Increasingly stringent oxides of nitrogen (NOx) and particulate matter (PM) regulations worldwide have prompted considerable activity in developing emission control technology to reduce the emissions of these two constituents from heavy-duty diesel engines. NOx has come under particular scrutiny by regulators in the US and in Europe with the promulgation of very stringent regulation by both the US Environmental Protection Agency (EPA) and the European Union (EU). In response, heavy-duty engine manufacturers are considering Selective Catalytic Reduction (SCR) as a potential NOx reduction option. While SCR performance has been well established through engine dynamometer evaluation under laboratory conditions, there exists little data characterizing SCR performance under real-world operating conditions over time.
This project evaluated the field performance of ten SCR units installed on heavy-duty Class 8 highway and refuse trucks. Additionally, five of these vehicles were operated with passive diesel particulate filters (DPFs) in tandem with the SCR units to further characterize the emission reduction capabilities of combining these technologies. Three of these vehicles were selected and comprehensively tested on a heavy-duty chassis dynamometer for criteria pollutants and ammonia (NH3). Testing was performed in two phases, the first after one year of in-use operation, and again after a second year.
The SCR units performed well with no deterioration in NOx performance after significant mileage accumulation. On average, NOx reductions after two rounds of testing were between 80% and 90%.
Hydrocarbons (HC) and carbon monoxide (CO) emission reductions met expectations based on previous test cell results [1,2,3]. PM emission reductions were below expectations possibly due to installation of non-degreened DPFs, sulfate-make, and/or system deterioration. It is difficult to draw conclusions from PM results without repeat of tests and more in-depth post-test PM analysis.