In 2013, the ICCT contracted with the Center for Alternative Fuels, Engines and Emissions at
West Virginia University to conduct in-use emissions tests on three light-duty diesel vehicles:
a Volkswagen Jetta, a VW Passat, and a BMW X5. The full results and analysis are available here
(http://www.theicct. org/use-emissions-testing-light-duty-diesel-vehicles-us).
The three test vehicles were certified to US-EPA Tier2-Bin5 and California LEV-II ULEV emissions
limits and were equipped with NOx after-treatment technologies: the Jetta was tested with a lean-
NOx trap (LNT), the Passat with a urea-based selective catalytic reduction (SCR) system, and the
BMW X5 with an SCR system. All three test vehicles were thoroughly checked for possible engine
or after-treatment malfunction codes using an on-board diagnostics (OBD) scanning tool, with none
of them showing any fault code or other anomalies. No reduction in catalytic activity due to aging
was expected, as the total mileage was relatively low (< 15,000 miles) for all test vehicles.
Real-world NOx emissions, as reported by the PEMS, were found to exceed the US-EPA Tier2-Bin5
(at full useful life) standard by a factor of 15 to 35 for the Jetta, and by a factor of 5 to
20 for the Passat, over five pre-defined routes categorized based on their predominant driving
conditions (highway, urban/suburban, and rural-up/downhill). The BMW was generally at or below
the standard and only exceeded the standard during rural uphill operating conditions.
The VW vehicles met the emission standard on FTP-chassis dynamometer tests, which include cold-
start NOx emissions. But the on-road emissions testing was performed with the engine and after-
treatment in warmed-up condition (i.e. warm/hot start), and the VW vehicle emissions were 5 to
35 times the standards during on-road testing, which did not include cold-start NOx emissions.
This inconsistency was a major factor in ICCT's decision to contact CARB and EPA about our test
results.
This project was part of a larger meta-analysis of PEMS data from EU (Euro 6) and US (Tier 2
Bin 5/ULEV II) diesel passenger cars. (For details on this project,
see http://www.theicct. org/real-world-exhaust-emissions-modern-diesel-cars)
This broader study analyzed the on-road emissions performance of fifteen new diesel passenger
cars, twelve certified to the Euro 6 standard and three to the US Tier 2 Bin 5 standard (which
is more stringent than Euro 6). Emissions were measured over 97 trips, totaling more than 140
hours of operation and 6,400 kilometers driven. On average, real-world NOx emissions from the
tested vehicles were about seven times higher than the limits set by the Euro 6 standard.
In most cases the exceedances found could not be attributed to “extreme” or “untypical”
driving. Instead, they were due to transient increases in engine load typical of everyday
driving (e.g., going up a slight incline), or to normal regeneration events in the diesel
exhaust aftertreatment systems.
Performance differences among the vehicles tested indicate that the technologies for real-world
clean diesels already exist. Some of the tested vehicles, such as the BMW X5, had average emissions
below Euro 6 emission limits, suggesting that the technologies to achieve that level of performance
are available.
