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What's the difference between SCR and EGR technology

2019-07-08 09:55:19
Nowadays, heavy diesel trucks come with the most current EPA compliant equipment. This equipment comes in the form of two different methods used in the after treatment of the exhaust emissions. These methods are Selective Catalytic Reduction (SCR) and Exhaust Gas Recirculation (EGR). Either are used to reduce NOx.

In the early days, most trucks had only an EGR system with a diesel particulate filter (DPF) inline with the exhaust system. So the question of SCR and EGR was relevant.

Both technologies use exhaust gas recirculation to pass a certain amount of a motors’ exhaust gas back to its combustion chambers and they both make use of a diesel particulate filter (DPF). This is what removes particulate matter from the exhaust.


Exhaust Gas Recirculation (EGR)


Over the past several years, both EGR and SCR have been coming standard on all diesel trucks. EGR by and large was implemented in 2008 and we first started seeing SCR in 2010.


Exhaust Gas Recirculation Limitations:
The engineers designed the EGR system in such a way that it recirculates the exhaust gases only when the engine forms the Nitrogen Oxide (NOx). The Exhaust Gas Recirculation system also has a thermal control valve in the vacuum line which prevents the operation of EGR at lower engine temperatures. This system is useful especially in the diesel engines where the catalytic converter cannot stimulate the chemical reduction due to high oxygen contents. So, the NOx emission remains the same in such conditions.

 
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