Direct injection injector angle & valve cleaning

[gregoron]

[img:left]https://flic.kr/p/wETvRh[/img]

Looking at the picture above of a VW EA888 1.8 liter 3rd generation turbo engine, one can see that the fuel injector angle allows fuel spray to hit the back of the intake valves during the intake cycle. Other pictures of GDI engines that I've seen have the fuel injectors at a steeper angle or even at the top of the cylinder head, which does not allow fuel to spray on the intake valves.

The reason I ask is that some older VW FSI engines had carbon deposit problems on the back of intake valves due to the fact that direct injection does not actually let fuel wash the back of intake valves. Could VW have modified the angle of the newer generation engines to allow some fuel coming from the injectors to spray on the back of valves? It's just my theory and I'm looking to see other's opinions and expertise on this.

 

[Dyusik]

My understanding is that the injectors fire after the valves are closed. If it sparys during the intake stroke that defeats the purpose of direct injection.

 

[gregoron]

Originally Posted By: Dyusik
My understanding is that the injectors fire after the valves are closed. If it sparys during the intake stroke that defeats the purpose of direct injection.


Thanks, I read up on GDI operation in Wikipedia and there are three combustion modes that injectors fire. On light loads, or "ultra lean burn" mode, the injector will fire shortly after the compression cycle when intake valves are closed. On moderate load conditions, the injector will fire during the intake cycle when the intake valves are open. This also applies to full power or heavy loads.

PS. If this is the case, would fuel spray hit the lower back side of the intake valves (not the stem) and clean it off carbon deposits if the angle of the injectors are flat enough, or perpendicular to the valve stems?

 

[Olas]

There's no question that fuel flow over the back of an inlet valve will keep it clean, but the sensible choice is to stop them getting dirty I the first place.

 

[demarpaint]

Originally Posted By: Olas
There's no question that fuel flow over the back of an inlet valve will keep it clean, but the sensible choice is to stop them getting dirty I the first place.


That would be a great choice, how is that accomplished with GDI?

 

[Joe90_guy]

As I see it, there are three bits of clever tech that can improve the efficiency of a petrol engine; GDI, low friction piston rings and low viscosity engine oils. I reckon you can have any two of these things but not all three otherwise you end up in the same pickle that Audi found themselves in a few years back.

 

[KrisZ]

Originally Posted By: demarpaint
That would be a great choice, how is that accomplished with GDI?


VW reportedly redesigned the oil separation unit for the PCV gasses. But the effectiveness of the new design is yet to be proven.

 

[d00df00d]

Interesting!

Are any other manufacturers doing this?

 

[d00df00d]

My impression of the problem in the older engines is that it was because of a combination of:

- Fuel quality
- Oil and OCI choice
- PCV
- ECU tunes

I think newer engines have better tunes, and I've heard at least some have coatings on the intake valves to prevent the gunk from sticking in the first place. Those things, combined with better oil formulations and PCVs, would greatly reduce the problem. With this injector angle thing, I'd imagine the problem would be mild enough that a DI engine could finally be a good long-term ownership prospect.

I wonder if there are any downsides to this configuration. One of the advantages of DI was that you could have a spray pattern that made the AFR different in different parts of the combustion chamber -- richer around the spark plug, leaner toward the cylinder walls. Can't imagine that'd be as easy to do with the injector so far from the spark plug.

 

[Quattro Pete]

Originally Posted By: gregoron
The reason I ask is that some older VW FSI engines had carbon deposit problems on the back of intake valves due to the fact that direct injection does not actually let fuel wash the back of intake valves. Could VW have modified the angle of the newer generation engines to allow some fuel coming from the injectors to spray on the back of valves? It's just my theory and I'm looking to see other's opinions and expertise on this.

Not really sure on that, but what VW actually did on some versions of this engine is introduce a secondary multipoint fuel injection (in addition to direct injection). The primary reason for doing it was to meet the latest EURO emissions standards, but a secondary benefit is that it helps wash off the valves. But AFAIK, North American versions of this engine does not include this secondary MPI.

 

[SteveSRT8]

Extra injector strategy is for part throttle cylinder filling issues. While it had nothing to do with valve deposits it may (should) help.

PCV strategies have not proven effective at the do it yourself level, catch cans seem to have a negligible effect. Perhaps a mfgr designed setup will be more effective?

Frankly, if the spray pattern appears to include the intake valves how is the incoming air not going to reduce the "washing" effect?

 

[demarpaint]

Originally Posted By: KrisZ
Originally Posted By: demarpaint
That would be a great choice, how is that accomplished with GDI?


VW reportedly redesigned the oil separation unit for the PCV gasses. But the effectiveness of the new design is yet to be proven.



Exactly. Give it some time then we'll know for sure just how good it is/isn't.

 

[gregoron]

Good insights. As SteveSRT8 said above, the incoming air from the intake valves would deflect the spray pattern from the injector. But wouldn't the high pressure spray swirling around the cylinder cavity be enough to expose the back side of the valves to some fuel to "clean" it off even for a brief period of time? At least it's better than not being exposed to it if the injectors are right on top and center of the cylinder. In a way, this angle is sort of like a port injection if (and that's a big IF) the fuel spray do come in contact with the valves.

Another thing, if on the 3 GDI burn modes mentioned above, the ultra lean burn mode happens when the engine is in light engine loads such as idling and constant freeway speed. It's during this mode that the intake valves are closed when fuel is injected shortly after compression. That means that the back of the valves are not exposed to fuel spray. That would mean that it's during this mode that carbon has the most chance of building up compared to the other two modes (i.e. moderate and full load) when valves are open and fuel is sprayed during the intake cycle.

