What Is Gasoline Direct Injection (GDI) Technology? And What Advantages Does It Have?

Gasoline Direct Injection (GDI)/(FSI) Fuel Stratified Injection technology is a stratified fuel injection method that injects fuel directly into the cylinder via a nozzle. This technology significantly enhances the thermal efficiency of gasoline engines and reduces emissions.

1.Working Principle
GDI technology employs two distinct combustion modes: homogeneous combustion and stratified combustion. In homogeneous combustion, fuel is injected at the end of the intake stroke, thoroughly mixing with air during the intake and compression strokes to form a uniform mixture in the cylinder for stable ignition. Stratified combustion involves injecting fuel during the compression stroke, creating a concentration gradient from the spark plug to the cylinder wall, ensuring effective ignition and normal flame propagation, thereby improving fuel economy.

2. Advantages of Direct Injection Engines over Port Injection Engines

A. Under high load conditions, direct injection engines inject fuel into the combustion chamber during the intake stroke. The fuel jet moves slower than the piston’s downstream speed, resulting in lower pressure around the jet, which facilitates rapid diffusion and evaporation of fuel, forming a homogeneous combustion mixture.

B. During medium and low load conditions, GDI engines use stratified combustion mode, distributing most air near the cylinder walls, preventing heat transfer to the water jacket and enhancing combustion thermal efficiency.

C. In cold start scenarios, port injection engines suffer from incomplete fuel vaporization due to low cylinder temperatures, leading to excessive fuel injection and potential misfires or incomplete combustion, increasing HC emissions. Conversely, direct injection engines can precisely control the air-fuel ratio in each cycle, reducing HC emissions during cold starts through stratified combustion technology.

D. Direct injection engines adopt mass-based control, injecting fuel according to each cylinder’s actual demand, minimizing cylinder-to-cylinder variations and improving uniformity, typically within 3% compared to port injection engines.

3. Core Components

A. Cylinder Head
The cylinder head, particularly its combustion chamber and air channel structure, plays a crucial role in airflow movement, mixture formation, and flame propagation.

B. Intake Manifold
For GDI engines using stratified combustion, the intake manifold must meet specific requirements regarding diameter, length, resonance chamber volume, and often includes variable flow and pipe length structures. This complexity increases manufacturing costs and calibration challenges. Turbocharged direct injection engines also require intake pipes to withstand positive pressures up to 0.2MPa, necessitating additional vacuum pumps for system demands.

C. High-Pressure Fuel Pump
GDI engines typically operate at injection pressures of 10-15MPa to ensure proper fuel atomization and penetration. The high-pressure pump is driven by a cam on the intake camshaft, with a lift of 2.5-4mm. A lift of approximately 3.5mm generally meets usage requirements, balancing engine performance, roller tappet life, cam profiles, and manufacturing processes.

D. Injector
Fuel injector is the core component of direct injection system, the arrangement of fuel injector in the combustion chamber, nozzle structure, the spray shape of the oil beam directly affects the atomization of fuel, oil and gas mixing and combustion process, and finally affects the performance of the engine. In addition, the injector nozzle is placed in the combustion chamber, by the fuel quality has a greater impact. If the fuel oil quality is not good, combustion is not sufficient, it is very easy to generate carbon deposits and plug the nozzle, affecting the quality of the spray and the life of the injector itself.

E. Piston
The shape of the top surface of the piston of the cylinder direct injection engine has a great influence on the movement of the airflow in the combustion chamber and the formation of the mixture, therefore, the cylinder direct injection engine will be the piston as a key component for the key components of the design and development. Whether it is wall guiding, airflow guiding or jet guiding, all of them need special top surface pit of the piston to adapt, so as to achieve more ideal oil and gas mixing effect, and form a homogeneous distribution or gradient distribution of oil and gas concentration to ensure the smooth combustion.

As we’ve explored, GDI (Gasoline Direct Injection) technology isn’t just a buzzword—it’s a meticulously engineered solution to the twin challenges of fuel efficiency and emission control. By mastering the dance between homogeneous combustion and stratified combustion modes, this innovation squeezes every drop of performance from fuel while slashing hydrocarbon (HC) emissions—a critical win for both your wallet and the planet.