“…GDI is a strategy to improve fuel efficiency that can relatively easily replace existing port fuel injected (PFI) engines, and is already seeing widespread availability. But it similarly faces technical challenges to meet future PM emissions standards. , This technology has evolved considerably over the past decade and half, and is still undergoing development. Early versions of direct injection employed a stratified injection strategy which included late fuel injection and charge air motion to produce a stoichiometric air/fuel mixture in the vicinity of the spark plug and, thereby, avoid pumping losses from the need to throttle the engine at light load. , The drawback is that direct injection of fuel into the combustion cylinder risks liquid fuel impingement onto the piston and cylinder surfaces and inhomogeneous air fuel mixing; consequentially PM formation is higher than in conventional PFI gasoline engines. , This is difficult to avoid during late injection as the piston approaches the top of its stroke, therefore more recent development of GDI technology has focused on early injection, or so-called homogeneous operation. , …”