Fuel leak diagnostic system

A fuel leak diagnostic system comprising:

• a high-pressure pump configured to pressurize liquid fuel supplied from a fuel tank;
• a pressure accumulator configured to store the liquid fuel discharged from the high-pressure pump;
• an in-cylinder injection valve configured to inject the liquid fuel in the pressure accumulator directly into a cylinder of an engine;
• and
• a diagnostic device configured to diagnose a leak of the liquid fuel from the in-cylinder injection valve, wherein
• the diagnostic device includes
• an acquisition unit configured to acquire a first temperature and a first pressure of the liquid fuel and a second temperature and a second pressure of the liquid fuel, the first temperature and the first pressure being a temperature and a pressure of the liquid fuel in the pressure accumulator when the engine is in a stopped state, and the second temperature and the second pressure being a temperature and a pressure of the liquid fuel in the pressure accumulator after the engine is stopped and before the engine is started,
• a determination unit configured to determine whether the second temperature is higher than the first temperature,
• a first calculation unit configured to, when the determination unit makes an affirmative determination, calculate an ideal pressure of the liquid fuel based on the first temperature, the second temperature, the second pressure, a volume of the pressure accumulator, a coefficient of thermal expansion of the liquid fuel, and a bulk modulus of the liquid fuel, assuming that there is no leak of the liquid fuel from the in-cylinder injection valve while the engine is stopped, the ideal pressure being an ideal pressure of the liquid fuel in the pressure accumulator before the engine is started,
• a second calculation unit configured to calculate an amount of leakage of the liquid fuel from the in-cylinder injection valve while the engine is stopped, based on a difference between the ideal pressure and the second pressure, and
• a diagnostic unit configured to diagnose the leak of the liquid fuel from the in-cylinder injection valve, based on the amount of leakage.