Study On The Influencing Factors Of Particle Deposition In Leakage Current Particulate Matter Sensor

With the rapid growth of national economy and automobile ownership,diesel engine is widely used in many fields such as commercial cars,agricultural machinery,etc.,which brings a series of environmental pollution problems.At present,the Diesel Particle Filter(DPF)is used to remove the Particulate matter emitted by the Diesel engine.In order to realize the real-time and accurate monitoring of DPF,ensuring the normal and reliable work of DPF and avoid exceeding the standard of particulate concentration in the exhaust,it is urgent to study the new particulate sensor that can meet the emission regulations.In this paper,the leakage current particulate matter sensor was studied by establishing a mathematical model and verified through experiments,studied the particle deposition rate change rule combined with the exhaust conditions,predicted the failure of particle sensor,and helped the reliability research of the particle sensor.In this paper,a 3 D model of exhaust pipe and sensor was established by using Comsol Multiphysics,and the deposition mechanism of particulate matter within the sensor was analyzed.Combined with the structure and principle of the sensor,the turbulent flow model,the steady-state electrostatic field model and the solid and fluid heat transfer model were selected and added to the three-dimensional model of the sensor.The mesh was divided,and the multi-physical field coupling model of the sensor was established.Pilot tube was used to measure the exhaust velocity at the end of the exhaust pipe,and the simulation results were compared to verify the model.Based on the established leakage flow particle sensor physical model,the distribution of flow field,electric field and temperature field in the sensor was simulated and studied,and the particle deposition law under the coupling of multiple physical fields was analyzed by changing the exhaust temperature,exhaust velocity,particle size and particle concentration.It was shown by the simulation results that the velocity of the exhaust gas decreased obviously when it was near the sensor.The flow rate of the exhaust gas increases to a certain extent when it entered the outside protection zone of the sensor,and the flow rate of the exhaust gas basically remains unchanged when it stayed in the concentration test area.The direction of electric field intensity was from the high voltage electrode to the grounding electrode.When the exhaust gas flowed into the concentration test area,a temperature gradient was generated in the concentration test area from the high voltage electrode to the ground housing.The increase of temperature led to an increasing trend of deposition velocity in all three mechanisms.With the increase of the flow rate,the thermophoretic deposition rate decreased,and the electrophoresis deposition rate increased slowly,and the inertial collision deposition rate increased rapidly.The variation of particle size has little effect on the deposition velocity of the three mechanisms.The concentration of particulate matter increased in equal proportion to the total deposition amount,and electrophoresis played a dominant role in the three deposition mechanisms.A diesel engine test bench was built to analyze the change rule of sensor signals under different working conditions,and the sensor failure time was predicted by combining the deposition mechanism and sensor signals,and the simulation results were verified.The failure time was determined according to the sensor constant and exhaust condition,and the sensor was heated and regenerated by heating module.It was found that the failure time of the sensor increased with the increase of load and decreased with the increase of temperature at the same rotating speed.With the increase of engine load,the particle deposition velocity in both simulation and test showed an increasing trend.At low load,the particle deposition velocity of test was lower than that of simulation.