Investigation On The Charged Characteristics Of Particulate Matter In The Leakage Current Particulate Matter Sensor

With the development of national economy and the increase of car ownership,diesel engine is widely used in transportation,mechanical engineering and other industries due to its advantages of high thermal efficiency,low emission and reliable operation.The promulgation and implementation of the China 6 emission regulation further tightening the limit requirements of diesel engine particulate matter emission.At present,the most widely and effective controlling method of particulate matter(PM)is to use Diesel Particulate Filter(DPF)to reduce the PM in diesel engine exhaust.In order to ensure the reliable operation of DPF,it is necessary to use particulate matter sensor to detect the concentration of particles in exhaust gas and monitor the working condition of DPF in real time.In this paper,a new type of leakage flow particulate matter sensor was studied through the methods of numerical simulation and experiment,the charge characteristics and movement state of PM in the sensor are analyzed under different air flow state and particle morphology,which provides theoretical basis for the next step of sensitivity and accuracy analysis of sensor signal output and optimizes the sensor performance.Firstly,the three-dimensional geometrical model of the particulate matter sensor mounted on the exhaust pipe is established by using the Comsol Multiphysics software.According to the coupling law of the flow field,the electric field distribution and the flow law of the particle phase in the sensor,the appropriate physical field model is selected,and the calculation model of the coupling distribution of the multiple physical fields in the sensor is established.The simulation velocity distribution at the section is compared with the test results to verify the accuracy of the model.The model is used to simulate the flow field and electric field distribution in the sensor.Based on the distribution coupling law of multiple physical fields,the charge characteristics and movement state of particles under different exhaust velocity and particle size are simulated.The simulation results show that after the exhaust gas flows through the particulate matter sensor,there is a relatively obvious speedboundary,and the flow velocity on the leeward side of the sensor decreases significantly,while the flow velocity at the lower end of the sensor inlet and the junction between the two sides of the sensor and the exhaust pipe increases slightly.After the exhaust gas enters the sensor,the flow velocity decreases rapidly,the exhaust flow velocity in the outer protection zone and the concentration test zone is relatively stable.The electric field in the sensor is non-uniform,and the electric field intensity direction at any point is from the high-voltage electrode to the grounding electrode and decreases continuously.With the increase of exhaust flow rate,the electric charge of unit particle will decrease,but the cumulative electric charge shows a slow growth trend,and the particle migration to the grounding electrode decreases.With the increase of exhaust temperature and particle size,the electric charge of particles increases,the migration of particles to the ground electrode also increases with the increase of the exhaust temperature and particle size.The simulation results are verified and the output signal laws of the particulate matter sensors under different air flow conditions and particle sizes are analyzed by build a test beach.The electric change of particles in the test is consistent with the simulation.At the same time,it is found that the output signal of the sensors increases with the increase of exhaust flow rate,but the increasing trend is not obvious.With the increase of exhaust temperature,the output signal of the sensors increases obviously.At the same time,with the increase of particle size,the output signal of the sensor increases.