Log in | Subscribe

Emission Standards

EU: Heavy-Duty Truck and Bus Engines

Regulatory Framework

European emission standards for new heavy-duty diesel engines are commonly referred to as Euro I ... VI. Sometimes Arabic numerals are also used (Euro 1 ... 6). We will use Roman numerals when referencing standards for heavy-duty engines, and reserve Arabic numerals for light-duty vehicle standards. Another convention followed by some authors is to use the “Euro” designation for light-duty standards and “EURO”, in all capitals, for heavy-duty engine regulations.

Please log in to view the full version of this article | Subscription required.

Euro V and earlier emission standards apply to all motor vehicles with a “technically permissible maximum laden mass” over 3,500 kg, equipped with compression ignition engines or positive ignition natural gas (NG) or LPG engines. Euro VI standards apply to M1, M2, N1 and N2 motor vehicles with a reference mass exceeding 2,610 kg and to all M3 and N3 motor vehicles. The Euro VI standards are also not limited to any particular engine types but apply to all motor vehicles including those with compression ignition engines, positive ignition engines (including NG/biomethane, petrol, LPG and E85) as well as dual fuel engines.

Heavy-duty standards were originally introduced with Directive 88/77/EEC [2871], followed by a number of amendments. In 2005, the standards were re-cast and consolidated by Directive 05/55/EC [1569]. Beginning with the Euro VI stage, the legislation was simplified; “directives”—which needed to be transposed into national legislation—were replaced by “regulations” which are directly applicable. The following are some of the most important rulemaking steps in the heavy-duty engine regulations:

  • Euro I standards were introduced in 1992, followed by the introduction of Euro II standards in 1996. These standards applied to both truck engines and urban buses, the urban bus standards, however, were voluntary.
  • In 1999, the EU adopted Directive 1999/96/EC [2870], which introduced Euro III standards (2000), as well as Euro IV/V standards (2005/2008). This rule also set voluntary, stricter emission limits for extra low emission vehicles, known as “enhanced environmentally friendly vehicles” or EEVs.
  • In 2001, the European Commission adopted Directive 2001/27/EC [3491] which prohibits the use of emission “defeat devices” and “irrational” emission control strategies, which reduce the efficiency of emission control systems when vehicles operate under normal driving conditions to levels below those achieved during the emission testing procedure.
  • Directive 2005/55/EC [1569] adopted in 2005 introduced durability and on-board diagnostic (OBD) requirements, as well as re-stated the emission limits for Euro IV and Euro V which were originally published in 1999/96/EC. In a “split-level” approach, the technical requirements pertaining to durability and OBD—including provisions for emission systems that use consumable reagents—were described in the Commission Directive 2005/78/EC [3492].
  • Euro VI emission standards were introduced by Regulation 595/2009 [3493] followed by a number of ‘comitology’ packages that specified technical details and by other amendments [3494][3496][4374][3495][4611]. The new emission limits, comparable in stringency to the US 2010 standards, became effective from 2013/2014. The Euro VI standards also introduced particle number (PN) emission limits, stricter OBD requirements and a number of new testing requirements—including off-cycle and in-use PEMS testing.

Emission Standards

The following tables contain a summary of the emission standards and their implementation dates. Dates in the tables refer to new type approvals—the dates for all vehicles are in most cases one year later.

There are two sets of emission standards, with different type of testing requirements:

