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Gurdas Sandhu
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HC, that is a good question and is well answered in part by Anne. To elaborate what she said, the EPA regulation is based on strictly defined duty cycle. A duty cycle is a speed vs time profile. Vehicles almost never experience the same duty cycle in real life. They may come close or be far off. The NOx control device that has been introduced starting from 2010 model years, Selective Catalytic Reduction (SCR), is sensitive to exhaust temperatures and maybe other variables which do no yet fully know. So, in short, a vehicle could meet EPA's regulation under the defined duty cycle but does it meet it under real-life conditions? That is what this news story highlights. But the paper and the research go beyond that. One important conclusion of this study was how to compare on-road real-world emissions such that the findings are robust to cycle-to-cycle variations. For example, if you drove a truck from point A to B and I drove a different truck from point C to D, what method can be used to compare your emission rates with mine. Okay, that is a long post! I encourage you to read the full paper to see why the research dollars are well spent :)
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Apr 19, 2012