A TOGNUM GROUP BRAND Engine technology Diesel Particulate Filter: Exhaust aftertreatment for the reduction of soot emissions Guido Schàffner Design Exhaust Aftertreatment A diesel particulate filter (DPF) can remove virtually all the soot particulates (PM) from the exhaust gas emitted from a diesel engine to ensure compliance with very strict emission standards. Regardless of the actual emission limit, diesel particulate filters satisfy the needs of operators who place importance on achieving extremely low soot emissions. Klaus Rusch Design Exhaust Aftertreatment Pre-Development Exhaust Aftertreatment Thermodynamics and Turbocharging Systems Diesel particulate filters mean less soot The emission regulations for diesel engines are becoming increasingly stricter worldwide, which makes modifications to the drive systems necessary. As a basic principle, MTU's ap- proach to achieve compliance is to reduce emission levels by means of internal engine enhancements. Depending on the specific emission limits, it may be possible to do with- out a diesel particulate filter altogether. Howev- er, there is a relationship between the production of soot particulates and nitrogen oxides when internal engine measures are used - if fewer soot particulates are produced during the combustion process, the quantity of nitrogen oxides increases, and vice versa. In situations where emission requirements are very strict, therefore, adding a diesel particu- ate filter is necessary, since it removes 90 percent or more of the soot particulates For example, very stringent emission limits are due to come into force for diesel locomotives in

Europe as of 2012. The EU Stage NIB standard lowers the limit for particulate matter emissions from its current level of 0.2 g/kWh by nearly 90 percent to 0.025 g/kWh. To comply with this requirement, MTU is equipping the new Series 4000 engine for rail applications with a particu- ate filter; nitrogen oxide levels, on the other hand, are reduced from 6.0 g/kWh to 3.5 g/kWh solely by internal engine measures using MTU's patented donor cylinder exhaust gas recircula- tion system. Due to its extremely effective cleaning effect, a particulate filter also satisfies the needs of users who - regardless...

CRT = Continuous Regeneration Trap □_ without thermal management with thermal management Fig. 3: Diagram of the "passive diesel particulate filter regeneration strategy" Under normal operating conditions, the engine's exhaust gas temperatures are high enough to continuously remove soot deposited in the diesel particulate filter. Under extreme conditions, regeneration is supported by thermal management, resulting in a significant increase in the exhaust gas temperature and therefore in soot burn-off. MTU's proprietary ECU (Engine Control Unit) engine management system, which was devel- oped in-house,...

Active regeneration If an engine runs under very low load, the exhaust gas temperature can drop to a point where continuous regeneration can no longer be com- pletely guaranteed. In order to prevent the diesel particulate filter being overloaded when operating under such conditions for a long time, additi- onal thermal energy must be introduced for a short time into the exhaust gas. That can be done, for instance, by injecting fuel into the combustion chamber in one or more post injection sequences or injecting fuel directly into the exhaust system. This fuel is then completely burned in the...

Passive regeneration/CRT effect (Continuous Regeneration Trap) MTU uses the CRT effect for regenerating the diesel particulate filter. This is based on chemical reactions that take place in the engine's exhaust aftertreatment system. First of all, nitrogen dioxide (N02) is produced in the oxidation catalyst from the nitrogen monoxide (NO) in the exhaust gas. In the diesel particulate filter, the process is reversed and the soot deposited in the diesel particulate filter is continuously burned off. Hence the name "Continuous Regeneration Trap" (CRT), i.e. a continu- ously regenerating filter....

Wall-flow diesel particulate filter In the case of a wall-flow diesel particulate filter, the entire exhaust flow Is passed through the fine porous ceramic walls of the filter element. This makes very high particle filtration rates of over 90 percent possible. However, filter regeneration must be possible In a wide range of engine applications, to prevent clogging. The resulting high exhaust backpressu- re would lead to higher fuel consumption and, In the worst case, to filter and engine damage. Consequently, Including the engine's thermal manage- ment measures Is of particular Importance In...