Citation: Mamakos, A.; Rose, D.; Melas, A.; Gioria, R.; Suarez-Bertoa, R.; Giechaskiel, B. Diesel Particle Filter Requirements for Euro 7 Technology Continuously Regenerating Heavy-Duty Applications. Vehicles 2023, 5, 1634–1655. https://doi.org/ 10.3390/vehicles5040089 Academic Editor: Mohammed Chadli Received: 16 September 2023 Revised: 23 October 2023 Accepted: 4 November 2023 Published: 7 November 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Diesel Particle Filter Requirements for Euro 7 Technology Continuously Regenerating Heavy-Duty Applications Athanasios Mamakos 1 , Dominik Rose 1 , Anastasios Melas 2 , Roberto Gioria 2 , Ricardo Suarez-Bertoa 2 and Barouch Giechaskiel 2, * 1 Corning GmbH, 65189 Wiesbaden, Germany; mamakosa@corning.com (A.M.); rosedw@corning.com (D.R.) 2 European Commission, Joint Research Centre, 21027 Ispra, Italy; anastasios.melas@ec.europa.eu (A.M.); roberto.gioria@ec.europa.eu (R.G.); ricardo.suarez-bertoa@ec.europa.eu (R.S.-B.) * Correspondence: barouch.giechaskiel@ec.europa.eu; Tel.: +39-0332-78-5312 Abstract: The upcoming Euro 7 regulation for Heavy-Duty (HD) vehicles is calling for a further tightening of the Solid Particle Number (SPN) emissions by means of both lowering the applicable limits and shifting the lowest detectable size from 23 nm (SPN 23 ) to 10 nm (SPN 10 ). A late-technology diesel HD truck was tested on a chassis dynamometer in order to assess the necessary particle filtration requirements for a continuously regenerating system. The study showed that passive regeneration under real-world operating conditions can lead to a significant release of SPN 10 particles from the current technology Diesel Particulate Filter (DPF) when soot-loaded, even exceeding the currently applicable emission limits. The actual emissions during passive regeneration and following the clean-up of the DPF exceeded the proposed Euro 7 limits by more than an order of magnitude. A prototype DPF, exhibiting a 99% filtration efficiency when clean, was shown to effectively control SPN 10 emissions under both operating conditions. The shift to SPN 10 also necessitates control of nanoparticles forming inside the Selective Catalytic Reduction (SCR) system, which for the tested truck exceeded the proposed (hot) limit by up to 56%. A dedicated particle filter specifically designed to capture these particles was also evaluated, showing a better than 60% efficiency. The key message of this study is that SPN emissions can be kept at low levels under all conditions. Keywords: DPF; SCR; particle number; SPN10; heavy-duty vehicle; transport emissions 1. Introduction The introduction of progressively tighter emission standards in the European Union (EU) has brought significant reductions in automotive exhaust emissions since their first implementation in the early 90s. The continuous development of emission control sys- tems was of paramount importance in achieving the set emission targets. However, road transport remains a major source of air pollution, accounting for 39% of NOx, 11% of fine particulate matter (PM 2.5 ) and 26% of black carbon [1]. Consequently, a proposal for a new (Euro 7) emission standard was recently published, calling for further emission reduction over a wider range of operating conditions and an extended useful life, taking advantage of state-of-the-art emission control technologies [2,3]. With respect to particulate emissions, the elevated solid particle number (SPN) levels during and immediately after the regeneration of the Diesel Particulate Filter (DPF), as well as the emission of sub-23 nm nanoparticles, were identified among the most relevant unregulated conditions [2]. The SPN regulation was introduced in 2011 for Euro 5 light-duty cars [4] and in 2013 for Euro VI Heavy-Duty (HD) engines [5] as a more sensitive technique from the conventional gravimetric method (PM), with the intention to require the installation of DPFs in all diesel-fueled vehicles to reduce particulate emissions. The SPN methodology is targeting solid particles (defined as those surviving thermodilution at 300 ◦ C to 400 ◦ C). Currently, the regulation requires particle counters with a lower detection size at 23 nm Vehicles 2023, 5, 1634–1655. https://doi.org/10.3390/vehicles5040089 https://www.mdpi.com/journal/vehicles