MBRedux

Enlighten me.

MBRedux

Okay here we go...... !!!!!!!!!!!!

I did a little poking around and found this... and it looks good... maybe! The new DI engines are designated M276 and M278, (V6 - V8). Both utilize the same head design although the V8 is turbocharged. But for our discussion, we are more interested in the set up of the injectors, which are piezo-electric direct petrol injection and the location of the intake valves relative to the injector. The new engine has a reduced V-angle between the cylinder banks, 60 now vs. 90, making the engine naturally balanced, enabling the designers to eliminate the friction hogging balancer shaft. The fuel efficiency numbers are truly astonishing for this engine, more than 24% more economical than the previous engine!

Let's look at the pix...

M276 V6

^ See where they placed the direct injected fuel injector?.... TDC! Now look at this picture...


M278 V8 but same head design.

^ You can better see in this picture that because of where the piezo electric injector is located, (not to the side but above the intake valves) Kevibk2 may have hit the nail on the head! The intake valves (the larger ones) are perfectly located to take full advantage of the injectors spray pattern cleansing properties.

__________________________________________________ ___________

The following is taken from Autoholics:

"In contrast to the V8, the new V6 engine is naturally aspirated, and has the potential for future use of a turbocharger thanks to the modular design concept.

A completely new intake and exhaust gas system with a variable-resonance intake manifold and optimised airflows was also developed for the new V6. This enabled the output of the 3499 cc engine to be increased to 225 kW (306 hp) (Previous engine of the same displacement in the S-Class: 200 kW/272 hp). Torque has increased from 350 Nm to 370 Nm, and is available between 3500 and 5250 rpm.

Key figures for the new V6 engine

No. of cylinders
V6
Displacement (cc)
3499
Bore (mm)
92.9
Stroke (mm)
86
Compression ratio:
12.2:1
Output (kW at rpm)
225 at 6500
Torque (Nm at rpm)
370 from 3500-5250

Both the new V6 and the new V8 from Mercedes-Benz have aluminium crankcases, pistons and cylinder heads. The crankshaft, connecting rods and valves are of special forged steel.

Mercedes-Benz has achieved this considerable leap in efficiency with the use of innovative technology – including newly developed, third-generation direct petrol injection with spray-guided combustion, multiple injection and multi-spark ignition. With this new generation of V-engines, Mercedes-Benz is clearly demonstrating that with concerted further development, internal combustion engines still have a great deal of potential, and that V6 and V8 engines with their great running refinement are fit for the future.

The technology package in the new engine generation includes a number of new developments that are unique in this combination:

• In combination with multi-spark ignition, a further developed, third generation direct fuel injection system with spray-guided combustion and piezo-electric injectors offers further possibilities for fuel savings – in the V8 by means of an improved, homogeneous combustion process, and in the V6 by a new, stratified combustion process with a considerably extended characteristic map and fuel-efficient lean-burn technology.

• In conjunction with start/stop technology, shift point adjustment and specific friction-reducing measures, improvements in day-to-day fuel consumption by more than 20 percent are possible.

• Power consumption by ancillary units has been reduced. These include an optimised water pump with second generation thermal management, a demand-controlled oil pump, a volume-controlled high-pressure fuel pump and an intelligent generator management system.

Lightweight construction techniques and detailed improvements have also reduced in-engine friction considerably compared to the previous engine.

Third generation direct petrol injection

Direct petrol injection with spray-guided combustion, which Mercedes-Benz was the first car manufacturer to introduce in series production, has been developed further as a third generation. The system pressure is up to 200 bar, the pressure being variably optimised according to the engine’s characteristic map. Completely newly developed piezo-electric injectors allow up to five injections per intake stroke for the best possible mixture formation.

The crystalline structure of the piezo-ceramic changes in microseconds under an electric voltage, and with a precision of just a few thousandths of a millimetre. The central component of a piezo-electric injector is the piezo-stack, which directly controls the metering needle. With a response time of just 0.1 milli-seconds, the fuel injection can be very sensitively and precisely adjusted to the current load and engine speed, with a beneficial effect on emissions, fuel consumption and combustion noise.

The multiple injections even in tiny quantities made possible with piezo-electric injection technology were used by Mercedes-Benz engineers to control a wider characteristic map with the efficient lean-burn process, and to provide the conditions for further functions:

• As the first new operating mode, Mercedes-Benz engineers have developed “Homogeneous stratified combustion” (HOS). As the name implies, HOS is a combination of homogeneous lean-burn and classic stratified combustion. The first injection is sprayed into the intake stroke, forming a homogeneous basic mixture. Actual “stratified” injection takes place during the compression stroke before ignition, and is a single or double injection depending on the characteristic map.

