Directinjection

Direct injection is a method of delivering fuel directly into the combustion chamber of an internal combustion engine, rather than into the intake manifold or port. The fuel is injected at high pressure by a dedicated injector controlled by the engine management system, and timing is synchronized with the piston position and ignition cycle.

It is used in both gasoline engines (gasoline direct injection, GDI) and diesel engines (diesel direct injection). In diesel engines, injection occurs at high pressure during the compression stroke, with precise timing and metering for each cylinder. In gasoline engines, direct injection allows greater control of the air-fuel mixture and enables strategies such as stratified charging at certain operating conditions or homogeneous charging at others.

Benefits include higher thermal efficiency, increased power density, and flexibility to downsize with turbocharging. Direct injection reduces pumping losses and can improve part-throttle efficiency, while enabling higher compression ratios in some designs. It also provides more precise control over combustion timing and emissions in modern engines.

Disadvantages include higher emissions of NOx and particulates in some gasoline direct injection configurations, especially under certain operating conditions. There is also a risk of carbon buildup on intake valves due to reduced fuel washing, along with increased peak pressures that demand more robust components. The system requires high-pressure fuel pumps, sophisticated control electronics, and more complex calibration, contributing to higher cost and maintenance requirements.

History: Direct injection has long been used in diesel engines and became widespread in gasoline engines in the late 1990s and 2000s as part of broader trends toward downsizing and turbocharging. It remains a core technology in contemporary engines and is often paired with variable valve timing and advanced fuel-management systems.