Direct injection carbon buildup on intake valves could be thing of the past

Considering the real problem is emissions components, they do not go into enough detail about what design improvements have been made to EGR, PCV, and other vent systems. Other than filtration, I can't figure out how any design improvements would nullify all of that vaporized oil and soot which is cycled back through those systems. Manipulating injector pulse width, valve timing, spark advance, etc. can only do so much to indirectly manage these byproducts.
I would guess that the problem has been reduced by these means, but certainly not eliminated.
 
Considering the real problem is emissions components, they do not go into enough detail about what design improvements have been made to EGR, PCV, and other vent systems. Other than filtration, I can't figure out how any design improvements would nullify all of that vaporized oil and soot which is cycled back through those systems. Manipulating injector pulse width, valve timing, spark advance, etc. can only do so much to indirectly manage these byproducts.
I would guess that the problem has been reduced by these means, but certainly not eliminated.
The video is purely about reducing carbon build-up on the intake valves. Not about reducing carbon or soot (or emissions) overall.

It's actually a bit simplistic, since valve overlap (especially with turbo engines) is often used for increased power and efficiency. The video does not mention all the tradeoffs with its approach of not injecting/firing until the intake valve is closed. In fact it's a bit "duh" statement! :)
 
It is simplistic; if the hydrocarbon does not get sprayed on the back of the intake valve than the soot from those emissions components won't combine with the fuel and cause the carbon formation on the back of the valve. This must be why the GM GDI 3.6 hasn't had problems with carbon buildup on the back of the intake valves.
 
I read that the Mazda fixed this by designing the intake valve so that it would stay hotter. This keeps the oil/fumes from the crankcase from depositing on the back of the valve and valve stem...
 
It is simplistic; if the hydrocarbon does not get sprayed on the back of the intake valve than the soot from those emissions components won't combine with the fuel and cause the carbon formation on the back of the valve. This must be why the GM GDI 3.6 hasn't had problems with carbon buildup on the back of the intake valves.
Actually, one of the reasons DI engines have the issue is BECAUSE fuel doesn't wash the backs of the valves clean (as happens with port injection).

And I meant simplistic (not simple) because any engine manufacturer could easily do this. They don't necessarily though, because there are other good design reasons for NOT doing it!
 
Actually, one of the reasons DI engines have the issue is BECAUSE fuel doesn't wash the backs of the valves clean (as happens with port injection).

I agree with you. Without the fuel washing the back of the intake valve with PFI the carbon would build up on the back of the intake valve. In the video though they state that they solved the problem of the carbon buildup on GDI engines in part because the fuel is injected after the intake valve completely closes. In the engines where there was carbon buildup (early adopters of GDI) the injector sprayed the fuel while the intake valve was still open suggesting that some of the fuel was sticking to the intake valve because of that. This is where I guess it gets confusing.

And I meant simplistic (not simple) because any engine manufacturer could easily do this. They don't necessarily though, because there are other good design reasons for NOT doing it!

I'm curious to know what those good design reasons are?
 
I'm curious to know what those good design reasons are?
Engine and combustion design are extremely complex. Depending on the circumstances (load/no load, revs, etc) it can be better to 'fire' the charge while there is still inrush from the open intake valve. This (for example) can increase swirl in the combustion chamber and promote a better burn with less knock (and so leaner fuel mix). In fact many engines have valve overlap that means BOTH the intake and the exhaust valves are open at the same time for better scavenging.

This is way more complicated than a simple forum post can explain (and certainly more than a simple couple-of-minute youtube video)!

The other point here is that the carbon buildup can be, in fact most likely is, from engine oil being carbonized in the heat, NOT fuel which would tend to burn off. That's why it builds up without the port-injected fuel flow being present to wash it off. The other post about some manufacturers raising the valve temps to burn it off is, frankly, hogwash. It's that heat that causes the problem! Designers do everything they can to COOL the valves to prevent seat burning - that's why many modern engines have sodium-filled valves - for the cooling properties.
 
Engine and combustion design are extremely complex. Depending on the circumstances (load/no load, revs, etc) it can be better to 'fire' the charge while there is still inrush from the open intake valve. This (for example) can increase swirl in the combustion chamber and promote a better burn with less knock (and so leaner fuel mix). In fact many engines have valve overlap that means BOTH the intake and the exhaust valves are open at the same time for better scavenging.

This is way more complicated than a simple forum post can explain (and certainly more than a simple couple-of-minute youtube video)!

The other point here is that the carbon buildup can be, in fact most likely is, from engine oil being carbonized in the heat, NOT fuel which would tend to burn off. That's why it builds up without the port-injected fuel flow being present to wash it off. The other post about some manufacturers raising the valve temps to burn it off is, frankly, hogwash. It's that heat that causes the problem! Designers do everything they can to COOL the valves to prevent seat burning - that's why many modern engines have sodium-filled valves - for the cooling properties.

