Fuel Injection

[Rhonn]

Hello,

I would like which is the difference between direct fuel injection (this used in road cars) than this used in F1 engines. If direct injection enhances fuel combustion in the cylinder, why engineers chose the injection in the air inlet? Yes, the pump pressure is lower and it makes a weight reduction, but I ever ask to my self which are the benefits of this kind if injection.
Could someone tell me where is the key?

Thanks

[koenda]

In the Netherlands they have raced with the Mitsubishi GDI engine. The biggest problem they encountered were: getting enough fuel into the engine, getting it there at the right time and have a good distribution of the fuel in the air.

Normally you can get more fuel by increasing the fuel-pressure, but then the spray might hit the piston or cylinderwall. And this fuel will not burn.

Timing: all of the fuel has to be delivered at about 1/2 of a stroke, for a f1 engine revving at 18000 rpm this means the injectors have 1/1200 second to deliver all of the fuel required. so the injector has to be very fast...
With fuel injection in the inletmanifold the timing is not that important and the spraying can be continuous. The fuel will be mixed when the air is entering the cylinder.

[desmo]

Probably the biggest sigle issue limiting the application of GDI tech in F1 is the time limit on the vapor gas exchange which takes a finite amount of time to occur. It apparently isn't possible to accomplish this in a 300cc cylinder 150 times per second. Preheating fuel which may have been done during the turbo era could concievably help some- at some cost in VE in an NA engine- but not enough for 18krpm. I've heard that F1 FI systems employ what are referred to as ramp and hold injectors which are fast enough to enable two discrete injection pulses per intake stroke. Fuel presentation is critical to F1 BMEPs and airbox resonances and ram effect makes getting good data about this on the test bed nearly impossible.