A control system for an engine, the engine having a combustion chamber, an injector, and a spark plug, the combustion chamber being formed by a cylinder, 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 to, in a first operating range (A1_a), adjust an opening of the swirl valve to generate a swirl flow inside the combustion chamber, control fuel injection amounts by the injector, of a pre-injection in which fuel is injected into the combustion chamber and a post-injection in which fuel is injected again after the pre-injection, output a control instruction to the injector to increase, as an engine speed increases, a ratio of an injection amount of the post-injection to a total amount of fuel to be injected into the combustion chamber in one cycle, and output an ignition instruction to the spark plug so as to ignite after the swirl generation and the fuel injection, so that partial compression-ignition combustion, in which the mixture gas combusts by flame propagation and then combusts by compression ignition, is performed, characterized in that the controller is configured to, during a partial compression-ignition combustion in a second operating range (A1_b) with a higher load than that of the first operating range (A1_a), cause the swirl valve to generate the swirl flow and control the injector so that the pre-injection and the post-injection are performed and the ratio of the injection amount of the post-injection to the total amount of fuel to be injected into the combustion chamber in one cycle is reduced as the engine speed increases. 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 to, in a first operating range (A1_a), adjust an opening of the swirl valve to generate a swirl flow inside the combustion chamber, control fuel injection amounts by the injector, of a pre-injection in which fuel is injected into the combustion chamber and a post-injection in which fuel is injected again after the pre-injection, output a control instruction to the injector to increase, as an engine speed increases, a ratio of an injection amount of the post-injection to a total amount of fuel to be injected into the combustion chamber in one cycle, and output an ignition instruction to the spark plug so as to ignite after the swirl generation and the fuel injection, so that partial compression-ignition combustion, in which the mixture gas combusts by flame propagation and then combusts by compression ignition, is performed, characterized in that the controller is configured to, during a partial compression-ignition combustion in a second operating range (A1_b) with a higher load than that of the first operating range (A1_a), cause the swirl valve to generate the swirl flow and control the injector so that the pre-injection and the post-injection are performed and the ratio of the injection amount of the post-injection to the total amount of fuel to be injected into the combustion chamber in one cycle is reduced as the engine speed increases.