An engine, the engine having a combustion chamber, an injector, and a spark plug, 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, and a control system, which comprises: a swirl valve provided to an intake passage of the engine; and a controller 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 change an opening of the swirl valve, and output a control instruction to the swirl valve to make the opening of the swirl valve smaller as an engine speed decreases, output a control instruction to the injector to inject the fuel in an intake stroke towards a swirl flow, and output an ignition instruction to the spark plug so as to ignite, so that the partial compression-ignition combustion is performed, the injector has at least a first nozzle port and a second nozzle port, the first and second nozzle ports are disposed at a center portion of a 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 configured to simultaneously inject the fuel, the swirl flow is an inclined swirl flow flowing nonparallel to a plane perpendicular to the cylinder axis of the combustion chamber, and the first and second nozzle ports are positioned and oriented 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 that a first fuel portion injected by the first nozzle port that has reached the swirl flow moves downstream along the swirl flow and then joins with a second fuel portion injected by the second nozzle port that has reached the swirl flow. a swirl valve provided to an intake passage of the engine; and a controller 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 change an opening of the swirl valve, and output a control instruction to the swirl valve to make the opening of the swirl valve smaller as an engine speed decreases, output a control instruction to the injector to inject the fuel in an intake stroke towards a swirl flow, and output an ignition instruction to the spark plug so as to ignite, so that the partial compression-ignition combustion is performed, change an opening of the swirl valve, and output a control instruction to the swirl valve to make the opening of the swirl valve smaller as an engine speed decreases, output a control instruction to the injector to inject the fuel in an intake stroke towards a swirl flow, and output an ignition instruction to the spark plug so as to ignite, so that the partial compression-ignition combustion is performed, the injector has at least a first nozzle port and a second nozzle port, the first and second nozzle ports are disposed at a center portion of a 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 configured to simultaneously inject the fuel, the swirl flow is an inclined swirl flow flowing nonparallel to a plane perpendicular to the cylinder axis of the combustion chamber, and the first and second nozzle ports are positioned and oriented 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 that a first fuel portion injected by the first nozzle port that has reached the swirl flow moves downstream along the swirl flow and then joins with a second fuel portion injected by the second nozzle port that has reached the swirl flow.