Challenges and Solutions to Meet the Euro 7 NOx Emission Requirements for Diesel Light-Duty Commercial Vehicles

Abstract

The improvement of air quality requires a further reduction of pollutant emissions, especially in urban areas. The Euro 7 regulations aim at the development of a new generation of internal combustion engine vehicles capable of achieving ultra-low pollutant emissions under demanding, real-world operating conditions. They introduce new technical challenges in the holistic design of a vehicle’s powertrain and emission control system. To identify these, four real-world Euro 7 driving scenarios are investigated, covering demanding urban, highway and mountain driving situations. Technical solutions are then presented to address these challenges and ensure compliance with the Euro 7 emission requirements as set out in the latest regulation proposal of the European Commission. The study focuses on the NOx emissions of an N1 Class III light commercial vehicle with 3.5 t mass and a P2 diesel mild-hybrid powertrain. To ensure emission compliance, a Euro 6e exhaust gas aftertreatment system with enlarged catalysts is combined with NOx raw emission improvements. For low-load cold starts, a 4-kW electric heater in the exhaust system is considered in addition to a 2-l DOC and a 6-l DPF with SCR coating. For high-load cycles with high raw emissions, a 10-l underfloor SCR is considered to ensure the necessary deNOx performance.

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Vol.:(0123456789)
Emission Control Science and Technology (2024) 10:123–139
https://doi.org/10.1007/s40825-024-00240-9
Challenges andSolutions toMeet theEuro 7 NOx Emission
Requirements forDiesel Light‑Duty Commercial Vehicles
TheodorosKossioris1 · RobertMaurer1 · StefanSterlepper1 · MarcoGünther1 · StefanPischinger1
Received: 8 November 2023 / Revised: 7 March 2024 / Accepted: 7 May 2024 / Published online: 4 June 2024
© The Author(s) 2024
Abstract
The improvement of air quality requires a further reduction of pollutant emissions, especially in urban areas. The Euro 7
regulations aim at the development of a new generation of internal combustion engine vehicles capable of achieving ultra-low
pollutant emissions under demanding, real-world operating conditions. They introduce new technical challenges in the holistic
design of a vehicle’s powertrain and emission control system. To identify these, four real-world Euro 7 driving scenarios are
investigated, covering demanding urban, highway and mountain driving situations. Technical solutions are then presented
to address these challenges and ensure compliance with the Euro 7 emission requirements as set out in the latest regulation
proposal of the European Commission. The study focuses on the NOx emissions of an N1 Class III light commercial vehicle
with 3.5 t mass and a P2 diesel mild-hybrid powertrain. To ensure emission compliance, a Euro 6e exhaust gas aftertreatment
system with enlarged catalysts is combined with NOx raw emission improvements. For low-load cold starts, a 4-kW electric
heater in the exhaust system is considered in addition to a 2-l DOC and a 6-l DPF with SCR coating. For high-load cycles
with high raw emissions, a 10-l underfloor SCR is considered to ensure the necessary deNOx performance.
Keywords Euro 7 NOx emissions· Exhaust gas aftertreatment technology· RDE cycles· Light commercial diesel vehicle
1 Introduction
In Europe, the first vehicle emission standards, known as
Euro 1, were introduced in 1992. Since then, increasingly
stringent emission standards have been a major driver of
technological progress in internal combustion engine vehi-
cles [1].
In addition to the drastic reduction of the regulated emis-
sion limits, the vehicle test conditions for type approval have
been continuously tightened since then. In 2017, the rather
outdated NEDC cycle was replaced by the more dynamic
WLTC (see below section). Subsequently, the introduc-
tion of the Real Driving Emissions (RDE) testing under the
Euro 6d-TEMP regulations [2] revealed significant differ-
ences between the NOx emission levels of diesel vehicles
measured in the laboratory and under real-world driving
conditions [3, 4], necessitating the implementation of new
emission reduction technologies and vehicle calibration
techniques. Despite these measures, major European city
centres are still struggling to comply with the air quality reg-
ulations [5, 6]. At the same time, the WHO had announced
even stricter air quality guidelines for 2021 [7].
Against this background, the Euro 7 regulations require
the development of a new generation of vehicles capable of
meeting ultra-low emissions limits under all possible real-
world driving conditions [8]. To this end, individual tech-
nologies have recently been intensively investigated. These
range from engine-related measures, such as the introduction
of advanced injection and boosting systems [9], dynamic
cylinder deactivation [10, 11] and lightweight structures
[9], to powertrain related measures, such as close-coupled
exhaust gas aftertreatment systems [12, 13], electric exhaust
gas heaters [11, 14] and fuel burners in the exhaust system
[15, 16]. However, there is very little work that addresses
the holistic emission-based design of Euro 7 diesel vehicles,
taking into account all aspects introduced by the upcoming
regulations.
This study first aims to highlight the technical chal-
lenges for the holistic emission-based development of Euro
7 diesel vehicles in the context of the diversity of regulated
* Theodoros Kossioris
kossioris@tme.rwth-aachen.de;
theodoros.kossioris@rwth-aachen.de
1 Chair ofThermodynamics ofMobile Energy Conversion
Systems, RWTH Aachen University, Aachen, Germany
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124 Emission Control Science and Technology (2024) 10:123–139
RDE operating conditions. It then presents the required
technological upgrades for the powertrain and the exhaust
gas aftertreatment system to meet the Euro 7 NOx emis-
sion requirements compared to current Euro 6 vehicles.
