What system helps control nitrogen-oxide emissions by forcing some of the gases back into the cylinders?

The exhaust-gas-recirculation (EGR) system is specifically designed to reduce nitrogen oxide (NOx) emissions in internal combustion engines. It works by recirculating a portion of the engine's exhaust back into the combustion chambers. By doing this, the EGR system lowers the peak combustion temperatures when the engine is running, which is essential because NOx emissions are primarily formed at high temperatures.

This method effectively dilutes the air-fuel mixture entering the cylinders, making it less reactive and resulting in reduced formation of NOx. It is a common emission control strategy used in many modern engines to help meet stringent environmental regulations. The function of the EGR system directly addresses the issue of nitrogen oxide emissions, highlighting its role in maintaining cleaner air standards.

In contrast, the other systems listed do not specifically focus on controlling NOx emissions in this manner. The catalytic converter system facilitates chemical reactions to reduce harmful emissions but does not recirculate exhaust gases back into the cylinders. The turbocharger system increases the engine's efficiency and power by forcing more air into the combustion chamber but is not primarily designed for emission control. The fuel injection system manages the amount of fuel entering the engine for optimal performance but does not directly address NOx emissions