Experiment And Simulation Study On Non Road Diesel Engine Aftetreatment System

Diesel engines are the main power source of non-road mobile machinery,and emissions from non-road mobile machinery account for a large proportion of the overall environmental emissions from mobile sources.Therefore,the use of non-road diesel engines has brought serious environmental pollution and resource scarcity problems.To cope with these problems,strict emission regulations for non-road mobile machinery have been formulated worldwide.In the face of the strict non-road emission regulations,aftertreatment technology has been applied to a large number of non-road diesel engine types and has achieved good emission reduction effect.In this paper,a 9.41L non-road diesel engine was used as the research object,and according to the experimental requirements of GB 20891-2014《Limits and measurement methods for exhaust pollutants from diesel engines of non-road mobile machinery（CHINAⅢ,Ⅳ）》,the non-road transient test cycle（NRTC）condition and the non-road steady-state test cycle（NRSC）condition were used.The experiments on the performance and emission characteristics of the non-road diesel engine were carried out under the NRTC and NRSC conditions.A detailed study of the aftertreatment system was carried out through a combination of simulation and experiment,aiming to meet the latest non-road national IV emission regulations while providing some reference for further emission reduction of non-road diesel engines.The main research contents of this paper as follows:（1）Through bench experiments,the emission characteristics of the aftertreatment system integrated with other catalytic converters were studied to grasp the emission reduction characteristics of the diesel oxidation catalytic（POC）for each emission,to identify the problems of the POC system in the face of more stringent emission standards in the future,and to propose ideas and solutions.（2）The non-road diesel engine performance model and the simulation model of diesel particulate filter（DPF）based aftertreatment system were built,the diesel engine performance model was calibrated,and the entrance boundary conditions of the complete and accurate DPF system model were obtained.Finally,the simulation model analysis was conducted to study the influence characteristics of each catalytic converter on emissions,including conversion rate,filtration efficiency,exhaust velocity,temperature and pressure,and the interaction between different catalytic converters.（3）The simulation results based on the DPF system show that the diesel oxidation catalytic reactor（DOC）can achieve zero emission of CO and HC.The NO reaction rate is closely related to the DOC inlet temperature,the average conversion efficiency of NO to NO₂ in DOC is 40.36%,and the inlet pressure of DOC has almost no effect on the conversion of HC and CO.When the temperature of selective catalytic reduction（SCR）is higher than 500 K,the average NOx conversion efficiency of SCR is up to 98.74%.The ammonia purification catalyst（ASC）can further reduce NO emissions while absorbing the slipped NH₃.When the inlet temperature of DPF is greater than 520 K,it has almost no effect on the oxidation of PM.The PM conversion efficiency of DPF system is mainly influenced by the PM collection efficiency,DPF catalyst’s average PM collection efficiency of DPF catalyst is 53.32%,and the PM conversion efficiency of DPF system is 91.54%.Although the DPF catalyst converts PM to CO,these CO cannot be completely converted to CO₂,so the CO conversion efficiency of the DPF system is lower than that of the DOC catalyst.（4）Experimental comparison analysis of POC system and DPF system was conducted,and the results show that both POC system and DPF system can effectively reduce PM and NO_X emissions under NRSC experimental working conditions.The DPF system has better purification effect than the POC system,and the effect on PM is especially obvious.Under NRSC experimental conditions,the conversion rate of DPF system for PM is as high as 87%,while the conversion rate of POC system for PM is only 60%.The conversion rates of NO_X and HC exceeds 95%.The conversion rates of PM,NO_X,HC and CO under the NRTC experiment are 92.83%,96.99%,96.86%and81.45%for the DPF system,60.12%,95.45%,92.82%and 79.51%for the POC system,respectively.Both POC system and DPF systems are able to meet the emission regulation limits.