Control system for compression-ignition engine

1. A control system for a compression-ignition engine, comprising:

an engine having a combustion chamber formed by a cylinder, a piston and a cylinder head;

an injector attached to the engine and configured to supply fuel into the combustion chamber;

a spark plug disposed to be oriented into the combustion chamber;

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, the controller including a processor configured to execute:

a swirl adjusting module configured to change an opening of the swirl valve, the swirl adjusting module outputting a control instruction to the injector to inject the fuel after a control of the swirl valve; and

a combustion controlling module to output an ignition instruction to the spark plug so as to ignite at a given ignition timing after an exhaust gas recirculation (EGR) ratio adjustment, so that partial compression-ignition combustion in which a mixture gas combusts by flame propagation and then combusts by compression ignition within a predetermined partial compression-ignition combustion operating range, is performed,

wherein the swirl adjusting module outputs a control instruction to the swirl valve to make the opening of the swirl valve smaller as an engine load decreases within the partial compression-ignition combustion operating range, and make the opening of the swirl valve smaller as an engine speed decreases within the partial compression-ignition combustion operating range.

2. The control system of claim 1 , wherein the swirl adjusting module controls the swirl valve so that a change rate of an intensity of swirl flow in a low engine speed range below a given engine speed is less than the change rate in a high engine speed range above the given engine speed.

3. The control system of claim 1 , wherein during the partial compression-ignition combustion, the swirl adjusting module controls the opening of the swirl valve within a given opening range larger than the fully-closed state.

4. The control system of claim 1 , wherein at least in a part of the partial compression-ignition combustion operating range, the swirl adjusting module controls the swirl valve to perform the partial compression-ignition combustion while forming an air-fuel (A/F) lean environment in which an air-fuel ratio that is a ratio of air to fuel inside the combustion chamber is larger than a stoichiometric air-fuel ratio.

5. The control system of claim 1 , wherein the injector at least has a first nozzle port and a second nozzle port 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 simultaneously injecting the fuel,

wherein the swirl flow is an inclined swirl flow flowing nonparallel to a plane perpendicular to a center axis of the combustion chamber, and

wherein 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 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.

6. The control system of claim 1 , wherein during the partial compression-ignition combustion, the combustion controlling module adjusts a given control amount at least including a timing of the spark ignition so that a spark ignition (SI) ratio that is a ratio of a heat generation amount by the spark ignition combustion to a total heat generation amount matches a target SI ratio determined in advance for each operating condition of the engine.

7. A control system for a compression-ignition engine including an injector configured to supply fuel into a combustion chamber and a spark plug configured to ignite a mixture gas containing fuel supplied from the injector and air, the engine performing partial compression-ignition combustion including spark ignition (SI) combustion performed by combusting a portion of the mixture gas through spark ignition by the spark plug, followed by compression ignition (CI) combustion performed by causing the rest of the mixture gas to self-ignite, comprising:

a swirl mechanism configured to adjust an intensity of swirl flow to be generated inside the combustion chamber; and

a processor configured to, during the partial compression-ignition combustion within a predetermined partial compression-ignition combustion operating range;

cause the injector to inject the fuel toward the swirl flow while controlling the swirl mechanism to:

make an opening of the swirl mechanism smaller as an engine load decreases; and

make the opening of the swirl mechanism smaller as an engine speed decreases; and

cause the spark plug to perform spark ignition at a given ignition timing so that the SI combustion of the mixture gas is performed followed by the CI combustion.

8. The control system of claim 7 ,

wherein within a segment below a boundary speed within the partial compression-ignition combustion operating range, the processor is configured to set the opening of the swirl mechanism to a constant opening regardless of the engine speed; and

wherein within a segment above the boundary speed within the partial compression-ignition combustion operating range make the opening of the swirl mechanism smaller as the engine speed decreases.