Exhaust system and method for reducing particulate and no2 emissions

An exhaust system for reducing particulate and NO2 emissions from diesel engine exhaust gases, the system comprising:

• a diesel particulate filter;
• an inlet for receiving exhaust gases from a diesel engine;
• a first conduit capable of providing a first fluid connection between the inlet and the diesel particulate filter;
• a second conduit capable of providing a second fluid connection between the inlet and the diesel particulate filter;
• a diesel oxidation catalyst in the second conduit, the diesel oxidation catalyst catalysing hydrocarbon combustion and the formation of NO2 and having high HC activity and high NO2activity;
• a valve mechanism for selectively directing exhaust gases from the inlet to the diesel particulate filter through the first conduit or the second conduit;
• wherein exhaust gases that pass from the inlet to the diesel particulate filter through the first conduit but not the second conduit will not encounter a diesel oxidation catalyst;
• and
• a fuel injector for injecting fuel upstream of the diesel oxidation catalyst.