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Researchers from Bochum, Germany, and San Diego, California, say they’ve found the precise mechanisms that allowed diesel Volkswagens and Audis to engage or disengage emissions controls depending on whether the cars were being driven in a lab or driven under real-world conditions. As a bonus, the researchers also found previously-undisclosed code on a diesel Fiat 500 sold in Europe.
Auto manufacturers have been cheating on emissions control tests for decades, but until recently, their cheats were fairly simple. Temperature-sensing or time-delay switches could cut the emissions control system when a car was being driven under certain conditions.These days, cars are an order of magnitude more complex, making it easier for manufacturers to hide cheats among the 100 million lines of code that make up a modern, premium-class vehicle.
In 2015, regulators realized that diesel Volkswagens and Audis were emitting several times the legal limit of nitrogen oxides (NOx) during real-world driving tests. But one problem regulators confronted was that they couldn’t point to specific code that allowed the cars to do this. They could prove the symptom (high emissions on the road), but they didn’t have concrete evidence of the cause (code that circumvented US and EU standards).
Luckily, subsequent subpoenas of e-mails between executives revealed the kind of broad-brush information that helped federal investigators secure settlements from Volkswagen and its supplier Bosch. Investigators were also able to get a plea deal with a former VW engineer.
This latest research finally offers a smoking gun. For more than a year, researchers studied 926 firmware images from the VWs and Audis identified by the EPA in 2015, and they found a potential defeat device in 406 of those firmware images. All the cars studied had Engine Control Unit (ECU) systems developed by Bosch.
Interestingly, Volkswagen may not have written any of the code that enabled its scandal, although it may have requested certain functions from Bosch. The researchers note: “We have found no evidence that automobile manufacturers write any of the code running on the ECU [Engine Control Unit]. All code we analyzed in this work was documented in documents copyrighted by Bosch and identified automakers as the intended customers.”
Discovering a hidden cheat
The researchers, led by University of California San Diego computer scientist Kirill Levchenko, faced a number of challenges in their quest to find the offending code.
Firmware images were gleaned from car-tuning forums and from an online portal maintained by Volkswagen for car repair shops. Documentation, in the form of so-called “function sheets,” was harder to come by. The function sheets were necessary to give the binary context, but the sheets are copyrighted by Bosch and generally not shared with the public. The research team ended up turning to the auto-performance tuning community again. These hard-core hobbyists and professionals share leaked function sheets so they can make aftermarket modifications to their cars.
“[T]he vehicle can switch to an operating regime favored by the manufacturer for real driving rather than the clean regime necessary to pass the emission test.”
Once the researchers were able to study the code running on the faulty diesels, they discovered that Volkswagen’s defeat devices were far more nuanced than anything found previously. Levchenko told Eurekalert that the “Volkswagen defeat device is arguably the most complex in automotive history.”
The researchers found that the cars assumed they were being tested in a lab until a sensor reading ruled out a lab test. At that point, “the vehicle can switch to an operating regime favored by the manufacturer for real driving rather than the clean regime necessary to pass the emission test,” the research paper noted (PDF).
Earlier, more basic versions of the software checked for three conditions to decide whether a lab test was being conducted. But by 2009, some firmware versions included 10 different checks for a lab test. The cars checked for things like how long and how far the car had been driven (in the US, emissions cycle tests last no more than 31 minutes and the car drives exactly 11.04 miles). Some cars also may have conducted steering wheel checks—if the steering wheel deviated more than 20° from neutral position, it was probably not being tested in the lab.
As each check ruled a lab test in or out, a different function of the Engine Control Unit—like fuel injection timing, how exhaust gas is recirculated through the vehicle, and how much urea should be injected into the exhaust—could respond.
Hidden in plain sight
In many of the function sheets, the code to cheat emissions tests was labeled as modifying the “acoustic condition” of the engine—a label that helped the cheat fly under the radar for as long as it did. But the “acoustic condition” wasn’t simply labeling legerdemain. Originally, “acoustic condition” code really did apply to the sound of the engine on startup.
