Design, Development and Testing of Catalytic Converter

Abstract

Air pollution generated from the automobile source is playing a vital role in green house gas effect so it is a problem of general interest. The pollutants like CO, CO2, HC, NOX, SOX and Particulate Matters are generated at the end of combustion in the engine. These pollutants have negative impact on the environment, air quality and health. To control these pollutants various stringent norms of pollutants emission are applicable in various countries. To reduce the emission levels of the engine there are primary and secondary approaches. Primary approach of reduction in engine emission includes improvement in engine design, fuel pretreatment, use of alternative fuels, fuel additives. In secondary approach exhaust gases are reacted with catalysts after releasing from engine. This method of after treatment of exhaust gases using catalytic converter is one of the most effective way in which harmful exhaust gases are converted into eco friendly gases. Traditionally platinum group metals are used as catalysts in CC. However to overcome limitations of these noble metals in present work palladium doped pervoskite catalysts is used in catalytic converter. To reduce the emission effectively proper design of catalytic converter is necessary. Catalytic converter consists of inlet pipe, diffuser, outlet pipe, nozzle and monolith (substrate). Out of this monolith is a chemical reactor consists of large number of small channels where catalyst is coated and it reacts with exhaust gas. Design of monolith includes selection of material and shape of monolith, type of channel size and channel density. A substantial amount of work is done on monolith design hence parameters are decided based on literature survey. Based on literature survey a circular shape of ceramic monolith with square channel shape having density 600 cells per square inch (cpsi) is preferred for better performance. Thermal and hydraulic design of inlet pipe, diffuser, monolith, nozzle and outlet pipe includes CFD analysis of the catalytic converter and it is simulated using Fluent Software. The flow through monolith is modeled as flow through porous media. Three dimensional CFD study involves determination of pressure drop across catalytic converter, flow distribution at the inlet of monolith, surface temperature of catalytic converter. Uniformity of flow distribution at the inlet of monolith is evaluated using uniformity index. Thermal and hydraulic analysis is carried out for conventional diffuser, two stage diffuser, short diffuser and enhanced diffuser. CFD analysis of total 20 different configurations of catalytic converter is carried out. Out of these, conventional 20° with short inlet outlet configuration, pressure drop found to be minimum and two stage diffuser with 15° configuration uniformity index is found to be maximum. When space and cost are limitation, at that time Short Diffuser configuration is preferred. Diameter of inlet and outlet pipe is selected as per outlet pipe diameter of I C engine. Based on CFD analysis it is found that length of Inlet pipe and outlet let pipe, smaller is better. For nozzle also 15o angle gives better results however to decrease the length of catalytic converter 30o nozzle angle is selected without much compromising on performance of catalytic converter. To carryout testing work based on results of numerical simulation, four geometries having different inlet pipe and diffuser geometries and same monolith, nozzle and outlet pipe are fabricated. These geometries are conventional diffuser angle 15°, conventional 20° with curved inlet 15°, two stage 5° plus 15° and short diffuser with combination of 15o and 45° diffuser angle. Performance of these four catalytic converter is tested on Maruti 800 car. All configurations converts harmful pollutant to less harmful pollutant effectively however pressure drop is found to be least for short diffuser and conventional diffuser with inclined inlet configurations.