Patent ID: 6823662
Filing Date: 2004-11-30
Classification: B01D,B01J,F01N,F02D

Abstract:
A method of purifying exhaust gas from a combustion device provided with an exhaust gas purifying system including a NOx treating disposed in an exhaust gas passageway of the combustion device, a NOx treating catalyst reducing NOx in presence of reducing components in exhaust gas, said method comprising:increasing a ratio of hydrogen to total reducing components in at least one of combustion gas or exhaust gas to be supplied to the NOx treating catalyst so as to meet relations represented by the following formulae (1) and (2), when reduction of NOx is carried out by said NOx treating catalyst: [H2/TR]d>[H2/TR]uâ€ƒâ€ƒ(1) [H2/TR]d&gE;0.3â€ƒâ€ƒ(2) where [H2/TR]u is a ratio between a concentration [H2]u of hydrogen and a concentration [TR]u of total reducing components in at least one of exhaust gas in the exhaust gas passageway upstream of said hydrogen enriching or combustion gas in a state before undergoing the hydrogen ratio increasing; and [H2/TR]d is a ratio between a concentration [H2]d of hydrogen and a concentration [TR]d of total reducing components in exhaust gas in the exhaust gas passageway upstream of the NOx treating catalyst and in a state after undergoing the hydrogen ratio increasing, wherein said ratio of hydrogen to total reducing components is increased by at least one selected from the group consisting of producing hydrogen in at least one of combustion gas or exhaust gas, decreasing the reducing components other than hydrogen in at least one of combustion gas and or exhaust gas, and suppressing consumption of hydrogen in at least one of combustion gas or exhaust gas, wherein increasing said ratio of hydrogen to total reducing components is carried out by a device including a catalyst containing at least one of a first catalytic component including platinum and zirconium oxide or a second catalytic component including rhodium and zirconium oxide, and a combustion control device for controlling at least one selected from the group consisting of operating parameters of an internal combustion engine and combinations of the operating parameters, the operating parameters including fuel injection amount, fuel injection timing, spark timing, opening and closing timings of intake and exhaust valves of the internal combustion engine, to control at least one of combustion gas or exhaust gas flowing into the catalyst; and increasing a ratio of hydrogen to carbon monoxide in the total reducing components in exhaust gas so as to meet a relation represented by the following formula [H2/CO]d>1 where [H2/CO]d is a ratio between a concentration [H2]d of hydrogen and a concentration [CO]d of carbon monoxide in the total reducing components in exhaust gas in the exhaust gas passageway immediately upstream of the NOx treating catalyst and downstream of said device including a catalyst, when reduction of NOx is carried out by said NOx treating catalyst.