Diesel engines in personal vehicles have gone through a yoyo ride. Initially they were considered as dirty, suitable only for commercial vehicles which needed high torque which these engines could generate. Then came period when, due to their better efficiency and low CO2 emission per Km, they were touted as the green option till people got concerned with NOx and PM2.5 emissions. The diesel engines were on the receiving end of the green lobby’s wrath, especially in India with the courts banning them left right and center. Along came technologies like selective catalytic reduction and AdBlue, reducing the NOx to nearly petrol levels while maintaining a low CO2 footprint.

The Touareg, is the flagship SUV model from Volkswagen. The Touareg V8 TDI is the flagship Touareg with a diesel engine. The twin turbo, V8 diesel engine in this car generates a rubber burning 421 PS of power and shaft twisting 900 N-m of torque. These are the vehicles which are green hunter’s favourite targets. But now, there is a twist. The Euro 6 norms require engines to produce a maximum of 80 mg/Km of NOx. Any car producing so much of NOx can legally run on the roads. These tests are to be done in the test laboratories under the Worldwide Harmonized Light Vehicles Test Procedure (WLTP) norms.

Image Courtesy VW

However, European Union has now introduced a new testing norm called the Read Driving Emission (RDE) which are to be conducted in the real world. These tests supplement the WLTP tests. Volkswagen has installed the Touareg V8 TDI with multi-stage exhaust gas treatment system featuring a very large NOx storage unit with high-grade coating. This unit can store up to 2.3 litres of NOx. The car is also fitted with an SCR (selective catalytic reduction) which converts NOx to harmless steam and nitrogen using AdBlue. AdBlue is a synthetic Urea solution which is injected into the exhaust. Further the the Touareg V8 TDI features a diesel particulate filter.

In addition to exhaust treatment, the Touareg V8 TDI is also installed with twin turbochargers which operate sequentially. At low engine speed from 1250 rpm only one turbo charger feeds air into the cylinders minimising both consumption and emissions. As the engine rpm increase to 2200 and beyond, the second turbo charger kicks in using an electrical valvelift system.

Emission Analytics, a third party tester carried out tests under the RDE on the VW Touareg V8 TDI in actual traffic in three locations to cater for the road inclines and altitude. Diesel engine performance is dependent on the altitude, being a compression ignition process. These tests were carried out in the flat regions of Lower Saxony. Two further tests were conducted on routes in Baden-Württemberg and Bavaria, areas where the region is hilly and there are differences in Altitude. The results were surprising. The Touareg V8 TDI, with its clean exhaust system and dual turbo chargers, the Touareg V8 TDI produced only 10mg/ Km of NOx in Saxony, 13 mg/ Km in Bavaria and 20 mg/ Km in Baden-Württemberg, averaging 14 mg/ Km of NOx, making it even cleaner than even petrol Euro 6 engines.