7. Evolution of Catalytic Converters for Spark Ignition Engines to Control Emissions

Engine exhaust species such as nitrogen oxides (NOx), carbon monoxide (CO) and unburnt hydrocarbons (HC) are hazardous and pose a significant threat to the environment and the human health. Catalytic converter is installed in the engine exhaust manifold of modern vehicles for emission reduction. This device plays a significant role by simultaneous catalytic oxidation and catalytic reduction reactions. Catalytic converters themselves do not take part in chemical reactions but catalyse these reactions. There is a drastic reduction in CO, HC and NOx emissions in the exhaust, and these species are converted to harmless products exiting through the tailpipe. Catalytic converters are among the most developed and matured technologies to control exhaust emissions. Emissions concentrations of different emission species can be analysed upstream and downstream of the catalytic converter to evaluate their conversion efficiencies. Also, real-time catalyst temperatures can be determined by 1-D thermal modelling of the three-way catalytic converters. This chapter gives insights into the flow behaviour along with the transient temperature field across the catalytic converter, which helps understand overall working of the catalytic converter. Also, catalyst temperature distributions are discussed based on engine operating conditions in order to understand the effect of exhaust gas temperature on the catalytic converter efficiency.