Engine control method and engine control device

1. An engine control device comprising:

a combustion chamber of an engine that executes a cycle including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke;

a spark plug arranged in the combustion chamber; and

an injector configured to supply a fuel into the combustion chamber, wherein

the injector supplies the fuel in the combustion chamber at a timing when the spark plug makes a flame in the combustion chamber so that an air-fuel mixture is generated at least around the spark plug, the air-fuel mixture having an air-fuel mass ratio A/F or a gas-fuel mass ratio G/F, in which gas includes air, higher than a stoichiometric air-fuel ratio,

the spark plug is configured to make the flame in the combustion chamber at a predetermined timing in the compression stroke;

the injector is configured to supply the fuel into the combustion chamber in the compression stroke to increase a fuel concentration of the air-fuel mixture in the combustion chamber after the spark plug has made the flame; and

a total amount of the fuel supplied into the combustion chamber in the compression stroke from ignition to a start of combustion is smaller than a total amount of the fuel supplied to the combustion chamber before the ignition.

2. The engine control device of claim 1 , wherein

the spark plug makes the flame during or before a post-mid stage, where the compression stroke is divided into four stages of a pre-stage, a pre-mid stage, the post-mid stage, and a post-stage.

3. The engine control device of claim 2 , wherein

the spark plug makes the flame at a middle stage, where the compression stroke is divided into three stages of an initial stage, the middle stage, and a final stage.

4. The engine control device of claim 1 , wherein

the injector is configured to supply the fuel into the combustion chamber so that the A/F or G/F of the air-fuel mixture in the combustion chamber is lower than or equal to the stoichiometric air-fuel ratio after the spark plug has made the flame.

5. The engine control device of claim 1 , wherein

the engine has a geometric compression ratio of 14 or more.

6. An engine control method of executing a cycle including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in a combustion chamber of an engine, the method comprising:

a first fuel supply step for supplying a fuel into the combustion chamber using an injector at a timing when a spark plug makes a flame in the combustion chamber so that an air-fuel mixture is generated at least around the spark plug, the air-fuel mixture having an air-fuel mass ratio A/F or a gas-fuel mass ratio G/F, in which gas includes air, higher than a stoichiometric air-fuel ratio;

after the first fuel supply step, an ignition step of making the flame in the combustion chamber in the compression stroke using the spark plug; and

after the ignition step, a second fuel supply step of supplying the fuel into the combustion chamber in the compression stroke using the injector to increase a fuel concentration of the air-fuel mixture in the combustion chamber, wherein

a total amount of the fuel supplied into the combustion chamber in the compression stroke from ignition to a start of combustion is smaller than a total amount of the fuel supplied to the combustion chamber before the ignition.

7. The engine control method of claim 6 , wherein

the spark plug makes the flame during or before a post-mid stage, where the compression stroke is divided into four stages of a pre-stage, a pre-mid stage, the post-mid stage, and a post-stage.

8. The engine control method of claim 7 , wherein

the spark plug makes the flame at a middle stage, where the compression stroke is divided into three stages of an initial stage, the middle stage, and a final stage.

9. The engine control method of claim 6 , wherein

the injector supplies the fuel into the combustion chamber in the second fuel supply step so that the A/F or G/F of the air-fuel mixture in the combustion chamber is lower than or equal to the stoichiometric air-fuel ratio.

10. The engine control method of claim 6 , wherein

the engine has a geometric compression ratio of 14 or more.

11. An engine control method of executing a cycle including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in a combustion chamber of an engine, the method comprising:

a first fuel supply step for supplying a fuel into the combustion chamber using an injector at a timing when a spark plug makes a flame in the combustion chamber so that an air-fuel mixture is generated at least around the spark plug, the air-fuel mixture having an air-fuel mass ratio A/F or a gas-fuel mass ratio G/F, in which gas includes air, higher than a stoichiometric air-fuel ratio;

after the first fuel supply step, an ignition step of making the flame in the combustion chamber in the compression stroke using the spark plug; and

after the ignition step, a second fuel supply step of supplying the fuel into the combustion chamber in the compression stroke using the injector to increase a fuel concentration of the air-fuel mixture in the combustion chamber, wherein

the injector supplies the fuel into the combustion chamber in the second fuel supply step so that the A/F or G/F of the air-fuel mixture in the combustion chamber is lower than or equal to the stoichiometric air-fuel ratio.

12. The engine control method of claim 11 , wherein the spark plug makes the flame during or before a post-mid stage, where the compression stroke is divided into four stages of a pre-stage, a pre-mid stage, the post-mid stage, and a post-stage.

13. The engine control method of claim 12 , wherein the spark plug makes the flame at a middle stage, where the compression stroke is divided into three stages of an initial stage, the middle stage, and a final stage.

14. The engine control method of claim 11 , wherein the engine has a geometric compression ratio of 14 or more.