Quote:
Originally Posted by Baldturbofreak
Geoff, when you are WOT, the DI system operates like a PFI system.
IT injects fuel during the intake stroke to create a homogenous charge.
The benefit of DI when in this mode is the reduced droplet size from 2200psi, and the latent heat of vaporization occuring within the chamber.
Adding up to 30% fuel upstream will change nothing while in this mode of operation. Nor would 30% of proper AFR be ignitable.
Only in a few light light loading situations(and low rpm too) does the system actually wait until the comrpession stroke to inject fuel.
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"Here’s how DI works. Fuel is injected directly into the combustion chamber instead of the intake port. It’s done at very high pressure; this overcomes high cylinder pressure and improves mixture homogeneity. The injection point is coincident with the spark plug, and you’ll see why in a moment. The important thing to remember is that there are three basic regimes that direct injection gasoline engines operate in: ultra-lean burn mode (for light cruise and idle), Stoichiometric for part throttle, and enrichment mode for full power.
In ultra-lean mode, the fuel is actually injected during the tail end of the compression stroke, not the intake stroke. This allows the fuel to remain in the vicinity of the spark plug, and be ignited in a toroidal pattern. (This is sometimes called a stratified charge, as the fuel is not distributed homogenously throughout the combustion chamber.) The air in the rest of the combustion chamber has little or no fuel, which reduces emissions, and greatly improves fuel economy. Air/fuel ratios can be as high as 65:1.
At part throttle, the air/fuel ratio is increased to 14.7:1 (stoichiometric); fuel is introduced during the normal intake cycle, and the engine behaves more like what we’re accustomed to seeing. At fuel throttle, the fuel mixture is enriched for max power, and to eliminate detonation, and is also a practice we’re used to seeing here in the hot rodding world. "
Cheers!