Gasoline is injected into each engine cylinder and ignited by a spark plug after air and the atomized fuel mix. With conventional port injection, the fuel is injected in the manifold to mix with air before entering the cylinders.
There are two types of GDI engines. Lean-burn GDI uses less gasoline in the mix than the theoretical, or stoichiometric, ideal. Lean-burn engines are very fuel efficient at low speeds, but high-sulfur gasoline can increase NOx emissions. The NOx levels must be lowered using a self-regenerating catalytic converter, which only works well on low-sulfur gasoline.
Homogeneous GDI engines use only the amount of air necessary to completely burn the fuel in the cylinder. The air-fuel mixture must be very uniform to avoid emitting partially burned fuel. Fuel consumption improves less but performance and especially low-end torque are greater.