| 摘要 |
PURPOSE:To perform excellent emission of exhaust gas through reduction of production of NOx without lowering an engine output, by a method wherein, when the octane number of working fuel is high, an air-fuel ratio is controlled so that it is further rich than a target air-fuel ratio. CONSTITUTION:In a control circuit 20, it is decided by ON/OFF of a change- over switch 34 whether low octane number fuel is used. When the octane number of working fuel is high, an ignition timing is advanced compared with that at a time when it is low, and an air-fuel ratio is controlled to a target value by feedback based on an output from an O2 sensor 32 for detecting residual oxygen concentration in exhaust gas. In which case, when the octane number of the working fuel is high, an air-fuel ratio is controlled so that it is further rich than a target air-fuel ratio. By advancing an ignition timing and controlling an air-fuel ratio to the rich side when high octane number fuel is used, the combustion temperature of an air-fuel mixture is decreased as an output is prevented from lowering, and an exhaust amount of NOx is reduced.
|
