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 ... VII. Sometimes Arabic numerals are also used (Euro 1 ... 7). Since the Euro 7/VII regulations for both light- and heavy-duty vehicles and engines are contained in a single regulation, they are commonly referred to as Euro 7. We will continue to use Roman numerals when referencing standards for heavy-duty engines (Euro I to VII), and reserve Arabic numerals for light-duty vehicle standards (Euro 1 to 7).

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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.
• Euro VII emission standards were introduced by Regulation 2024/1257 [6204]. For the first time, regulations for light-duty and heavy-duty vehicles and engines are covered by a single regulation. The changes for M2, M3, N2 and N3 vehicles are considerable compared to Euro VI. Limits for WHSC and WHTC are harmonized, NOx, CO limits tightened, PN size limit changed to 10 nm from 23 nm in Euro VI and gravimetric limits on N₂O and NH₃ introduced. Also, RDE limits are introduced alongside WHSC and WHTC limits. Some trailers become regulated with respect to CO₂ emissions and control of non-tailpipe particulate emissions from brakes and tires is introduced. Implementing acts for M2, M3, N2 and N3 vehicles are to be adopted by 2026.11.29.

Applicability. 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—since the Euro III stage—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/VII 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.

Euro 7/VII standards apply to all motor vehicles since there are no separate regulations for light- and heavy-duty vehicles. However, M1 and N1 vehicles have their emission limits expressed in mg/km while M2, M3, N2 and N3 have their emission limits expressed in mg/kWh as has been done for these vehicles in previous light- and heavy-duty regulations respectively. For N2 vehicles between 3.5 and 5 t maximum mass originating from an N1 vehicle, type-approval using the light-duty procedures is still an option as was been the case for Euro 5/V and 6/VI.

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 three sets of emission standards, with different types of testing requirements:

• Steady-State Testing: Table 1 lists emission standards applicable to Euro I and later diesel (compression ignition, CI) engines only, with steady-state emission testing requirements.
• Transient Testing: Table 2 lists standards applicable to Euro III and later diesel and positive ignition (PI) engines, with transient testing requirements.
• Real Driving Emissions Testing: Table 3 lists emission standards applicable to Euro VII CI and PI engines, with RDE testing requirements.

Additional provisions of the Euro VI regulation include emission limits and requirements for off-cycle emission and in-service conformity testing, discussed later.

Additional provisions of the Euro VII regulation include:

• On Board Monitoring (OBM).
• On-board fuel and energy consumption monitoring (OBFCM).
• Geofenced hybrid vehicles with sufficient electric driving range may be designated as ‘Euro 7G’ and can only drive in zero-emission zones when a zero-emission mode is activated. Driving using the combustion engine for 5 km is allowed if the battery is depleted.
• Category O3 (3.5 t > max. mass ≤ 10 t) and Category O4 (max. mass > 10 t) trailers have their energy efficiency regulated.
• Battery durability for BEVs and PHEVs have minimum performance standards. For M2, M3, N2 and N3 vehicles, legislation is under development at the UNECE and thresholds are yet to be defined.
• Non-tailpipe particulate emissions from brake and tire wear are regulated.
• Anti-tampering measures apply to emission control, OBD, OBM and OBFCM systems.

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.

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”).

Euro VII introduced an “additional lifetime” beyond the “main lifetime” during which emission limits are adjusted using a durability multiplier. For M2, and N1 vehicles, the multiplier is 1.2 while for N2, N3, and M3 vehicles, it will be defined after an analysis to be performed by the European Commission by December 2025.

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 5 [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].

Non-Tailpipe Emissions. Particulate emissions from tire and brake wear are regulated for Euro 7/VII. While brake particle limits and test procedures for light-duty vehicles apply initially, limits and test procedures for M2, N2, M3 and N3 vehicles will apply from 2030 onwards and have yet to be defined. For tires, the abrasion limits will be implemented 2028.07 for light-duty vehicles (C1 tires), 2030.04 for medium load heavy-duty vehicles (C2 tires), and 2032.04 for high load heavy-duty vehicles (C3 tires). Tire abrasion limits have not been defined yet.

Testing

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.
• Euro VII testing:
  • Type approval testing:
    • WHSC + WHTC + RDE test for diesel engines; WHTC + RDE test for positive ignition engines,
  • In-service conformity (ISC): RDE test.

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 6.

Euro VII: The provisions of UN Regulation No. 49 apply for all exhaust emission tests conducted on the engine dynamometer. For verifying emissions from Euro VII engines and vehicles under real driving conditions, most of the provisions of UN Regulation No. 49 apply with two important exceptions:

• The conformity factor for all pollutant species is set to 1.0 and the limits in Table 3 apply.
• The power threshold, used to assess the validity of the windows used in the moving average window (MAW) evaluation, is lowered to 6% from 20% in UN Regulation No. 49 and 10% for Euro VI-E. This captures more low-load and low-speed operation.

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 6.

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 90^th 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].