Porpoise Hork
Well-Known Member
It's not a missed opportunity, just a forced shift in the industry that was placed on them by governments to meet stricter efficiancy and mileage standards.
The fuel delivery happens during the compression stroke on GDI engines just like most 4 stroke desiel engines. This is why all GDI and TGDI engines have a mechanical HPFP (High Pressure Fuel Pump) driven off the intake cam. They need this secondary pump to increase the 35-50psi supplied by the primary electric pump and increase it to 2000psi or more. The system needs these high pressures to properly atomize the fuel and to overcome the rapidly increasing air pressure in the cylinder as the piston reaches TDC. So with this design there is no possible way for fuel to come into contact with the top side of the intake valves.
By moving the fuel delivery directly into the combustion chamber and delivering at the time of compression, engineers were able to significantly improve power and fuel economy over the port injection systems. The trade off was early GDI engines would develop excessive carbon buildup by oil laden blowby gasses from the PCV system mixing with hot exhaust fumes when the EGR system was active. The current generation of GDI and TGDI engines are designed to minimize this buildup by adding factory oil/air separators to the PCV system significantly reducing the oil vapor in the PCV system. Other engine disigns are also now adding dual port injection systems as well as oil/air separation. Dual pot injection systems provide the best of both worlds by utilizing port injection during driving conditions when that delivery method is more efficient than direct injection. Then will switch to the high pressure direct injection system under heavy throttle and higher rpm situations. Engineers have also made updates to how/when the EGR system operates to further minimize the contact time that led to the build up. The end result of these systems along with better quality oils like those used in Europe (who didn't have the issues we did with GDI) is significantly less deposit buildup and less long term drive-ability issues than what was experienced in the early GDI engines.
