Volkswagen’s Little Engine That Couldn’t

In the early 2000s, engineers at Volkswagen embarked on an audacious plan, one that seemed like it should have worked.

The company had bet that their technical prowess in crafting powerful and efficient diesel engines would help them meet increasingly tighter emissions regulations and fuel efficiency standards. Their wager on diesel was a technically simple solution to a problem that several other automakers were addressing with complex hybrid electric powertrains. Even in compact cars where widely-used clean diesel technology is bulky and costly, the company forged ahead, making small diesel cars a cornerstone of their fleet.

A Volkswagen 2.0-liter turbodiesel

For nine years, that bet paid off. Volkswagen engineers touted their 2.0-liter TDI diesel engine as an exemplar of efficiency and low emissions. At conferences and in published papers, they reveled in their engineering abilities—after all, they were the only company to have mastered the new emissions regulations using a compact, inexpensive treatment system. It allowed them to roll out diesel engines in one small car after another at relatively low prices. Since 2007, the company has sold 11 million cars worldwide with the so-called EA 189 engine.

Then, last week, they lost their bet. The U.S. Environmental Protection Agency had been tipped off that cars with that engine were releasing ten to 40 times the amount oxides of nitrogen (NOx) than was permitted by law. For over a year, the EPA pressed Volkswagen to explain the discrepancy between emissions released during the testing procedure and real-world driving. Finally, the company admitted last Friday that it had installed what’s known as a defeat device that engaged emissions controls during testing but disabled them otherwise, allowing the engines to emit toxic exhaust.

Volkswagen has said that the software that dupes emissions tests is installed on 11 million vehicles worldwide. The company states that the defeat device affects only a portion of those engines, though no one will know exactly how many until independent tests on those cars are completed. And while the fallout has so far been limited to Volkswagen, it’s possible that other manufacturers could be deploying their own emissions hacks. “We have no knowledge about whether other manufacturers are doing this, but it is a question that needs to be asked,” says John German, senior fellow and U.S. co-lead at the International Council on Clean Transportation, the independent nonprofit that discovered Volkswagen’s emissions discrepancies.

Volkswagen’s malfeasance is troubling in part because of its sophistication. The company had to write software that would recognize when the car was undergoing an emissions test, a potentially complex algorithm that might incorporate everything from differences in front and rear wheel speeds to variations in steering inputs and even barometric pressure.

There were signs that something was amiss even before the cars were shipped to U.S. dealers. In 2007, Volkswagen announced that new 2.0-liter diesel models were being delayed due to a technical problem, which a report from the time claims was related to the emissions system.

But just a year later, shortly after the recalled cars went on sale in the U.S., Volkswagen engineers were traveling the world extolling their design. They claimed to have cracked the low emissions, high fuel economy conundrum even while the polluting cars were driving off dealers’ lots.

A Long History

By the mid-2000s, Volkswagen had been making diesel engines for decades, and in Europe, they sold tens of thousands of diesel-powered cars every year. In the U.S., they had carved out a profitable niche selling small diesel cars to iconoclastic American consumers who reveled in their peppy acceleration and good fuel economy. But the company faced a challenge: In 2008, all diesel-powered cars sold in the U.S. had to meet to significantly stricter emissions standards that were a part of so-called “Tier 2” regulations. The EPA was looking to rid diesel of its sooty, noxious ways.

For years, engineers across the industry had struggled to find a way to keep the best parts of diesel engines—torque and efficiency—while ditching the bad—soot, nitrogen oxides (NOx), and sulfur dioxide emissions. To reduce NOx emissions, there are two main approaches. One is selective catalytic reduction, or SCR, which involves injecting urea into the exhaust stream to react with NOx and turn it into harmless nitrogen and oxygen. The approach is incredibly effective, but it requires an additional tank to store the urea, a heater to keep it fluid, a pump, a valve, a mixer, and a catalyst to speed the reaction. Despite that, most automakers ended up settling on SCR, in part because it worked so well.

For larger, more expensive vehicles, hiding the extra kit involved in SCR is easier, both in terms of packaging and price. But on smaller cars like the Volkswagen Golf and Jetta, SCR is less than ideal. There’s not a lot of room to put the urea tank, pump, and other equipment, and price-conscious consumers may balk at the added expense, which costs the manufacturer about $50 more for a 2.0-liter engine than the alternative, according to a study by ICCT. That equates to a cost savings of over $500 million over 11 million cars.

