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J

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Discussion Starter #1
I know that VW got rid of pumpe duse, but was it because of emissions? This was the worst time to stop making diesels for the us. Not making any diesels for the US in all of 2007 really hurt a company that could use the sales.
 

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To make a long story short, it was just that: emissions. The only reason they made pumpe duse was so that they could avoid paying licensing fees on the common rail technology. Pumpe duse works but common rail is better.
 
D

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I'll 2nd that. Here is some more info from the vortex.

If anything, common-rail fuel injection systems ordinarily require more power to operate than P-D or other mechanical injection systems. Mechanical injection systems pressurize only the fuel that they want to squirt into the cylinders. Common-rail systems pressurize fuel at maximum delivery rate all the time and spill what they don't use back to the tank through a high pressure relief valve.

Common-rail engines don't get fantastically better mileage than their mechanically-injected (but still direct-injected) predecessors. You can look at the Cummins pickup truck engines for an example of this.

The VW TDI in mechanically-injected form is already one of the most efficient automotive diesel engines produced. Further efficiency gains beyond that point get very difficult to find. You are not going to get 30% better efficiency overnight from an engine whose thermal efficiency already peaks around 42%.

And, the new particulate-trap and de-NOx catalysts require a regeneration cycle, which requires the engine to periodically go into a "rich-running high-exhaust-temperature" mode. If the driver is gentle and doesn't put enough load on the engine to do this on its own (i.e. is a typical granny or economy-minded driver) then the engine will do this by injecting extra fuel late in the power stroke for the sole purpose of making a high-temperature exhaust stream which is slightly rich (not the usual diesel lean). This is going to use *extra* fuel.

Taller gearing doesn't magically give better mileage, either. I have 8% taller 5th gear than stock in my P-D, and on the overall, the difference in consumption is about 2%, only slightly more under ideal conditions.

Prediction: the new model is going to have close to the same consumption ratings as the P-D. Which is good ... but not 60 mpg US.

The 60 mpg US figure, from what I can tell, came from ONE statement made by ONE non-engineering person, and has been bounced around ever since. I wish it would stop. It is setting up for a big disappointment when the real numbers become available.

And I'll say the same thing about Honda's upcoming Accord diesel. It might be possible to get 60 mpg US under certain ideal conditions (as it is with the VW diesels) but a 60 mpg US EPA highway rating is not going to happen in a vehicle of that size.
 
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