  • Steady-State Testing: Table 1 lists emission standards applicable to diesel (compression ignition, CI) engines only, with steady-state emission testing requirements.
  • Transient Testing: Table 2 list standards applicable to both diesel and positive ignition (PI) engines, with transient testing requirements.
Table 1
EU emission standards for heavy-duty CI (diesel) engines: Steady-state testing
Euro I 1992, ≤ 85 kW ECE R-49
1992, > 85 kW
Euro II 1996.10
Euro III 1999.10 EEV only ESC & ELR 0.15
2000.10 2.10.665.00.10a0.8
Euro IV 2005.10 1.50.463.50.020.5
Euro V 2008.10 1.50.462.00.020.5
Euro VI 2013.01WHSC×1011
a PM = 0.13 g/kWh for engines < 0.75 dm3 swept volume per cylinder and a rated power speed > 3000 min-1
Table 2
EU emission standards for heavy-duty CI (diesel) and PI engines: Transient testing
Euro III 1999.10 EEV onlyETC 3.00.400.652.00.02
2000.10 5.450.781.65.00.16c
Euro IV 2005.10 4.00.551.13.50.03
Euro V 2008.10 4.00.551.12.00.03
Euro VI 2013.01WHTC 4.00.16d0.50.460.016.0×1011e
a for gas engines only (Euro III-V: NG only; Euro VI: NG + LPG)
b not applicable for gas fueled engines at the Euro III-IV stages
c PM = 0.21 g/kWh for engines < 0.75 dm3 swept volume per cylinder and a rated power speed > 3000 min-1
d THC for diesel (CI) engines
e PN limit for PI engines applies for Euro VI-B and later [4374]

Additional provisions of the Euro VI regulation include:

  • Emission limits and requirements for off-cycle emission and in-service conformity testing, discussed later.
  • An ammonia (NH3) concentration limit of 10 ppm applies to CI (WHSC + WHTC) and PI (WHTC) engines.
  • A maximum limit for the NO2 component of NOx emissions may be defined at a later stage.

Emission Durability. Effective 2005.10/2006.10, manufacturers should demonstrate that engines comply with the emission limit values for useful life periods which depend on the vehicle category, as shown in the following table.

Table 3
Emission durability periods
Vehicle Category†Period*
Euro IV-VEuro VI
N1 and M2100 000 km / 5 years160 000 km / 5 years
N3 ≤ 16 ton
M3 Class I, Class II, Class A, and Class B ≤ 7.5 ton
200 000 km / 6 years300 000 km / 6 years
N3 > 16 ton
M3 Class III, and Class B > 7.5 ton
500 000 km / 7 years700 000 km / 7 years
† Mass designations (in metric tons) are “maximum technically permissible mass”
* km or year period, whichever is the sooner

Effective 2005.10/2006.10, type approvals also require confirmation of the correct operation of the emission control devices during the normal life of the vehicle under normal conditions of use (“conformity of in-service vehicles properly maintained and used”).

Early Introduction of Clean Engines. EU Member States are allowed to use tax incentives in order to speed up the marketing of vehicles meeting new standards ahead of the regulatory deadlines. Such incentives have to comply with the following conditions:

  • they apply to all new vehicles offered for sale in the market of a Member State which comply in advance with the mandatory limit values set out by the Directive,
  • they cease when the new limit values come into effect
  • for each type of vehicle they do not exceed the additional cost of the technical solutions introduced to ensure compliance with the limit values.

Euro VI type approvals, if requested, must have been granted from 7 August 2009, and incentives could be given from the same date. Euro VI incentives can also be given for scrapping existing vehicles or retrofitting them with emission controls in order to meet Euro VI limits.

Early introduction of cleaner engines can be also stimulated by such financial instruments as preferential road toll rates. In Germany, road toll discounts were introduced in 2005 which stimulated early launch of Euro V trucks.

Dual Fuel Engines. The Euro VI regulation extended the applicability to dual fuel (DF) engines. A number of different types of dual fuel engines are defined based on the average Gas Energy Ratio (GER) over the hot part of the WHTC, Table 4 [3494]. In dual fuel engines, the ‘service mode’ is activated for the purpose of repairing or moving the vehicle from traffic when operation in the dual-fuel mode is not possible. Prior to Euro VI, the regulations were not applicable to dual fuel engines. UNECE Regulation 49 also defines dual fuel engines using similar terminology but with some differences in the details [4369].

