A thermal insulation film is formed on a bottom surface of a cylinder head facing a top surface of a piston. The thermal insulation film in a region (a circumferential region) of a bottom surface of the cylinder head configuring a squish area in a circumferential edge of a cavity region is formed to be thinner than the thermal insulation film in a region (a cavity region) of the bottom surface of the cylinder head facing a cavity. The thermal insulation film in the circumferential region is polished, and surface roughness thereof is equal to or lower than 3 μm. The thermal insulation film in the cavity region is not polished, and surface roughness thereof is 3 to 8 μm on average.

An object is to enable stable diesel combustion in an internal combustion engine using a fuel having a relatively high self-ignition temperature. In the internal combustion engine, pre-injection and ignition of pre-spray fuel are performed, and thereafter main injection is performed to cause a portion of main-injected fuel to be burned by diffusion combustion. Injection ports of a fuel injection valve are provided in such a way that the quantity of the main injected fuel injected to a predetermined region defined by a predetermined angle equal to or smaller than 90 degrees about the fuel injection valve from the location of an ignition device in the direction of rotation of the swirl is relatively small.

An outboard motor includes a cylinder block, a cylinder head unit, a delivery pipe, a plurality of injectors, a fuel pump, and a fuel pipe. The cylinder block includes a plurality of cylinders. The cylinder head unit is connected to the cylinder block. The delivery pipe is attached to the cylinder head unit. The injectors are attached to the delivery pipe. The fuel pump is attached to the cylinder head unit. The fuel pipe is attached to the delivery pipe and the fuel pump. A first attachment direction of attaching the fuel pump to the cylinder head unit is parallel or substantially parallel to a second attachment direction of attaching the fuel pipe to the delivery pipe.

An object is to improve the combustion condition in an internal combustion engine equipped with a supercharger and performing diesel combustion using fuel having a relatively high self-ignition temperature in an operation state in which the engine load is increased or decreased. A control apparatus performs first injection during the compression stroke, causes spray guide combustion to occur, and starts to perform second injection at such a second injection time that combustion of injected fuel is started by flame generated by the spray guide combustion, thereby causing self-ignition and diffusion combustion of fuel to occur. During a response delay period in changing the boost pressure when changing the engine load of the internal combustion engine to a target engine load, the ratio of the quantity of fuel injected by the first injection to the total fuel injection quantity in one combustion cycle is made higher than the ratio of the quantity of fuel injected in the first injection to the total fuel injection quantity in one combustion cycle during the time when the engine load is equal to the target engine load and the actual boost pressure is equal to a target boost pressure corresponding to the target engine load.

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.

An internal combustion engine includes a combustion chamber with a cylinder head, a cylinder, and a piston. The internal combustion engine also includes at least one intake valve and at least one exhaust valve that are connected to the combustion chamber, a fuel injector that injects fuel into the combustion chamber, at least two ignition devices arranged in the combustion chamber, and control means that control the valves, the injector, and the ignition means. The control means operate the engine according to different combustion modes including a controlled ignition combustion mode, a compression ignition combustion mode, and an assisted compression ignition combustion mode. The control means activate the ignition means in the assisted compression ignition combustion mode.

A fuel injection control device for an engine is provided. A swirl generator generates a swirl flow inside a combustion chamber. A fuel injector with multiple nozzle holes injects fuel into the combustion chamber, and forms a lean mixture gas inside the combustion chamber. A spark plug ignites the lean mixture gas to cause a portion of the mixture gas to start combustion accompanied by flame propagation, and then combusts by self-ignition. The fuel injector has first and second nozzle holes, and a first atomized fuel spray injected from the first nozzle hole and a second atomized fuel spray injected from the second nozzle hole separate from each other by the swirl flow. The fuel injector performs the fuel injection in an intake stroke, and retards a start timing of the injection when an engine load is high compared to that when the load is low.

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.

An engine is provided, which includes a combustion chamber defined by a piston crown surface, an inner wall surface of a cylinder, and a pentroof ceiling surface formed in a cylinder head, and an ignition part of a spark plug disposed at the ceiling surface to achieve flame propagation combustion inside the combustion chamber. A cavity recessed in a spherical cap shape is formed in a central area of the crown surface. An opening of an intake port is formed in the ceiling surface (intake side) and an opening of an exhaust port is formed in the ceiling surface (exhaust side). When seen in a cross-sectional view taken along a cylinder axis, the ignition part is located above the cavity to be offset toward the exhaust side with respect to a cylinder axial line whereas a cavity center point is located to be offset toward the intake side.