Direct Injection's Achilles Heel

[1BMW4fun]

Apparently, Lexus has a patent on a dual injector system – where most fuel is sprayed directly into the combustion chamber, while a little is sprayed into the valve to “wash” it clean: “D-4S Direct Fuel Injection” Featuring two injectors per cylinder, D-4S (Direct-injection 4-stroke Superior version) is the latest evolution of Lexus’ direct fuel injection technology. One injector is installed in the combustion chamber, a second in the intake port. In this way the engine combines the strengths of both direct and port injection, ensuring optimum engine performance and efficiency. Torque is improved, while fuel consumption and emissions are reduced.

[ruff]

Originally Posted by swamp2

Seems to be a case of a Achilles Heel to Audi's RS4 direct injection. Much, much more evidence would be required to call this an Achilles Heel in general.

Swamp,

I am surprised at your lack of knowledge on this issue. There is mounting evidence of carbon build up in numerous DFI engine configurations. I listed just the one source because the 4.2 litre is probably the closest match to the S65.

[JAJ]

Originally Posted by ruff

Swamp,

I am surprised at your lack of knowledge on this issue. There is mounting evidence of carbon build up in numerous DFI engine configurations. I listed just the one source because the 4.2 litre is probably the closest match to the S65.

I don't understand this comment at all. The S65 doesn't have DI.

There are two separate issues being discussed. The high sulfur issue keeps the manufacturers from implementing the high-fuel-efficiency lean-burn mode on the engine. It's used in Europe but not North America because of the sulfur issue.

The second issue is that combustion byproducts in the crankcase - "blow-by" gas - is recycled into the intake and forms deposits on the valves. Better fuel and better engine oil can reduce it, but it's a design problem that plagues real-world DI engines. The Lexus system noted above washes the contamination off the valves and they stay clean. But, what's the point? You can't run lean-burn so there's no mileage benefit and now you have twice as many injectors.

[foosh]

Excellent thread, from which I've learned a great deal!

After sifting through the info here, and in the Audi Forum, I'm awfully glad I let my RS4 go at 15K miles, in favor of the E93. The RS4 powerplant was certainly a wonderful engine, which spooled up much faster than the S65, and I only had one misfire and associated code during that period. But, I never had the opportunity to look inside the intake to see how much trouble was brewing for the future.

[Neil McRae]

Originally Posted by footie

The sulfur amount in fuel has been a long running issue in the UK, I remember an article run in one of the car mags stating that BMW advised it's owners not to use supermarket fuel. I can't say if this is still the case but it appears to be an on-going concern for BMW.

It's interesting that they see fit to offer it with turbo engines but not N/A engines. All I can say is that I have owned four DFI engined cars, 2 turboed and 2 N/A ones and none have caused any problems, I have always used super unleaded fuel either BP or Texaco. Maybe a quality brand of fuel is the most important thing.

footie, I thought most of the fuel in the UK comes from the same few terminals though irrespective of brand? The only difference being the RON.

[footie]

Originally Posted by Neil McRae

footie, I thought most of the fuel in the UK comes from the same few terminals though irrespective of brand? The only difference being the RON.

This is true but each brand name has their own additives that they add when filling the fuel tanker truck before taking it to the petrol station. In Northern Ireland there in the big BP terminal which most other companies draw out of, but none of them get to use BP's additive. The same is true for Texaco, Shell, Esso, etc.

All fuels are basically the same, this is true for the USA and it's only the additives that make them different.

[Radiation Joe]

Originally Posted by footie

This is true but each brand name has their own additives that they add when filling the fuel tanker truck before taking it to the petrol station. In Northern Ireland there in the big BP terminal which most other companies draw out of, but none of them get to use BP's additive. The same is true for Texaco, Shell, Esso, etc.

All fuels are basically the same, this is true for the USA and it's only the additives that make them different.

Why does this myth continue to be presented as fact?

