What is an EGR System and How Does it Work?

Posted on July 13, 2012 There have been 0 comments


On nearly all diesel engines manufactured today, incorporated into the design of the engine is an EGR System. EGR stands for exhaust gas recirculation and that’s exactly what it does, recirculates a portion of the exhaust gas back through the intake and into the cylinders. These systems are incorporated to lower the overall emissions and hydrocarbon out-put emitted by the engine, which are by-products of the combustion process. Two of the most common problems associated with the EGR systems are failures of the EGR Valve and the EGR Cooler.


Each manufacture has their own configuration and some incorporate a few different components, but here is the basic path that the exhaust gas will travel to flow back to the engine. The gas leaves the cylinder head and flows into the exhaust manifold. From there, the gas travels to the turbocharger. Now, it’s typically between the cylinder head and the turbocharger that you will find an access port that will allow a portion of the gas to enter the EGR cooler. The gas flows through the EGR cooler to reduce the temperature before reaching the EGR valve. The valve is the component (usually located in the intake manifold) that regulates when AND how much exhaust gas is permitted to flow into the engine.


The EGR Cooler is subject to very high exhaust temperatures. During normal operation, a diesel engines exhaust gas temperatures range from 400-1400 degrees Fahrenheit. The purpose of the EGR cooler is to remove as much heat as possible from the portion of the gas that is being introduced into the intake manifold to mix with the fresh air from the turbo. The EGR cooler is simply a heat exchanger that utilizes the engine coolant flowing around the core that the exhaust travels through and removes heat by means of conductive heat transfer. Eventually, the core of the cooler will crack, and allow coolant to leak into the exhaust passages of the core. As the exhaust gas travels through the cooler, coolant mixes with it. This results in coolant loss, poor engine performance and white smoke from the exhaust as the coolant cannot burn when introduced into the cylinders and is present during the combustion process.


The EGR valve is an electronic actuator which functions as a metering device, limiting the quantity of exhaust gas permitted to flow into the engine. The EGR valve is controlled by the engine ECU (electronic control unit) and is energized to allow exhaust gas flow into the intake manifold when the ECU recognizes that ideal conditions are met. Over time, the exhaust flowing through the EGR valve will leave carbon deposits on the valve causing it to “stick” and not function properly, resulting in insufficient flow of the gases through the valve. The valve is also subject to electronic failure as it is exposed to elevated temperatures for extended periods of time.

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