Exhaust gas purifying method and exhaust gas purifying system

摘要

To provide an exhaust gas purifying method for purifying the exhaust gas of an internal combustion engine (1) by an exhaust gas purifying system (10) having an oxidation catalyst (3a), which comprises the steps of estimating the quantity of unburnt hydrocarbon accumulated in a support of the oxidation catalyst (3a), performing a hydrocarbon removal control when an estimated accumulation quantity (Vhc) of the unburnt hydrocarbon exceeds a predetermined judgment value (Vhc0) and raising an exhaust gas temperature (T) to activate the oxidation catalyst (3a) and oxidizing and removing the accumulated unburnt hydrocarbon. Thereby, it is possible to prevent a white fume from being produced after a low exhaust temperature state of an idling operation or the like continues for a long time.