Exhaust Gas Recirculation (EGR) Engines
The NOx emissions reduction technique lies within the engine, wherein the engine re-circulates a portion of the exhaust gas back to the engine cylinders depriving it of certain amount of oxygen thereby leading to lower temperature burn. This reduces NOx emissions, but produces more PM which is reduced using diesel oxidation catalyst (DOC) and particulate filter.
EGR technology will be beneficial for low or medium duty cycles (e.g. city bus applications, short haul rated load applications etc.)
What is an EGR System?
EGR system recirculates the exhaust gas back in the engine, which contains unburnt fuel and carbon, reduces the combustion temperature, hence bringing down NOx.
While doing so, PM increases, which is then controlled outside the engine using a filter. It is an easy to use system with low initial cost. However the EGR system has a lower combustion efficiency and a higher heat rejection. This causes unburnt carbon and fuel to enter the system, and possibly impacts its reliability and durability.
EGR System Working
Cummins ISB5.9 BSIV EGR Engine Specifications: