EGR vs. SCR

EGR vs. SCR

There are two paths to regulatory compliance: EGR and SCR. Learn how each delivers in terms of energy, economy and ecology:

EGR: How it Works


EGR or Exhaust Gas Recirculation recirculates exhaust gases back into the cylinder and burns them again.

A portion of the exhaust gases are first cooled through a heat exchanger and then blended with fresh air before being returned to the cylinder. The exhaust gases have less oxygen and more carbon dioxide than the rest of the incoming air. This lowers the combustion temperature which results in reduced nitrogen oxides (NOx). The challenge is to reduce the temperature without having an excessive impact on combustion efficiency.

This approach involves extensive exhaust gas cooling systems, recirculation valves to divert a portion of the exhaust or ultra-high pressure injection, and a Diesel Particulate Filter (DPF) which needs active regeneration to avoid blockages which leads to higher fuel consumption. EGR also increases ash and soot in the oil.

SCR: How it Works


SCR or Selective Catalytic Reduction is the technology behind e3.

With SCR, the nitrogen oxide (NOx) reduction process takes place after combustion - so as to not diminish engine performance.

The process is simple: Diesel Exhaust Fluid (DEF, also known as AdBlue in Europe) is sprayed into the hot exhaust gases. The fluid consists of urea and deionized water. This mixture passes through a catalytic chamber.

When the hot exhaust combines with the Diesel Exhaust Fluid within the catalytic chamber, the exhaust is broken down into harmless nitrogen and water vapor - two natural components of the air we breathe.

Bottom line, EGR:
Adds cost
Adds complexity
Hotter running performance
Increased engine noise
Bottom line, SCR delivers:
Cost savings
Simplicity
Cooler running performance
Quieter sound levels

SCR provides a clear path toward meeting tomorrow's emission standards.

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