Abstract: In a direct fuel-injection engine equipped with a pentroof-shaped piston, cross-sectional shapes containing a piston central axis (Lp) of a cavity recessed in a central part of the piston having a top face with the height varying in the circumferential direction are set so as to be basically identical at each position in the circumferential direction (see broken line).

Abstract: A direct fuel-injection engine includes a piston, a cavity recessed in a central part of a top face of the piston, and a fuel injector. At a main injection collision point of a fuel-injection axis when main injection is performed while the piston is near top dead center, a main injection collision angle formed between its tangent and the fuel-injection axis is set at an obtuse angle. Fuel colliding with the main injection collision point is deflected towards a cavity open end side. At a secondary injection collision point of the fuel-injection axis when performing secondary injection with the piston is further from top dead center, a secondary injection collision angle formed between its tangent and the fuel-injection axis is set at one of a right angle and an acute angle. Fuel colliding with the secondary injection collision point is deflected primarily in the circumferential direction of the cavity.

Abstract: In a cross section in which squish flow from an outer peripheral part of a piston (13) toward a cavity (25) is large due to a width (W2) of a squish area (SA) being large and a squish clearance (C2) being small, a collision angle (?2) at which a fuel injection axis (Li2) collides with the cavity (25) is made large, whereas in a cross section in which squish flow is small due to the width of the squish area (SA) being small and the squish clearance being large, the collision angle at which a fuel injection axis collides with the cavity (25) is made small. This enables a tendency for fuel to flow out to the exterior of the cavity (25) in a cross section where the squish flow is small to be weakened, and a tendency for fuel to flow out to the exterior of the cavity (25) in a cross section where the squish flow is large to be strengthened, thereby making the conditions in which fuel and air are mixed uniform throughout the entire region of the cavity (25).

Abstract: In a direct fuel injection diesel engine having a piston with a pentroof-shaped top face, with regard to a pentroof-shaped piston (13) with a cavity (25) recessed in a central part of the top face, a radial width S of a squish area (26) formed between an outer peripheral part of the top face and a lower face of a cylinder head (14) changes in the circumferential direction of the piston (13). By setting a squish clearance H large for a portion where the radial width S of the squish area (26) is large and setting the squish clearance H small for a portion where the radial width S of the squish area (26) is small, more specifically, by setting S/H so that it is constant in the circumferential direction, it is possible to make the strength of the squish flow uniform in the circumferential direction of the piston, thus promoting the mixing of air and fuel and reducing harmful exhaust components.

Abstract: In a direct fuel injection diesel engine equipped with a pentroof-shaped piston, when fuel is injected into a cavity (25) recessed in a central part of a piston (13), for which the height of a top face changes in the circumferential direction, from a fuel injection point (Oinj) of a fuel injector disposed on a piston central axis along a plurality of fuel injection axes (Li1,Li2), if a cross-section of the cavity (25) passing along the fuel injection axis (Li1,Li2) is defined as a fuel injection cross-section (Sn), a cross-sectional shape (see shaded portion) of the cavity (25) defined by first to third specific points (An, Bn, Cn) on the fuel injection cross-section (Sn) is set so as to be substantially equal for each fuel injection cross-section (Sn). By so doing, the conditions in which fuel and air are mixed in each fuel injection cross-section (Sn) can be made uniform, the engine output can be improved, and harmful exhaust substances can be reduced.

Abstract: In a direct fuel injection diesel engine equipped with a pentroof-shaped piston, a collision angle (?) at which fuel injected in a direction in which the height of the top face of a piston (13) is high collides with a cavity (25) is set larger than a collision angle (?) at which fuel injected in a direction in which the height of the top face of the piston (13) is low collides with the cavity (25).

Abstract: In a direct fuel-injection engine equipped with a pentroof-shaped piston, cross-sectional shapes containing a piston central axis (Lp) of a cavity recessed in a central part of the piston having a top face with the height varying in the circumferential direction are set so as to be basically identical at each position in the circumferential direction (see broken line).

Abstract: In a direct fuel injection diesel engine equipped with a pentroof-shaped piston, when fuel is injected into a cavity (25) recessed in a central part of a piston (13), for which the height of a top face changes in the circumferential direction, from a fuel injection point (Oinj) of a fuel injector disposed on a piston central axis along a plurality of fuel injection axes (Li1,Li2), if a cross-section of the cavity (25) passing along the fuel injection axis (Li1,Li2) is defined as a fuel injection cross-section (Sn), a cross-sectional shape (see shaded portion) of the cavity (25) defined by first to third specific points (An, Bn, Cn) on the fuel injection cross-section (Sn) is set so as to be substantially equal for each fuel injection cross-section (Sn). By so doing, the conditions in which fuel and air are mixed in each fuel injection cross-section (Sn) can be made uniform, the engine output can be improved, and harmful exhaust substances can be reduced.

Abstract: A direct fuel-injection engine includes a piston, a cavity recessed in a central part of a top face of the piston, and a fuel injector. At a main injection collision point of a fuel-injection axis when main injection is performed while the piston is near top dead center, a main injection collision angle formed between its tangent and the fuel-injection axis is set at an obtuse angle. Fuel colliding with the main injection collision point is deflected towards a cavity open end side. At a secondary injection collision point of the fuel-injection axis when performing secondary injection with the piston is further from top dead center, a secondary injection collision angle formed between its tangent and the fuel-injection axis is set at one of a right angle and an acute angle. Fuel colliding with the secondary injection collision point is deflected primarily in the circumferential direction of the cavity.

Abstract: In a cross section in which squish flow from an outer peripheral part of a piston (13) toward a cavity (25) is large due to a width (W2) of a squish area (SA) being large and a squish clearance (C2) being small, a collision angle (?2) at which a fuel injection axis (Li2) collides with the cavity (25) is made large, whereas in a cross section in which squish flow is small due to the width of the squish area (SA) being small and the squish clearance being large, the collision angle at which a fuel injection axis collides with the cavity (25) is made small. This enables a tendency for fuel to flow out to the exterior of the cavity (25) in a cross section where the squish flow is small to be weakened, and a tendency for fuel to flow out to the exterior of the cavity (25) in a cross section where the squish flow is large to be strengthened, thereby making the conditions in which fuel and air are mixed uniform throughout the entire region of the cavity (25).

Abstract: In a direct fuel injection diesel engine having a piston with a pentroof-shaped top face, with regard to a pentroof-shaped piston (13) with a cavity (25) recessed in a central part of the top face, a radial width S of a squish area (26) formed between an outer peripheral part of the top face and a lower face of a cylinder head (14) changes in the circumferential direction of the piston (13). By setting a squish clearance H large for a portion where the radial width S of the squish area (26) is large and setting the squish clearance H small for a portion where the radial width S of the squish area (26) is small, more specifically, by setting S/H so that it is constant in the circumferential direction, it is possible to make the strength of the squish flow uniform in the circumferential direction of the piston, thus promoting the mixing of air and fuel and reducing harmful exhaust components.

Abstract: In a direct fuel injection diesel engine equipped with a pentroof-shaped piston, a collision angle (?) at which fuel injected in a direction in which the height of the top face of a piston (13) is high collides with a cavity (25) is set larger than a collision angle (?) at which fuel injected in a direction in which the height of the top face of the piston (13) is low collides with the cavity (25).