Abstract: An exhaust gas recirculation system for returning part of exhaust gas of an engine to an intake system has at least one EGR gas introduction port for directing the EGR gas into an intake air passage downstream of a throttle valve. The EGR introduction port opens, into the intake passage, in a tangential direction to produce a circumferential flow along an inside curved surface of the intake air passage around a central back flow region behind the throttle valve to mix the EGR gas efficiently with the fresh intake air and to prevent deposits on the throttle valve.

Abstract: A predetermined firing delay time B.sub.1 is added to a value obtained by dividing a total gas weight Gcyl in a cylinder by an unburnt gas density basic value DENS and a laminar flow flame velocity basic value FLML. The value obtained by this calculation is unit converted and then set as a basic ignition timing for which a minimum ignition advance value or MBT is obtained. In this way, ignition timing control is optimized for various engine running conditions without preparing a plurality of maps.

Abstract: A fuel injection valve includes a valve body to which liquid to be injected is supplied. A nozzle tip is connected with an end portion of the valve body. A valve member is installed in the valve body to stop and start a supply of the liquid to the nozzle tip. The nozzle tip has first and second nozzle holes which are formed so that fluid injected through the first nozzle hole is collided with fluid injected through the second nozzle hole and that a ratio between a square root of a cross-sectional area of the first nozzle hole and a square root of a cross-sectional area of the second nozzle hole is within a range 1.25 to 3.5. Therefore, the collided fuel is effectively atomized as a result of a resonance phenomenon by the collision.

Abstract: A valve operating mechanism for an internal combustion engine having a plurality of exhaust valves per cylinder comprises a device for driving the exhaust valves in a same cylinder at such a valve timing that makes opening of the exhaust valves with a phase difference, i.e., at different timings relative to a crank angle. In one aspect of this invention, the exhaust valves open at the different times and close at the same time.