Simulation Analysis And Structure Optimization Of Diesel Engine Urea SCR System

Nitrogen oxides(NO_x),one of the harmful emissions from diesel engine,have been paid more and more attention.The International Maritime Organization(IMO)has stipulated upper limit value for marine diesel engine NO_x emission in three tiers in MARPOL 73/78 Annex VI,and the Tier III standard has come into force formally in 2016.Selective catalytic reduction(SCR)is one of the most effective techniques for the Tier Ⅲ standard.The simulation analysis of SCR system is of great significance to the design and test of SCR system.In this thesis,the SCR system of the 6105AZLD diesel engine is modeled and simulated,and the simulation results are analyzed from several aspectsat the same time,the influence of the catalyst and the structure parameters of the injection system on the SCR system is simulated.The following studies have been carried out:Firstly,the basic principle of SCR system is expounded,and the modeling of 6105AZLD diesel engine SCR system is established by FIRE software,mathematical model and numerical calculation methods were selected reasonably.Determine the parameters of exhaust gas,injection parameters,chemical reaction dynamic parametersthrough experiment and calculation,complete mesh solver and settings,which lay the foundation for 3D numerical simulation.Secondly,the calculation of the model is completed.The results show that the atomization effect of spray droplets is consistent with the calibration parameters;for the de-nitration rate of SCR system,the simulation results are in good agreement with the experimental data,which verifies the rationality of the model.Then,the simulation results are analyzed from the aspects of velocity field,pressure field,atomization effect and reaction process.Through the analysis of the pressure field,it is concluded that the pressure drop of the SCR system mainly comes from the local pressure loss of the catalyst;Based on the spray particle size distribution,the atomization process and law of droplets were analyzed;The process of selective catalytic reduction of NH3 and NO under the action of catalyst was analyzed from the point of view of the variation of NO with time.Finally,on the basis of the model,the influence of the structure parameters of the catalyst and injection system of the SCR system is analyzed through control variable method.The pressure drop and NO_x conversion rate were used to evaluate the rationality of catalyst design.The optimal structural parameters of the injection system were selected by using the mixing uniformity and the NO_x conversion rate as the evaluation criteria.