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A comment on Volkswagen Chief Martin Winterkorn Resigns Amid Emissions Scandal. Parent comment

Re:Volkswagen Chief Martin Winterkorn Resigns Amid Emissions... by HNaTTY on Wednesday September 23, 2015 @01:12PM (#10266346)
From what I've read so far, this has to do with heat necessary for the catalytic converter to absorb NOx -- without enough heat, NOx isn't absorbed, so in emissions test mode, they're just running the engine in such a way that more heat is generated to make sure the cat works properly.
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Re:Volkswagen Chief Martin Winterkorn Resigns Amid Emissions... by mzs on Wednesday September 23, 2015 @01:22PM (#10266436)
Fuel economy improves at higher temperatures, but NOx production increases dramatically then. Conventional catalytic systems cannot keep-up so either a selective catalyst (expensive) or improved egr system (performance sapping) must be used.
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Re:Volkswagen Chief Martin Winterkorn Resigns Amid Emissions... by harryh on Wednesday September 23, 2015 @01:15PM (#10266376)
Interesting! How much heat are we talking about here? When an engine is just running in normal operation it generates a fair amount of heat naturally. I guess that's not enough?
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Re:Volkswagen Chief Martin Winterkorn Resigns Amid Emissions... by ams6110 on Wednesday September 23, 2015 @02:25PM (#10266963)
Diesel engines run with a surplus of air so they only burn the fuel they need to. They don't really generate a lot of heat unless they are under load (relative to gas engines). Just cruising down the highway a diesel will not need much fuel and will run fairly cool.
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Re:Volkswagen Chief Martin Winterkorn Resigns Amid Emissions... by durin42 on Wednesday September 23, 2015 @03:46PM (#10267635)
The owners manual for the VW TDIs actually warns you to not try and preheat the engine by letting it idle in the winter, because it won't work.
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