FIG. 7 illustrates the condition of the interior of a combustion chamber when a shock wave is generated in the combustion chamber. A shock wave 59 is generated upon the opening of the intake valve 4 when one of the foregoing conditions for shock wave generation expressed by Expressions (1) to (5) is satisfied, and the fuel 20 injected simultaneously with the opening of the intake valve 4 is vibrated and atomized by the pressure energy of the shock wave. Having a small mass, the atomized particles of the fuel are easily carried by air currents and disperse in sprays 57 and 58.
In this embodiment, intake valve opening timing is varied by the variable valve timing mechanism to generate a shock wave in the combustion chamber, and the fuel is injected in synchronism with the generation of the shock wave to atomize the fuel as shown in FIG. 7.