(Please Note: This may be the answer I've been looking for! HOS can be programmed to spray multiple times during the power stroke, and at any rpm! (Amazing but so does my GT-R) This means that Mercedes engineers quite possibly took advantage of this technology to spray off the intake valves during those milliseconds! See next point below.)

• Another new operating mode is known as “Homogeneous Split” (HSP). In this homogeneous combustion process, more than 95 percent of the fuel is singly or multiply injected, followed a very small “ignition” injection to stabilise combustion. This is used when combustion conditions are difficult.

The characteristic map of the new Mercedes-Benz V6 engine is therefore basically divided into up to four areas:

− idling range (homogeneous)
− low partial load up to 4 bar and 3800 rpm (stratified)
− medium partial load 4 to 8 bar and up to 4000 rpm (HOS)
− high load and entire engine speed range (homogeneous or HSP)
__________________________________________________ _____________________

Well there you have it! This is the best possible proof I can find to date that the boys over in the new sub-plant of the Untertürkheim engine werks, lies the new V-engine factory at Bad Cannstatt, knew what they were doing!


M276 V6

^ This picture doesn't help our discussion at all but I thought is was very cool so I included it.

MinnBobber

MBRedux,
thanks for the pics.
Someone correct me if I'm wrong, but isn't the carbon buildup in the valvestem area, outside the combustion chamber/ in the intake ports?

So, with DI all the spraying is inside the combustion chamber and even with the multiple injections/injections during the intake and compression strokes etc, it is still inside the combustion chamber. Thus, the intake ports get no direct cleansing by raw fuel and the issue remains. They are upstream from the fuel spray.
Outside of minor seepage/swirl back into the intake port, no real fuel source cleans the intake ports and therein lies the (potential) problem.

madhermit

As a new owner of a C3504M and reader of this forum, I always keep an eye out for your responses. You are clearly educated, informed, not into rampant speculation, and carry yourself in a very professional manner. Kudos!

I look forward to more measured responses in the future.

Jason

Glyn M Ruck

Thank you Jason. I wish I had a clap smiley for the naysayers now they have done their homework. As I said when I got embargoed - "I'm sure you will find their (MB's) comments reassuring". I was itching to comment but had agreed not to. Kevink2 is a good engineer & he basically had it sorted.

BTW - I'm allowed to say this. It came from MBSA. In high temp endurance testing down here in Southern Africa at extreme mileage no detrimental depositing was found on the new DI engines.

As I have said before Benz also understands captive breather & oil control in DI engines both diesel & gasoline.

Glyn M Ruck

It's all in the valve tulip protrusion into the combustion chamber & valve timing & overlap. 'Nuff said.

EDIT: Benz was building stratified charge DI engines in Europe in 2003.

2012c350

Glyn, it's not that people (myself included) are naysers. It's more the fact that if I'm putting out ~$50K for a car, and hearing horror stories about DI engines, and no (to date) response from direct inquiries to MB that it's a logical assumption that no news is not good news. I certainly hope that they know what they're doing and the latest post here (along with your latest comment about endurance testing) starts to give reason to believe that things may be fine. Again, when you have a financial investment in something it only makes sense to want to ensure that your money is being well spent.

As always, I enjoy reading your knowledgeable contributions to this and other topics.

Glyn M Ruck

Understood! There should not have been horror stories.

Of technical note: See how the piston design is adopting diesel characteristics - obviously of far lighter construction.

MinnBobber

I too look forward to Glyn's responses, even if they now need to be more measured.
Please don't drive him away by dumping on him/his motives etc. A consultant has to respect their companies wishes or else...
He is a valuable resource here.
Bob in MN, US

kevink2

Nice work MBRedux, and Glyn enjoy your Retirement in that wonderful location.

.

MBRedux

Well thank you kevin, very well appreciated!

Unfortunately it appears that some here refuse to understand the process of a public forum. Asking questions and receiving answers, especially if it is known by one or more, is what makes a place like this worth while, am I right? It's rare that the person who asks the question and/or starts a thread is left to answer it for him or herself... and is then demonized for previously citing known cases where DI has proven itself to be a major performance issue by the very person in charge... who then states that "wrong questions were asked", who possibly had the answer all along since he professes to know the "right questions"!

