Volkswagen going on about FSI

All petrol engines have their air supply controlled via the throttle valve [1] and the fuel is injected in reponse to the amount of air to get the perfect burn at all speeds and loads.

What you have with the FSI, and indeed Mitsis GDI (4 yrs ago this was in production!) is direct fuel injection into the cylinder, instead of into the inlet manifold. i.e. down stream of the inlet valves instead of conventionally upstream.

With this, you can get much more complete fuel mixing with the air, as you can design the combustion chamber to create lots of swirl, as opposed to having to do it in the inlet manifold.

You can also do nice things such as shut off one of the inlet valves at cirtain speeds, and alter the point when fuel is injected into the chamber. For instance, at low revs and low load you'd inject the fuel sooner and over a onger period to counter poor gas flow and poor cylinder filling whilst the valve is open, whereas at high revs and load you may be able to dump it in more quickly.

In essence its done to reduce emissions primarily, and aid MPG, rather than actually give more HP.

tim..

PS.

[1] = apart from BMW's valve tronic which has no (conventional) throttle valve for controlling air flow[2] [2] - there is a throttle valve in the inlet controlled by the computer for 2 uses- shutting to create brake servo vacuum and when the valvetronic malarky goes wrong to stop the engine revving til it blows to bits.

Tim..

That GDI engine was on sale at least as far back as 1997

-- James

It has direct fuel injection (rather like a diesel), the fuel is injected directly into the cylinders rather than into the inlet manifold / throttle body.

Alfa Romeo (JTD)/ Fiat, Ford, Peugeot / Citroen (HPI) and Mitsubishi (GDI) all have petrol direct injection engines, others have too but offhand those are all that I can name.

-- James

Where is the fuel injected? The head or in the side of the cylinder wall?

AFAIUI, the mercedes benz engines in the second world war had injectors in beside the spark plug, top of the combustion chamber. The idea was then to light the tail of the fuel and have the flame front spread to wherever it had penetrated.

I'd wondered what the contigency was for failure...

and apart from some odd problems with noisy cams / valvegear (meaning many needed 60-90k mile rebuilds) the engines were ace. My S40 GDI averaged 39mpg over its time with me, often cracking mid forties on 80-90mph runs. Would power to good speeds too and was never very thirsty.

Alfa JTS only has a low RPM limit for the "lean" mode though - IIRC the mitsy engine ran in lean mode to about 3500rpm and the alfa is about 2200 rpm

Head and shaped piston crown.

-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

Wrong way round! At low speed fuel is injected into the cylinder near the end of the compression stroke. It only needs a little bit and at very high pressure it is atomised really well.

Due to large volume of fuel required injection starts during inlet of air.

It gains on better and more complete combustion due to near 100% vapourisation = more power for the same fuel. Cleaner too as normal port injection only vaporises 80% of the fuel every drop of the remaining liquid fuel is the nucleus of a little particle of soot.

This shows high speed and power inlet stroke injection and stratified lean burn light load (upto 120 km/h cruise) compession stroke injection.

may like to start at page 1. more of the same on the white arrow on a red backgound >

Because the Europeans (including us in the UK) are crap drivers who demand manual gear boxes but won't change down to accelerate (scared of Max Power?) they had to introduce a special 2 phase injection mode to supply the fuel required when some idiot just cloggs at low rpm.

FSI doesn't have the vertical ports, it uses a throttle butterfly valve near the port to conrol and direct the air flow into the required swirl pattern. ran FSI in high power mode at LeMans.

-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

The Mitsubishi ones have a specially shaped area on the piston crown which the fuel is sprayed at, I presume it has to evapourate off this surface. Evapourating the fuel in the cylinder charge cools the engine meaning it can have higher compression / later ignition etc.

I had heard of a 2 stroke motorbike engine doing the same sort of thing but being a 2 stroke it tended to end up with much residue stuck to the piston crown.

-- James

Supposedly part of the reason that they won was that the engine was more fuel economical than the competitors were so they didn't have to carry as much fuel or have stop for fuel as often

-- James

I should learn to spell evaporate properly.

-- James