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Since the implementation of Euro 6 in September 2014, diesel engines are facing another drastic reduction of NOx emission limits from 180 to only 80 mg/km during NEDC and real driving emissions (RDE) are going to be monitored until limit values are enforced from September 2017. Considering also long term CO2 targets of 95 g/km beyond 2020, diesel engines must become cleaner and more efficient. However, there is a tradeoff between NOx and CO2 and, naturally, engine developers choose lower CO2 because NOx can be reduced by additional devices such as EGR or a catalytic converter. Lower CO2 engine calibration, unfortunately, leads to lower exhaust gas temperatures, which delays the activation of the catalytic converter. In order to overcome both problems, higher NOx engine out emission and lower exhaust gas temperatures, new aftertreatment systems will incorporate close-coupled DeNOx systems.

Diesel particulate filters (DPF) are a common component in emission-control systems of modern clean diesel vehicles. Several DPF materials have been used in various applications. Silicone Carbide (SiC) is common for passenger vehicles because of its thermal robustness derived from its high specific gravity and heat conductivity. However, a segmented structure is required to relieve thermal stress due to SiC's higher coefficient of thermal expansion (CTE). Cordierite (Cd) is a popular material for heavy-duty vehicles. Cordierite which has less mass per given volume, exhibits superior light-off performance, and is also adequate for use in larger monolith structures, due to its lower CTE. SiC and cordierite are recognized as the most prevalent DPF materials since the 2000's. The DPF traps not only combustible particles (soot) but also incombustible ash. Ash accumulates in the DPF and remains in the filter until being physically removed.

Diesel engines are more fuel efficient due to their high thermal efficiency, compared to gasoline engines and therefore, have a higher potential to reduce CO2 emissions. Since diesel engines emit higher amounts of Particulate Matter (PM), DPF systems have been introduced. Today, DPF systems have become a standard technology. Nevertheless, with more stringent NOx emission limits and CO2 targets, additional NOx emission control is needed. For high NOx conversion efficiency, SCR catalysts technology shows high potential. Due to higher temperature at the close coupled position and space restrictions, an integrated SCR concept on the DPFs is preferred. A high SCR catalyst loading will be required to have high conversion efficiency over a wide range of engine operations which causes high pressure for conventional DPF materials.

Ammonia Selective Catalytic Reduction (SCR) and Lean NOx Trap (LNT) systems are key technologies to reduce NOx emission for diesel on-highway vehicles to meet worldwide tighter emission regulations. In addition DeNOx catalysts have already been applied to several commercial off-road applications. Adding the DeNOx catalyst to existing Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) emission control system requires additional space and will result in an increase of emission system back pressure. Therefore it is necessary to address optimizing the DeNOx catalyst in regards to back pressure and downsizing. Recently, extruded zeolite for DeNOx application has been considered. This technology improves NOx conversion at low temperature due to the high catalyst amount. However, this technology has concerned about strength and robustness, because the honeycomb body is composed of catalyst.

Diesel engines are widely used to reduce CO2 emission due to its higher thermal efficiency over gasoline engines. Considering long term CO2 targets, as well as tighter gas emission, especially NOx, diesel engines must become cleaner and more efficient. However, there is a tradeoff between CO2 and NOx and, naturally, engine developers choose lower CO2 because NOx can be reduced by a catalytic converter, such as a SCR catalyst. Lower CO2 engine calibration, unfortunately, leads to lower exhaust gas temperatures, which delays the activation of the catalytic converter. In order to overcome both problems, higher engine out NOx emission and lower exhaust gas temperatures, close-coupled a diesel particulate filter (DPF) system with integration of SCR catalyst technology is preferred. For SCR catalyst activity, it is known that the catalyst loading amount has an influence on NOx performance, so a high SCR catalyst loading will be required.

Diesel Particulate Filters (DPF) made of cordierite are generally used for diesel engine aftertreatment systems in both on-road and commercial off-highway vehicles to meet today’s worldwide emission regulations. PM/PN and NOx emission regulations will become more stringent worldwide, as represented by CARB2027 and Euro7. Technologies that can meet these strict regulations are required. As a result, aftertreatment systems have become more complex with limited space. Recently, off-highway OEMs have been interested in downsizing the aftertreatment system using concepts such as DOConFilter in an effort to reduce the size of the exhaust system. DOConFilter can effectively replace DOC + CSF or DOC + bare DPF systems with a single zone coated particulate filter. DOConFilter systems have an increased amount of coating compared to CSF as higher-filtration filters will become the norm. An undesirable increase in pressure drop is expected by adopting this new technology.