In a combustion cycle in which fuel for forming a homogenized air-fuel mixture in the combustion chamber is injected from the first fuel injector, ignition-use fuel for forming an ignition-use air-fuel mixture in the vicinity of the electrode part is injected from the second fuel injector, and lean combustion is performed by an excess air rate of 2.0 or more, the ignition-use fuel is injected by at least an injection rate of 1.0 mm.sup.3/ms or more for a duration of 250 μs or more in an interval from a crank angle advanced by exactly 20 degrees from an ignition timing of the spark plug to the ignition timing, and the quantity of the ignition-use fuel is 2.0 mm.sup.3/st or less.

A combustion chamber structure in which an installation hole of the injector is improved to realize a rapid combustion and to reduce an unburned hydrocarbon. In the combustion chamber, a leading end of an injector is withdrawn from an upper end of an opening of an installation hole, and an additionally expanded surface area is formed on an upper inner surface of the installation hole from a portion to which the leading end of the injector is situated. to an opening end of the installation hole. An angle between the additionally expanded surface area and a joint surface of a cylinder head is narrower than an angle between a center axis of the installation hole and the joint surface.

A combustion system is provided for an internal combustion engine including a cylinder head and a piston. In one example, a combustion system may include a cylinder head with a second cylinder surface angled relative to a first cylinder surface, an intake port coupled to the first cylinder surface, an exhaust port coupled to the second cylinder surface, and a piston with a first piston surface parallel to the first cylinder surface and a second piston surface parallel to the second cylinder surface.

An electronic control unit of an internal combustion engine is configured to control the fuel injection valve and to control a spark plug if necessary such that fuel is combusted by pre-mixture compression ignition combustion or flame propagation combustion. The electronic control unit is configured to perform homogeneous combustion in a flame ignition operation range when switching failure has not occurred, the homogeneous combustion being combustion in which fuel homogeneously diffused into the combustion chamber is ignited using the spark plug and is combusted by flame propagation combustion. The electronic control unit is configured to perform spray-guided stratified combustion in a second operation range when the switching failure has occurred, the spray-guided stratified combustion being combustion in which fuel in the fuel injection path is ignited using the spark plug and is combusted by the flame propagation combustion.

An internal combustion engine for gaseous fuel includes a cylinder and a piston for reciprocal movement in the cylinder along a reciprocal axis, whereby a combustion chamber is at least partially delimited by the cylinder and the piston. The piston includes a piston crown facing the combustion chamber, a piston crown projection of the piston crown in a direction parallel to the reciprocal axis and onto a piston crown plane extending transversally to the reciprocal axis having a piston crown center point, the piston crown comprising a piston bowl surface defining a piston bowl and a piston rim portion enclosing the piston bowl surface. A piston bowl opening is the intersection between the piston rim portion and the piston bowl surface. The piston bowl opening has an opening center of gravity in the piston crown plane. The opening center of gravity is offset from the piston crown center point.

An object of the present invention is to, while forming a heat insulating layer on a squish area surface of a top surface of a piston main body, prevent generation of large cracks on the heat insulating layer and suppress damages and peeling of the heat insulating layer. To achieve this object, in the present invention, a heat insulating layer on a squish area surface of a top surface of a piston main body is made thinner than a heat insulating layer on a cavity surface of the top surface of the piston main body.

An intake device of an engine having cylinders is provided. The intake device includes a cylinder head formed with two intake ports per cylinder, and a forced induction system. One of the two intake ports is designed to have a smaller passage cross-sectional area at a throat portion thereof than that of the other intake port, and to cause a strength of a tumble flow strength of intake air formed within a combustion chamber to be stronger when a flow of the intake air into the combustion chamber is assumed to be caused only from the one of the two intake ports, than only from the other intake port. A tumble ratio of the intake air flow within the combustion chamber is a predetermined value or greater when the intake air is forcibly induced and flows into the combustion chamber from the two intake ports.

A combustion chamber structure for an internal combustion engine includes a recessed portion formed in a pent roof of a cylinder head on an upstream side of a tumble flow with respect to a spark plug.

Various aspects of the present disclosure are directed to a cylinder head for an internal combustion engine. In one example embodiment, the cylinder head includes at least one spark plug having at least one earth electrode, a precombustion chamber accommodating the at least one spark plug, and a fuel channel which leads into the precombustion chamber. The fuel channel having a flow axis at an outlet that is oriented in the direction of the at least one earth electrode. An axis of rotation of the at least one spark plug has an offset with respect to the flow axis between 0 and 15% of the greatest precombustion chamber diameter.

In a combustion cycle in which fuel for forming a homogenized air-fuel mixture in the combustion chamber is injected from the first fuel injector, ignition-use fuel for forming an ignition-use air-fuel mixture in the vicinity of the electrode part is injected from the second fuel injector, and lean combustion is performed by an excess air rate of 2.0 or more, the ignition-use fuel is injected by at least an injection rate of 1.0 mm.sup.3/ms or more for a duration of 250 μs or more in an interval from a crank angle advanced by exactly 20 degrees from an ignition timing of the spark plug to the ignition timing, and the quantity of the ignition-use fuel is 2.0 mm.sup.3/st or less.