What are the advantages and challenges of gasoline direct injection (GDI)?

GDI injects fuel directly into the combustion chamber at high pressure (50-350 bar) instead of the intake port. Advantages include precise fuel metering, charge cooling for higher compression ratios, stratified charge lean operation possible, and improved efficiency (up to 15%). Challenges include higher particulate emissions (requiring particulate filters), injector deposit formation, potential intake valve carbon buildup (no fuel washing), and higher fuel system cost. Modern port+direct injection systems address some drawbacks.