The Exhaust Gas Recirculation System: Reducing Engine Emissions
The exhaust gas recirculation (EGR) system is an emission control technology used in internal combustion engines. EGR works by recirculating a portion of the exhaust gas back to the engine cylinders. This dilutes the oxygen in the intake manifold and combustion chambers, which lowers the combustion temperature and reduces the formation of nitrogen oxides (NOx).
EGR systems contain valves, piping, and a control module to regulate the amount of exhaust gas that is recirculated back to the engine. The EGR valve opens and closes to control the flow rate of the exhaust gas. It is controlled by the EGR control module based on inputs from sensors that monitor the engine operating conditions.
When the engine is idling or under low load, the EGR valve remains closed. At higher engine loads, the EGR valve opens to allow some exhaust gas to enter the intake manifold. The recirculated exhaust displaces some of the normal intake air and inert gases like carbon dioxide and water vapor. This lowers the combustion temperature, which reduces the formation of NOx pollutants.
However, too much exhaust gas recirculation can negatively impact engine performance and fuel economy. The EGR control system monitors engine sensors to determine the optimal EGR rate under different driving conditions. The goal is to maximize NOx reduction without significantly sacrificing performance.
The amount of exhaust gas recirculation needs to be precisely controlled under different engine loads and speeds. Typically, the EGR valves are more open at higher engine loads when the most NOx forms. At idle or low loads, the EGR valve closes completely for maximum performance. Accelerating or heavy throttle requires less or no EGR for good engine response.
EGR technology is a very effective method for reducing NOx emissions from internal combustion engines. By recirculating inert exhaust gas, the peak combustion temperatures can be lowered, which inhibits the chemical reactions that form NOx pollutants. EGR systems, when properly controlled, can reduce NOx by up to 50% or more. Many engines use EGR in combination with other technologies like catalytic converters to minimize emissions and meet emissions standards.