From: C. E. White on

"EdV" <systmengr(a)hotmail.com> wrote in message
news:2e0036d7-156b-4b0e-9625-11ef7fab6a74(a)i36g2000prf.googlegroups.com...
> This is how I understand GDI (gasoline DIRECT injection), feel free
> to
> correct my mistake
>
> Fuel and air mixture are injected in some kind of pressure tank
> where
> the pressure is increased, by compressing the mixture I suppose. At
> this stage the ratio of the fuel and air is adjusted for optimum
> burn.
>
> This pressure tank sometimes called as a *common rail*? has a nozzle
> that will release the pressurized fuel-air mixture directly into the
> chamber chamber via the intake valves. This high pressure coupled
> with
> optimum ratio allows the engine to run more fuel efficiently and, of
> course, more powerful. The VVTi (toyota) will then adjust the
> opening
> of the valves whether to inject the mixture during the intake stroke
> or slightly delayed.

In the direct engine engines I have researched, there is no tank that
mixes the fuel and air. There is an injector in the combustion chamber
instead of in the intake tract before the intake valves. Air is
admitted into the combustion chamber by the valves. Fuel is injected
directly into the combustion chamber, instead of being mixed with the
air in the intake tract before the intake valves. By injecting the
fuel directly into the combustion chamber, you can create a
"stratified charge." In other words a non-uniform mixture of gasoline
vapor and air. Gasoline is very difficult to ignite if you don't have
the proper air/fuel mixture. By creating a stratified charge, you can
have a proper A/F mixture in the area of the spark plug and a lean
mixture everywhere else. The spark plug can then easily ignite the
proper mixture in the area of the spark plug and this in turn will
burn the leaner mixture elsewhere in the combustion chamber. This
allows an overall leaner mixture to be burned, resulting in higher
efficiency. Chrysler tried this years ago with carbureted engines with
limited success (tried to manipulate the mixture with combustion
chamber and intact tract shape). Honda tried something a little
different with a three valve design in the late 70's (two "regular"
valves and one smaller valve to richen the mixture near the plug).
Neither worked very well. There are a lot of great claims being made
for direct injection engines. However, the direct injected manual
transmission Mazda 5 gets worse EPA gas mileage than the regular old 4
cylinder automatic Toyota RAV4 (which is larger and heavier...).

Ed

From: EdV on
On Jul 18, 11:05 am, "C. E. White" <cewhi...(a)removemindspring.com>
wrote:
There is an injector in the combustion chamber
> instead of in the intake tract before the intake valves. Air is
> admitted into the combustion chamber by the valves. Fuel is injected
> directly into the combustion chamber, instead of being mixed with the
> air in the intake tract before the intake valves.

Ahh, so the intake valves is just for the AIR and the injector for the
FUEL. no pre-mixing involved. The mixing occurs directly inside the
combustion chamber. The fuel is pressurized and not the air like in a
turbo setup. Thanks!
From: Retired VIP on
On Fri, 18 Jul 2008 08:36:01 -0700 (PDT), EdV <systmengr(a)hotmail.com>
wrote:

>On Jul 18, 11:05 am, "C. E. White" <cewhi...(a)removemindspring.com>
>wrote:
> There is an injector in the combustion chamber
>> instead of in the intake tract before the intake valves. Air is
>> admitted into the combustion chamber by the valves. Fuel is injected
>> directly into the combustion chamber, instead of being mixed with the
>> air in the intake tract before the intake valves.
>
>Ahh, so the intake valves is just for the AIR and the injector for the
>FUEL. no pre-mixing involved. The mixing occurs directly inside the
>combustion chamber. The fuel is pressurized and not the air like in a
>turbo setup. Thanks!

Yep, you got it Edv. But the fuel is injected into the combustion
chamber, not the intake manifold.

Of the three types of fuel injection, the direct injection has the
capability of being the most efficient. The air/fuel mixture can be
precisely adjusted for each individual cylinder and for each
individual power stroke.

Throttle body injection is the least precise of the three. It is
basically just a computer controlled carb that uses a injection jet
instead of a metering jet. It's better than a carburetor but not by
much.

Multi-port injection places one injector in the manifold runner to
each cylinder. This is a better scheme that allows more precision but
it is limited on how much the mixture can be leaned out before
pre-ignition occurs.