The labelling checks out with a story in a legal complaint filed by the New York Attorney General in July 2016. The state’s top lawyer wrote that, as early as 2004, Audi was looking for a way to stop the rattling sound that diesel engines are known to make as the engine starts up. They allegedly solved the problem by injecting extra fuel as the engine initiated combustion. The extra fuel increased emissions. So, the “acoustic condition” was modified to discern when lab testing was occurring so that the Audis in question could pass their emissions tests and also have nice quiet start-ups that customers would find inoffensive.
According to that same 2016 complaint from the New York Attorney General, Volkswagen later struggled with building its selective catalytic converter—the company felt that the kind licensed by Mercedes-Benz was superior, and VW’s solution required an extra tank that stored “gallons” of Diesel Exhaust Fluid. Volkswagen then tried to build a “Lean Trap” for the catalytic converter to trap NOx, but engineers found that the car could only go 50,000 miles before the Lean Trap broke.
At this point, according to the NY AG, engineers turned back to that “acoustic condition” code for a little help to meet strict emissions regulations. Those engineers were also on a deadline to put forward a product that could compete with competitors’ diesel passenger vehicles.
That legal assessment of the defeat device scandal seems to have held up as the researchers analyzed the cars’ code. The VWs and Audis in question checked for a number of parameters at startup, and if a lab test was a possibility, the car would start with that assumption, enabling full emissions controls. The code permitted the car “to operate... as if two distinct personalities took turns controlling the vehicle,” the paper’s authors wrote.
The paper also notes that the researchers tested the diesel Fiat 500X because it used the same Engine Control Unit from Bosch as the Volkswagens and Audis did. There was no mention of the “acoustic condition” in the Fiat’s function sheet, but some undisclosed code was discovered controlling how the car regenerates its NOx Storage Catalyst (NSC).
“Unlike the Volkswagen defeat device, the FCA [Fiat Chrysler Automobiles] mechanism relies on time only, reducing the frequency of NSC regenerations 26 minutes 40 seconds after engine start,” the paper notes. In a normal system, the NSC reduces NOx emission by trapping it in a catalyst and then regenerating the catalyst as it gets full.
But regeneration hurts a car’s fuel economy numbers and puts a lot of load on the Diesel Particulate Filter (DPF). “By reducing the frequency of NSC regeneration, a manufacturer can improve fuel economy and increase DPF service life, at the cost of increased NOx emissions,” the researchers explained.
This problem? It’s an arms race.
To do a lot of their analysis, the authors of the paper developed a static analysis system that could scan auto firmware to look for defeat devices. They were largely successful with Volkswagens and Audis, but they stressed that more work has to be put into this problem. Staying ahead of automakers is difficult when they know precisely what regulators are looking for. Automakers, of course, stand to gain considerably if they can hide emissions cheats and deliver cars with performance superior to their competitors. Consumers will be excited to get better gas mileage—they won’t necessarily know that their car is spewing an outsized chunk of NOx into the air behind them.
The researchers also say that it’s high-time regulators dispense with the kind of lab tests that US and EU governments have required for years. Instead, some kind of active scan for illegal code needs to be developed. This problem, the paper notes, “drives a critical research agenda going forward that will only become more important as regulators are asked to oversee and evaluate increasingly complex vehicular systems (e.g., autonomous driving).”
cylinder pressures and friction from larger bearings required to withstand the resulting higher loads in the engine.
The diesel-engine-powered vehicles also achieve more miles per gallon than SI gasoline powered vehicles due to the higher heating value of diesel fuel (128,450 Btu/gal) vs. gasoline (116,090 Btu/gal). The approximately eleven percent higher heating value results in an eleven percent better fuel consumption on a volumetric basis. At the pump, diesel fuel also costs more than regular gasoline in most areas of the United States. For the first 6 months of 2014, the average price of diesel fuel was $3.87/gal, while regular gasoline was $3.59/gal, or approximately 8 percent higher costs for diesel fuel. However, early projections of diesel fuel prices in 2015 expect a national average of $2.84/gal and a rise to $3.24 in 2016 (EIA 2015). The effect of this price decrease on diesel vehicle penetration in the U.S. market is currently unknown.
The exhaust emissions from diesel engines have been regulated since the 1960s for light-duty diesels and 1973 for heavy-duty diesels. The current regulations of the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) require control of criteria emissions of hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx), and particulate matter (PM). The CO emissions of diesels are inherently low due to lean combustion, and HC emissions are low compared to gasoline engines. The NOx and PM emissions have been controlled through engine technology, but recently more stringent standards have resulted in aftertreatment being used for PM (which is reduced with diesel particulate filters [DPF]) and NOx (which is controlled with selective catalytic reduction [SCR]). This is discussed in greater detail later in the chapter.