Luckily for Volkswagen, the company’s engineers were hard at work on the alternative, one based on research Toyota had done in the mid-1990s on an idea known alternately as a NOx storage catalytic converter or a lean NOx trap, or LNT. LNT uses a catalyst to absorb and store NOx so it doesn’t escape into the atmosphere. When the catalytic converter is full, the system burns off the stored NOx by pumping an extra burst of fuel into the cylinders, most of which passes through to the converter where it burns the NOx into harmless nitrogen and oxygen.

When working properly, LNT systems tend to run a fuel-rich mixture for a second or two “every minute or so, sometimes more often,” says German, the ICCT senior fellow. “You’re injecting a lot of extra fuel.” Running rich that often can depress fuel economy, one of the main selling points of diesel cars.

An Apparent Breakthrough

But by the mid-2000s, Volkswagen seemed to have cracked the emissions-fuel economy tradeoff. In August 2006, Richard Dorenkamp, head of the company’s lowest emission engines and exhaust aftertreatments department, spoke at a meeting of clean diesel engineers in Detroit.

Lean NOx traps weren’t quite as good at reducing emissions than urea-based systems, but they were substantially cheaper, he said. If engineers could tune the engine just right, they could use diesel engines in small cars using LNT while also meeting the Tier 2 limits.

The trick was to reduce the engine’s emissions before the exhaust made it to the catalytic converters. In diesel engines, a simple way to reduce NOx emissions is to lower the combustion temperature. One solution is to draw cooled exhaust back into the cylinder. Because it’s deprived of oxygen, it won’t burn as hot as fresh air and will lower the combustion temperature.

But exhaust gas recirculation comes with its own set of problems. The lower combustion temperature reduces the engine’s power, and sooty exhaust can clog the system’s pipes, leading to higher maintenance costs. “EGR is kind of detrimental to many engine systems because of soot deposits that are going to go through intake,” says Arvind Thiruvengadam, a research assistant professor at West Virginia University and member of the team that discovered the engine’s emissions discrepancies. “Proper management of an EGR is always a challenge.”

Volkswagen engineers worked to reconcile the competing demands of emissions, power, and fuel economy, likely plowing through a series of engine tunings trying to find the right balance. They seemed to have figured it out. In 2008, a group of them presented a talk titled “Volkswagen’s New 2.0 l TDI Engine Fulfils [sic] the Most Stringent Emission Standards” at an industry conference in Vienna and published two papers outlining their strategy in MTZ worldwide, a technical journal that focuses on engine technologies. Their approach was three-pronged: One, they closely monitored and adjusting combustion conditions, and two, they used a two-stage exhaust gas recirculation system. Both of these reduced initial emissions. Finally, they handled the remaining emissions using a lean NOx trap.

Later that year, Achim Freitag, a testing engineer in the company’s diesel development department and a specialist in lean NOx traps, delivered a talk on the EA 189 at a diesel emissions conference in Michigan. “The implemented measures reduce engine emissions, which then make it possible to employ a NOx storage catalytic converter without any noteworthy increase in fuel consumption,” he wrote in the conference booklet.

Signs of Trouble

Volkswagen had rolled out the EA 189 engine in Europe without a hitch, but the American version was hit with an unexpected delay. The company had pulled its small diesel cars from many U.S. markets after the 2007 model year because the old engines didn’t meet new emissions standards, but it wouldn’t have new ones ready until the summer of 2008. Volkswagen broke the news to their dealer network in an email, which was posted in an Volkswagen diesel enthusiast forum. Automotive News picked up on the story and did some digging.

“A problem with the emissions system in Volkswagen’s new Jetta TDI will delay the launch of the diesel sedan for about six months,” reporter Richard Truett wrote in November 2007. “VW spokesman Keith Price confirmed Friday that the delay will be announced this week at the Los Angeles auto show. He would not give specifics about the technical problem, but he said it has been fixed. The car, though, must go through emissions testing and validation again, Price said. U.S. sales were expected to begin in early spring but now won’t start until late summer.” In response to a NOVA Next request for comment, Volkswagen could only confirm that the delay was “durability related.”

We may not ever learn the true motivation behind Volkswagen’s decision to cheat on emissions tests. But one thing is for certain: The swagger that once defined Volkswagen and its diesel cars has faded. Back in 2008 at the Beijing introduction of the Audi Q5, Wolfgang Hatz, head of engine and transmissions for the company, said, “Those who bought a diesel model will never return to gasoline.” Time will tell.