Combustion chamber structure of engine

An engine system, comprising:

• a combustion chamber including a cylinder formed in an engine and a piston configured to reciprocate inside the cylinder;
• a spark plug disposed in a ceiling part of the combustion chamber;
• and
• a water injection device configured to inject water into the combustion chamber through a plurality of nozzle holes facing the inside of the combustion chamber,
• wherein the piston has a cavity in an upper surface thereof,
• wherein the water injection device injects water into the cavity in a compression stroke at a timing when an extension of axes of at least some of the nozzle holes intersect the cavity,
• wherein the cavity has a bottom part where the water injected by the water injection device collides, and a raising part configured to raise the water spreading along the bottom part toward the water injection device,
• wherein the water injection device is disposed in the ceiling part, and at least a part of an injection surface of the water injection device, where the nozzle holes open, is located at a position of the cavity in a direction perpendicular to an axis of the cylinder,
• wherein the spark plug is installed at a position offset from the cavity in the direction perpendicular to the axis of the cylinder,
• wherein when the compression stroke is divided into three stages of an early stage, a middle stage, and a late stage, the water injection device performs a water injection during a period from the early stage to the middle stage of the compression stroke, and
• wherein the water injection is completed in the middle stage of the compression stroke regardless of an engine load.