No horror stories here Glyn, it's the TRUTH, defined as factual. Look, Mercedes is STILL not out of the woods here! The true horror story is what happened here IMO.

Lacking information is one thing, but intentionally withholding it or criticizing members for seeking it out on their own is NO WAY to run a public forum where information is crucial to the operations of the site. I do not appreciate it Glyn. That is no way to run a forum.... period.

Incorrect, the piston crown shown in these pictures are not "adopting diesel characteristics". They're recessed simply to allow for valve clearance. The deep pocket is to increase volume capacity. Chamber vortex properties aside, these pistons are standard fare in any high performance, high efficiency engine seen today.

That said, my post above is in no way proof that Mercedes has solved the issue, and you know it. It's "hope" where there was none before that Mercedes may have addressed it. I'm trying to be "optimistic" where information was lacking, and I must add, STILL IS lacking despite my post.

These Piezo injectors fire off 3 or 4 ultra fine bursts a millisecond but only during the intake stroke... hardly enough to time to "clean off" any carbon deposits since they are not *continuous* in nature as in some port injected cars. If you took the time to read the entire post, then you must have read this:


I said "quite possibly"! There's NO PROOF that Mercedes did. Again, this is optimistically speculative, not a "horror story".... not yet anyways! Only time will tell. Field testing doesn't prove much. Audi said the same thing, but was tragically wrong.

So to all, I would still keep your fingers crossed.

MBRedux

So, we must be cautious until further evidence on either side comes to light.

Glyn M Ruck

The pistons are most certainly following diesel design other than the valve relief. For the rest You go on scratching!

axhoaxho

Good thread, and is getting informative.

Thanks,

MBRedux

Again... elighten me then. What's the saying? "Put up, or shut up?"

MDMercedesGuy

I have an idea... let's keep this about the potential issue (read: potential, not definite) and fixes, and less about attacking other members who for whatever reason may not be able to disclose all that they know.

2012c350

+1

Glyn M Ruck

Previous generation M272, M273 piston crowns. Flat + valve relief.



The new M276 you posted above with diesel influenced crown for DI.



The OM642 Diesel "Bluetec" engine from Benz.

MBRedux

Thanks... but no cigar... I don't see it. What I do see in the diesel is a true cone shaped crown, just a typical diesel piston completely absent from with no resemblances to the M276 piston. That cone does have a purpose, know what it is?

MBRedux

You are confusing "attacking" with *defending*.

madhermit

+2

MinnBobber

Hi,
I believe the DI M276 cone shaped piston crown centralizes the stratified charge/lean burn mixture around the spark plug to get a better burn/more complete burn from a mixture that is well leaner than the stoichiometric ideal mixture of 14.7 : 1
It also enables, in conjunction with the multi-squirt injectors, the engine to run at very lean mixtures at higher load/higher rpm levels, not just at idle and very minimal load levels.
It provides a home base for the DI ticky-ticky noise

Bob

Glyn M Ruck

I'm not going to be provoked by the purveyor of cigars.

The direction of DI piston design in both diesel & petrol engines is to low turbulence for better emissions control & fuel consumption. This of course aided by very high pressure multipulse injectors with full electronic control. The toroidal recess with cone, which is fast becoming the design of choice in these DI engines, controls the desired swirl within a defined area for complete combustion. Diesel engines require a more aggressive cone due to the nature of the fuel & droplet size. As injection improves so cones require to be less aggressive.

There are also cooling, structural & weight considerations. DI gasoline pistons started showing cracking in the outer "squish" band of the piston similar to diesels & have now been strengthened in this area with the broad diesel type band while trying to keep weight under control. DI petrol engine pistons are nevertheless higher in weight due to strength requirements & longer skirts.

The result of this is that DI petrol engine crowns start looking like DI diesel crowns.

MBRedux

Diesels have spark plugs?

MBRedux

Contradictory?

Are we looking at the same pictures? There is no cone on this new Mercedes Direct Injected M278 piston, nor is there an extended flush skirt, nor anything resembling a diesel crown or piston design. I'm sorry, but piston design is going in the opposite direction. Diesel engine design is adopting gasoline attributes. Audi has repeated proven this to be the case with their world class TDI designs and cars. Lighter designs improve efficiency, new alloy compositions improve strength without power sacrificing weight. I'm on the track every season networking with the best engine builders out there and I simply think you're either out of touch, or dreaming. You haven't convinced me.



This new Mercedes DI piston has NOTHING in common with a diesel... period.