Removal of soot particles from Diesel exhaust

~ Pergamon

J. I/ero.ol Sci.• Vol. 27.Suppl. I. pp. S70S-S706, 1996

Copyright iC 1996Elsevier Science Ltd Printed in Great Britain. All righlS reserved 0021·8502/96 SIS.OO + 0.00

PII: 80021-8502(96)00425-9

REMOVAL OF SOOT PARTICLES FROM DIESEL EXHAUST TOMASZ CIACH and TOMASZ R. SOSNOWSKI Warsaw University of Technology, Department of Chemical andProcess Engineering Warynskiego 1,00-645 Warszawa, Poland This work is a continuation of our studies reported recently (Ciach et al., 1995, J. Aerosol Sci., 26, 5273,). Our investigations were focused on developing and testing efficient methods for elimination of aerosol particles from Diesel exhaust. Base on the laboratory scale experiments we found out that filtration in a fibrous filter with simultaneous application of the high voltage (5-8 kV) electrostatic field serves a highly effective way of removal of submicron soot particles from a gas stream. In this system much better filtration efficiencies could be achieved at shorter residence times of the aerosol than in a classical electrostatic precipitator or a regular fibrous filter. Also the pressure drop in this system was reasonably low. Here we discuss the possibility of application of electrodynamic coagulation for pretreatment of Diesel aerosols and we report experiments on testing the prototype device which might be used in a real Diesel-engine driven system. Electrodynamic coagulation was tested in a laboratory system (Fig. 1) using 10kV 50Hz AC in the agglomerator and 12 kV DC in the corona charger in the inlet to the device. Aerosol distribution was tested with the use of LAS-X (PMS) and PortaCount (TSI) in parallel. For aerosol concentration of 4,5 glm3 and residence time about 4 s we observed an increase in the number of particles 0,2-0,4 J.1m with the reduction of fraction below 0,17 J.1m. On the other hand, we observed practically no effect on size ditribution of model soot aerosol at lower concentrations and higher flows through the agglomerator. This result suggests that agglomeration in the electric field cannot be effectively used for Diesel aerosols as a method of "growth"of soot particles. electric agglomerator outlet

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S706

Abstracts of the 1996 European Aerosol Conference

The prototype filtering device was constructed as a chamber (vol. = 0,096 m') packed with a glass fiber. Electrostatic field was perpendicular to the flow of aerosol. Model soot aerosol was initially charged by a corona what significantly improved the filtration efficiency (Figs.2,3). It was demonstrated that penetration through the filter did not depend significantly on temperature. At the residence time ... 0,5 s penetration less than lOO/cl was achieved for voltage 13 kV and discharge current 0,25 rnA heater

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Voltage [kV] Fig. 3. Influence of a coronacharging on filtration efficiency in the prototype filter. During tests in the exhaust system of a car driven by a Diesel engine the operation of the prototype was disturbed by initial condensation of humid. This led to a short-circuit in the device and made it malfunction. It seems that also other effects, absent in the experimental system, should be taken into account before the adaptation of the device, and some construction changes must be done. We plan to work on these problems in our future studies. ACKNOWLEDGEMENT: This workwas supported by KBN grant # 7520301206