Stations that purchase their base stocks from the same refinery get the same gasoline prior to additives. HOWEVER, there isn't just one refinery on the planet, nor in the British Isles, nor in California. I believe there are at least three refineries in just the SF bay area. Each uses it own proprietary processes to refine gasoline. I didn't even mention the variable quantities of alcohol added (up to 10%).

So depending which station you purchase your gasoline from, you CAN get very different products.

[foosh]

Originally Posted by Radiation Joe

Why does this myth continue to be presented as fact?

Stations that purchase their base stocks from the same refinery get the same gasoline prior to additives. HOWEVER, there isn't just one refinery on the planet, nor in the British Isles, nor in California. I believe there are at least three refineries in just the SF bay area. Each uses it own proprietary processes to refine gasoline. I didn't even mention the variable quantities of alcohol added (up to 10%).

So depending which station you purchase your gasoline from, you CAN get very different products.

Perhaps partially true, although it's doubtful that those refining processes differ significantly from the standpoint of removing sulfur content. All of their processes yield a product, which is close to predetermined standards.

However, from a practical standpoint, you're getting the same product whether it is BP, Shell, Exxon/Mobil, or whatever. Yes, each brand has its own proprietary additive packages added to each tanker load.

If there are multiple refinery choices hooked to the pipelines supplying your area, that gasoline from the different refineries is all passed through the same set of supply pipelines, and is mixed in storage tanks where it waits for pickup by the distributors. You'd then be getting a mixture of multiple refineries or a product of a single refinery.

Unless you move around a lot, you're probably getting the majority of your fuel from retailers relatively close to where you live. That means your gasoline is likely coming a single distribution center, serviced by one or more refineries, and if it is multiple, it is all mixed together.

[mapezzul]

Originally Posted by JAJ

I don't understand this comment at all. The S65 doesn't have DI.

There are two separate issues being discussed. The high sulfur issue keeps the manufacturers from implementing the high-fuel-efficiency lean-burn mode on the engine. It's used in Europe but not North America because of the sulfur issue.

The second issue is that combustion byproducts in the crankcase - "blow-by" gas - is recycled into the intake and forms deposits on the valves. Better fuel and better engine oil can reduce it, but it's a design problem that plagues real-world DI engines. The Lexus system noted above washes the contamination off the valves and they stay clean. But, what's the point? You can't run lean-burn so there's no mileage benefit and now you have twice as many injectors.

I don't think he was saying the S65 has DI more so that its closest Audi model in the RS4 does.

Your analysis of why BMW has not implemented DI in NA engines is spot on, they do not see the point in the US since there is no chance of lean burn. The N53 in the EU is a lean burn mode engine and has been successful.

The reason for the DI in the FI engines escapes my mind at the moment...

[footie]

Originally Posted by Radiation Joe

Why does this myth continue to be presented as fact?

Stations that purchase their base stocks from the same refinery get the same gasoline prior to additives. HOWEVER, there isn't just one refinery on the planet, nor in the British Isles, nor in California. I believe there are at least three refineries in just the SF bay area. Each uses it own proprietary processes to refine gasoline. I didn't even mention the variable quantities of alcohol added (up to 10%).

So depending which station you purchase your gasoline from, you CAN get very different products.

All I know for sure is that in the UK all unleaded fuels have to meet a basic standard prior to additives, I assume that meet all brands of unleaded fuel are basically the same and only differ when the additive is added. If this opinion is wrong then hopefully someone can answer where each brand differ.

I do know for certain that in Northern Ireland the majority of brands over here draw out of the BP depot in Belfast, so this is why I have my opinion.

[GT3 Tim]

Originally Posted by foosh

However, from a practical standpoint, you're getting the same product whether it is BP, Shell, Exxon/Mobil, or whatever. Yes, each brand has its own proprietary additive packages added to each tanker load.

