Experimental And Simulation Research On Working Characteristics Of Metallic Diesel Particulate Filter

Compared with gasoline engines,diesel engines have a one-third lower fuel consumption and nearly one-half lower carbon dioxide emissions.Because of their large torque and low fuel consumption,they are widely used in commercial vehicles,passenger cars,construction machinery,ships and others.Various non-road machinery fields have output surging power for the economic development of the society.However,diesel engine PM emissions are much higher than gasoline engines,accounting for 90% of the total vehicle particulate emissions.Reducing particulate emissions in exhaust gas is a prerequisite for further widespread application of diesel engines.Diesel particulate traps are the most successful post-treatment technology for reducing particulate emissions.Now ceramic-based DPF has been used in large-scale commercial applications,but it is not perfect.It lacks thermal shock resistance and structural strength,while metal material DPF can Make up for this defect.In this paper,a series of experiments are carried out based on the metal material DPF and the DOC used in combination with it,to explore its capture characteristics,and perform CFD simulation analysis on it according to the physical parameters obtained from the experiment,to improve the structure and optimize its flow field distribution.According to the needs of the research content,a related diesel engine test bench was built in this research.The relevant test operating points were selected in the working condition interval of the stable operation of the engine bench in combination with the current WHSC test cycle standard of the six national standards.Under selected working conditions,DOC performance test,DOC+metal material DPF filtration efficiency test,metal material DPF pressure drop test,variable injection parameter and boundary parameter influence test are carried out.The various performances of DOC and DPF and the influence on engine combustion after installation are explored.On the basis of the pressure drop test data,the viscous resistance coefficient and inertial resistance coefficient of the metal material DPF are obtained,and then the computational fluid dynamics simulation model of the metal material DPF is established in the simulation software FLUENT.The flow field distribution of the DPF is improved by changing the structural parameters.Through experiments and simulation analysis,the main conclusions are as follows: DOC has a conversion effect on a variety of harmful substances in exhaust gas,and the conversion efficiency of carbon monoxide(CO)is the highest,which can reach more than 90%.At the same time,DOC has a better effect on nuclear particles smaller than 50 nm.The strong conversion effect makes the particle size move toward the aggregate state,which is beneficial to improve the trapping efficiency of the metal material DPF;the overall trapping efficiency of the DOC + metal material DPF for the particulate matter is above 90%,and the specific trapping characteristics are less than 30 nm The capture efficiency of nuclear particulate matter is high,and the capture efficiency of 110-120 nm aggregate particulate matter is the highest,while the capture efficiency of 70-80 nm and 280-320 nm aggregate particulate matter is relatively low;a small amount of post-injection can improve engine particulate matter emissions,The post-spray angle based on time needs to be shortened according to the increase in speed.EGR rate below 8.3% is not much different from no EGR.The increase of EGR rate above 16.7% will cause the particle size to migrate towards the aggregate state and reach the70-80 nm metal DPF low-efficiency trapping zone;the exhaust speed is increased,The high pressure area at the front end of the filter body is getting bigger and bigger,and there is stress in the middle part.Even a reverse arcuate pressure area will be produced;a too short or too long convergent deflation section can cause the internal pressure of the DPF to concentrate,and the air flow is unevenly distributed.A too short inlet cone angle will also cause a relatively strong vortex,and the strength of the vortex will be stronger.Larger,the longer the airflow stays in the DPF,the greater the air resistance.The vortex area on both sides of the baffle disappears after the baffle is installed,which proves that the baffle can isolate the vortex,and the pressure and flow rate can diverge faster and evenly after the baffle is installed,which improves the capture of DPF particles.