RI A6

If valve deposit formation occurs on the back side of the valve and the valve stems, how will gasoline detergents help, if they are injected directly into the cylinder, without being sprayed and moved across the valve stem, as they are in manifold injection?

There is some research on direct injection engines which seems to indicate that valve deposits are due to burnt volatile oil components, and not fuel. Fuel varnish clogs injectors, but does not seem to make it to the back side of the valves. If this is true, then valve deposits are very sensitive to oil formulation, and not as sensitive to fuel detergent additives.

daveak05

I don't know, you tell me. However, if you're suggesting that the valves on an FSI engine will remain in pristine condition, not gonna happen. The air around there may be free of fuel, but not combustion byproducts.

How would you suggest getting rid of valve deposits on an FSI engine, whether fuel or oil...or carbon? Non FSI engines are just as susceptible to the other 2, by the way.

daveak05

What do you think it's all about? If you're saying fuel can't get on valves thru FSI, then what in hell is VAG issuing fuel deposit warnings for on their FSI engines?

Vijay

Let's just hope there is not some critical design flaw and all our engines will fail at 30,000 miles or something like that

gtikid98

is there some sort of overlap durring the intake stroke that would cause the fuel to get to the backside of the valve?
another question...could the emission systems have something to do with the deposits? doesnt the blow by get recirculated and ran back through the intake manifold? without the fuel to help clean wouldnt it cause excessive build up of materials? just wondering.

RI A6

But it will never be the volume the is seen with manifold injection. There can't be. That is the point of DI. There is actually quite a developing body of research on just this problem in all DI engines. It seems that everyone thought that the deposits were due to left behind gunk in the fuel. It turns out that it many be burnt oil after all. That's why I think this dilution problem is a big deal. Once the oil degrades, it is then capable of forming deposits.

You can see clearly from the following discussion that the injector positioning has been optimized. (look who's V6 engine is in the side bar) since the injector is between the intake valve, it may be that some fuel does get on the valves, but the design is optimized to evenly distribute the fuel in the combustion chamber.

Read the 2nd to last paragraph carefully.<ul><li><a href="http://www.avl.com/wo/webobsession.servlet.go/encoded/YXBwPWJjbXMmcGFnZT12aWV3Jm5vZGVpZD00MDAwNTQwNDE_3D .html">Discussion of DI design concepts</a></li></ul>

RI A6

But at the same time there is intake flow, which should keep most contained in the cylinder. There won't be nearly the volume of fuel that flows by the intake valve in manifold injection.

McQueen993

Don't worry too much...FSI technology has been around for a while

daveak05

carbon and oil deposits on valves? Not that it's unique to RS4, but carbon would have me concerned with an already high 12.5:1 compression ratio.

Anyway, Audi is talking about fuel deposits, so there is something going on which makes that an issue.

PetrolDave

- if it's in stratified (economy) mode it injects while the cylinder is on the compression stroke and the valves are closed.

- if it's in stoichiometric mode it injects during the induction stroke when the inlet valve is open.