Direct port ignition for SI engine

[TuscanR]

Could anyone please explain to me the principles of Direct Port injection for an SI (spark ignition) engine, I have seen and understand the principles for it on a CI engine, But I recently read an interview with Alan Mcnish and he was talking about the noticeable power difference he felt now the Audi had Direct Port injection. Have the priniples stayed the same if so how do you avoid detination?, is there a swirl pot or is it mixed somewhere down the line to get a stoichiometric ( hope I spelt that right ) ratio ( I know not 14.7:1 something like 7or8:1 ) and then compressed and then spat out by the injector nozzle or is this a closley guarded secret. Could some one please help as I have been trying to figure it out on my own without much success
:confused:
And I know that we have more than one or two race engineers on here that can hopefully put me out of my misery

Thanks for your time
Paul

[graham bahr]

yes Vw call it an FSI engine.

in a nutshell it does away with the need of throttles to control the power output it does it like a diesel by controlling the fuel intake rather than air, which reduces pumping losses (it wastes energy creating the vacuum), the problem with controlling the power output in this manor creates very lean mixtures and high levels of NOX. it has to be said in production terms the goal is ecconomy not power its just lean burn technology brought into this century, the main problem with a lean burn is it produces NOX or nitrogen oxides which couldn't be delt with back in the 80's when lean burn engines started appearing, now days they have NOX cats, which basically just store the NOX up, and then with a retarted spark set fire to it when the cats full.

this engine has two modes of operation normal and stratified,

in stratisfied mode a plate blocks off 50% of the inlet port to raise the airspeed through it and direct it accross the back of the valve instead of all the way round it, it then opens the throttle wide open and controls the power by the amount of fuel added, the piston crown is a very special shape to control the movement of the air mixture around the cylinder, this is used in conjustion with the part closed of intake port, what this all contrives to do is arrange things so that when the injector injects fuel directly into the cylinder there is a small area of mixture at a chemically correct 14.1 around the spark plug which burns as per normal, however the the rest of the cylinder is filled with basically fresh air! if you check whats coming out the cylinder its very very lean but whats burnt is normal. the engine only operates in this mode at small throttle openings and when feed 97+ octane fuel.

the rest of the time the engine works as per any other petrol engine, the only difference is the injector location.
doing away with the normal pumping losses will increase power output upto the point at which the half blocked off intake runs out of airflow.

[TuscanR]

Ive just looked at the title of this post and realised that I have made a monumental mistake in calling it ignition and not injection WHAT A DOUGHNUT!

Thanks for the reply Graham, I take that the design of the piston surface (crown) now does away with the need for a swirl pot? Are there any other engines apart from the Audi from the racing world that have direct port INJECTION and that are not to closely guarded a secret. I would love to be able to view a cut-away Diagram of how the thing is constructed, like the ones I used to get when I was a college all those years ago.