| 摘要 |
<p>A catalyst (22) suitable for reducing NOx in an exhaust gas by using ammonia in the presence of an excessive oxygen is disposed in an exhaust passage (18, 21). A urea solution is supplied via a flow rate control valve (33) into the exhaust passage (21) upstream of the catalyst (22). When the catalyst (22) is low in temperature, a large amount of a urea solution is supplied to store urea contained in the urea solution in the catalyst (22). When the temperature of the catalyst (22) rises due to an acceleration operation, ammonia is released from the catalyst (22) little by little to reduce NOx in the exhaust gas by the released ammonia.</p> |
