| 摘要 |
<p>The present invention is particularly applicable to lean burn engines that produce exhaust containing insufficient amounts of unburned hydrocarbons to satisfactorily reduce NOx emissions without undermining engine performance. In the exhaust purification system (10), ethanol or another suitable hydrocarbon (19) is injected into the exhaust stream at an appropriate location between the engine and the catalytic converter (12). A deNOx catalytic converter (22, 122, 222) is positioned within the exhaust downstream from the ethanol injection point. The combination engine application, ethanol injection and suitable deNOx catalyst combine to reduce NOx to satisfactory levels without producing significant amounts of undesirable secondary nitrogen containing compounds. An oxidation catalytic converter (24, 124, 224) is positioned in the exhaust downstream from the deNOx catalytic converter (22, 122, 222). The oxidation catalyst serves to convert any remaining unburned hydrocarbons (19) into carbon dioxide and water. At the same time, only small amounts of secondary nitrogen compounds are converted back into NOx compounds upon passage through the oxidation catalyst. The end result being an overall reduction in both HC and NOx compounds particularly for lean burn engines to satisfactory levels.</p> |
