BenK wrote:
Do tell...please teach me how Ford and the others now do so without
having to have a port injector?
oughtsix wrote:
snip....
The reason for Port injection over direct injection isn't because the direct injectors are not able to inject enough gasoline. The reason for the port injection is to achieve a stratified mixture of gasoline/air in the combustion chamber. It is difficult to achieve a good mix of gasoline and air with direct injection. By injecting gasoline in the intake port the gasoline has much more time to mix with the air and the air movement itself helps with the mixing.
If you do some reading on direct injection a very common theme is problems getting a stratified mixture. Much research money has been spent on injector design, injector spray pattern, injector timing, multiple injection events, chamber design and piston head design to achieve a good mixture of gas and air in the cylinder at ignition time in a direct injected engine. At full power levels is when it is most important to have a full cylinder of well mixed gas and air. Port injection was used to augment the mixing of gas and air in the earlier direct injection engines as an easy way to over come these mixing issues.
Direct injection allows lean burn mode where the mixture is greater than stoich (14.7:1 air to fuel). So in the early direct injection engines direct injection was used for lean burn to greatly increase mpg. Then when full power was needed the port injection was used to give the best mixing of air and fuel.
Fuel is metered in fuel injections systems by how long the fuel injector is held open. If the problem in early direct injection engines was simply a matter of not being able to get enough fuel in the cylinder this could have been easily fixed by holding the injector open longer and just using a bit bigger injector orifice. But the actual problem was mixing the fuel with the air and this is why port injection was used to augment the direct injection.
There are hundreds of papers available on the internet discussing the internal flow patterns of how gasoline mixes with air under compression inside a cylinder with direct injection and how to optimize the geometries to optimize the mixing of air and fuel. In other words Ford must be doing something right with their EcoBoost engines since they no longer need the port injection. I am sure it is the result of many trillions of computer calculations in computer simulations of fuel and air mixing in a combustion chamber when the fuel is directly injected into the cylinder. This excites me to see advances in direct injection technology.
