Dinex (Finland)

Future emission limits (Stage 6) for off-road engines will require more efficient removal of nitrogen oxides. The dual-SCR system has in addition of conventional main SCR catalyst after diesel oxidation catalyst (DOC) and particulate filter (DPF), a second SCR catalyst near to engine to enhance catalyst activity at low temperature periods. However, DPF regeneration requires periodic diesel fuel injection to DOC + DPF to oxidize carbonaceous particles at elevated temperatures. Late post-injection of diesel fuel was used during the regeneration period of a DPF. The study investigated how this strategy affects the performance of a close-coupled vanadium-based SCR with an ammonia slip catalyst. The exhaust aftertreatment system (SCR, DOC, DPF) was incorporated into the exhaust line of a high-speed, common-rail, diesel engine, designed for off-road applications fulfilling the latest emission legislation (Stage 5). Extensive bench experiments determined how late diesel injection through the close-coupled vanadium-SCR and ammonia slip catalyst affected the exhaust gas temperature, and whether high hydrocarbon concentrations from late diesel injection changed the catalyst performance. The SCR inlet temperatures ranged from 250 to 400 °C. Accumulation of hydrocarbons on the close-coupled vanadium-SCR catalyst at low exhaust temperatures was also examined. The studýs overall conclusion is that the strategy of late diesel injection is feasible to adopt during the regeneration period of a particulate filter only at sufficiently high SCR-inlet temperatures (≥ 320 °C). At lower temperatures, hydrocarbons might be stored in the catalyst. When the temperature increases again, exothermic reactions generated in the SCR may lead to notable catalyst deactivation.

Abstract. Oxidation flow reactors used in secondary aerosol research do not immediately respond to changes in the inlet concentration of precursor gases because of their broad transfer functions. This is an issue when measuring the vehicular secondary aerosol formation in transient driving cycles because the secondary aerosol measured at the oxidation flow reactor outlet does not correspond to the rapid changes in the exhaust flow rate. Since the secondary aerosol production factor is determined by multiplying the secondary aerosol mass by the exhaust flow rate, the misalignment between the two leads to incorrect production factors. This study evaluates the extent of the error in production factors due to oxidation flow reactor transfer functions using synthetic and semi-synthetic exhaust emission data. It was found that the transfer-function-related error could be eliminated when only the total production factor of the full cycle was measured using constant-volume sampling. For shorter segments within a driving cycle, a narrower transfer function led to a smaller error. Even with a narrow transfer function, the oxidation flow reactor could report production factors that were more than 10 times higher than the reference production factors if the segment duration was too short.

Particle emissions and secondary aerosol formation from internal combustion engines deteriorate air quality and significantly affect human wellbeing and health. Both the direct particle emissions and the emissions of compounds contributing to secondary aerosol formation depend on choices made in selecting fuels, engine technologies, and exhaust aftertreatment (EAT). Here we study how catalytic EATs, particle filtration, and fuel choices affect these emissions concerning heavy-duty diesel engine. We observed that the most advanced EAT decreased the emissions of fresh exhaust particle mass as much as 98% (from 44.7 to 0.73 mg/kWh) and the formation of aged exhaust particle mass ∼100% (from 106.2 to ∼0 mg/kWh). The composition of emitted particles depended significantly on the EAT and oxidative aging. While black carbon typically dominated the composition of fresh exhaust particles, aged particles contained more sulfates and organics. The fuel choices had minor effects on the secondary aerosol formation, implicating that, in diesel engines, either the lubricant is a significant source of secondary aerosol precursors or the precursors are formed in the combustion process. Results indicate that the utilization of EAT in diesel engines would produce benefits with respect to exhaust burden on air quality, and thus their utilization should be promoted especially in geographical areas suffering from poor air quality.

Emission regulations and legislation inside the European Union (EU) have a target to reduce tailpipe emissions in the transportation sector. Exhaust gas aftertreatment systems play a key role in low emission vehicles, particularly when natural gas or bio-methane is used as the fuel. The main question for methane operating vehicles is the durability of the palladium-rich aftertreatment system. To improve the durability of the catalysts, a regeneration method involving an efficient removal of sulfur species needs to be developed and implemented on the vehicle. This paper tackles the topic and its issues from a fundamental point of view. This study showed that Al2(SO4)3 over Al2O3 support material inhibits re-oxidation of Pd to PdO, and thus hinders the formation of the low-temperature active phase, PdOx. The presence of Al2(SO4)3 increases light-off temperature, which may be due to a blocking of active sites. Overall, this study showed that research should also focus on support material development, not only active phase inspection. An active catalyst can always be developed, but the catalyst should have the ability to be regenerated.

In order to meet stringent emission limits, after-treatment systems are increasingly utilized in natural gas engine applications. In this work, two catalyst systems were studied in order to clarify how the catalysts affect, e.g. hydrocarbons, NO x and particles present in natural gas engine exhaust. A passenger car engine modified to run with natural gas was used in a research facility with possibilities to modify the exhaust gas properties. High NO x reductions were observed when using selective catalytic reduction, although a clear decrease in the NO x reduction was recorded at higher temperatures. The relatively fresh methane oxidation catalyst was found to reach reductions greater than 50% when the exhaust temperature and the catalyst size were sufficient. Both the studied catalyst systems were found to have a significant effect on particulate emissions. The observed particle mass reduction was found to be due to a decrease in the amount of organics passing over the catalyst. However, especially at high exhaust temperatures, high nanoparticle concentrations were observed downstream of the catalysts together with higher sulphate concentrations in particles. This study contributes to understanding emissions from future natural gas engine applications with catalysts in use.