Since the first automotive positive crankcase ventilation system was mandated by the Environmental Protection Agency in the 1960s, automotive emissions have been tightly regulated by the EPA.
Manufacturers must certify new models as emissions compliant, and the EPA monitors vehicle emissions under the Clean Air Act. Occasionally, vehicles are found to emit more than the allowed levels, and the EPA acts to force a product recall.
Volkswagen Inc., representing the Volkswagen and Audi brands in America, has today been issued a Notice of Violation of the Clean Air Act by the EPA.
But this is far from a routine notification regarding an out-of-spec system.
The EPA alleges that four-cylinder VW and Audi diesel cars made between 2009 and 2015 include special software designed to circumvent testing of the EPA’s emission standards for certain air pollutants, specifically oxides of nitrogen (NOx).
Essentially, Volkswagen Inc.’s special software in the powertrain control module sensed when the vehicle was under an emissions test, and recalibrated the air fuel parameters to produce NOx values up to 40 times lower than those emitted during real-world operation.
According to the EPA, the software produced by Volkswagen is a “defeat device,” which is expressly prohibited by the Clean Air Act. The defeat device was discovered through independent analysis by researchers at West Virginia University, working with the International Council on Clean Transportation, a nongovernmental organization.
In September, after the EPA and the California Air Resources Board demanded an explanation for the emissions level discrepancies, VW revealed that the cars contained defeat software. Volkswagen may be liable for civil penalties, or they could be compelled to recall the affected vehicles.
482,000 diesel passenger cars sold in the US since 2008 are affected, including models of the Jetta, New Beetle, Audi A3, Golf and Passat. The EPA noted that the Notice of Violation covers exhaust emissions only, and there is not a safety issue. According to administration, owners of affected vehicles do not need to take any action at this time.
While it may seem incredible that one of the world’s largest automakers would incorporate a device intended to cheat on a government mandated test, from an engineering viewpoint it’s not hard to see VW’s motivation.
Acceptance of diesel powered passenger cars has been glacially slow in the United States, despite the popularity of diesels in light and medium duty pickup trucks. One reason is a lingering perception of diesel vehicles as noisy and smoky, conditions which are no longer true due to the advanced fuel air management capabilities of software-controlled common rail fuel injection.
Another issue is drivability. Diesels used to mimic the heavy truck experience, meaning very high torque at low engine RPM, presenting a driving experience unfamiliar to American drivers.
Proper calibration of modern multispeed automatic transmissions has gone a long way to changing this, but diesels are still a specialty market in the passenger car arena in the United States.
To sell diesels in the US, the driving experience has to match that of gasoline powered vehicles as closely as possible, while delivering significantly better fuel economy in order to justify the additional cost of diesel vehicles.
And that’s where the NOx issue comes in. Oxides of nitrogen are potent pollutants, and controlling them is more difficult than, for example, cleaning up carbon monoxide with catalytic converters.
The problem is simple: the best efficiency and power comes from the highest possible combustion chamber temperatures. These are heat engines, after all, and every first-year engineering student knows that the delta T matters.
Unfortunately, though combustion air is only 16% oxygen, it is also 78% nitrogen, and at the elevated temperatures of high compression engines such as diesels, temperatures are high enough to bind oxygen to nitrogen in the form of mixed oxides.
The simplest way to reduce NOx formation is to cool the combustion chamber, which can be achieved by fuel/air ratios that are either very lean or very rich compared to the stoichiometric.
This naturally has a serious effect on economy and drivability, so the alternative is exhaust gas recirculation. Unfortunately, stuffing the combustion chamber with inert combustion by-products doesn’t help the economy or drivability, either.
However, it is preferable to difficult to manage air/fuel ratios, plus it’s a proven technology in gasoline engines since the mid-1970s.
Turbocharged diesels, probably the ultimate in internal combustion engine efficiency, have closed the drivability gap with gasoline powered cars and light trucks.
Is it possible that Volkswagen isn’t alone in cheating on the NOx standard?
No doubt the EPA and CARB will be investigating the control software in more vehicles now that this has come to light.
It’s highly unlikely that the affected Volkswagen vehicles can be retrofitted or re-flashed to reduce emissions to mandated levels without killing drivability and economy. It’s also highly unlikely that VW will be forced to recall these vehicles, although the resale value of vehicles known to be noncompliant may be affected, especially in environmentally sensitive jurisdictions like California.
At the very least, VW has the mother of all PR problems on its hands, although not as serious as GM’s ignition switch scandal.
Will heads roll at VW engineering?
How many people knew about the defeat software?
It’s unlikely that knowledge of the software was limited to only one or two engineers at Volkswagen. It will be interesting to see who falls on their sword at VW, and how they plan to reengineer their diesel engines to actually meet to the NOx standard while maintaining drivability.
We’ll keep you informed.
