Heavy-Duty Diesel Engines with Aftertreatment

Hannu Jääskeläinen, W. Addy Majewski

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Abstract: Emission aftertreatment—diesel particulate filters and SCR catalysts—was widely introduced on heavy-duty diesel engines to meet US 2007 emission standards. However, there were differences in the technology paths—some manufacturers initially attempted to meet the 0.2 g/bhp-hr NOx limit using high EGR rates, without NOx aftertreatment. In medium-duty vehicles, there has been a trend to chassis certify complete Class 2b and Class 3 trucks. In Europe, Euro VI emission standards required the addition of particulate filters to Euro V engines with SCR technology.


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.

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


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.

Table 1
Emission control strategies for meeting US 2007 emission standards
Manufacturer2007-20092010 and laterComments
StrategyEmission Limits (NOx+HC/PM, g/bhp-hr)StrategyEmission Limits, NOx/PM
CaterpillarLP EGR + DPF1.3/0.01--Active regeneration with burner
CumminsHP EGR + DOC+DPF1.1–2.5/0.01HP EGR + DOC + DPF + SCR0.2-0.5/0.01 g/bhp-hrSeveral engine families had NOx FELs above 0.20 g/bhp-hr from 2010-2012. After 2013, most engines certified to 0.20 g/bhp-hr, a small number of families used FELs of 0.30-0.35 g/bhp-hr.
Active regeneration with DOC
HP EGR + DOC + DPF + NAC0.2-0.4/0.02 g/mileDodge Ram pick-ups 2007-2012. Legally equivalent to 0.2 g/bhp-hr NOx.
HP EGR + DOC + DPF + SCR0.2-0.4/0.02 g/mileDodge Ram pick-ups 2013 and later. Legally equivalent to 0.2 g/bhp-hr NOx.
DaimlerHP EGR + DOC + DPF + SCR0.2-0.4/0.02 g/mile2010 and later 2500 and 3500 series Mercedes-Benz Sprinter, Freightliner and Dodge vans
SCR: Fe zeolite
DDCHP EGR + DOC+DPF1.3/0.01HP EGR + DOC + DPF + SCR0.2/0.01 g/bhp-hr
GMHP EGR + DOC+DPF1.3/0.01-0.02HP EGR + DOC + DPF + SCR0.46/0.01 g/bhp-hr
0.2-0.4/0.02 g/mileSCR: Cu zeolite
Ford--HP EGR + DOC + DPF + SCR0.2/0.01 g/bhp-hr
HP EGR + DOC + SCR +DPF0.2-0.4/0.02 g/mileSCR: Cu zeolite
HinoHP EGR + DOC+DPF1.2/0.01HP EGR + DOC + DPF + SCR0.2/0.01 g/bhp-hr
IsuzuHP EGR + DOC+DPF1.2-1.4/0.01HP EGR + DOC + DPF + SCR0.2/0.01 g/bhp-hr
HP EGR + DOC + DPF + SCR0.2-0.4/0.02 g/mileSCR: Fe zeolite
IvecoHP EGR + DOC + DPF + SCR0.2/0.01 g/bhp-hr
MitsubishiHP EGR + DOC+DPF1.2/0.01
NavistarHP EGR + DOC+DPF1.1-1.9/0.01HP EGR + DOC + DPF0.5/0.01 g/bhp-hrActive regeneration with DOC
Paccar--HP EGR + DOC + DPF + SCR0.2/0.01 g/bhp-hr
Volvo/MackHP EGR + DPF1.3/0.01HP EGR + DOC + DPF + SCR0.2/0.01 g/bhp-hr“Passive” regeneration