Design of Engine Exhaust System for Optimum Heating of Catalytic Converter and Back Pressure Control

Abstract

Pollution from automobiles is a major source of environmental pollution and mitigating this is an important task for human health and environmental protection. Catalytic converters are important instruments in this regard, helping eliminate major pollutants like unburnt hydrocarbons, carbon monoxide and nitrogen oxides. Thus increasing the efficiency of catalytic converters is need of the. Catalysts of a catalytic converter become appreciably active (> 50%) after they attain a certain temperature, called the ‘light-off temperature’. Cold start emissions are extremely high before catalysts reach the light-off temperature. Therefore, minimising the time taken to achieve light-off temperature is vital. This must be done without significantly increasing the back pressure on the engine, or damaging the catalysts. Through Computational Fluid Dynamics (CFD) analysis of a simple exhaust system with a catalytic converter,it was found that light-off time is minimum when the catalytic converter is placed closest to the exhaust pipe inlet. Back pressure was found to be within tolerable limits. Steady state analysis revealed that some steady state temperatures were above 800 °C, which increases the possibility of catalyst degradation. Finally, methods (some of which have already been proposed in existing literature) have been suggested to avoid this problem.