Final answer:
The EGR system reduces nitrogen oxide emissions in engines by recirculating a portion of the exhaust into the combustion chamber during the intake stroke as part of the cyclical process of a heat engine.
Step-by-step explanation:
The emission-control system described in the question is known as the Exhaust Gas Recirculation (EGR) system. This system works by redirecting a portion of an engine's exhaust gases back into the engine cylinders. During the intake stroke, instead of only fresh air or a mixture of gasoline and air being drawn into the combustion chamber, some of the exhaust gases are reintroduced.
This lowers the combustion temperature, reducing the formation of nitrogen oxides (NOx), which are harmful pollutants. The reintroduction of exhaust into the combustion process is a cyclical process, in line with how heat engines operate through cycles to convert heat into work.The EGR system reduces nitrogen oxide emissions in engines by recirculating a portion of the exhaust into the combustion chamber during the intake stroke as part of the cyclical process of a heat engine.