Simulation Analysis And Structure Optimization Of Marine Diesel Engine SCR System

The TIERIII standard of Annex VI of the MARPOL Convention places the most stringent requirements to date for the emission of nitrogen oxides from diesel engine exhaust.In several effective diesel engine exhaust aftertreatment systems,selective catalytic reduction(SCR)technology can effectively reduce nitrogen oxide emissions.In this paper,the 4135Ca diesel engine SCR system is taken as the research object,and its simulation modeling and experimental research are carried out.The simulation results are analyzed from various angles,and the influence of nozzle and catalyst structural parameters on the SCR system is simulated.The main research contents of the thesis are as follows:First,the principle of diesel engine SCR system is introduced,and the main factors affecting the efficiency of SCR are introduced.Using FLUENT software to model the 4135Ca diesel engine SCR system,select reasonable mathematical model and corresponding exhaust parameters,injection parameters and chemical reaction kinetic parameters,divide the grid and set the solver to lay the foundation for the flow field analysis of the catalytic converter.Second,solve the built model.The simulation results are analyzed from the velocity field,the concentration field,the pressure field and the turbulent energy distribution.The analysis of the velocity field shows that the expansion of the outlet causes the mixing of the reducing agent,and the analysis of the concentration field,the distribution of NH3 concentration is greatly affected by the velocity field,and the concentration in the middle is low,around is high.The analysis of the pressure field shows that the pressure is approximately the same between the expansion port and the catalyst cross section,and gradually decreases along the axis in the catalyst;Distribution analysis shows that the damping effect of multiple catalysts enhances the friction of the fluid,leading to the strengthening of turbulence.Then the ESC emission test is carried out on the SCR system.The experimental data is basically consistent with the simulation data,which verifies the rationality of the model.Last,based on the experimental bench model,the control variable method is applied.For factors affecting the mixing effect of ammonia and diesel engine exhaust,the SCR system is optimized from the perspective of the injection system and catalyst structure.The simulation results show that when the number of nozzle orifices is 8 and the axial injection,nozzle orifice diameter is 3mm,and the length of the expansion section is 90mm,the ammonia distribution uniformity of the catalyst inlet section is increased by 6.6%,7.6%,and 6.7%,respectively.By optimizing the injection system and the catalyst structure with this structure,the conversion efficiency of the diesel engine SCR device can be improved.