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For trucks today, the diesel particulate filter (DPF) and SCR catalysts are combined in this sequential order in diesel exhaust systems with the drawback of insufficient temperature for the SCR catalyst during cold start and large volume. The problems can potentially be solved by integrating the SCR catalyst into the particulate filter as one multifunctional unit. For off-road and heavy-duty vehicles applications with fully managed passive NO2-soot regenerations, integration of V-based SCR formulations on the DPF (V-SCRonDPF) represents an attractive solution due to high sulfur resistance accompanied by low-temperature NOx conversion and improved fuel economy. Engine bench tests together with an NO2-active DOC show that it is possible to manage the NO2/NOx ratio so both a high NOx conversion and still a low soot balance point temperature is obtained. The soot balance point is almost unaffected by the fast SCR reaction when urea is introduced.

Today, the DPF and SCR catalysts are combined sequentially in diesel exhaust systems. However, such sequential system configuration has several drawbacks: 1) large volume; 2) insufficient temperature for the SCR catalyst during cold start when DPF is placed in front of SCR; and 3) unfavorable conditions for passive soot regeneration if SCR is placed upstream of the DPF. The problems can potentially be solved by integrating the SCR catalyst into the particulate filter as one multifunctional unit. The study indicates that SCRonDPF based on Cu-zeolite type as SCR material can achieve the NOx conversion levels close to flow-through SCR catalysts for LDV (Light Duty Vehicles) using forced regenerations. Forced soot regeneration solves potential sulfur poisoning.

Silicon carbide diesel particulate filter (DPF) is now recognized as the most effective and robust way to reduce not only the mass but also the number of emitted particles on diesel passenger cars. Widespread use of expensive catalytic platinum-containing coatings has contributed to increased harmful NO₂ emissions. A novel low-cost palladium-base metal coating, BMC-211, was developed which assists soot regeneration by oxygen transport and which actively removes NO₂ still having comparable passive and active soot regeneration properties. The novel coating was tested against a traditional commercial platinum coating on a modern series-produced car, on chassis dynamometer and on engine test bench.

Nitrogen dioxide (NO2) concentrations in European city street air have not decreased after year 2000 in spite of stringent Euro 3 and Euro 4 NOx limits for diesel passenger cars. NO2 emissions from modern diesel vehicles are caused by platinum catalysed Diesel Oxidation Catalysts (DOC) and platinum catalysed Diesel Particulate Filters (cDPF). The NO2 formed on DOC and cDPFs are used for passive soot regeneration but the excess of NO2 out of the filter is not controlled. A Euro 4 diesel passenger car equipped with a DOC and a palladium base metal cDPF was compared with DOC plus a platinum based cDPF using NEDC test cycle with both cold and hot start, FTP-75, and Artemis test cycles. Emissions of NO2 and NOx were measured online in the raw exhaust, and with standard bag sampling method. Relative to cold NEDC the NOx and NO2 levels increased with a warm engine.

To reach the EPA ‘10 and Euro VI strict regulations of PM and NOx for heavy duty trucks it will be necessary to apply integrated catalytic solutions for removal of both PM and NOx. The described system consists of an alternative catalytic configuration where the SCR catalyst is placed downstream of the diesel engine followed by diesel injection over an oxidation catalyst (DOC) and a catalysed diesel particulate filter (cDPF). One of the advantages of this system configuration is that the SCR catalyst in this way is protected from high temperatures during filter regeneration and that the SCR catalyst has the fastest heat up required for good performance in cold test cycles. The SCR catalyst can therefore be of a standard V-based type that is already proven technology for Euro IV and Euro V compliance in Europe. Another advantage is that the DOC and cDPF act as clean-up catalysts for any possible ammonia slip from the SCR catalyst.

To counter the adverse impact on the formation of harmful unregulated emissions such as nitro-polycyclic aromatic hydrocarbons (NPAH), catalyst companies and researchers have been developing catalytic coatings that have the capability of suppressing the formation of NO2. NO2 is formed at low exhaust temperatures with potentially greater concentrations at part load engine operation. Haldor Topsoe, a catalyst company from Denmark, developed such a catalytic coating for DPFs. A sample was provided to Southwest Research Institute (SwRI) to conduct this research with a view of potentially improving NO2-suppressing formulations in the future. The Haldor Topsoe diesel particulate filter (DPF) with its novel coating was tested together with three other DPFs and the results confirmed the capability of this DPF to suppress the formation of NO2. This characteristic was apparent in all five engine test modes selected to cover the full engine operating range.

Due to concerns over NO2 emissions from platinum catalysts a base metal catalysed diesel particulate filter (DPF) has been developed and used in combination with fuel borne catalysts (FBC). Results are presented showing reductions in HC, NOX, NO2, and PAH emissions along with an assessment of the emissions of metals used in the FBC and the catalysed DPF. This data is used to show the likely reduction in overall iron and other metal emissions as a result of using the catalysed DPF/FBC system. A similar system has also been assessed for durability for over 2000 hours when fitted to a bus in regular service in Switzerland.

In order to meet the Euro V heavy-duty diesel emission standard legislation limits, a diesel engine can be optimized by internal means to give low particulate emissions and lower fuel consumption. These modifications of the engine lead inevitably to higher NOx emissions due to the NOx/PM trade off. An efficient Urea SCR after-treatment system is then able to reduce the higher NOx emission to below the Euro V 2.0g/kWh legislation limit. This paper presents tests made on a PM optimized 12 liter heavy-duty diesel engine together with a urea SCR after-treatment system. The optimized engine had engine out particulate emissions of about 0.04 g/kWh and NOx emissions of 9 g/kWh for the ESC and 8,5 g/kWh for the ETC. The fuel consumption of the optimized engine was 194 g/kWh for the ESC and 198 g/kWh for the ETC as compared to state of the art Euro III engines of typically 210 g/kWh for the ESC, giving significant fuel savings of 7.5 %.