Selective Catalytic Reduction (SCR)

By 2010, the Environmental Protection Agency (EPA) will require all medium- and heavy-duty vehicles to run cleaner. A lot cleaner. Nitrogen oxide (NOx) exhaust emissions – which contribute to acid rain, smog and greenhouse gas levels - must be reduced to 0.2g/bhp-hr, an 83% reduction from 2007 levels.

Thomas Built Buses and its engine partner, Cummins Inc., have worked hard to meet the EPA 2010 emission requirements while still maintaining maximum fuel efficiency and engine performance. Our proven technology, Selective Catalytic Reduction (SCR), not only reduces NOx emissions to near-zero, but Cummins testing shows a 5-9% fuel economy advantage compared to In-cylinder EGR. This proven, road-tested technology provides significant advantages for the environment, and your bottom line.

What is SCR?

SCR stands for Selective Catalytic Reduction. This technology reduces tailpipe nitrogen oxide emissions, NOx, by treating the exhaust stream with a spray of DEF (diesel exhaust fluid). DEF, along with the heat of the exhaust and a catalyst, converts NOx into nitrogen and water vapor, which are clean, harmless and present in the air we breathe every day.

Thomas Built's complete line of diesel buses will be equipped with SCR technology to meet the EPA 2010 emission standards. Thomas Built's mission is to provide reliable, durable, safe and innovative buses to our customers. And SCR technology with its near-zero emissions was the environmental choice when meeting these new standards.

SCR technology uses the existing engine architecture, diesel oxidation catalyst and diesel particulate filter, plus SCR hardware. This technology allows the engine to function at higher, more optimal combustion temperatures, which increases fuel efficiency and reliability. Take a look at the diagram below to see how SCR works.

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When looking at both systems, Thomas Built decided that SCR was the more reliable and fuel-efficient option. The charts below outline the differences of In-cylinder Exhaust Gas Recirculation (EGR) and SCR technology.