So, an Italian Tune Up that allows the engine to go through various acceleration and full load operation would expose the intake valves to some fuel spray, thus minimizing carbon deposits on those valve's back side. Again, just a theory.

 

[Olas]

Originally Posted By: demarpaint
Originally Posted By: Olas
There's no question that fuel flow over the back of an inlet valve will keep it clean, but the sensible choice is to stop them getting dirty I the first place.


That would be a great choice, how is that accomplished with GDI?


From what I've seen on this site in the past Americans don't like to hear the answers (there are two of them)

Wet manifold
Or
No EGR & no PCV.

If you're lucky enough to have both of these the inlet tract will remain spotless forever. One or the other should still see pretty good results, too.
Neither, and things get very dirty very quickly.

 

[demarpaint]

Originally Posted By: Olas
Originally Posted By: demarpaint
Originally Posted By: Olas
There's no question that fuel flow over the back of an inlet valve will keep it clean, but the sensible choice is to stop them getting dirty I the first place.


That would be a great choice, how is that accomplished with GDI?


From what I've seen on this site in the past Americans don't like to hear the answers (there are two of them)

Wet manifold
Or
No EGR & no PCV.

If you're lucky enough to have both of these the inlet tract will remain spotless forever. One or the other should still see pretty good results, too.
Neither, and things get very dirty very quickly.


No EGR and no PCV in my state = illegal unfortunately. What this American wants to see is a legal fix.

 

[Olas]

Originally Posted By: demarpaint
Originally Posted By: Olas
Originally Posted By: demarpaint
Originally Posted By: Olas
There's no question that fuel flow over the back of an inlet valve will keep it clean, but the sensible choice is to stop them getting dirty I the first place.


That would be a great choice, how is that accomplished with GDI?


From what I've seen on this site in the past Americans don't like to hear the answers (there are two of them)

Wet manifold
Or
No EGR & no PCV.

If you're lucky enough to have both of these the inlet tract will remain spotless forever. One or the other should still see pretty good results, too.
Neither, and things get very dirty very quickly.


No EGR and no PCV in my state = illegal unfortunately. What this American wants to see is a legal fix.


You could fit a block off gasket to the egr but leave all the piping in place so it 'looks' correct, or if it's electronic you could map it out but still make it show 'ready'.
A well baffled catch can with a large volume in a cold (relatively) location in the engine bay will catch some goop, or alternatively reroute the PCV hose from the intake tract to the exhaust so the vapours are still being recycled but not gumming up your valves.

My car always had a wet manifold, never had EGR, never had PCV as such only a CCV system with no fresh air inlet and fixed orifice outlet venting into the clean side of the airbox. It's now a road draft tube venting to a low pressure zone under the car.
These factors along with my (currently) using a Mann OE filter keep the inlet tract absolutely spotless as witnessed when I did the inlet mani gasket in April this year.

So yeah, mapping and blanking gaskets and hose re-routing and you'll be golden

 

[demarpaint]

Originally Posted By: Olas

You could fit a block off gasket to the egr but leave all the piping in place so it 'looks' correct, or if it's electronic you could map it out but still make it show 'ready'.
A well baffled catch can with a large volume in a cold (relatively) location in the engine bay will catch some goop, or alternatively reroute the PCV hose from the intake tract to the exhaust so the vapours are still being recycled but not gumming up your valves.

My car always had a wet manifold, never had EGR, never had PCV as such only a CCV system with no fresh air inlet and fixed orifice outlet venting into the clean side of the airbox. It's now a road draft tube venting to a low pressure zone under the car.
These factors along with my (currently) using a Mann OE filter keep the inlet tract absolutely spotless as witnessed when I did the inlet mani gasket in April this year.

So yeah, mapping and blanking gaskets and hose re-routing and you'll be golden

If that fix doesn't trip a CEL I like it!
I really like the idea of a catch can. Or better yet buy something w/o DI and install a catch can.

 

[andyd]

What is a "wet manifold"? I'm not familiar with the term. My BMW's engine just has a breather chucked into the air stream. They also had a coolant loop to take the chill off, but it didn't really help much, compared to its tendency to leak, hence a wet manifold?

 

[SteveSRT8]

Originally Posted By: andyd
What is a "wet manifold"? I'm not familiar with the term. My BMW's engine just has a breather chucked into the air stream. They also had a coolant loop to take the chill off, but it didn't really help much, compared to its tendency to leak, hence a wet manifold?

Andy, you need a carburetor to have a wet manifold. Since everything went fuel injection all the manifolds are optimized for airflow and they don't have to worry about fuel puddling here or there.

Olas, we can't all go back to 50's tech here. We have rules and regs. A road draft tube was on my 55 Desoto but you won't find one on any modern car. We have trucks with extremely high mileage that have spotless intakes and valves, but no DI here yet...

 

[Olas]

Originally Posted By: SteveSRT8
Originally Posted By: andyd
What is a "wet manifold"? I'm not familiar with the term. My BMW's engine just has a breather chucked into the air stream. They also had a coolant loop to take the chill off, but it didn't really help much, compared to its tendency to leak, hence a wet manifold?

Andy, you need a carburetor to have a wet manifold. Since everything went fuel injection all the manifolds are optimized for airflow and they don't have to worry about fuel puddling here or there.

Olas, we can't all go back to 50's tech here. We have rules and regs. A road draft tube was on my 55 Desoto but you won't find one on any modern car. We have trucks with extremely high mileage that have spotless intakes and valves, but no DI here yet...


If you don't want a road draft then use the exhaust to pull vacuum on the crank case - I bet you'll see lower pressure that way than you would using the normal system. And I'm not trying t be confrontational but I really can't believe that you have PCV vapour and egr soot mixing together and still have a clean inlet tract, is there an inverse oiler in there somewhere?