| 摘要 |
PROBLEM TO BE SOLVED: To improve a NOx removing rate in a spark ignition engine, especially in a gas engine. SOLUTION: An HC-SCR catalyst device 9 is disposed in an exhaust passage, propane is supplied to an exhaust upstream side inlet part 9a of the HC-SCR catalyst device 9, and a supplying quantity of the propane is controlled by an operating condition. An engine load, an engine rotating speed, and an excess air ratio are detected, a NOx quantity in exhaust gas is estimated from those detected elements, and the supplying quantity of the propane is controlled corresponding to the estimated NOx quantity.
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