Yep. I work closely with the guys that regulate CA fuels. The key differences are the additives. Most other attributes are fairly tightly regulated. The fuels tend to be "very close" to one another. Also, many companies "share" bulk tanks. The tankers fill up at them, add the specific additives for thier given destination, and then go drop it off.

So, there aint a hell of a lot of difference in CA fuels, minus the additives.

[swamp2]

Originally Posted by ruff

Swamp,

I am surprised at your lack of knowledge on this issue. There is mounting evidence of carbon build up in numerous DFI engine configurations. I listed just the one source because the 4.2 litre is probably the closest match to the S65.

http://www.m3post.com/forums/showpos...2&postcount=13

My ignorance should not be all that surprising. I don't follow every topic on evey car despite being a keen advocate of the benefits of DI.

[foosh]

Originally Posted by footie

All I know for sure is that in the UK all unleaded fuels have to meet a basic standard prior to additives, I assume that meet all brands of unleaded fuel are basically the same and only differ when the additive is added. If this opinion is wrong then hopefully someone can answer where each brand differ.

I do know for certain that in Northern Ireland the majority of brands over here draw out of the BP depot in Belfast, so this is why I have my opinion.

You are absolutely correct. As I said above, even if multiple refineries are producing a slightly different product, the differences are miniscule because of the standards. Whatever slight differences that do exist between refineries are rendered moot because product is piped through the same lines and ends up being mixed in fuel tank farms/distribution centers before being picked up for delivery to retailers.

[gr8000]

OK, I got a series of silly qns. Whoever can spare some time to explain will be most appreciated:

1. Why and how can carbon residue form on the part of the valves (all valves I assume) which is outside of the combustion chamber? Is it due to leakages through the valve seats?
2. How come the cylinder head on the inside of the combustion chamber is clean?
3. Why is this an issue only with DI? If fuel (with additives) helps the case of non-DI because the fuel / air mixture is sprayed close to / on the intake valves and cleans them, then what happens in the case of the exhaust valves? Carbon residue should build there in DI and non-DI engines, or?

Probably I have a simple issue awfully mixed up in my head...

[consolidated]

Originally Posted by gr8000

OK, I got a series of silly qns. Whoever can spare some time to explain will be most appreciated:

1. Why and how can carbon residue form on the part of the valves (all valves I assume) which is outside of the combustion chamber? Is it due to leakages through the valve seats?
2. How come the cylinder head on the inside of the combustion chamber is clean?
3. Why is this an issue only with DI? If fuel (with additives) helps the case of non-DI because the fuel / air mixture is sprayed close to / on the intake valves and cleans them, then what happens in the case of the exhaust valves? Carbon residue should build there in DI and non-DI engines, or?

Probably I have a simple issue awfully mixed up in my head...

Believe it's oil and not fuel residue, the air/oil separator is allowing for some oil to return back into the intake tract which is normal in my experience, with DI there's now no fuel air mixture to clean it off.

[aus]

Originally Posted by mapezzul

The reason for the DI in the FI engines escapes my mind at the moment...

DI in a forced induction setting cools the gases in they cylinder and allows higher compression ratio's and boost.

Originally Posted by gr8000

OK, I got a series of silly qns. Whoever can spare some time to explain will be most appreciated:

1. Why and how can carbon residue form on the part of the valves (all valves I assume) which is outside of the combustion chamber? Is it due to leakages through the valve seats?
2. How come the cylinder head on the inside of the combustion chamber is clean?
3. Why is this an issue only with DI? If fuel (with additives) helps the case of non-DI because the fuel / air mixture is sprayed close to / on the intake valves and cleans them, then what happens in the case of the exhaust valves? Carbon residue should build there in DI and non-DI engines, or?

Probably I have a simple issue awfully mixed up in my head...

The oil comes from around the cylinder with each intake stroke since there is suction. The valves are open during this time to allow the air/fuel into the cylinder. With port fuel injection, the fuel is sprayed just before the valves and the fuel will clean off the valves as it flows around them. With DI, the fule is injected directly into the cylinder and only air is passed through the valves.