Direct injection allows placing a rich fuel/air mixture around the
sparkplug and a much leaner mixture in the rest of the cylinder. By
the time the flame front moves out to the rest of the cylinder, the
piston has moved past top dead center and the much faster burn rate of
a lean mixture won't hurt the engine.

I hope this helps and if I've gotten anything wrong in this, I'm sure
someone will correct me.

Jack
From: EdV on
On Jul 18, 2:16 pm, Retired VIP <jackj.extradots....(a)windstream.net>
wrote:
> On Fri, 18 Jul 2008 08:36:01 -0700 (PDT), EdV <systme...(a)hotmail.com>
> wrote:
>
> >On Jul 18, 11:05 am, "C. E. White" <cewhi...(a)removemindspring.com>
> >wrote:
> > There is an injector in the combustion chamber
> >> instead of in the intake tract before the intake valves. Air is
> >> admitted into the combustion chamber by the valves. Fuel is injected
> >> directly into the combustion chamber, instead of being mixed with the
> >> air in the intake tract before the intake valves.
>
> >Ahh, so the intake valves is just for the AIR and the injector for the
> >FUEL. no pre-mixing involved. The mixing occurs directly inside the
> >combustion chamber. The fuel is pressurized and not the air like in a
> >turbo setup. Thanks!
>
> Yep, you got it Edv. But the fuel is injected into the combustion
> chamber, not the intake manifold.
>
> Of the three types of fuel injection, the direct injection has the
> capability of being the most efficient. The air/fuel mixture can be
> precisely adjusted for each individual cylinder and for each
> individual power stroke.
>
> Throttle body injection is the least precise of the three. It is
> basically just a computer controlled carb that uses a injection jet
> instead of a metering jet. It's better than a carburetor but not by
> much.
>
> Multi-port injection places one injector in the manifold runner to
> each cylinder. This is a better scheme that allows more precision but
> it is limited on how much the mixture can be leaned out before
> pre-ignition occurs.
>
> Direct injection allows placing a rich fuel/air mixture around the
> sparkplug and a much leaner mixture in the rest of the cylinder. By
> the time the flame front moves out to the rest of the cylinder, the
> piston has moved past top dead center and the much faster burn rate of
> a lean mixture won't hurt the engine.
>
> I hope this helps and if I've gotten anything wrong in this, I'm sure
> someone will correct me.
>
> Jack

Great! So this means its possible not to have VVTi and Direct
injection at the same time. The timing of the fuel comes from the
nozzle and not from the opening of the valves, although air enters
through the valves, its the fuel which is controlled and not the air.
From: Retired VIP on
On Mon, 21 Jul 2008 06:35:30 -0700 (PDT), EdV <systmengr(a)hotmail.com>
wrote:

>On Jul 18, 2:16 pm, Retired VIP <jackj.extradots....(a)windstream.net>
>wrote:
>> On Fri, 18 Jul 2008 08:36:01 -0700 (PDT), EdV <systme...(a)hotmail.com>
>> wrote:
>>
>> >On Jul 18, 11:05 am, "C. E. White" <cewhi...(a)removemindspring.com>
>> >wrote:
>> > There is an injector in the combustion chamber
>> Direct injection allows placing a rich fuel/air mixture around the
>> sparkplug and a much leaner mixture in the rest of the cylinder. By
>> the time the flame front moves out to the rest of the cylinder, the
>> piston has moved past top dead center and the much faster burn rate of
>> a lean mixture won't hurt the engine.
>>
>> I hope this helps and if I've gotten anything wrong in this, I'm sure
>> someone will correct me.
>>
>> Jack
>
>Great! So this means its possible not to have VVTi and Direct
>injection at the same time. The timing of the fuel comes from the
>nozzle and not from the opening of the valves, although air enters
>through the valves, its the fuel which is controlled and not the air.

No, I think it would still be possible to use variable valve timing
and direct injection at the same time. The amount of fuel is
controlled by the engine computer based on info it gets from the O2
sensor, throttle position, RPM, etc. VVTi would still be a valid way
to increase engine efficiency by controlling the amount of air, that's
really all it controls with multi-port injection also.

Jack
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