A mild-hybrid light-duty commercial vehicle (LCV) with
a diesel internal combustion engine (ICE) and automatic
(AT) gearbox is examined. LCVs combine in their operation
the characteristics of a light-duty (LD) passenger car and a
larger heavy-duty (HD) truck used for freight transport. This
makes it possible to apply the research results to both vehicle
types. The emission results presented in this study are based
on simulation and are focused on tailpipe NOx emissions.
2 Emission‑Based Euro 7 Design
Methodology andLegal Boundary
Conditions
An LCV of the N1 Class III class with a curb weight of
2.2 t and a gross combined weight of 3.5 t was selected for
the investigations. The vehicle is powered by a 2-l inline
4-cylinder diesel engine with a rated power of 115kW. The
power-to-mass ratio of the fully loaded vehicle is therefore
less than 35kW/t. The considered vehicle specifications are
listed in Table5 of the Appendix. The simulative investi-
gations were conducted in a MATLAB/Simulink environ-
ment, jointly developed by the Chair of Thermodynamics
of Mobile Energy Conversion Systems (TME) at RWTH
Aachen University and FEV Europe GmbH [17]. The plat-
form allows a holistic longitudinal vehicle simulation for
given driving cycles by combining existing models for all
powertrain sub-components (i.e. the ICE, the exhaust gas
aftertreatment system (EATS) and the vehicle). An over-
view of the structure and the prediction accuracy of these
models can be found in [18–25]. Data from previous Euro
7 light-duty vehicle projects were used to calibrate the
baseline models. These were scaled accordingly to meet
the powertrain specifications considered in this work. The
engine, vehicle and underfloor selective catalytic reduction
(SCR) catalyst (see Sect.4.2) calibrations were additionally
validated with dedicated experimental data from comparable
LCVs with the one investigated.
The Euro 7 emission-based design methodology adopts
a design approach that focuses on adverse RDE scenarios
for emissions formation. If compliance can be ensured in
these scenarios, it can be ensured in any other realistic RDE
test. Tables1 and 2 summarize the Euro 7 emissions limits
and testing conditions for normal driving proposed by the
EU commission and compare them to the Euro 6e standards
[2, 8, 26]. This provides a reference to the current regula-
tions. For driving situations that do not fall under normal
driving conditions, specific emission corrections should be
implemented, as per the Euro 7 regulation proposal. These
are summarized in Table3.
From Tables1, 2 and 3, the following conclusions can
be drawn about the expected regulations: (a) more stringent
emission standards are introduced compared to the Euro 6e
standards; (b) NH3 is a new regulated emission species; (c)
a minimum distance of 10km is specified for meeting the
emission requirements; (d) challenging driving situations,
including short urban trips, mountain driving, extreme cold
starts and trailer pulling, are part of the tested RDEs, with no
strict specification of the urban, rural and motorway shares;
and (e) The RDE conformity factor is no longer considered.
By considering the preceding, four critical scenarios for
emission compliance are investigated for the design of the
Euro 7 vehicle concept in the following. These cover a very
wide range of operation and ambient conditions. They are
selected to be challenging from all emission-relevant techni-
cal aspects. These scenarios are presented in Fig.1.
3 Challenges toMeet theEuro 7 NOx
Emission Requirements
In Fig.2, the profiles of the driving cycles that correspond to
the Euro 7 scenarios depicted in Fig.1 are shown.
A low-speed “Cold Urban” drive during traffic jams is
reflected in the first scenario (Fig.2, top left). For this, the
9-km “London Inter-Peak” cycle developed by the local
British government entity, Transport for London (TfL), is
used [27, 28]. As a worst-case scenario for normal cold
ambient conditions, a temperature of 0°C has been assumed.
The second scenario (Fig.2, top right) models “Moun-
tain Driving”. The driving cycle depicts mountain driving
with limited traffic flow, focusing solely on the uphill part
[29]. Due to hairpin curves, driving is aggressive with fre-
quent slowdown and acceleration. The road grade increases
Table 1 Comparison of the Euro 6e and the proposed Euro 7 emis-
sion limits for N1 Class III LCVs with a power-to-mass ratio of less
than 35kW/t [2, 8, 26]
a THC + NOx, bTHC
Emissions species Euro 6e standards Proposed
Euro 7 stand-
ards
NOx/ (mg/km) 125 75
CO/ (mg/km) 740 630
HC /(mg/km) 215a130b
PN/ (1/km) 6 × 1011 6 × 1011
PM/ (mg/km) 4.5 4.5
NH3 / (mg/km) - 20
RDE conformity factor
(NOx)/ (-)
1.1 1
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125Emission Control Science and Technology (2024) 10:123–139
continuously, averaging 9% for the cycle. The 16-km cycle
is a real-world driving profile that was derived from GPS
measurements. Since vehicles usually drive up and down
the mountain, a mountain downhill driving cycle of the
same distance follows the mountain uphill driving cycle in
the corresponding scenario presented in Fig.1. To model
a downhill driving profile, the uphill driving cycle and its
corresponding slope profile depicted in Fig.2 (top, right)
were mirrored round the horizontal axis towards increasing
time to mimic a return drive to the mountain bottom. The
Table 2 Comparison of the RDE normal testing conditions for N1 Class III LCVs with a power-to-mass ratio of less than 35kW/t under the
Euro 6e and the proposed Euro 7 standards [2, 8, 26]
RDE testing conditions Euro 6e Euro 7 proposal
Method Street driving + PEMS Street driving + PEMS
Altitude/ m ≤ 700 ≤ 700
Ambient temperature /°C 0–30 0–35
