In-Use NO_x Emissions from Model Year 2010 and 2011 Heavy-Duty Diesel Engines Equipped with Aftertreatment Devices

Abstract

The California Air Resources Board (ARB) undertook this study to characterize the in-use emissions of model year (MY) 2010 or newer diesel engines. Emissions from four trucks: one equipped with an exhaust gas recirculation (EGR) and three equipped with EGR and a selective catalytic reduction (SCR) device were measured on two different routes with three different payloads using a portable emissions measurement system (PEMS) in the Sacramento area. Results indicated that brake-specific NO x emissions for the truck equipped only with an EGR were independent of the driving conditions. Results also showed that for typical highway driving conditions, the SCR technology is proving to be effective in controlling NO x emissions. However, under operations where the SCR’s do not reach minimum operating temperature, like cold starts and some low load/slow speed driving conditions, NO x emissions are still elevated. The study indicated that strategies used to maintain exhaust temperature above a certain threshold, which are used in some of the newer SCRs, have the potential to control NO x emissions during certain low-load/slow speed driving conditions.

Real-World Emissions from Modern Heavy-Duty Diesel, Natural Gas, and Hybrid Diesel Trucks Operating Along Major California Freight Corridors

“…Over all routes, emissions on a per-mile basis range between 0.6 and 4.0 g/mi, which was slightly lower than the range of 2.0-8.9 g/mi reported by Thiruvengadam et al [31] over the chassis dynamometer UDDS cycle for MY 2010 and 2011 engines all equipped with SCR. Whereas these results indicate later MY engines have improved NOx control, the SCR conversion efficiency decreases at a threshold temperature somewhere between 200 and 250°C [20,31], and elevated brake-specific and per-mile NOx emissions were still observed during low-load driving conditions. To illustrate trends of real-world routes with high NOx emissions for all engine manufacturers, Fig.…”

“…Elevated emissions could result from poor durability of emission control devices (e.g. selective catalytic reduction (SCR), or diesel particulate filter (DPF) systems) [16], the generation of off-cycle NOx emissions when SCR temperatures are below catalyst light-off temperatures [19,20], or emissions generated during infrequent events such as DPF regeneration that are quantified during certification but may exhibit different emissions trends during real-world operation [21,22]. Improved control of actual in-use emissions, which include these known types of off-cycle events, begins with identifying the periods of inefficient emission control during real-world driving, especially during the introduction of new engine and aftertreatment technologies to achieve stringent emission standards.…”

On-road Heavy-duty Vehicle Emissions Monitoring System

“…24,25 Port operations can lead to low exhaust temperatures, poor SCR operation and higher NO x emissions on the 2010 compliant HDV's. 34 There are physical differences between the two weigh station sites with Peralta having an uphill exit compared to Cottonwoods slightly downhill grade and the entrance ramp at Cottonwood is significantly longer (1.1 km vs 0.3 km), which may account for the Cottonwood truck's having slightly lower average IR exhaust temperatures (210°C vs 225°C). Speeds and accelerations are also slightly higher at Peralta.…”

Investigating Real-World Emissions of China’s Heavy-Duty Diesel Trucks: Can SCR Effectively Mitigate NOx Emissions for Highway Trucks?

“…Fuel-based NO x emission factors under high and low loads for five HDDTs (Note: Four Euro II and III HDDTs (i.e., II-1, II-2, III-1 and III-2) emission tests were performed in Beijing and One Euro IV HDDTs (i.e., IV-1) in Guangdong). might achieve very low NO x emissions (e.g., lower than 1 g km -1 ), although some challenges still remain under unfavorable operating conditions, which are associated with lower exhaust temperatures (e.g., low speed, idle conditions and low load mass) (Misra et al, 2013;Spreen et al, 2014).…”