Moto IQ quoting MAZDA is the source of the "Hogwash" regarding keeping intake valves hot to burn off the oil. See the following link and copy us on your message to them correcting their technical article:
http://www.motoiq.com/magazine_arti...l-introducing-mazdas-skyactiv-technology.aspx
 
Engine and combustion design are extremely complex. Depending on the circumstances (load/no load, revs, etc) it can be better to 'fire' the charge while there is still inrush from the open intake valve. This (for example) can increase swirl in the combustion chamber and promote a better burn with less knock (and so leaner fuel mix). In fact many engines have valve overlap that means BOTH the intake and the exhaust valves are open at the same time for better scavenging.

This is way more complicated than a simple forum post can explain (and certainly more than a simple couple-of-minute youtube video)!

The other point here is that the carbon buildup can be, in fact most likely is, from engine oil being carbonized in the heat, NOT fuel which would tend to burn off. That's why it builds up without the port-injected fuel flow being present to wash it off. The other post about some manufacturers raising the valve temps to burn it off is, frankly, hogwash. It's that heat that causes the problem! Designers do everything they can to COOL the valves to prevent seat burning - that's why many modern engines have sodium-filled valves - for the cooling properties.

I know sodium filled valves have been used for exhaust valves but intake valves too? Back in my days of engine building this is how it was. I'm just not as up to date with engine designs such a Mazda's although their basic designs haven't actually changed much.

Just curious but what is your background if you don't mind sharing. You obviously know a few things and I respect your opinion.

There seems to be an assumption out there that if you have GDI that your engine will automatically suffer from carbon buildup on the intake valves and eventually reduce the engines performance. To be honest I can't find any evidence that current GDI designers of any make still suffer this fate. Some probably still do to some lesser degree but I find it hard to believe that manufacturers would continue to use GDI and not solve the problem that early adopters had of this technology.
 
I am new to the forum and interested in buying either 2013 Mazda 3 or 2014 mazda 6 with the skyactiv engine, does any one have the carbon build up issue on either model?

also since the skyactiv engine is out for only two years, is it reliable or there are any topics talked about it?

Thanks,
 
I just sold a 70,000 mile 2007 CX7 DI turbo and the engine has never had a problem with intake valves loading up. The day I sold it, it ran from idle to the red line without any hesitation and never had a CEL, except, during the first 200 miles (HP fuel pump). I tried to pick an oil with a lower than most evaporation value (NOACK), and ended up with 5w30 PP and used 6K oil changes. Several UOAs demonstrated that this was a good OCI and could have gone out to the 7,500 max quite easley but, I do my own so 6 K is a nice number. My new CX5 will probably get the recomended (in the US & CAN) 0w20 or maybe the 5w30 which is the recomended oil outside of CRAF :)). ED
 
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I just sold a 70,000 mile 2007 CX7 DI turbo and the engine has never had a problem with intake valves loading up. The day I sold it, it ran from idle to the red line without any hesitation and never had a CEL, except, during the first 200 miles (HP fuel pump). I tried to pick an oil with a lower than most evaporation value (NOACK), and ended up with 5w30 PP and used 6K oil changes. Several UOAs demonstrated that this was a good OCI and could have gone out to the 7,500 max quite easley but, I do my own so 6 K is a nice number. My new CX5 will probably get the recomended (in the US & CAN) 0w20 or maybe the 5w30 which is the recomended oil outside of CRAF :)). ED

No offense, but it is/was a big issue on the Mazda DISI engine. Just because you didn't notice the effects doesn't mean there wouldn't have been quite a mess if you peeled the IM/head off of that engine.

As for the S-G engines, there doesn't appear to be any clear information just yet. As posted in this thread, it appears Mazda may have implemented some clever engineering to assist in deterring carbon build-up.
What it will likely take is one or more members tearing into their engines to take a look. One day, after mine accumulates some more miles, I think out of curiosity, I might attempt to yank the IM off of the car to take a peek.

S-G engine reliability overall, however, looks to be above average. That much is clear.
 
I agree IHeart. However; Doom sayers seem to have over stated the problem to the point that people were expecting DI engines would be worthless in a short time, which is obviously not true. The engineering work at Mazda suggests they have found the answer by keeping the intake valves hotter. Ed
 
I agree IHeart. However; Doom sayers seem to have over stated the problem to the point that people were expecting DI engines would be worthless in a short time, which is obviously not true. The engineering work at Mazda suggests they have found the answer by keeping the intake valves hotter. Ed

Too early to tell. we need to see engines with 30K or so on them to see. One might see a CEL with a misfire if it happens. It's happened in the Mazda3's.

https://www.facebook.com/Mazda/posts/10152641383900363
 
By now we have many CX-5 owners w/Skyactiv engines at over 30K miles. Any issues related to CEL / carbon build up?
 
Bump thread.

Anyone with 30k plus miles report any effects due to DI carbon buildup?
 
MY 2007 DI CX7 was running like new when I sold it at ~ 80,000 miles and now Mazda claims they have solved the issue with later engines. Ed
 
50,000 on mine and it is still the same. Maybe I'll take out the gtech at some point and retest to see if it's still 7.5 seconds to 60.
 
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