Heavy-Duty Diesel Engines with Aftertreatment

Hannu Jääskeläinen, W. Addy Majewski

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• Introduction
• North American Engines
  • Manufacturers’ Strategies
  • Chassis Certification of Heavy Pickup Trucks and Vans
  • On-Board Diagnostics (OBD)
  • Aftertreatment Systems
• European Engines
  • Emission Strategies
  • Aftertreatment
  • Real World NOx Emissions

Introduction

Between 1994 and the end of 2006, emission standards for on-road heavy-duty diesel engines regulated by the US EPA focused on reducing NOx emissions. During this period, NOx emission requirements decreased from 5.0 to about 2.4 g/bhp-hr while PM emission limits remained static at 0.10 g/bhp-hr. Starting in 2007, emission limits for NOx and PM dropped considerably. A new PM limit of 0.01 g/bhp-hr (0.013 g/kWh) required an order of magnitude reduction in PM emissions for 2007 MY engines while a NOx limit of 0.2 g/bhp-hr (0.27 g/kWh) was phased-in between 2007 and 2010. For the period 2007-2009, 50% of a manufacturer’s engines had to comply with the new NOx limit of 0.2 g/bhp-hr while the remaining 50% of engines could continue to comply with the 2004 NOx+HC limit of 2.5 g/bhp-hr. The averaging, banking and trading options in the regulation allowed manufacturers to produce engines with NOx emissions between these two limits. As a result, most manufacturers designed almost all of their 2007-2009 engines to meet a NOx family emissions limit of around 1.1-1.2 g/bhp-hr. Additional regulatory requirements for on-board diagnostics (OBD) also started to be phased-in starting in 2007.

To meet the 0.01 g/bhp-hr PM limit, all engine manufacturers adopted diesel particulate filters (DPF). To meet the interim NOx requirements during the phase-in period most manufacturers chose to increase the levels of EGR from their 2004 engines to bring NOx down to 1.1-1.2 g/bhp-hr. One manufacturer, Cummins, chose to implement NOx adsorber catalysts in engines destined for Dodge Ram pick-up to meet an optional heavy-duty vehicle chassis certification limit that was legally equivalent to the 0.2 g/bhp-hr engine limit. For the full implementation of the 0.2 g/bhp-hr NOx limit starting in 2010, most manufacturers opted for urea SCR. The alternative to urea SCR, further increases in EGR was attempted by Navistar but ultimately proved to be unsuccessful.

Further reductions in NOx are required in the USA starting with model year 2024. In 2020, CARB adopted a rule that would see the NOx limit at 435,000 miles reduced to 0.050 g/bhp-hr in 2024 and 0.02 g/bhp-hr in 2027. The CARB rule also extends the FUL for HHDDEs in 2027 and 2031 to 600,000 and 800,000 miles respectively. At the federal level, the US EPA adopted a rule that set the FUL (650,000 miles) NOx limit at 0.050 g/bhp-hr starting in 2027. Both CARB and EPA rules also adopted a low load cycle (LLC) and in-use testing with PEMS using a moving average window (MAW) test procedure that will put further pressure to lower emissions, especially NOx, during low temperature operation and off-cycle conditions. The longer FUL starting in 2027 requires a significant increase in emission control system durability.

In Europe, Euro V standards for heavy-duty diesel engines came into effect starting near the end of 2008 that reduced NOx emissions to 2.0 g/kWh from the Euro IV level of 3.5 g/kWh. In 2013, Euro VI emission limits of 0.4 g/kWh NOx and 0.01 g/kWh PM came into effect. Also, a PN limit of 8.0×10¹¹ particle/kWh was introduced. OBD requirements were introduced at the Euro V level and increased in stringency for Euro VI. Off-cycle emission testing was introduced at the Euro VI level.

North American Engines

Manufacturers’ Strategies

Summary

Table 1 summarizes both the interim 2007-2009 and final 2010 emission control strategies for most manufacturers of heavy-duty diesel engines for the US market. Applications range from pick-up trucks rated at 8500 lb GVW (Class 2b) up to Class 8 trucks.

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