EGR

EGR, or exhaust gas recirculation, is an emissions-control technology used in internal combustion engines to reduce nitrogen oxides (NOx) in exhaust. It accomplishes this by routing a portion of the engine’s exhaust gas back into the intake manifold, where it mixes with incoming air. The exhaust gas is largely inert at typical combustion temperatures, which lowers peak temperatures and slows NOx-forming reactions.

Control and variants: An EGR valve meters the amount of gas recirculated, with electronic control common on modern engines. Some systems use an EGR cooler to lower the recirculated gas temperature, increasing NOx reduction. There are two main configurations: high-pressure EGR, which draws from the exhaust manifold upstream of the turbocharger, and low-pressure EGR, which draws from downstream after cooling and routes gas to the intake.

Components and operation: Core components include the EGR valve, EGR cooler, piping, and actuators, along with sensors that monitor valve position and differential pressure. Systems may also incorporate filters or screens to prevent deposits from entering the engine.

Benefits and limitations: EGR reduces NOx emissions to help meet regulatory standards. It can also affect engine performance and fuel economy, and if malfunctioning can cause rough idle, reduced power, or increased carbon buildup in the intake and EGR passages.

Maintenance and issues: EGR systems are susceptible to carbon buildup, valve sticking, cooler plugging, and leaks. Regular inspection, cleaning, or replacement of the EGR valve and cooler are common maintenance tasks.

Applications: EGR is widely used in gasoline and diesel engines, forming a standard part of modern emissions-control strategies.