Payload /(-) Up to 90% of the sum of the allowed passengers’ mass & vehicle
pay-mass
0 ÷ 100%
Driving phases/ (-) Urban, rural, motorway -
Speed limits/ (km/h) Urban (60), rural (90), motorway (145) 145
Minimum distance/ km Urban (16), rural (16), motorway (16) 10
Driving share/ (%) Urban (29–44), rural (23–43), motorway (23–43) No limitation
Total trip duration /min 90–120min No limitation
Maximum average wheel power < 2km/
(-)
Not specified < 20% of maximum wheel power
Table 3 Emissions corrective factors for the extended RDE driving conditions according to the Euro 7 regulation proposal [2, 8, 26]
RDE testing conditions Extended conditions Emissions corrective factor
Altitude /m > 700 (a) The emissions are divided by 1.6 for as long as one testing condition is
“extended”
(b) If two (or more) testing conditions are simultaneously “extended”, the emissions
are multiplied by 0
Ambient temperature /°C − 10 ≤ θ < 0; 35 < θ ≤ 45
Maximum average wheel power < 2km /(-) ≥ 20% of the maximum wheel power
Trailer traction/ (-) With trailer
Fig. 1 Considered Euro 7 scenarios
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126 Emission Control Science and Technology (2024) 10:123–139
slope profile was additionally multiplied by − 1 to model
the downhill road grades. Due to the considerably increased
overall system mass in the 7 t variant with trailer traction,
the vehicle was unable to launch or accelerate properly in
certain high dynamic phases, due to lack of power. Hence,
it could not satisfactorily follow the requested vehicle speed,
leading to its emissions results being incomparable with
these of the two other variants. The preceding indicates
that in reality, this system would operate differently in such
dynamic and high-slope scenarios (e.g. with less aggres-
sive acceleration and/or vehicle speed reduction) and hence
the selected “Mountain Driving” driving cycle was deemed
unsuitable to model the 7 t vehicle driving behaviour in such
a scenario. In normal ambient conditions, 0°C is the worst-
case cold temperature.
In the third scenario (Fig.2, bottom left), extreme “Hot
Urban” congestion is modeled during summer in southern
European cities like Madrid. The 11-km cycle is generated
from measurements by the Chair of Thermodynamics of
Mobile Energy Conversion Systems of the RWTH Aachen
University under congested situations with rapid accelera-
tion following a protracted stop. Similar to the “Mountain
Driving” scenario, the Madrid driving cycle was deemed
unsuitable to model the 7 t vehicle driving behaviour in
urban traffic congestion due to its very high dynamics, and
is therefore not further considered in this study. A 35°C
ambient temperature is the worst-case hot temperature for
normal ambient conditions.
The last scenario (Fig.2, bottom right) investigates “High
Speed Highway” driving. The driving style is aggressive
with dynamic acceleration and speed requests of over
170km/h. The scenario represents a winter highway journey
in Germany at worst-case normal cold ambient conditions
at 0°C. The 103-km cycle is generated from measurements
at the Chair of Thermodynamics of Mobile Energy Conver-
sion Systems of RWTH Aachen University. For the test case
“trailer towing”, the maximum vehicle speed was limited to
100km/h as required by the regulations in many European
countries [30].
To quantify the new challenges of the different cycles,
their key features as well as their impact on the ICE engine-
out exhaust conditions are analyzed in Table4, Figs.6 and
7, respectively. For reference, Table4 compares the key fea-
tures of the Euro 7 test cycles with those of the well-known
NEDC and WLTC dynamometer test cycles.
Table4 demonstrates that the Euro 7 regulations will
result in more dynamic urban driving with lower average
vehicle speeds and more frequent idling phases, such as
the City RDE Madrid and TfL London Inter-Peak driving
cycles. This will increase the formation of transient emis-
sions while simultaneously reducing the average exhaust
gas enthalpy, making it more challenging to attain the
Fig. 2 Driving cycles that correspond to the Euro 7 scenarios [31]
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127Emission Control Science and Technology (2024) 10:123–139
light-off temperature of the exhaust gas aftertreatment sys-
tem (EATS).
Simultaneously, scenarios with very high average speeds
(e.g. German Highway) or road gradients (e.g. Mountain
Driving) and thus very high ICE loads must be taken into
account. These result in high raw emissions, requiring a
high deNOx performance, and high exhaust temperatures,
potentially affecting the deNOx capability of the system. At
elevated temperatures, the NH3 storage capacity of SCR sys-
tems is drastically reduced. Consequently, there is a higher
risk for NH3 slip during high average load cycles. Figures6
and 7 of the Appendix depict the time-based distribution
of the ICE operating points over the engine-out NOx and
exhaust gas temperature maps for the four Euro 7 driving
cycles considered.
In summary, a Euro 7 powertrain must be able to handle
the following technical challenges: (1) ensuring proper heat-
ing of the EATS even under conditions of very low-load cold
starts, (2) reducing idling and transient emissions, and (3)
being appropriately sized and controlled to achieve emis-
sions compliance in conditions of both very low-load cold
starts and very high loads. Based on these requirements,
technical solutions for Euro 7 are discussed in the next
chapter.
4 Solutions toMeet theEuro 7 NOx Emission
Requirements
Meeting the Euro 7 emission standards requires the imple-
mentation of new powertrain technologies. These can be
divided into two main subcategories: (1) measures for ICE
raw emissions reduction and (2) measures to increase the
deNOx efficiency.
