| The non-road four-phase emission regulations are about to be implemented.The four-phase emissions are limited to a 90%reduction in PM,a 12%reduction in NOx,and a 12%reduction in HC when compared with the three-phase regulations,.DOC+DPF+SCR engine composite after-treatment system can achieve purification of HC,CO,PM and NOx effectively without relying on in-machine purification.By this system,few modifications can achieve the requirements of engine emission limits more quickly and good economics.This article focused on the off-road four-phase post-processing matching design.studied on the composite post-processing system of DOC+DPF+SCR.Starting from the structure of DOC,DPF,and SCR,the analysis of the emissions of each unit of the system The purification ability is verified on the engine bench,and the SCR working strategy is optimized,which has certain guiding significance for the design of the engine after-treatment system.The research object of this article is non-road four-cylinder high-pressure common rail electronically controlled supercharged diesel engine.surrounded the matching design of the off-road four-stage post-processing system.The results are the evaluated by the Non-Road Transient Cycle(NRSC)situation.Firstly,the layout of engine after-treatment system is determined as Diesel Oxidation Catalyst(DOC)-Diesel Particulate Filter(DPF)-Selective Catalytic Reduction(SCR)according to the content of diesel exhaust pollutants and the working characteristics.Then,we set up a diesel engine platform to obtain the basic engine operating parameters and the engine’s original engine emissions,and build a complete machine simulation model based on the engine’s structural parameters,three-dimensional model,and bench test data.Finally,the boundary conditions for the design of subsequent post-processing systems was provided.To study the effects of CO,HC and NO conversion efficiency on different carrier structures,a DOC simulation model was established.the results showed that the CO conversion efficiency was higher and less affected by the structural change;the HC conversion efficiency increased as the diameter increased;the NO treatment efficiency It increases with the diameter and the number of meshes;considering the pollutant removal efficiency and post-processing installation space,140 mm × 170 mm × 400 mesh is selected as the DOC carrier sizeTo match the DPF under NRSC cycle and the pressure drop characteristics of the DPF under different carbon loadings,The DPF simulation model was established to be coupled with the DOC model.the results show that the particle capture efficiency increases with increasing length;When the carrier mesh size is 150 meshes,the collection efficiency increases as the diameter increases,and when the carrier mesh size is 150 meshes,the collection efficiency decreases as the diameter increases When the DPF carrier size is selected to be 120 mm×150 mm×200 mesh,it can meet the control of particulate matter emissions and have a small impact on the engine work.To explore the influence of different SCR carrier mechanisms on NOx conversion efficiency and NH3 leakage,A SCR model of FE molecular sieve was established.The results showed that the significant NOx conversion efficiency increased with diameter,length,and mesh number;when the SCR structure was 170 mm × 250 mm × 300 mesh Under each working condition,NOx conversion efficiency is the highest and NH3 leakage is small.To test and verify the matched diesel engine system,the original engine model and the one-dimensional model of the after-treatment system were coupled.The results show that the matched post-processing system can meet the off-road four-stage emission requirements in the NRSC cycle.The urea injection strategy of the NRSC cycle in the SCR is optimized,which is more in line with the requirements of current emission regulations,reduces the cost of the after-treatment system,and the optimized NOx emissions and NH3 leakage meet the off-road four-stage emission standards. |
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