EU: Heavy-Duty Truck and Bus Engines

Regulatory Framework

European emission regulations 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.

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

The 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.

The regulations were originally introduced by the Directive 88/77/EEC [2871], followed by a number of amendments. In 2005, the regulations were re-cast and consolidated by Directive 05/55/EC [1569]. Beginning with the Euro VI stage, the legislation became simplified, as “directives”—which need to be transposed into all of the national legislations—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 regulations 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 would be reducing the efficiency of emission control systems when vehicles operate under normal driving conditions to levels below those determined 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” regulatory approach, the technical requirements pertaining to durability and OBD—including provisions for emission systems that use consumable reagents—have been described in the Commission Directive 2005/78/EC [3492].
• Euro VI emission standards were introduced by Regulation 595/2009 [3493], with technical details specified in a number of ‘comitology’ packages [3494][3496][3495]. 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 gas (positive ignition, PI) engines, with transient testing requirements.

Additional provisions of the Euro VI regulation include:

• An ammonia (NH₃) concentration limit of 10 ppm applies to diesel (WHSC + WHTC) and gas (WHTC) engines.
• A maximum limit for the NO₂ component of NOx emissions may be defined at a later stage.

Some Euro VI provisions, including OBD and certain testing requirements are phased-in by 2016/2017 (new types/all vehicles).

Test Cycles. The regulatory emission test cycles have been changed several times, as indicated in Table 1 and Table 2. Since the Euro III stage (2000), the earlier steady-state engine test ECE R-49 has been 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. The following testing requirements applied:

• Euro III: (1) ESC/ELR test for conventional diesel engines, (2) ESC/ELR + ETC testing for diesel engines with “advanced aftertreatment” (NOx aftertreatment or DPFs) and for EEVs, and (3) ETC test for positive ignition (NG, LPG) engines.
• Euro IV-V: (1) ESC/ELR + ETC testing for diesel engines, and (2) ETC test for positive ignition engines.

Since the Euro VI stage, diesel engines are tested over the WHSC + WHTC tests, while positive ignition engines are tested over the WHTC only.

Off-Cycle Testing. Euro VI regulation introduced off-cycle emissions (OCE) testing requirements. OCE measurements, performed during the type approval testing, follow the NTE (not-to-exceed) 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 random selection of three grid cells and emission measurement at 5 points per cell.

In-Service Conformity Testing. Euro VI regulation also introduced in-use testing requirements that involve field measurements using PEMS. The testing is conducted over a mix of urban (0-50 km/h), rural (50-75 km/h) and motorway (> 75 km/h) conditions, with exact percentages of these conditions depending on vehicle category. First in-use test should be conducted at the time of type approval testing.

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”).

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 on 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.

Defeat Strategies. For Euro IV and V heavy-duty engines, an ‘auxiliary emission control strategy’ (AECS) is defined as

an emission control strategy that becomes active or that modifies the base emission control strategy for a specific purpose or purposes and in response to a specific set of ambient and/or operating conditions, e.g. vehicle speed, engine speed, gear used, intake temperature, or intake pressure;

Also a ‘base emission control strategy’ (BECS) is defined as

an emission control strategy that is active throughout the speed and load operating range of the engine unless an AECS is activated.

An AECS can be activated to protect the engine or vehicle from damage, operational safety, to prevent excessive emissions and to trade-off the control of one regulated pollutant for another. An AECS should not be used under the following conditions unless there is a critical need to do so:

• altitude below 1,000 meters (or equivalent atmospheric pressure of 90 kPa) and
• an ambient temperature between 2 °C to 30°C and
• engine coolant temperature between 70°C to 100 °C.

A ‘defeat strategy’ is defined as:

an AECS that reduces the effectiveness of the emission control relative to the BECS under conditions that may reasonably be expected to be encountered in normal vehicle operation and use,

a BECS that discriminates between operation on a standardized type-approval test and other operations and provides a lesser level of emission control under conditions not substantially included in the applicable type-approval test procedures, or

an OBD or an emission control monitoring strategy that discriminates between operation on a standardized type-approval test and other operations and provides a lower level of monitoring capability (timely and accurately) under conditions not substantially included in the applicable type-approval test procedures;

Note that the term ‘emission control system’ is not used in the definition of defeat device as is the case for light-duty vehicles.

Full documentation of AECS and BECS details are required to be submitted upon application for certification.

For Euro VI heavy-duty engines, the terms Auxiliary Emission Strategy (AES) and Base Emission Strategy (BES) are adopted with similar definitions to AECS and BECS. The definition for ‘defeat strategy’ was changed to:

an emission strategy that does not meet the performance requirements for a base and/or auxiliary emission strategy.

The reasons for using a AES remained similar to those for Euro IV and V vehicles. However, the envelope of conditions under which an AES should not be used are not clearly spelled out. Rather, the vehicle is required to meet OCE and in-use PEMS testing requirements. Full documentation of AES and BES details are required to be submitted upon application for certification.