Direct Injection
A fuel delivery system design where fuel is sprayed directly into the combustion chamber under high pressure rather than the intake port.
Gasoline Direct Injection (GDI) is an advanced fuel delivery system where fuel injectors spray highly pressurized gasoline directly into the engine's combustion chambers. This differs from traditional port fuel injection, where fuel is injected into the intake runner, mixing with air before entering the cylinder. GDI operates at extremely high pressures (often over 2,000 PSI) to achieve fine fuel atomization and a cooling effect inside the cylinder.
The main benefits of direct injection are improved fuel economy, lower emissions, and increased power output. The cooling effect of the fuel vaporizing inside the cylinder allows for higher compression ratios and more advanced ignition timing without causing engine knock. However, GDI systems require complex high-pressure fuel pumps and specialized injectors.
A major drawback of direct injection is carbon buildup on the intake valves. Because fuel (which contains cleaning detergents) is sprayed directly into the cylinder, it no longer washes over the backs of the intake valves. Over time, PCV oil mist deposits cook onto the hot valves, restricting airflow and causing misfires, rough idling, and lost power, requiring specialized walnut blasting or intake cleaning services.