[Diy_efi] Re: GDI and why

[Phil Lamovie]

Hi All,

> I thought the concept was rather like a diesel.  Relatively high
pressure,
> fuel introduced as near the time of ignition as possible to reduce
the
> opportunity to detonate.  I would expect that time to be long after
the
> intake valve has closed.  Am I not understanding something about
GDI?

The purpose of GDI is to achieve things that cannot be accomplished by

indirect injection.

There is no factory system that uses less than two discrete injection
events
per compression. The most interesting use 4.

A fuel pulse equal to 70  or 80% of total required is applied after
the intake
valve is closed. This amount of fuel would in some engines reach an
A/F
ratio of 25:1. Clearly a well mixed but incombustible mixture.

Just before ignition the 2nd ( or 3rd or 4th) injection is used to
create a
rich zone near the plug. This rich zone fires easily and is used as an

ignition source for the ultralean 25:1.

This is the simplest strategy and is known as stratified charge
injection.

Good news is it has 20 to 30 % fuel saving and has better peak power
to boot.

Bad news is that it complicates things in the ECU area with dozens of
extra algorithms and subsequent calculation.

The "really trick" systems are stuck waiting for 48 volt vehicles in
about
18 months time. This will take the injection pressures to new and
dizzying heights.

There is a great deal of info available from the SAE if you have the
cash
and the Patent office in GIF form if you don't.

HTH

Phil


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