Figure3 shows the considered technology upgrades in
the simulation model, in order to comply with the Euro 7
Table 4 Comparison of the key-features of the Euro 7 driving cycles and the NEDC and WLTC
Stop share/
(%)
Maximum speed/
(km/h)
Average speed/
(km/h)
Min. acceleration/
(m/s2)
Max. acceleration/
(m/s2)
v*apos 95%ile/
(m2/s3)
Average gradient/
(%)
NEDC 23.8 120 33.3 − 1.6 1 8.2 0
WLTC 13.4 131 46.5 − 1.5 1.6 12.6 0
WLTC Low 26.4 57 18.9 − 1.5 1.5 8.1 0
City RDE Madrid 65.3 60 11.3 − 1.2 3.4 18.4 0
London TfL Inter-Peak 36.1 52 13.9 − 3.1 2.5 8.0 0
WLTC High & Extra High 4.9 131 71.2 − 1.5 1.6 13.8 0
German Highway 0.8 175 118.3 − 2.3 2.3 27.2 0
Alpine Uphill 1.4 98 61.6 − 2.6 2.3 16.5 9.3
Fig. 3 Euro 7 powertrain and EATS concept compared to the Euro 6 state-of-the-art technology
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128 Emission Control Science and Technology (2024) 10:123–139
standards, compared to the state-of-the-art Euro 6 technol-
ogy for this vehicle category [29]. As expected, the Euro
7 concept is significantly more complex than the Euro 6
reference system. The two deNOx unit layout, with a die-
sel particulate filter (DPF) with a selective catalytic reduc-
tion (SCR) coating (ccSDPF) followed by a second SCR in
underfloor position (ufSCR), remains the same. The Euro 7
EATS volume shows an overall increase of 2.8 times, with
the first deNOx unit being largely sized by 2 times and the
second deNOx unit by 5 times compared to the respective
Euro 6 catalysts. The powertrain is electrified with a 48V
system that provides the necessary power supply to the elec-
tric heater (E-heater) installed in front of the “close-coupled
(cc)” diesel oxidation catalyst (DOC) and the electric motor
(E-motor) installed in P2 position. Hence, faster heat-up of
the EATS and pure electric drive become possible in the
Euro 7 system.
Compliance should be ensured also under adverse RDE
operating conditions. To cover all possible payload condi-
tions, the emission compliance of the LCV was tested when
empty (2.2 t), fully loaded (3.5 t) and fully loaded with
trailer towing (7 t). All simulations started with a depleted
battery (State of Charge (SoC) = 15%) as an unfavourable
scenario for the usability of the electrified components. In
addition, a very low initial NH3 of 5% of the maximum was
assumed for both deNOx units, which minimizes the deNOx
capability of the exhaust gas aftertreatment system at the
beginning of a cold-started cycle.
In the following, the adopted technical solutions for Euro
7 in this study are described in more detail.
4.1 Reduction ofICE Raw Emissions
Strategies to reduce the ICE raw emissions are necessary
when the EATS efficiency is limited, such as during cold
start or high-load operation. To lower the ICE raw emissions
under these conditions, while still maintaining favourable
fuel efficiency, combined HP- and LP-EGR systems have
become state-of-the art [32]. Besides the proper ICE hard-
ware selection, dedicated low-NOx operation of the ICE is
essential to meet all Euro 7 emission requirements.
For the Euro 7 vehicle concept presented here, a
low-NOx mode for the cold start is implemented in the
model in which the stationary NOx raw emissions of
the ICE are reduced by 40% compared to the baseline
Euro 6 warm emissions calibration. The strategy is
implemented for as long as the upstream temperature
of the second deNOx unit, the ufSCR (see Fig.3, bot-
tom plot), remains below 240°C. Similarly, in the high-
load and high-speed range (i.e. above 3500 1/min and
80kW ICE power), a 20% reduction in NOx emissions
is considered compared to the baseline Euro 6 emis-
sions, to address the particularly high formation of raw
emissions in the considered high-power Euro 7 cycles.
The NOx raw emission reductions are realized in the
model by adjusting the EGR rate [18]. For this level of
NOx raw emission reduction, model calculations indi-
cate an average increase in EGR rate by 8.5% (EGR rate
units) at low-load cold starts and 3% (EGR rate units) at
high loads during the activation phase of the respective
strategy, compared to the Euro 6 baseline. Based on
available measurement data from comparable engines,
the impact of the EGR rate increase on combustion effi-
ciency worsening, and hence fuel consumption and CO2
emissions increase, lays in the range of 0.5–1% (com-
bustion efficiency units) for the investigated levels of
raw NOx emission reduction [33, 34]. Such a combus-
tion efficiency reduction can be considered negligible.
Based on the same data, an increase of soot emissions in
the range of 40–100% was estimated. This can be com-
pensated by the increased DPF volume in the Euro 7
system. The typically expected impact of the increased
EGR strategy on the engine performance at high loads
can be compensated by different measures, such as the
boost pressure increase. Last, it is worth noting that
when it comes to moderate driving conditions, the ICE
measures considered are expected to be activated for a
limited period of time. The baseline warm NOx emis-
sions calibration for this concept derives from a state-
of-the-art Euro 6 ICE and is depicted in Figs.6 and 7
in the Appendix.
A significant proportion of the NOx emissions in a driv-
ing cycle is due to the transient acceleration events and the
idling operation. Here, powertrain hybridization can be very
beneficial. By also considering the 2030 CO2 emissions tar-
gets [35], a P2 mild-hybrid system is considered for this
Euro 7 concept. The system enables higher energy recupera-
tion capability [17] and hence a CO2 emission reduction
compared to market-standard P0 concepts. Moreover, it ena-
bles pure-electric propulsion and ICE start-stop functional-
ity. The latter contribute to a raw NOx emissions reduction
[17, 22].
The implementation of the previous measures enabled a
raw NOx emissions level below 300mg/km in the classi-
cal WLTP procedure, which is characterized as minimum
requirement for typical LD applications to comply with the
Euro 7 standards [36].
