In-use emissions testing of light-duty diesel vehicles in the U.S.

Published: 2014.05.30

Gregory J. Thompson, Daniel K. Carder, Marc C. Besch, Arvind Thiruvengadam, Hemanth K. Kappanna (West Virginia University)

The ICCT contracted with the Center for Alternative Fuels, Engines and Emissions at West Virginia University to conduct in-use testing of three light-duty diesel vehicles, using a portable emissions measurement system (PEMS), over a variety of pre-defined test routes exhibiting diverse driving conditions pertinent to major United States population centers located in the state of California. Additionally, one vehicle was operated over an extended distance of nearly 4,000 kilometers predominantly composed of highway driving conditions between California and Washington State. Two of the three test vehicles were also tested on a chassis dynamometer at California Air Resources Board’s (CARB) El Monte, CA vehicle certification test facility.

The test vehicles were certified to US-EPA Tier2-Bin5 and California LEV-II ULEV emissions limits and were equipped with NOx after-treatment technologies, including one lean-NOx trap (LNT) and two urea-based selective catalytic reduction (SCR) systems.

Real-world NOx emissions were found to exceed the US-EPA Tier2-Bin5 (at full useful life) standard by a factor of 15 to 35 for the LNT-equipped vehicle, by a factor of 5 to 20 for one, and at or below the standard for the second urea-SCR fitted vehicle over five pre-defined routes categorized based on their predominant driving conditions, namely, i) highway, ii) urban/suburban, and iii) rural-up/downhill driving. The second urea-SCR equipped vehicle exceeded the standard only during rural-up/downhill operating conditions by a factor of ~10. Most importantly, distance-specific NOx emissions for the two high-emitting vehicles were below the US-EPA Tier2-Bin5 standard for the weighted average over the FTP-75 certification cycle during chassis dynamometer testing at CARB’s El Monte facility, with 0.022g/km ±0.006g/km (±1σ, 2 repeats) and 0.016g/km ±0.002g/km (±1σ, 3 repeats) for the LNT and urea-SCR equipped vehicles, respectively.

In general, CO and THC emissions were observed to be well below the regulatory level for all three test vehicles and driving conditions, with exception of two routes for the LNT-equipped vehicle where THC emissions were observed at slightly elevated levels.

As expected, highway driving showed lowest distance-specific CO2, whereas urban/suburban driving conditions led to highest CO2 emissions factors for all vehicles. Overall, urban/suburban driving leads to a 32%–39% reduction in fuel economy over highway driving.

Particulate number emissions, inferred from PPS measurements, were observed below the Euro 5b/b+ standard except during vehicle operation exhibiting DPF regeneration events where PN emissions significantly increased by two to three orders of magnitude, thereby exceeding the Euro 5b/b+ standard under all driving conditions for the LNT and first urea-SCR vehicles.

Staff contact: Francisco Posada