The diesel particulate filter (DPF) is a critical component for the abatement of the harmful pollutant particulate matter (PM) from diesel engines. Accumulation of PM in DPFs increases flow restrictions, resulting in elevated backpressure for the exhaust gases. To mitigate the increase in backpressure, a regeneration process is applied, by which the soot is removed by oxidation. To enhance the regeneration process the DPF can be coated with a catalyst. The ash originating from the engine oil, remains in the DPF and will eventually determine its lifespan. PM composition is not static, catalysts age, and ash varies in properties and distributions, all affecting the performance of DPFs. This thesis investigates the different aspects concerning DPF performance and durability. Soot oxidation, catalyst deactivation, low-temperature regeneration, and ash accumulation have been investigated and discussed regarding its role for the continuous and prolonged use of DPFs. To capture practical relevance, field-retrieved DPFs have been studied and compared to fresh and non-catalyzed DPFs, whereby the experiments have been conducted at different scales, in both laboratory and real engine environments. Soot from different sources was shown to have a low variation in reactivity and was therefore not considered to be a critical parameter for DPF functionality. Instead, DPFs collected from the field revealed a significant decrease in NO conversion capability as a result of catalyst poisoning. The lower NO conversion created unfavorable conditions for the low-temperature regeneration. Well-controlled regeneration was shown to be important for the control of the ash distribution pattern. However, the results showed that ash packing density had a stronger influence on the backpressure than the distribution pattern. The research provides a deeper understanding concerning the aging and performance of DPFs, which can enable extended use, reuse, and remanufacturing of DPFs.

För minskning av skadliga partikelutsläpp, PM (från engelskans particulate matter), från dieselmotorer används dieselpartikelfilter (DPF) som är en del av avgasefterbehandlingssystemet. Ackumulering av PM i partikelfilter ökar flödesrestriktionerna vilket resulterar i ett ökat mottryck för avgaserna. För att hämma uppbyggnaden av mottrycket genomförs en regenerering där sot avlägsnas genom oxidation. Regenereringen kan effektiviseras genom att DPF-substratet beläggs med en katalysator. Askan, som bildas från tillsatser i motoroljan, förblir i partikelfiltret efter regenereringen och kommer slutligen avgöra dess livslängd. Variation i PM-sammansättning, askans egenskaper och fördelning, och katalysatoråldring har påverkan på DPF-prestandan. Denna avhandling undersöker de olika aspekterna av prestanda och livslängd för partikelfilter. Sotoxidation, katalysatordeaktivering, lågtemperatur-regenerering, och askackumulering har studerats och diskuteras med avseende på dess roll för kontinuerligt och långvarigt användande av partikelfilter. För ökad praktisk relevans har prover från verklig drift undersökts och jämförts med färska och icke-katalyserade prover, varpå experiment har genomförts i flera olika skalor, i både laboratorie- och riktiga avgasmiljöer. Sot från olika källor visade sig ha en liten variation i reaktivitet och ansågs inte vara en kritisk parameter för funktionaliteteten hos partikelfilter. Däremot påvisade partikelfilter från verklig drift en tydlig minskning av förmågan att oxidera NO som ett resultat av katalysatorförgiftning. Den lägre omsättningen av NO skapade ogynnsamma förhållanden för lågtemperatur-regenerering. Välkontrollerad regenerering var viktigt för att styra inlagringsmönstret av aska; däremot visade resultaten att askans packningsdensitet hade en större betydelse för tryckfallet i jämförelse med inlagringsmönstret. Forskningens nytta finns i den ökade förståelsen av åldrandet av partikelfilter vilket är en förutsättning för ökad livslängd och även återanvändande och återtillverkning.

Oxidation catalysts can greatly improve the regeneration efficiency of diesel particulate filters (DPF) by providing sufficient levels of NO₂ for low-temperature soot oxidation. As for other automotive catalysts, catalyzed DPFs are subject to aging effects, resulting in decreased performance of the NO oxidation reaction. The life span of DPFs generally only considers the elevated back pressure as a consequence of the accumulation of ash. However, with reduced catalytic activity and impaired functionality of the regeneration process there is a risk of premature replacement of the catalyzed DPF or accumulation of soot above critical levels. In this study, a new exhaust aftertreatment system has been developed to accommodate laboratory-scale catalysts and DPFs for testing with full-size heavy-duty engines. The modified exhaust aftertreatment set-up was used together with a rig for accelerated soot and ash loading to assess the impact of catalyst aging on regeneration performance under real conditions. Experiments were conducted with and without diesel oxidation catalyst to limit or increase the concentration of NO₂. It could be demonstrated that the impaired catalytic activity can have a significant impact on the regeneration process. With a limited upstream concentration of NO₂ fed to the catalyzed DPF, a temperature increase from about 390 °C to 450 °C was required to initiate the oxidation of soot. Furthermore, an overall lower oxidation rate was observed. With the addition of a diesel oxidation catalyst, resulting in elevated upstream concentrations of NO₂, the effect of aging could be partially mitigated leading to more comparable soot oxidation rates with a temperature difference of 30 °C for soot ignition. These results highlight the importance of the catalytic activity for the functionality of the system, which should be considered for future catalyzed DPF design and regeneration strategies.

Low-temperature soot oxidation in catalytic diesel particulate filters (DPF) is important for maintaining high efficiency of heavy-duty vehicles. This can be achieved by coating DPFs with an oxidation catalyst. In this work, catalytic DPFs have been collected from real-world operating heavy-duty vehicles for assessment of their catalytic activity and subsequent characterization. Testing of catalytic activity revealed the diminishing nitric oxide (NO) oxidation of the aged catalysts. The apparent reaction rates showed that the number of available catalytic sites decreased with mileage explaining the loss in activity. Characterization of the samples showed a decreasing surface area as well as an accumulation of metals and poisonous elements. An important finding from SEM-EDS analysis is the evident accumulation of phosphorus and sulfur in the washcoat in the absence of other ash-related elements, potentially explaining the decreased activity.

Increasing concern for air pollution together with the introduction of new types of fuels pose new challenges to the exhaust aftertreatment system for heavy-duty (HD) vehicles. For diesel-powered engines, emissions of particulate matter (PM) is one of the main drawbacks due to its effect on health. To mitigate the tailpipe emissions of PM, heavy-duty vehicles are since Euro V equipped with a diesel particulate filter (DPF). The accumulation of particles causes flow restriction resulting in fuel penalties and decreased vehicle performance. Understanding the properties of PM produced during engine operation is important for the development and optimized control of the DPF. This study has focused on assessing the reactivity of the PM by measuring the oxidation kinetics of the carbonaceous fraction. PM was sampled from two different heavy-duty engines during various test cycles. The heavy-duty engines were 6- and 8-cylinder direct injection diesel engines rated at 550 and 650 hp respectively. Reaction kinetics of the samples and characteristic oxidation temperatures were assessed by the non-isothermal thermogravimetric analysis (TGA) employing a multiple-ramp rates method in a 10% oxygen atmosphere. The oxidation of the diesel soot was compared with a model soot, Printex-U, and values were compared with the existing literature. The calculated activation energies range between 114.8 and 155.8 kJ/mol for diesel soot as well as the Printex-U samples indicating similar reactivity despite differences in engine configuration, fuel chemistry or, aging.