4.2 Exhaust Gas Aftertreatment System
Regarding the catalytic system, a DOC-based system is
preferred over a Lean NOx Trap (LNT)-based system
due to the latter’s negative impact on fuel consump-
tion and rapid ageing at high operating temperatures
[36]. The requirement for high deNOx capability under
both cold-started low-load and high-load conditions
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129Emission Control Science and Technology (2024) 10:123–139
necessitates the installation of two deNOx units. In
cold-started low-load cycles with low average exhaust
gas temperatures (e.g. urban driving), the first deNOx
unit, a ccSDPF, is mainly responsible for the NOx
emission conversion. The catalyst is placed close to
the ICE, in “close-coupled (cc)” position, in order to
allow the catalyst light-off temperature to be reached
quickly. For the HC and CO emissions oxidation, a
ccDOC is placed upstream of the ccSDPF.
To further decrease the time to the first internal post fuel
injections, and hence enable the faster heating of the ccDOC
and the complete EATS, an E-heater is installed upstream
the ccDOC. The E-heater power is 4kW, which is the cur-
rent market standard for 48V mild-hybrid electric vehicles
(MHEVs) [37, 38]. The heater provides power to the exhaust
gases for as long as their temperature at the ccSDPF inlet
remains below 220°C. The implemented internal post fuel
injection strategy aims at optimum operating temperature
windows for both deNOx units. Post injections start when
the ccDOC inlet temperature is above 200°C and are deacti-
vated when the exhaust gas temperature downstream ofthe
ccSDPF is 240°C. A 20% reduction in the targeted boost
pressure for ICE loads below 25% provides additional sup-
port for preventing the EATS from cooling down during
low-load operation.
In addition to the measures mentioned so far, the P2 mild-
hybrid system creates improved conditions for the EATS
through its start-stop and ICE load-point shift functions [22].
In this concept, pure electric driving is activated only during
urban driving when the SoC level is above 20%. When pure
electric driving is not possible and the battery SoC level
is below 50%, a load point shift strategy is implemented
to avoid operation below 15% of the maximum ICE load.
This prevents the flow of cold exhaust gases through the
EATS, and hence its cooling down, avoids operation in areas
of poor ICE fuel efficiency and higher raw NOx emissions
and also recharges the battery. For NOx emission reduction
at higher loads and temperatures (e.g. mountain driving),
a larger second SCR is placed in underfloor position. The
catalyst is appropriately dimensioned to ensure the neces-
sary deNOx capacity, also at these operating conditions. Its
heat-up behaviour and deNOx performance were validated
using vehicle measurements from a comparable LCV with
the one investigated.
NH3 will become a regulated emission species in the new
Euro 7 regulations (see Table1). Therefore, an ufSCR unit
with an ammonia slip catalyst (ASC) coating in its last slices
is considered to avoid tailpipe NH3 slip. Combined with a
robust urea dosing strategy, a universal NH3 control concept
has been defined that can ensure compliance with the Euro 7
NH3 and NOx limits in all four scenarios. Figure4 visualizes
the toolchain for identifying the proper ufSCR sizing and a
universal Euro 7 compliant NH3 slip strategy.
In the following, the Euro 7 emission results of the vehi-
cle concept are discussed and analyzed in detail. In all sim-
ulations, aged catalysts (Euro 7—160,000km equivalent)
were considered.
5 Results andDiscussion
After the challenges to achieve the Euro 7 NOx emission
requirements were identified and solutions to address them
were discussed, the specified Euro 7 vehicle concept is tested
for emission compliance.
Figure5 summarizes the tailpipe NOx emission results.
The results both at 10km and at cycle end are shown, since
compliance is only achieved, if the system manages to reach
the Euro 7 limits after 10km of driving and stays below
these until the cycle ends. The “uncorrected” and the “cor-
rected” emissions results are shown in the same figure. The
“corrected” results include the necessary emission correc-
tions depending on the presence or not of “extended” driving
conditions, as described in Table3. In Tables6 and 7 of the
Appendix, a detailed explanation of the emissions correction
criteria is given.
As shown in Fig.5, after the necessary corrections are
applied, Euro 7 compliance is achieved in all scenarios. The
designed system shows very good emissions performance in
the Cold Urban and the High Speed Highway scenario. In
both, the emissions stay well below the Euro 7 limit, even
before the necessary emission corrections are applied. The
only exceptions are the two cases with the trailer towing. The
same is also verified by the tailpipe NOx emission course in
those scenarios, which are depicted in Figs.8 and 9 in the
Appendix.
In the Hot Urban and the Mountain Driving scenarios,
NOx emission compliance is also achieved. However, in
Fig. 4 Toolchain for identifying
the proper ufSCR sizing and a
universal Euro 7 compliant NH3
slip strategy
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130 Emission Control Science and Technology (2024) 10:123–139
these cases, fulfilling the Euro 7 emission limits is more
challenging.
Focusing on the first scenario, the combination of
prolonged idling phases followed by aggressive and
short acceleration events creates particularly demand-
ing boundary conditions for emissions compliance dur-
ing city driving. According to Table4, the v*apos in
the selected City RDE Madrid driving cycle for the
Hot Urban scenario is 2.3 times higher than in the TfL
London Inter-Peak cycle of the Cold Urban scenario.
This indicates that the first cycle has higher dynamics.
Combined with the also higher stop share by 1.8 times,
the City RDE Madrid appears more challenging for
emission compliance than the TfL London Inter-Peak,
which is known as a challenging emission cycle for
diesel light-duty vehicles. The prolonged idling phases
in such low-load cycles render the proper EATS heat-
up very difficult, due to the insufficient exhaust gas
enthalpy available for its heating.
