Simulation Study On Spray Atomization Of Diesel Engine Urea-SCR System

With the continuous increase of environmental pollution and the gradual upgrading of emission standards,the pollution problem brought by diesel engines has been paid more and more attention by the industry and the country.The urea-SCR of diesel engine is the current mainstream NOx aftertreatment technology for diesel engines.Based on Fluent software,the numerical simulation of urea aqueous solution injection,evaporation,hydrolysis pyrolysis and mixing in urea-SCR post-treatment technology was carried out.Firstly,the working principle and system composition of urea-SCR post-treatment technology are analyzed.The evaluation index of urea droplet atomization performance is discussed.The mathematical model of urea-SCR system spray atomization simulation is established.Based on Solidworks software,the system simulation geometry model was established.The ICEM software was used to mesh the grid.The boundary conditions for numerical simulation were set according to the common working conditions of the diesel engine,and the urea-SCR system simulation model was established.Secondly,based on Fluent software,the process of tail gas flow,urea aqueous solution injection,urea droplet evaporation and pyrolysis hydrolysis was simulated.The influence of urea nozzle spray atomization was studied by changing the urea nozzle structure parameters and system operation parameters.The results show that the uniformity coefficient and average mass fraction of NH₃ decrease with the increase of the distance between the nozzle and the exhaust gas inlet.With the increase of the number of orifices,the increase of the diameter of the orifice,the jet direction and the exhaust gas flow As the angle of the direction increases,the uniformity of NH₃ distribution at the front end of the carrier increases first and then decreases.With the increase of exhaust gas temperature,the uniformity of NH₃ distribution at the front end of the carrier increases gradually and then remains basically unchanged.The average mass fraction of NH₃ at the front end of the carrier gradually increases.With the increase of exhaust gas flow,the uniformity and average mass fraction of NH₃ at the front end of the carrier The average decreases gradually,and the decreasing range is basically consistent.With the increase of urea mass flow,the uniformity of NH₃ distribution at the front end of the carrier remains basically unchanged,and the average mass fraction of NH₃ at the front end of the carrier increases linearly.Finally,the effect of the type of mixer,the position of the mixer,and the number of mixers on the atomization of urea droplets was studied by designing and adding a mixing device to the system.The results show that the addition of mixer can significantly improve the uniformity of NH₃ distribution in urea-SCR system.The disturbance effect of mixer 2 on urea droplets is better than that of mixer 1.With the continuous shift of the position of the mixer,the NH₃ of the front end of the carrier is evenly distributed.The first increase and then decrease.When the position of the mixer is 6D,the NH₃ distribution at the end of the inlet tube is the most uniform.With the increase of the number of mixers,the uniformity of NH₃ at the end of the inlet trachea increases first and then decreases and the average mass fraction of NH₃ decreases.Then gradually increase.