The Acoustic Function that lead to the VW emissions scandal

Posted By on July 23, 2016


The development of Volkswagen’s emission defeating device may have initially had the best of intentions, according to Road and Track. It started with engineers in 1999 who were working to quiet the diesel clatter on an Audi V-6 engine. They were  using "Pilot Injection" to needleliftsensorpilotinjectioninject an additional amount of fuel to a cylinder when the engine was at idle to reduced the "clatter" that has plagued diesel engines since their invention. The downside was that adding fuel also increased emissions. In the VW engineering circles this was called an "Acoustic Function" and they implement it in Audi branded 3.0-liter European diesels from 2004 – 2008.

Then in 2006, Volkswagen engineers made the decision to adapt the the technology for use in their Generation 1 EA189 2.0-liter TDI engine (the  TDI diesel engine at the heart of the scandal) as a way to avoid licensing SCR technology from Mercedes-Benz. The commonplace selective catalytic reduction (SCR) technology uses liquid urea to reduce nitrogen oxide (NOx) emissions and is the norm on all larger diesels. But for VW, the bread and butter small diesels could avoid the licensing and the added cost of a urea tank and exhaust injection system by using a "Lean Trap," which traps NOx and breaks it down in a catalytic converter by cycling to a fuel-rich mode as needed. Unfortunately this also brought on another problem as the Lean Trap choice also allowed too much build up of diesel particulates in the soot filter (DPF) resulting in premature failure. Engineers decided they could use the "Acoustic Function" to correct the problem … which was in turn approved by management. As sales for these highly efficient small diesel grew in popularity, Volkswagen leaned on this treatment technic further and further.


In the early days Volkswagen engineers may have pursued the development of the "Acoustic Function" with the best of intentions, even when using it to extend the life of the diesel particulate filter. But somewhere along the line they decided to use the feature to cheat the emissions tests and continued to promote and market these small TDI "clean diesels."  Oh … the $15 BILLION web they weaved … not to mention the black-eye which will haunt the company for years.

Additional reading:
Road and Track has an interesting article on the "fix" that may not really be a fix.


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