Fuel injection control system and fuel injection control method for diesel engine

A fuel injection control system for a diesel engine, the fuel injection control system comprising:

• a combustion chamber of an engine, formed with a lower surface of a cylinder head, a cylinder, and a crown surface of a piston;
• a fuel injection valve configured to inject fuel into the combustion chamber;
• and
• a fuel injection control device including a processor and configured to control an operation of the fuel injection valve;
• wherein
• the crown surface of the piston includes a cavity,
• the cavity includes:
• a first cavity portion disposed in a radial central region of the crown surface,
• the first cavity portion including a first bottom having a first depth in a cylinder axial direction;
• a second cavity portion disposed on an outer peripheral side of the first cavity portion in the crown surface, the second cavity portion including a second bottom having a depth shallower than the first depth in the cylinder axial direction;
• and
• a joint portion connecting the first cavity portion and the second cavity portion,
• the fuel injection valve is configured to inject the fuel toward the cavity and is disposed at or near a radial center of the combustion chamber,
• the fuel injection control device is configured to cause the fuel injection valve to execute at least:
• a first injection to inject the fuel at timing when the piston is positioned near a compression top dead center;
• a second injection to inject the fuel at timing earlier than the first injection;
• and a third injection to inject the fuel at timing earlier than the second injection or timing later than the first injection,
• the fuel injection control device is configured to execute:
• a first injection control module to execute at least one of the first injection or the second injection at timing of injecting the fuel toward the joint portion;
• and
• a second injection control module to execute the third injection,
• the second injection control module:
• estimates a rotational diameter of a rotational flow generated in the first cavity portion based on injection pressure, injection amount, and injection timing of the first injection or the second injection by the first injection control module, the rotational flow being an in-cylinder flow of an air-fuel mixture containing the injected fuel;
• estimates an oxygen residual feasible region generated in the radial central region of the combustion chamber based on the estimated rotational diameter;
• and
• executes the third injection to spray the fuel only into the estimated oxygen residual feasible region, and
• an injection amount of the third injection is smaller than an injection amount of the second injection and smaller than an injection amount of the first injection.

A fuel injection control method for a diesel engine, the diesel engine including:

• a combustion chamber formed with a lower surface of a cylinder head, a cylinder, and a crown surface of a piston;
• and a fuel injection valve configured to inject fuel into the combustion chamber, wherein the crown surface of the piston of the diesel engine includes a cavity, the cavity including:
• a first cavity portion disposed in a radial central region of the crown surface, the first cavity portion including a first bottom having a first depth in a cylinder axial direction;
• a second cavity portion disposed on an outer peripheral side of the first cavity portion in the crown surface, the second cavity portion including a second bottom having a depth shallower than the first depth in the cylinder axial direction;
• and a joint portion connecting the first cavity portion and the second cavity portion, the fuel injection valve is configured to inject the fuel toward the cavity and is disposed at or near a radial center of the combustion chamber, the fuel injection control method comprising:
• a first injection step in which the fuel injection valve injects the fuel at timing when the piston is positioned near a compression top dead center;
• a second injection step in which the fuel injection valve injects the fuel at timing earlier than the first injection;
• and
• a third injection step in which the fuel injection valve injects the fuel at timing earlier than the second injection step or timing later than the first injection step, wherein
• the third injection step includes:
• a step of estimating a rotational diameter of a rotational flow generated in the first cavity portion based on injection pressure, injection amount, and injection timing of the first injection step or the second injection step;
• the rotational flow being an in-cylinder flow of an air-fuel mixture containing the injected fuel,
• a step of estimating an oxygen residual feasible region generated in the radial central region of the combustion chamber based on the estimated rotational diameter, and
• a step in which the fuel injection valve sprays the fuel only into the estimated oxygen residual feasible region, and
• an injection amount of the third injection step is smaller than an injection amount of the second injection step and smaller than an injection amount of the first injection step.