Although diesel fuel has higher energy content per gallon than gasoline, it also has a higher carbon density that results in approximately 15 percent more carbon dioxide emitted per gallon of diesel fuel relative to a gallon of gasoline. Diesel produces 10,180 g of carbon dioxide per gallon when burned, while gasoline produces 8,887 g of carbon dioxide per gallon (EPA/NHTSA 2012a). The EPA/National Highway Traffic Administration (NHTSA) Joint Technical Support Document refers to the additional carbon dioxide released from the burning of a gallon of diesel, relative to the burning of a gallon of gasoline, as the “carbon penalty” (EPA/NHTSA 2012b). Due to the cited “carbon penalty,”a diesel vehicle yields greater fuel economy improvements compared to its CO2 emissions reduction improvements. Another consideration is that diesel fuel is generally slightly more efficient to refine than gasoline, and there is a potential CO2 and energy benefit when refining crude oil to diesel as compared with refining crude to gasoline. This possible offset is not accounted for in the Agencies’ regulations.
This issue is amplified in the final CAFE rule, which states that the “163 g/mi [carbon dioxide standard] would be equivalent to 54.5 mpg, . . . [assuming] gasoline fueled vehicles (significant diesel fuel penetration would have a different mpg equivalent)” (EPA/NHTSA 2012a). EPA and NHTSA cite the additional carbon dioxide released from burning diesel fuel, compared to burning gasoline, as one of the reasons why manufacturers might not invest significantly in diesel engine technologies as a way to comply with the CAFE and GHG standards for MY 2017-2025 (EPA/NHTSA 2012b).
EPA/NHTSA 2017-2025 CAFE Rulemaking
The Agencies’ CAFE rulemaking for the 2017-2025 time frame relies heavily on the analysis done in the previous 2012-2016 rulemaking. The 2017-2025 rulemaking acknowledges the benefits of diesel engines regarding reduced pumping losses, improved torque, diesel fuel’s higher energy content compared to gasoline, and lean combustion. In spite of these benefits, EPA and NHTSA’s Joint Technical Support Document (TSD) recognizes the challenges that manufacturers will face regarding tailpipe emissions of diesel vehicles due to the “carbon penalty” and the NOx reductions required in the U.S. Tier 2 Bin 2 standards. In addition, it is recognized that diesels will also need to meet the EPA Tier 3 rules (EPA/NHTSA 2012b; EPA 2014a) introduced in March 2014 (see Chapter 2).
In order to meet the stricter CAFE/GHG standards, the Agencies acknowledged the potential need for vehicle manufacturers to include diesels in their product strategies. According to the TSD, several vehicle manufacturers have indicated to the Agencies that diesels will be part of their strategy to meet the midterm goals. Manufacturers that produce more diesel-engine-powered vehicles have also informed the Agencies that they expect diesel technologies to be part of a feasible strategy for reducing fuel consumption, carbon dioxide, and NOx emissions in the future.
In analyzing the technology, the TSD discusses the challenges of reducing diesel emissions to meet future requirements while acknowledging the fuel consumption reduction benefits of diesel engines. The approach to reducing emissions will include a combination of improvements to the combustion system to reduce emissions leaving the engine and improvements to the aftertreatment system. Technologies to improve the combustion system include fuel systems with higher injection pressures and multiple injection capabilities, advanced control systems, higher levels of cooled exhaust gas recirculation (EGR) to reduce NOx emissions, and advanced turbocharger systems. The aftertreatment system will continue to consist of a diesel oxidation catalyst followed by a DPF, or a catalyzed DPF and an SCR system for NOx reductions.
During the analysis, the Agencies used performance as the equalizing metric to compare diesel and gasoline vehicles. For smaller vehicles, the Agencies applied an I4 diesel engine with a displacement of 2.0L to replace a larger displacement I4 gasoline engine. For large cars and mid-sized trucks, a large I4 diesel engine with a displacement of 2.8L was used instead of a larger displacement V6 gasoline engine. For