| 摘要 |
<p>A low-octane fuel and a high-octane fuel stored in a low-octane fuel tank ( 5 ) and a high-octane fuel tank ( 7 ), both having known octane numbers, are injected from fuel injection valves ( 13 a, 13 b) into an intake port ( 12 ) at a mixing proportion that achieves a standard octane number set in accordance with the engine operation state. If knocking occurs during a predetermined steady engine operation state, the knocking is detected by a knock sensor ( 10 b) and, corresponding to the knocking, the ignition timing is retarded from a basic ignition timing. A deviation in octane number is determined from the amount of ignition timing retardation with reference to a map, and is then corrected by the intake air pressure. On the basis of the corrected deviation in octane number, a deviation in the mixing proportion of the high-octane fuel is determined with reference to a map. The thus-determined deviation is added to a target mixing proportion computed corresponding to the standard octane number, thereby computing the present mixing proportion.</p> |