The short acceleration events increase significantly
the transient NOx emissions. Both phenomena appear in
a worst-case combination when the LCV is driven fully
loaded. However, even in this case, the advanced Euro 7
emission measures considered marginally succeed in ensur-
ing emissions compliance after the necessary corrections are
applied. This is also confirmed by the tailpipe NOx emission
courses depicted in Fig.10 for this scenario.
In the Mountain Driving scenario, on the other hand, the
technical challenges arise from the high NOx raw emissions
and high exhaust temperatures. The critical variant for com-
pliance with the emission limits is also the 3.5 t LCV, which
shows very high average ICE load demand during uphill
driving. Indicative of this is the cumulative ICE work over
the travel distance. This is found 2.4 times higher for the
uphill part of the Mountain Driving scenario driven with
the 3.5 t LCV than for the WLTC driven with the 3.5 t LCV
while towing a 3.5 t trailer (i.e. 0.5 kWh/km and 1.19 kWh/
km, respectively).
The critical Euro 7 distance of 10km falls in the uphill
portion of the Mountain Driving scenario, as shown in
Fig.11. Combined with the extended driving conditions in
the first 2km after the cold start due to the driving cycle
dynamics (see Tables6 and 7), this results in extremely chal-
lenging operating conditions for the EATS. Hence, compli-
ance cannot be achieved at 10km, as shown in Fig.5. Con-
sidering that vehicles driving up a mountain usually drive it
down afterwards, the vehicle certification that accounts only
the emissions of the uphill part for the emissions compliance
evaluation is not representative of the overall vehicle opera-
tion in such a driving situation. Therefore, the emissions
at the end of the cycle, after the vehicle has descended the
mountain again, were taken into account for the evaluation
of compliance with the Euro 7 standard in this scenario.
As shown in Figs.5 and 11 of the Appendix, the
specified Euro 7 system achieves the NOx emissions
requirement of 75mg/km in the case of the 3.5 t LCV,
when it reaches the bottom of the mountain again. In
the uphill part, the tailpipe emissions clearly exceed
the Euro 7 NOx limit after the first 8km, when the
average vehicle speed and slope reach their highest
level. However, in the downhill part, the vehicle is
mainly coasting down with the ICE switched off, thus
minimizing the emission formation and compensating
for the significantly high emissions of the uphill part.
The previous are confirmed by the tailpipe NOx emis-
sion courses depicted in Fig.11 for this scenario.
Fig. 5 Evaluation of Euro 7 NOx emission compliance: Tailpipe NOx emission results at 10km and at cycle end in the four driving scenarios
considered
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131Emission Control Science and Technology (2024) 10:123–139
For a more thorough understanding of the antipollution
performance of the investigated EATS concept and to further
support future work on the optimal dimensioning of diesel
catalytic systems, the contribution of each deNOx unit in the
conversion of the engine-out NOx emissions is presented
in Fig.12 in the Appendix. In addition, in Figs.13 and 14,
the time-based engine-out conditions are illustrated for all
cases investigated.
6 Conclusions
Following a holistic emission-based vehicle design
approach, a novel vehicle concept was presented that can
meet the NOx emission requirements of the Euro 7 stand-
ards as set out in the latest Euro 7 proposal of the European
Commission. The design was based on four RDE scenarios
that are particularly unfavourable for NOx emission forma-
tion. These were selected accordingly to cover all possible
operating situations of a light commercial vehicle.
The specified Euro 7 system consists of a close-cou-
pled DOC-based EATS with a 6-l ccSDPF, combined
with a 4-kW E-heater, a P2 mild-hybrid system, and
dedicated low-NOx ICE operation. In underfloor posi-
tion, a 10-l SCR with an ASC coating in its last slices
is installed. The system was able to ensure Euro 7 NOx
emission compliance even in the Madrid City RDE
cycle, which is significantly more challenging than the
already harsh TfL London Inter-Peak cycle in terms of
emissions compliance. Despite the aggressive driving
style and the required vehicle speeds of up to 175km/h,
emission compliance appeared noncritical in the inves-
tigated High Speed Highway scenario.
As expected, the uphill driving scenario proved to be
the most challenging, as the average ICE load demand is
very high when driving uphill. With kilometre-specific
vehicle certification, scenarios of permanent uphill driv-
ing could lead to emission compliance issues. However,
this largely depends on the driving speed and the road
gradient. If both the uphill and the downhill part of the
Mountain Driving scenario are considered for the Euro
7 emissions certification, compliance does not appear
critical.
Closing, the required emissions technology and, con-
sequently, the overall vehicle costs are highly dependent
on the RDE scenarios considered, and how demanding
they are from the emission formation perspective. The
more demanding the scenarios, the more sophisticated
will be the necessary antipollution technology. The
specified Euro 7 EATS system is considerably larger
dimensioned than the reference Euro 6 system. Future
research should explore the feasibility of decreasing the
catalyst sizing while imposing dedicated, temporal ICE
power limitations. Moreover, alternative EATS con-
cepts, such as placing the ccSDPF before the ccDOC,
should also be investigated, as they could prove benefi-
cial in terms of antipollution efficiency and catalysts
size reduction.
Concerning the design methodology followed, this was
based on adverse RDE scenarios for emission formation.
In the future, an even more precise design method should
additionally consider the frequency of occurrence of such
driving situations on an average day of the year and also
relate the selection of the RDE testing scenarios more
strongly with air quality aspects. Regarding the latter,
recent studies have highlighted that although mountain
uphill driving scenarios are typically very challenging
for emissions compliance, they remain uncritical from
an air quality point of view [29]. Adopting the previous
measures would enable more justifiable emission tech-
nology upgrades and, consequently, limited increases in
vehicle costs.
