How I became a diesel believer again

Like many proponents of the diesel, my faith in the fuel-efficient technology was undermined by revelations that the industry systematically abused regulatory loopholes governing harmful nitrogen oxide emissions. Current sales figures suggest I am not alone. The diesel appears to be in terminal decline.

Yet the supplier most linked to the industry’s deceit, Robert Bosch, which is alleged to have developed the original defeat device for Volkswagen Group, may have found a solution that could turn around the diesel’s decline. Using a VW Golf GTD with a 146-hp engine and manual transmission as a platform, Bosch has developed an after-treatment process that can lower NOx to a fraction of the future legal limit.

The key is an intelligent software that ensures the main selective catalytic reduction (SCR) system almost always operates at its optimal temperature of 200 degrees Celsius regardless of the engine load. Engineers achieved this by integrating the SCR system into the diesel particulate filter positioned next to the warm engine block. This breakthrough required precise control of the filter’s soot incineration process to ensure temperatures do not exceed 800 degrees Celsius, which would cause the SCR system’s platinum catalytic coating to start to degrade. Bosch also uses the Golf GTD’s high-pressure recirculation system to ensure cool exhaust gases do not accidentally lower the operating temperature of the system too far.

Bosch claims the system can achieve an average NOx output of just 13 milligrams per kilometer, far below the Euro 6d’s stringent upcoming target of 80mg/km. Bosch believes the technology is on par with the cost of improving gasoline engines, and it could be ready for series production in two to three years.

To allay any suspicion, the company gave me a chance to test it on the road using a Portable Emissions Measurement System. While these PEMS devices are imperfect – Euro 6d currently accounts for a deviation as high as 40mg/km – the advantage is that a reading cannot be manipulated.

The entire 94.4 km test drive was split roughly evenly between urban, rural and highway environments to ensure it mimicked the new regulatory “real world driving emissions” test called RDE, including the prescribed cold start that is responsible for a third or more of NOx emissions. I drove fairly aggressively building in intentional gear shift delays to ensure the engine was challenged. A log was kept using the vehicle’s own NOx sensors located in the tailpipe. My initial finding: After just 7.83 kilometers the car was performing below the 80mg/km threshold and that number was expected to keep dropping.

Today, many automakers’ engine management systems are designed to switch off the car’s exhaust gas after treatment once the vehicle is driven too far or reaches certain altitudes or ambient temperatures. This is supposed to prevent the system from becoming clogged with soot. Bosch’s new system, I was told, works for all driving styles, at all temperatures and in all weather conditions.

After nearly two hours, I returned anxious to hear the PEMS results. Due in part to my demanding driving style, the reading was abnormally high, according to Bosch. On average I emitted 18 mg/km of NOx at a mean consumption of 6.5 liters of fuel and 0.17 liters of AdBlue urea solution per 100 km.

For the first time since diesel sales started to collapse last March, I finally found an answer that might restore my faith in the powertrain. I can only hope environmental groups have a chance to independently verify the performance of Bosch’s technology. The diesel’s only chance of survival is if there is absolute transparency regarding emissions.

My RDE results indicate it’s not too late to salvage the powertrain. The diesel isn’t dead. Not yet.