CARBON DEPOSIT DETERMINATION METHOD, CARBON REMOVAL METHOD, AND SPARK IGNITION DIRECT INJECTION ENGINE

PROBLEM TO BE SOLVED: To easily determine that carbon is deposited on a heat insulating layer 21c formed at least at the rear side portion of an umbrella 21a in an air intake valve 21, and to easily remove the carbon when it is determined that the carbon is deposited, in a spark ignition direct injection engine 1.SOLUTION: An accumulated operation time at the number of revolutions of an engine which is not smaller than a prescribed number of revolutions is detected, and when the accumulated operation time exceeds a prescribed time, it is determined that the carbon is deposited on a heat insulating layer 21c. Furthermore, in the case that the determination is performed, when an acceleration opening after the requirement of acceleration is brought into a constant state that the opening becomes not larger than a prescribed opening, a burnt gas is introduced into an air intake port 18 by the overlap of valve-opened periods of the air intake valve 21 and an exhaust valve 22, thus burning and removing the carbon deposited on the heat insulating layer 21c.