Appendix Tables5, 6 and 7.
Figures6, 7, 8, 9, 10, 11, 12, 13 and 14.
Table5 summarizes the LCV specifications that were
taken into consideration for the investigations. The vehicle
coast down and gearbox data derived from a VW Crafter
vehicle used as LCV demonstrator by the Chair of Thermo-
dynamics of Mobile Energy Conversion Systems of RWTH
Table 5 Specifications of the investigated N1 Class III LCV
Vehicle
GCW/kg 3500
Vehicle curb weight/kg 2200
Tire radius / m 0.345
CDA/ m21.57
CRR/(-) 0.0091
Transmission
Transmission type Automatic
Transmission gear number 8
Transmission gear ratios 4.7–3.14–2.1–1.67–
1.29–1.00–0.84–
0.67
Rear axle ratio 4.7
Engine
Displacement/l 2
Layout/(-) 4 inline
Power/kW 115 @ 3500 1/min
Torque/Nm 360 @ 1750 1/min
Idling speed/(1/min) 800
Turbocharger 1-Stage, VGT
EGR HP/LP cooled
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132 Emission Control Science and Technology (2024) 10:123–139
Aachen University [17, 39]. These were also validated with
literature values [40]. The engine specifications derive from
a state-of-the-art Euro 6 ICE, which was measured on the
test bench.
In Figs.6 and 7, the Euro 7 design requirements
deriving from the engine-out conditions are visualized
in the form of a time-based distribution of the ICE oper-
ating points over the engine-out NOx emissions and the
warm exhaust temperature maps in the four Euro 7 driv-
ing cycles considered. The depicted ICE mapping was
generated through simulation with the utilized engine
model. The latter was validated with experimental test
bench data from a state-of-the-art Euro 6 ICE, and was
used as the basis for the Euro 7 ICE for the studied LCV
concept. The results shown correspond to the 3.5 t fully
loaded N1 Class III LCV.
Tables6 and 7 provide supplementary information
regarding the correction of the NOx emissions in the
Euro 7 scenarios presented in Fig.5. More specifically,
in Table6 the wheel power criterion in the first 2km
of driving after a cold-start is evaluated. In Table7, the
necessary emissions corrections resulting from the pres-
ence of extended conditions in the virtual emissions test-
ing are explained in detail.
In Figs.8, 9, 10 and 11, the simulated courses of
the cumulative tailpipe NOx emissions for the three
LCV variants in the four Euro 7 cycles are presented.
A Euro 7 compliant variant should demonstrate emis-
sions performance below the illustrated Euro 7 limit
over the complete driving cycle. In the first 10km,
the 750mg budget limit applies. After 10km until the
end of the driving cycle, the 75mg/km limit should
be fulfilled [8]. In the diagrams, the 75mg/km limit
is depicted in the form of its cumulative equivalent in
[mg] over time.
Fig. 6 Engine-out NOx emissions of the 3.5 t N1 Class III LCV in the Euro 7 driving cycles: time-based distribution of the ICE operating points
over the baseline Euro 6 warm engine-out NOx map
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133Emission Control Science and Technology (2024) 10:123–139
The specified critical distance of 10km defines indi-
rectly for the system a driving cycle-specific maximum
time margin after a cold start to achieve emissions
compliance [8]. However, this does not guarantee for
cycles longer than 10km that the same emission per-
formance is preserved until the vehicle parks again,
which is the aim of the regulator, in order to label a
vehicle real-world emission compliant. Hence, the
cumulative emission trace over the complete driving
cycle and the cumulative emission value at the end
of the cycle become also of significant importance to
ensure the desired real-world emissions compliance. As
analyzed in detail in Sect.5, in the case of the Moun-
tain Driving scenario only the emissions at the end of
the driving cycle are considered for the Euro 7 compli-
ance evaluation.
In Fig.12, the contribution of each deNOx unit in
the conversion of the engine-out NOx emissions is pre-
sented for each considered vehicle variant in all four
Euro 7 scenarios. Figures13 and 14 show the cumula-
tive engine-out NOx emissions and the exhausts tem-
perature over time respectively, which correspond to
the results shown in Figs.8, 9, 10, 11 and 12. For bet-
ter visualization and correlation with the results shown
in Figs.8, 9, 10, 11 and 12, the 10km critical distance
Fig. 7 Engine-out exhausts temperature level of the 3.5 t N1 Class III LCV in the Euro 7 driving cycles: time-based distribution of the ICE oper-
ating points over the baseline Euro 6 warm exhausts temperature map
Table 6 Maximum average wheel power 2 km after a cold-start as
percentage of the maximum wheel power for each Euro 7 scenario
Euro 7 scenario Empty LCV
(2.2 t)
Fully-loaded
LCV (3.5 t)
Fully-loaded LCV with
trailer (7 t)
Cold Urban 3% 5% 9%
Mountain Driving 23% 34% -
Hot Urban 17% 21% -
High Speed Highway 14% 21% 35%
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134 Emission Control Science and Technology (2024) 10:123–139
Fig. 8 Evaluation of Euro 7
NOx emissions compliance
in the Cold Urban scenario:
tailpipe NOx emissions course
over the complete driving cycle
(SE, single extended, only one
testing condition is extended)
Tailpipe NOx / mg
0
200
400
600
800
1000
1200
1400
Distance / km
0 2 4 6 8 10 12 14 16
18
Euro 7 limit: 750 mg
75 mg/km
2.2 t LCV - Uncorrected emissions
3.5 t LCV - Uncorrected emissions
7 t LCV - Uncorrected emissions
7 t LCV - Corrected emissions: SE in complete cycle
10 km
Fig. 9 Evaluation of Euro 7
NOx emissions compliance in
the High Speed Highway sce-
nario: tailpipe NOx emissions
course over the complete driv-
ing cycle (SE, single extended,
only one testing condition is
extended; DE, double extended,
two testing conditions are
extended)
Tailpipe NOx/mg
0
1000
2000
3000
4000
5000
6000
Distance /km
010 20 30 40 50 60 70 80 90 100
Euro7limit:
750mg
75 mg/km
10 km
2.2tLCV-Uncorrected emissions
2.2tLCV-Correctedemissions:SE>145km/h
3.5tLCV-Uncorrected emissions
3.5tLCV-Correctedemissions:SE<2km&SE >145 km/h
7tLCV-Uncorrectedemissions
7tLCV-Correctedemissions:DE<2km&SE >2km
Table 7 Emissions correction resulting from the presence of extended driving conditions
Euro 7 scenario Empty LCV (2.2 t) Fully-loaded LCV (3.5 t) Fully loaded LCV with trailer (7 t)
Cold Urban No emission correction No emission correction Single extended below 2km: trailer traction.