Table 4
Different dual fuel engines defined under Euro VI legislation
TypeGERWHTCIdle on dieselWarm-up on dieselOperation on diesel solelyOperation in absence of gasEmission limitsComments
Type 1AGERWHTC ≥ 90%Not allowedAllowed only on service modeAllowed only on service modeService modeIn dual fuel mode, PI engine emission limits applyNo diesel mode
Type 1BGERWHTC ≥ 90%Allowed only on diesel modeAllowed only on diesel modeAllowed only on diesel & service modesDiesel modeHas a diesel mode
Type 2A10% < GERWHTC < 90%AllowedAllowed only on service modeAllowed only on service modeService modeIn dual fuel mode, CI engine emission limits apply except:
PN limits based on average GER;
NG/biomethane engines THC, NMHC, CH4 limits based on average GER
No diesel mode
GERWHTC ≥ 90% allowed
Type 2B10% < GERWHTC < 90%AllowedAllowed only on diesel modeAllowed only on diesel & service modesDiesel modeHas a diesel mode
GERWHTC ≥ 90% allowed
Type 3ANeither defined nor allowed
Type 3BGERWHTC ≤ 10%In dual fuel mode, CI engine emission limits applyHas a diesel mode


The regulatory emission test cycles have been changed several times, as indicated in Table 1 and Table 2. At the Euro III stage (2000), the earlier steady-state engine test ECE R-49 was replaced by two cycles: the European Stationary Cycle (ESC) and the European Transient Cycle (ETC). Smoke opacity was measured over the European Load Response (ELR) test. Since the Euro VI stage, engines are tested over the WHSC and WHTC tests. In addition, the Euro VI regulation introduced off-cycle and in-service conformity testing. The following are some of the important testing requirements:

  • Euro III: ESC/ELR test for conventional diesel engines; ESC/ELR + ETC testing for diesel engines with “advanced aftertreatment” (NOx aftertreatment or DPFs) and for EEVs; ETC test for positive ignition (NG, LPG) engines.
  • Euro IV-V: ESC/ELR + ETC test for diesel engines; ETC test for positive ignition engines.
  • Euro VI testing:
    • Type approval testing:
      • WHSC + WHTC test for diesel engines; WHTC test for positive ignition engines,
      • Off-cycle emission (OCE) testing:
        • NTE engine testing over the WNTE cycle, and
        • PEMS vehicle test.
    • In-service conformity (ISC): In-use vehicle PEMS testing.

Some Euro VI provisions, including OCE/ISC testing and OBD requirements, are phased-in over several years. The corresponding stages of the emission standards are referred to as Euro VI-A through Euro VI-E, Table 5.

Table 5
Euro VI stages and OCE/ISC requirements
StageImplementation DateOCE/ISC Requirements
Type approval (new types/all vehicles)Last date of registrationPEMS power thresholdCold start included in PEMSOCE
A2013.01/2014.012015.0820%NobNOx 0.60
THC 0.22
CO 2.0
PM 0.016
B (CI)2013.01/2014.012016.12
B (PI)2014.09/2015.092016.12
a For PI engines and type 1A and 1B dual fuel engines in dual fuel mode, PN CF applies 2023.01/2024.01
b evaluation starts when coolant temperature reaches 70°C
c evaluation starts when coolant temperature reaches 30°C

Off-Cycle Testing. Euro VI regulation introduced off-cycle emissions (OCE) testing requirements. OCE measurements, performed during the type approval testing, have two elements: laboratory testing following the NTE (not-to-exceed) limit approach and in-use PEMS testing.

In the NTE limit approach, a control area is defined on the engine map (there are two definitions, one for engines with a rated speed < 3000 rpm, and another for engines with a rated speed ≥ 3000 rpm). The control area is divided into a grid. The testing involves the random selection of three grid cells and emission measurement at 5 points per cell. The Euro VI emission limits for NTE testing are shown in Table 5.

The PEMS procedure at type approval is similar to PEMS testing for In-Service Conformity (ISC).

In-Service Conformity Testing. The Euro VI regulation also introduced in-use testing requirements that involve field measurements on vehicles that have accumulated a minimum of 25,000 km using PEMS. A conformity factor (CF) of 1.5 applies to gaseous emissions. To pass the test, the 90th percentile of the measured emissions must not exceed the CF × WHTC emission standard for the respective components. Starting with Euro VI-E, ISC testing includes partial cold start as well as PN emissions with a CF = 1.63 [4611].