Large two-stroke diesel engine with an exhaust gas purification system

摘要

The invention relates to a large turbocharged two stroke diesel engine of the crosshead type comprising a plurality of cylinders that are each connected to an exhaust gas receiver. A selective catalytic reduction reactor is arranged downstream of the exhaust gas receiver. An exhaust conduit connects the outlet of the selective catalytic reduction reactor to a turbine of a turbocharger. The turbine drives a cornpressor of the turbocharger that delivers scavenge air via a scavenge air path to a scavenge air receiver. The scavenge air receiver is connected to the plurality of cylinders. An auxiliary blower in the scavenge air path assists the turbine at low bad conditions. A controllable by pass line extends from the scavenge air receiver to the exhaust conduit. At low engine bad a controlled flow of scavenge air is directed from the scavenge air receiver to the exhaust conduit at a position downstream of the selective catalytic reduction reactor and upstream of the turbine of the turbocharger. This measure increases the temperature of the exhaust gases entering the selective catalytic reduction reactor. Further, a cooler in the scavenge air path can be controlled so as to the cooling effect partially or completely. Alternatively, the cooler can be controlled to become a heater or a heater is installed in the scavenge air path.