Single extended after 2km: trailer traction
Mountain Driving Single extended below
2km: wheel power
Single extended below 2km: wheel power -
Hot Urban No emission correction Single extended below 2km: wheel power -
High Speed Highway Single extended,
when vehicle
speed > 145km/h
Single extended below 2km: wheel
power. Single extended, when vehicle
speed > 145km/h
Double extended below 2km: wheel power &
trailer traction. Single extended after 2km:
trailer traction
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135Emission Control Science and Technology (2024) 10:123–139
Fig. 10 Evaluation of Euro 7
NOx emissions compliance in
the Hot Urban scenario: tailpipe
NOx emissions course over the
complete driving cycle (SE, sin-
gle extended, only one testing
condition is extended)
Tailpipe NOx/mg
0
250
500
750
1000
1250
1500
1750
2000
Distance /km
0 2 4 6 8 10 12 14 16 18 20 22
Euro 7limit:750 mg
75 mg/km
2.2tLCV-Uncorrected emissions
3.5tLCV-Uncorrected emissions
3.5tLCV-Correctedemissions:SE<2km
10 km
Fig. 11 Evaluation of Euro 7
NOx emissions compliance in
the Mountain Driving scenario:
tailpipe NOx emissions course
over the complete driving cycle
(SE, single extended, only one
testing condition is extended)
75 mg/km
Mountain Driving - Downhill Part
Tailpipe NOx / mg
0
500
1000
1500
2000
2500
3000
Distance / km
0 5 10 15 20 25 30
Euro 7 limit:
750 mg
Mountain Driving - Uphill Part
10 km
2.2 t LCV - Uncorrected emissions
2.2 t LCV - Corrected emissions: SE < 2 km
3.5 t LCV - Uncorrected emissions
3.5 t LCV - Corrected emissions: SE < 2 km
for Euro 7 is also depicted. As expected, the higher the
payload, the higher the NOx raw emissions mass and
the average engine-out exhaust gas temperature level.
The exceptions are the 3.5 t and the 7 t variants in the
German Highway scenario. In the first case, the higher
overall mass in the 3.5 t case compared to the 2.2 t
case leads to less aggressive accelerations and lower
maximum vehicle speed being reached in the high-
speed sections of the German Highway cycle due to
ICE power limitations. This results to the 3.5 t variant
demonstrating lower engine-out NOx emissions mass
flow rates in those cycle sections, where it drives more
slowly than the 2.2 t variant. Similarly, in the 7 t case
the maximum vehicle speed is limited at 100km/h, as
already explained in Sect.3. This allows the ICE to
operate at lower loads and less dynamic conditions,
resulting in lower exhaust gas temperature levels and
the formation of less engine-out NOx emissions over
the complete cycle than the 2.2 t and the 3.5 t variant.
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136 Emission Control Science and Technology (2024) 10:123–139
Fig. 12 Percentage of NOx emissions reduction over the EATS and in each deNOx unit in respect to the engine-out NOx emissions in each Euro
7 scenario for all LCV variants investigated
Fig. 13 Cumulative engine-out NOx (uncorrected) emissions over time in each Euro 7 scenario for all LCV variants investigated (Cum., cumula-
tive; EO, engine-out)
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137Emission Control Science and Technology (2024) 10:123–139
Acknowledgements The authors would like to thank Dr.-Ing. Frank
Bunar (IAV GmbH), Dr.-Ing. Markus Ehrly (FEV Europe GmbH),
Dr.-Ing. Andreas Balazs (FEV Europe GmbH), Arwa Abidi (TME,
RWTH Aachen University) and Melih Ayyildiz (TME, RWTH Aachen
University) for their contributions to this paper.
Author Contributions T.K.: Conceptualization, Methodology, Inves-
tigation, Visualization, Writing—Original Draft; R.M.: Conceptual-
ization, Methodology, Funding Acquisition; S.S: Writing—Review &
Editing; M.G.: Resources, Writing—Review & Editing, Project admin-
istration; S.P.: Supervision.
Funding Open Access funding enabled and organized by Projekt
DEAL. This research was funded by FVV e.V.//Science for a moving
society, project number 1412.
Data Availability Data are partly available on request from the corre-
sponding author with the permission of FVV e.V.//Science for a mov-
ing society and its members.
Declarations
Ethics Approval Not applicable.
Competing Interests The authors declare no competing interests.
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
were made. The images or other third party material in this article are
included in the article’s Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not included in
the article’s Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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