Euro 7 extension

Decisions and discussions around Euro 7 – the latest in a long line of standards to cut emissions of commercial vehicle engines – are ongoing. But there has been plenty of movement in the past 12 months, including a revised timescale. Toby Clark assesses the landscape

Since we described the upcoming Euro 7 emissions legislation last year (see June 2023 issue of Transport Engineer), the European Parliament has proposed a substantial list of revisions, which were confirmed by a vote on 13 March. Sigrid de Vries, director general of ACEA, the industry group that represents the major European OEMs, said: “Make no mistake: Euro 7 still tightens exhaust emissions and test procedures. In particular, truck and bus manufacturers will face significantly more stringent rules, as they already face an uphill climb to meet rapidly approaching 2030 decarbonisation targets.”

Most dramatically, the timescale has eased from what was originally planned. John Goodwin, regulatory affairs director at Johnson Matthey, explains: “What has been agreed is an implementation date of +48 months from [the] entry into force date (EIF). Assuming the EIF will come in June this year, this places the first implementation at June/July 2028 (for new vehicle types) followed by 2029 for all vehicle types. This is versus a 2027 start date for all heavy-duty vehicles in the original proposal.” So the fact that we still haven’t seen any Euro 7-compliant trucks shouldn’t come as a surprise.


The amendments generally see a slight easing of limits compared with the proposed hot-running transient test (see table), but Euro 7 still represents a serious tightening of emissions compared with Euro VI – and over a longer period. For instance, John Goodwin says: “The main lifetime durability mileage now includes a longer compliance duration versus Euro VI, for N3 vehicles. This is 700,000km or 12 years, whichever comes first (vs seven years for Euro VI). There is also a new additional lifetime requirement which extends the mileage from 700,000km to 875,000km (or 15 years lifetime, whichever comes first).”

The particulate emissions limit (PN) appears more liberal than Euro VI, but it includes smaller particles, says Goodwin. “The move from 23nm [nanometres] to 10nm still forces consideration of improved filtration in the exhaust system.”

As the particles emitted by engines are reduced, so those from other sources — primarily tyres and brakes — become more significant. In February, the UNECE agreed a methodology of lab and on-road tests to measure emissions from tyre abrasion (expressed in mg/km per tonne of load on the tyre). Trade body ETRMA says it expects the method “to be expanded to heavier vehicles with C2 and C3 types of tyres during 2026 and 2027”.

Of course, emissions change according to whether the engine is hot or cold, and whether it is running in a steady state or in a transient condition. The global ECE standard lab test cycles are a hot-start steady state test (WHSC) and a 30-minute transient test cycle (WHTC) covering both cold and hot starts, which came in with Euro VI.


The European Commission’s original Euro 7 proposals used separate ‘cold’ and ‘hot’ WHTC tests, with different emissions limits, as well as a separate limit for longer trips combining hot and cold running — and a NOx limit under idle. The European Parliament’s amendments simplify matters: now there is a single limit for a stationary and transient running, as well as higher limits under a new standard called RDE (REAL Driving Emissions).

“WHSC and WHTC are both lab tests,” says Goodwin. “The WHTC is a transient test, which is designed to represent usual driving conditions, while the WHSC is a steady state test that looks to cover the full map of engine operation. The RDE is what used to be called ‘in-service compliance’ (ISC). Here, measurements need to be carried out using portable equipment on the actual application. The RDE limits are typically higher to allow for the more variable nature of real-world testing.”

Could removing the distinction between ‘hot’ and ‘cold’ emissions mean less of a cost increase for end users? Goodwin isn’t sure: “Yes, with less emphasis on cold start emissions, there will be less of a need to have additional system heating. This might mean cost savings in some instances, but [it’s] not likely to be a large difference versus total truck price, and some OEMs may maintain [their] original design plans.” So the latest revisions still mean that EGR-only engines are unlikely to survive.

“Overall, the provisional Euro 7 agreement could have been more ambitious, especially with important aspects such as cold emissions,” he adds. “Comparatively speaking, regions such as the USA will take the lead in reducing pollutant emissions from this section.”

Reference: The proposed amendments to Euro 7 are contained in European Parliament report A9-0298/2023, available at: www.tinyurl.com/5apmuayj


The latest version of the Euro emissions standard has seen the nomenclature changed from Roman (VI) to Arabic (7). Previously, Roman indicated the standards for HGVs/PSVs (eg Euro IV), while Arabic was for cars, vans and motorbikes (eg Euro 4). The latest standards are supposed to be more closely (although not totally) aligned – and the script has been altered to reflect this.


One of the most obvious changes in the past couple of rounds of emissions regulations is that as the limits have got much lower, they have started to be defined in milligrams (mg/kWh) rather than grams (g/kWh). NOx, for instance, is at around one-thirtieth of the Euro II limit of the late 1990s. And, given that overall truck efficiency (in terms of km per kWh) has probably risen noticeably since the turn of this century, the real-world improvements should be even greater. But some pollutants have become more significant in Euro 7.

Euro 7 separates the definition of nitrogen oxides – NOx, referring only to NO (nitric oxide) and NO2 (nitrogen dioxide) – from nitrous oxide (N2O). As a greenhouse gas N2O stays in the atmosphere for a very long time, on average 121 years. This scenario gives it a Global Warming Potential (GWP) over 100 years of 265 times that of CO2. Worse still, it damages the ozone layer, letting more harmful solar radiation through to the ground; since the banning of CFCs, it has become the dominant source of ozone depletion.

An exception to the general loosening of the amendments comes with ammonia (NH3) emissions, which drop slightly from 65 to 60mg/kWh.

While ammonia is not directly a greenhouse gas, it helps to form N2O and is implicated in the formation of harmful fine particulates. ‘Ammonia slip’ comes from the DPF/AdBlue solution passing through the SCR system without reacting. This happens if the dose is excessive, if the catalyst has been poisoned, or (most likely) if the temperature is too low. This process can be countered by pre-heating the catalyst (electrically, with a pilot burn of fuel, or with an exothermic reaction from the diesel oxidation catalyst) or using a two-part SCR unit with the first section ‘close-coupled’ to the engine to maintain temperature. “Ammonia slip is already well controlled for Euro VI systems,” says Johnson Matthey’s John Goodwin. “The broad expectation is that ammonia slip catalysts… in today’s systems will continue to be used.”

The emphasis on ammonia might also reflect the possibility of ammonia-fuelled engines. Ammonia has a high hydrogen content and (obviously) no carbon, and it can be produced using renewable energy as ‘green’ ammonia, so as a liquid fuel it could help reduce CO2. This idea is being tested by marine diesel manufacturers, and ammonia-fuelled heavy trucks have been demonstrated in North America.

Since Euro III, the legislation has limited NMHC (Non-Methane Hydrocarbons) and Methane (CH4) separately. But from Euro 7 NMHC is being superseded by NMOG (Non-Methane Organic Gases), a marginally higher figure which includes NMHC plus volatile organic compounds (VOCs) such as ethanol, formaldehyde and acetaldehyde. These can react with NOx and sunlight to form ground-level ozone (O3), which leads to smog, lung irritation and asthma.

Formaldehyde (HCHO) is itself an irritant, and is now defined separately in the Euro 7 proposals. Even if it is added to NMOG, Euro 7 means a substantial (34%) reduction in overall NMOG/NMHC emissions.

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