How does EGR Exhaust Gas Reticulation work, why is it needed and common faults explained

In all internal combustion engines, undesirable nitrogen oxides (NOₓ) are formed when combustion takes place at high temperatures with excess air. These gases can be largely avoided, however, through the use of exhaust gas recirculation (EGR), EGR returns a high proportion of the exhaust gas to the combustion chambers. This reduces the amount of fresh, oxygen-rich air in the chambers. The exhaust gas also inhibits the chemical reactions taking place in the combustion chamber. Both of these effects cause combustion temperatures to fall, thereby significantly reducing the amount of NOₓ produced. To increase efficiency, water-cooled EGR systems are used on all engines today. On its way back to the engine, the exhaust gas flows through a water cooler with a map-controlled cooling capacity. This additional cooling of the exhaust gas allows a greater amount of exhaust gas to be recirculated, while also reducing the initial temperature in the combustion chamber. manufactures have significantly increased efficiency in this area of technology, for example, the separate low-temperature cooler has been eliminated, along with its pump drive. Modern engine have a dedicated high- and low-temperature circuit that does an excellent job supplying the EGR cooler. The efficiency of the entire cooling system has increased significantly.

Despite the emissions benefits, EGR systems can encounter issues. Here are some common faults:

1. **EGR Valve Malfunction**: Sticky or clogged valves can restrict exhaust gas flow, leading to performance issues or increased emissions. The build up of carbon and oil which is in the exhaust gasses clog up the valve which stops it from working correctly. Sometimes the valve can be cleaned but also they can seize solid and replacement is needed. Some valves are electronically operated or vacuum operated. A seized valve can damage the vacuum diaphragm or electric solenoid or motor.

2. **EGR Cooler Failures**: Leaks or blockages in the cooler can cause overheating and reduced efficiency. It can be quite common to have a coolant leak from the EGR cooler.

3. **Sensor Failures**: Faulty sensors can misinform the ECU, disrupting the EGR process and potentially causing engine knock or poor fuel economy, or increased smoke.

4. **Carbon Build-Up**: Over time, carbon deposits can accumulate on the EGR valve and cooler, reducing their effectiveness.


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