An engine having a combustion chamber, an injector, a spark plug, and a control system, the combustion chamber being formed by a cylinder having a cylinder axis, a piston, and a cylinder head, the injector being attached to the engine and configured to supply fuel into the combustion chamber, the spark plug being disposed to be oriented into the combustion chamber, the control system comprising: a swirl valve to be provided to an intake passage of the engine; and a controller to be connected to the injector, the spark plug, and the swirl valve, and configured to output a control signal to the injector, the spark plug, and the swirl valve, respectively, wherein the controller is configured, during partial compression-ignition combustion in which a mixture gas combusts by flame propagation and then combusts by compression ignition, to adjust an opening of the swirl valve to generate an inclined swirl flow, which is nonparallel to a plane perpendicular to the cylinder axis, inside the combustion chamber, control a timing or crank angle of the fuel injection by the injector, output a control instruction to the injector, and output an ignition instruction to the spark plug so as to ignite after the swirl generation and the fuel injection, so that the partial compression-ignition combustion is performed, the injector is disposed in a center portion of a ceiling surface of the combustion chamber, and its tip portion opposes to a center portion of a crown surface of the piston, the injector is a multi-port injector having a plurality of nozzle ports at its tip portion, the ports are configured to simultaneously inject the fuel such that center lines (L1-L10) of sprays of fuel injected from the respective nozzle ports intersect the cylinder axis at an angle (α) of about 30° to 60° so as to reach the inclined swirl flow, the injector has at least a first nozzle port and a second nozzle port, the first and second nozzle ports are disposed at the center portion of the ceiling surface of the combustion chamber and separated from each other in a circumferential direction of the injector, the first and second nozzle ports are positioned and oriented so that a first fuel portion injected by the first nozzle port that has reached the inclined swirl flow moves downstream along the inclined swirl flow and then joins with a second fuel portion injected by the second nozzle port that has reached the inclined swirl flow, and the controller is configured to control the injector to retard the fuel injection as an engine speed increases, during the partial compression-ignition combustion in which the inclined swirl flow is generated. a swirl valve to be provided to an intake passage of the engine; and a controller to be connected to the injector, the spark plug, and the swirl valve, and configured to output a control signal to the injector, the spark plug, and the swirl valve, respectively, wherein the controller is configured, during partial compression-ignition combustion in which a mixture gas combusts by flame propagation and then combusts by compression ignition, to adjust an opening of the swirl valve to generate an inclined swirl flow, which is nonparallel to a plane perpendicular to the cylinder axis, inside the combustion chamber, control a timing or crank angle of the fuel injection by the injector, output a control instruction to the injector, and output an ignition instruction to the spark plug so as to ignite after the swirl generation and the fuel injection, so that the partial compression-ignition combustion is performed, adjust an opening of the swirl valve to generate an inclined swirl flow, which is nonparallel to a plane perpendicular to the cylinder axis, inside the combustion chamber, control a timing or crank angle of the fuel injection by the injector, output a control instruction to the injector, and output an ignition instruction to the spark plug so as to ignite after the swirl generation and the fuel injection, so that the partial compression-ignition combustion is performed, the injector is disposed in a center portion of a ceiling surface of the combustion chamber, and its tip portion opposes to a center portion of a crown surface of the piston, the injector is a multi-port injector having a plurality of nozzle ports at its tip portion, the ports are configured to simultaneously inject the fuel such that center lines (L1-L10) of sprays of fuel injected from the respective nozzle ports intersect the cylinder axis at an angle (α) of about 30° to 60° so as to reach the inclined swirl flow, the injector has at least a first nozzle port and a second nozzle port, the first and second nozzle ports are disposed at the center portion of the ceiling surface of the combustion chamber and separated from each other in a circumferential direction of the injector, the first and second nozzle ports are positioned and oriented so that a first fuel portion injected by the first nozzle port that has reached the inclined swirl flow moves downstream along the inclined swirl flow and then joins with a second fuel portion injected by the second nozzle port that has reached the inclined swirl flow, and the controller is configured to control the injector to retard the fuel injection as an engine speed increases, during the partial compression-ignition combustion in which the inclined swirl flow is generated.