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The rapid growth of motor vehicles during the twentieth century resulted in significant air pollution problems across the world. Internal combustion engines emit harmful pollutants such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). These pollutants contribute to environmental degradation, smog formation, respiratory diseases, and climate change. In response to these challenges, governments introduced increasingly strict emission regulations. Modern emission control technologies such as Exhaust Gas Recirculation (EGR), Three-Way Catalytic Converters (TWC), Selective Catalytic Reduction (SCR), and Diesel Particulate Filters (DPF) have played a crucial role in enabling the automotive industry to meet these stringent global emission standards. Exhaust Gas Recirculation (EGR) is one of the earliest and most widely used technologies for controlling nitrogen oxide emissions in internal combustion engines. Nitrogen oxides are produced during high-temperature combustion processes when nitrogen and oxygen in the air react together. EGR works by recirculating a portion of the engine’s exhaust gases back into the intake manifold where they mix with the incoming air-fuel mixture. The presence of exhaust gases reduces the oxygen concentration and lowers the combustion temperature within the cylinder. Since NOx formation is highly dependent on high temperatures, reducing combustion temperature significantly decreases the formation of nitrogen oxides. Modern EGR systems are electronically controlled and can precisely regulate the amount of exhaust gas recirculated depending on engine load, speed, and operating conditions. Advanced cooled EGR systems further improve efficiency by passing exhaust gases through a heat exchanger before recirculation, which lowers the temperature even more. This technology has become a standard feature in both gasoline and diesel engines to meet modern emission limits. Three-Way Catalytic Converters (TWC) represent a major breakthrough in gasoline engine emission control. Before the introduction of catalytic converters, vehicles emitted large amounts of CO, _______ _____ ____ ___ __________ ____ _________ _____ _________ ________.
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