It may come as little consolation to beleaguered executives at Volkswagen but the automotive giant could turn out to have been a victim of its own sophisticated software. The United States Environmental Protection Agency (EPA) has accused the company of deliberately rigging its computer-controlled diesel engines to behave differently at the regulatory agency’s official test facility than they do on the road. However, a Canadian specialist in diesel engines suggests that any automotive firm should check carefully to make sure their own vehicles would not do the same thing.
According to Ming Zheng, a professor of mechanical, automotive and materials engineering at the University of Windsor, new passenger cars now have more computer code controlling their engines than some of the world’s most sophisticated jet aircraft. This code issues commands to an engine that will be dedicated to achieving and maintaining operational efficiency. However, minimizing pollution might take a lower priority than maximizing fuel economy unless the program is modified accordingly, Zheng warns.
Zheng is director of the Clean Combustion Engine Laboratory, a $3.5 million research centre dedicated to high efficiency diesel and hybrid powertrains. For him, the trade-off in performance is clear. The most obvious way of lowering the production of nitrogen oxide and nitrogen dioxide during diesel combustion is to lower the flame temperature in the cylinder. This decreases the outstanding combination of power and fuel economy that is prized by so many diesel drivers.
Some high-end models address this problem through a selective catalytic converter that reacts engine emissions with an on-board supply of a gaseous reductant such as anhydrous ammonia, aqueous ammonia or urea. This approach converts nitrogen oxides into diatomic nitrogen and water without compromising the engine’s performance. The supply of reductant must be replenished regularly, about as often as the vehicle’s oil should be changed.
Volkswagen did not adopt this strategy in many of its models, relying instead on computer controls to intensify exhaust gas recirculation as a means of emission suppression. A group of university researchers then inadvertently discovered that this software carefully distinguished between typical road operation and the EPA testing conditions, setting emissions on the road to be much higher than those found by the EPA during their tests.
Zheng does not find this result surprising, citing the extraordinary gap in the progress between emissions standards versus emissions testing. “Thirty years ago there were almost no restrictions on nitrogen oxide,” he says. “It was 10 grams per kilowatt-hour; currently it is 0.2 grams per kilowatt-hour for commercial truck engines. Meanwhile, the primary testing procedures for passenger cars, which emphasize low-load and low-speed transient operations, haven’t changed in 45 years.”
At the time when those procedures were developed, Zheng adds, cars functioned primarily under mechanical controls, with no electronics or on-board computers. Today, mechanical control systems have been overshadowed by high tech automation. As Volkswagen’s case demonstrates, the underlying software can readily obscure the emission compliance that regulators are expecting.
Nor is it clear what kind of new testing regime would be able to keep up with such software. Automobile manufacturers continue to add ever more code to their products while keeping the content of that code as confidential as possible. For the time being, notes Zheng, regulatory bodies like the EPA continue to count on the cooperation of company engineers to help them determine what is really happening with each car’s emissions on the highway. “We hope that the manufacturers will optimize their cars for emissions all the time, irrespective of real-world driving or laboratory testing,” he says. “But we know that this is not actually required — though expected — by the regulations.”