EXHAUST GAS

RECIRCULATION VALVES

EGR stands for ‘exhaust gas recirculation’. An EGR valve helps reduce NOx emissions. NOx is produced during the combustion process. It is created when high combustion temperatures and pressures enable the nitrogen and oxygen present in the air-fuel mixture to combine. To reduce these harmful emissions, the EGR valve takes exhaust gases from the exhaust manifold and reintroduces them into the intake manifold, mixing them with fresh air. Since the intake air contains less oxygen, the combustion temperature cannot reach the same levels, which is why less NOx is produced during the combustion process.  

EGR valves help to reduce NOx emissions, which have negative health and environmental effects. To be sold in the EU, vehicles must comply with applicable European emissions standards, which continue to evolve over time. This means that the EGR valve has a key role to play.

The EGR valve in a diesel engine performs the same role as it does in any other engine type, namely reducing NOx emissions by returning exhaust gas back to the engine's combustion chambers through the intake manifold, and ultimately reducing peak temperatures. There are two different types of EGR valves for diesel engines: diesel high pressure EGR valves and diesel low pressure EGR valves.
High pressure EGR valves: here, exhaust gas that is high-flow and high in soot is diverted by the EGR valve before it enters the diesel particulate filter. The gas is then returned to the inlet manifold. A vacuum is created by a secondary valve in the inlet manifold.
Low pressure EGR valves: here, exhaust gas that has already passed through the diesel particulate filter is diverted back to the inlet manifold through a pipe. This gas contains significantly less soot as it has already passed through the diesel particulate filter, but has a lower flow.