Death comes to us all. Life's but a walking shadow | I may have spoken to soon. I have been very curious as to the actual technical details of the failures which led VW to cheat. While these details haven't been published in the media this paper presented in 2008 gives some possible clues and maybe answers your question about using biodiesel to answer the problem.
Effects of Biodiesel Operation
on Light-Duty Tier 2 Engine and
Emission Control Systems
Preprint
M. Tatur, H. Nanjundaswamy, and D. Tomazic
FEV Inc.
M. Thornton
National Renewable Energy Laboratory
Presented at SAE 2008 World Congress
Detroit, Michigan
April 14–17, 2008
Below is page 11 from this paper. If you look at figure 19 you see following three charts. On top is test driving cycle showing the vehicle speed as it simulates a standard driving event with startup, the various acceleration, deccelerations etc during a road trip. These standard driving cycles are the basis of the EPA's test protocals. The middle chart shows the accumulated nitrogen oxide emissions from the engine itself and out the tailpipe after the exhaust gas goes through the absorber/converter. You see that NOx emissions from B20 blend are higher than ULSD just from the engine but lower out the tailpipe after the absorber/converter. The explanation is the higher exhaust temperature when using ULSD reduces the efficency of the absorber/converter, specifically during some acceleration events. They go on to say that in order to keep their test engine in compliance they needed to retune the engine which resulted in a 12% reduction in fuel economy. Essential the evidence about VW's mis-step has been available since 2008.
You can see the consequences clearly in the righthand portion of figure 20 where the mpg declines from about 35 to just over 30. However the really important point of fig 20 is the lefthand bar graph labelled "tailpipe emissions". Here the tailpipe emissions for the B20 blend is 0.03 vs the 0.05 for ULSD. The signficance of these numbers is that the ave. vehicle fleet standard is 0.07. The magic number is 0.07. By this criteria the 0.03 is 40% better than the 0.05 grams per mile.
To quote: Vehicle results showed some benefits for a vehicle
operating on B20 fuel blend with the NAC system.
This is a result of the calibration work being
performed using the 20% biodiesel fuel blend. The
resulting higher exhaust temperatures with ULSD
resulted in lower NAC system effectiveness.
I would also point out that the centane rating for B20 is 45 vs that of 41 for ULSD. This probably explains the higher exhaust temperatures for ULSD. The B20 ignites at a lower temperature in the combustion cycle resulting in slightly lower exhaust gas temperatures , lower engine operating temperatures and maybe less engine wear.
Lots to think about.
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JonSCKs, Biodiesel & the VW scandal, you may be correct.
