Secondly,the theory and method of water film adsorption on particles are studied.The collision and adsorption process of exhaust particles with horizontal water film and vertical water film is analyzed and the corresponding adsorption models are established respectively.As a result,the relationship between the thickness of the water film and the adsorption of exhaust particles is obtained.And for the adsorbed particles,the sedimentation process in the liquid is also analyzed.In addition,the model for the collision and separation process between exhaust particles and mist droplets is built,and the impact on the particle sedimentation process after the two collision is calculated.Thirdly,the innovative theory and method of wave adsorption unit group for purification of exhaust particulate matter is proposed and researched.The model for the formation of an equal pressure-differential water film is established,and through simulation,the diffusion process of droplets on the vertical plate is analyzed,providing a basis for the arrangement of micropores for the formation of a continuous water film.Besides,aiming at the regeneration requirement of the purification device,that is,the regeneration of the water film,the dynamic model of the water film is established.What’s more,the influence of the fluid boundary layer on the flow process of the water flow in the pore is investigated,and the effect of temperature on the regeneration process is also analyzed.Finally,a device for purifying exhaust particulates based on water film adsorption is designed and manufactured in the thesis.Through simulation experiments comparing the concentration and composition of exhaust particulate matter and exhaust gas flow rate and diesel engine bench experiments,the effectiveness and feasibility of the device for the separation and purification of exhaust particulate matter is verified.