[aus]

Originally Posted by GT3 Tim

I recall my Dad telling me he had to "blow out the carbon once in a while" way back when I was a lil pup. lol. I guess he was right!

I think he was talking about a carburetor engine. A lot of the old school V8 guys will rev the engine right before turning it off.

I'm not sure how flogging a DI engine would prevent this build up?

Originally Posted by Dascamel

Wonder how the N54 valves look after 50k miles while running a tune.

It's been shown on E90 boards already.

[gr8000]

Originally Posted by aus

The oil comes from around the cylinder with each intake stroke since there is suction. The valves are open during this time to allow the air/fuel into the cylinder. With port fuel injection, the fuel is sprayed just before the valves and the fuel will clean off the valves as it flows around them. With DI, the fule is injected directly into the cylinder and only air is passed through the valves.

Got ya - thanks.

I read above about this oil/air seperator which helps the case of DI. Where does this fit in? If air with some (escaping) oil is sucked in each stroke from the intake port, then I guess oil is sucked from the top of the cylinder head through the intake valves causing the residue build up on the valves. So where is this oil/air seperator fitted to avoid / minimise oil running through the intake valves? I guess it needs to be dumping the clean air as close as possible (i.e. just before) the intake valves, but then I wonder how is this possible without disturbing the smooth air flow...

[JAJ]

Originally Posted by gr8000

Got ya - thanks.

I read above about this oil/air seperator which helps the case of DI. Where does this fit in? If air with some (escaping) oil is sucked in each stroke from the intake port, then I guess oil is sucked from the top of the cylinder head through the intake valves causing the residue build up on the valves. So where is this oil/air seperator fitted to avoid / minimise oil running through the intake valves? I guess it needs to be dumping the clean air as close as possible (i.e. just before) the intake valves, but then I wonder how is this possible without disturbing the smooth air flow...

The oil and other combustion by-products in the intake air come from the crankcase ventilation system. The crankcase is vented into the intake tract so that gases are burned rather than escape unburnt into the atmosphere. The crankcase has a lot of oil spraying around inside and the small droplets get carried along with the rest of the crankcase gases into the intake tract. The factory puts an oil separator in the tubing that carries the gases into the intake, but they're not 100% efficient and some gets by.

The small amount of remaining contamination hits the back side of the intake valve and gets burned on from the heat of the valve itself. It takes many cycles to build up but that's what engines do - many cycles over thousands of miles. What's worse, as the buildup collects, it insulates the metal valve from the cool intake air rushing into the cylinder, causing it to run even hotter, turning the coating of oily residue into hard carbon.

The after-market separator traps oil that got past the factory separator before it gets into the intake tract and that keeps it from collecting on the back of the valves. It doesn't solve the problem but it does slow it down a lot.

[gr8000]

Originally Posted by JAJ

The oil and other combustion by-products in the intake air come from the crankcase ventilation system. The crankcase is vented into the intake tract so that gases are burned rather than escape unburnt into the atmosphere. The crankcase has a lot of oil spraying around inside and the small droplets get carried along with the rest of the crankcase gases into the intake tract. The factory puts an oil separator in the tubing that carries the gases into the intake, but they're not 100% efficient and some gets by.

The small amount of remaining contamination hits the back side of the intake valve and gets burned on from the heat of the valve itself. It takes many cycles to build up but that's what engines do - many cycles over thousands of miles. What's worse, as the buildup collects, it insulates the metal valve from the cool intake air rushing into the cylinder, causing it to run even hotter, turning the coating of oily residue into hard carbon.

The after-market separator traps oil that got past the factory separator before it gets into the intake tract and that keeps it from collecting on the back of the valves. It doesn't solve the problem but it does slow it down a lot.

Very comprehensive response - all clear. Many thanks for your time!