| 摘要 |
A method of purifying NOX contained in exhaust gas, the method including a first NOX purification method and a second NOX purification method, wherein the first NOX purification method and the second NOX purification method include injecting hydrocarbons into an exhaust gas passage at predetermined feed intervals, wherein in the first method, the injected hydrocarbons are partially oxidized and an air-fuel ratio flowing into an exhaust purification catalyst is lean, and in the second method, the injection of the hydrocarbons occurs at intervals longer than the predetermined feed intervals in the first method, and an air-fuel ratio is switched from lean to rich. |
| 主权项 |
1. A method of purifying NOX contained in exhaust gas, the method comprising a first NOX purification method and a second NOX purification method, wherein the first NOX purification method and the second NOX purification method comprise:
supplying exhaust gas containing NOX to an exhaust gas passage; injecting hydrocarbons in the exhaust gas passage at predetermined feed intervals to form a mixture with the exhaust gas containing NOX; feeding the exhaust gas or the mixture to an exhaust purification catalyst; and reducing the NOX contained in the exhaust gas, wherein
a precious metal catalyst is carried on the exhaust purification catalyst,a basic layer is formed on the exhaust purification catalyst,a hydrocarbon feed valve injects the hydrocarbons in the exhaust gas passage, whereinin the first method, the injected hydrocarbons are partially oxidized, and an air-fuel ratio of the exhaust gas and an air-fuel ratio of the mixture flowing into the exhaust purification catalyst is lean, thereby, the exhaust purification catalyst chemically reduces NOX contained in the exhaust gas without storing nitrates, or with storing a fine amount of nitrates, in the basic layer formed on the exhaust purification catalyst, and the first method further comprises:
reacting the NOX and the partially oxidized hydrocarbons contained in the mixture at the precious metal catalyst to produce a reducing intermediate containing nitrogen and hydrocarbons;holding the produced reducing intermediate on the basic layer; andchemically reducing the NOX contained in the exhaust gas by a reducing action of the reducing intermediate held on the basic layer, thereby chemically reducing the NOX contained in the exhaust gas without storing nitrates, or with storing a fine amount of nitrates, in the basic layer formed on the exhaust purification catalyst, andin the second method, the injection of the hydrocarbons from the hydrocarbon feed valve occurs at intervals longer than the predetermined feed intervals in the first method, wherein
when the feed intervals of the hydrocarbons are longer than the predetermined feed intervals of the first method, the exhaust purification catalyst increases in a storage amount of NOX, thereby physically reducing the NOX contained in the exhaust gas, andwhen the feed intervals of the hydrocarbons are longer than the predetermined feed intervals of the first method, and when an air-fuel ratio of the mixture is switched from lean to rich, NOX is chemically reduced, andat the time of engine operation, the first NOX purification method and the second NOX purification method are selectively performed in accordance with an operating state of an engine. |
