Characterization of NOx emissions from Light-Duty Diesel Vehicles during off-cycle operation

Persisting air quality problems in the US have triggered several policy responses that are targeted at lowering the emissions of light-duty vehicles. In addition, the promulgation of Clean Air Act of 1963 and other stringent emissions regulations in the recent times (USEPA Tier 2 Bin 5) to improve the quality of ambient air, mandated the OEMs to develop advanced engine combustion strategies and after-treatment pathways to minimize NOx, PM emissions and attain these ultra-low regulatory targets. Significant difference in emissions rates between certification cycles and real world operation has been observed.;The objective of this study is to conduct in-use emissions testing of light-duty diesel vehicles. Four light duty diesel trucks were tested over four pre-defined, on-road routes, certification and non-certification chassis dynamometer cycles to investigate the difference in emission rates during off-cycle operation. Exhaust emissions were measured using Portable Emissions Measurement System (PEMS).;Results from on-road tests show that NOx emission rate from one of the four vehicles exhibited 1.2 times higher than the combined average of the other three. All vehicles exhibited NOx emission rates of 4 -- 35 times higher during off-cycle operation compared to FTP-75 standard of 0.04 g/km. CO emissions during the warm engine starts were 48% lower than tests with cold start. Of all the vehicles, one vehicle exhibited CO 2 emission rate 3% lower than the combined average of the other three. Fuel economy observed on highway routes is 3% more than other urban and rural routes. On-road emissions rates are 4-35 times higher when compared to emissions from similar cycles on dynamometer, establishing that real world driving emissions are significantly different from those measured on certification cycles.