Research On Integrated Design Of Marine Diesel Engine Soot Filtration And Noise Reduction

With the continuous increase of environmental protection efforts,domestic and foreign will further limit the marine diesel engine’s particulate matter emission,then catalytic converters,particle traps and mufflers need to be installed in the exhaust system.The space of the ship’s engine room is limited,and the additional devices will increase the exhaust back pressure of the diesel engine,which will affect the power performance and economic performance.The monolith for exhaust gas purification is honeycomb porous structure,which has the functions of reactive and dissipative noise reduction performance,and as the SCR catalyst coated on the wall surface of the particulate trap can form a SCRF device with particle purification and denitration functions.This paper studies the purification and noise reduction characteristics of the marine particle filter,and combines the noise reduction element to carry out the integrated design of particle capture and noise reduction.In this thesis,the soot loading and regeneration process of the particulate filter and its influencing factors are firstly studied.The DOC+DPF one-dimensional model was established in AVL-Boost software,and the relevant parameters in the model were calibrated using the test data of the experimental bench.According to the calibrated DPF performance parameters,a 3D model of DPF is established in AVL-Fire.The flow velocity and soot distribution changes during the loading process of DPF were simulated and analyzed,and the effects of different DPF pore mesh numbers,wall thicknesses and ratios of inlet and outlet pore width on the pressure drop and soot distribution during loading were compared;The soot distribution and temperature distribution changes during the continuous regeneration of DPF were simulated and analyzed,and the effects of different inlet temperature,inlet NO₂concentration,inlet flow and initial soot loading on the continuous regeneration rate and pressure drop were compared;The soot distribution,temperature and temperature gradient changes during the active regeneration of DPF were simulated and analyzed,and the effects of different initial soot distribution forms on the maximum temperature and oxidation rate during the active regeneration of DPF were compared.The acoustic performance of DOC and DPF monolithes in particle traps were then investigated.Based on the transfer matrix method,the acoustic models of the two monolithes were established,and the two-load method was used in the impedance tube to conduct the experimental test.The transmission loss calculated by the model was in great agreement with the experimental measurement data.The effects of different monolith’s pore mesh number,wall thickness,length and medium temperature on the transmission loss of DOC and DPF monolithes were analyzed by the model.An acoustic test device containing a square monolith was further designed,the impedance transfer method and the lumped parameter method were used to study the acoustic calculation of the device containing the monolith,and the transmission loss of the device was calculated and compared with the experimental value.The results show that the impedance transfer method is more accurate over the entire calculated frequency range.Finally,the integrated design of soot capture and noise reduction is carried out.Based on the spectrum analysis of exhaust noise,using Helmhertz resonant cavity,insertion tube,perforated plate,DOC and DPF monolith structure,a diesel engine exhaust treatment device with particle trapping and noise reduction functions is designed.Under the rated load of the diesel engine,the simulated exhaust pressure loss of the device is 2183Pa,the inlet velocity uniformity index of the DOC is 0.991,and the noise transmission loss basically reaches 25d B,which meets the design requirements of the exhaust device’s back pressure,flow field uniformity and noise reduction performance.