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piezoelectric injectors in the CDI?

23K views 21 replies 9 participants last post by  Mr2weenie 
#1 ·
Question: does the E320 CDI use piezoelectric injectors? I think I read that it does.

If so, how do they work?

Is it that they receive an electrical charge and the shape of the injector changes enough to allow an opening for the fuel to flow? Trying to get an understanding of the mechanics of the thing.

What are the drawbacks of such a system?

Thanks!
 
#2 ·
Found this information:

Automotive Business Review said:
Mercedes C250 CDI to premiere Delphi's Direct Acting Piezo injector

US-based automotive parts manufacturer Delphi has announced that, following the development in cooperation with Daimler engineering teams, the new Mercedes C250 CDI will premiere Delphi's Direct Acting Piezo injector.

According to Delphi, its new Direct Acting Common Rail (CR) represents a radical break-through in diesel injection technology as the injector needle is directly activated by the piezo stack, removing the hydraulic circuit and its associated lag and energy consumption. This change enables vehicle manufacturers to comply with future emission legislations while providing more power and fuel economy.

Delphi's Direct Acting CR system uses a patented direct-acting concept in which the injector needle is set in motion directly by a piezo ceramic actuator instead of being moved via an electro-hydraulic circuit as with existing fuel injection technologies.

The piezo ceramic actuator directly operates the needle valve of the injector for initial lifts, such as those obtained in pilot injections, and a motion amplifier is used to help complete the lift for large injections. This enables the injector to spray fuel into the combustion chamber faster, with much improved spray momentum and accuracy, at higher pressures.

Jose Avila, general manager of Delphi Diesel Systems, said: "Today, Delphi surpassed a major milestone in diesel technology history and there is no better way to write this new chapter than to be partnered with Mercedes-Benz, the company with the industry's longest history in diesel engines."
Very neat, can anyone confirm if this is used in the I6 CDI engine?
 
#4 · (Edited)
Very neat, can anyone confirm if this is used in the I6 CDI engine?
I think it's new for the V6 (OM642) diesel only. (And some recent 4-cyl diesels not in North America such as the 250 in the example ... which is not Mercedes' first use of piezo electrics but it's probably first use of follower Delphi's stuff.)

Remember, the I6 CDI (OM648) really dates back to 1998.

Piezo appears to have started here: http://www.bosch-presse.de/TBWebDB/...1-D753-204E-2A05D10FA8414D00&Search=1&id=2508
 
#7 · (Edited)
Much more reliable! The cycle rate is 10 injections per combustion stroke, although MB is not using the injectoion system anywhere near its full capability.

The injection events are broken up to "shape" the combustion pressure rise in the cylinder. To do this, they inject multiple times as the piston approaches TDC as well as vary the amount of fuel inejected during each injection sequence. This lower emissions by injecting fuel at specific points in the combustions process that promote the most efficient/lowerst emissions burn. Older diesels simply dumped in one big slug of fuel and when it ignited resulted in a rapid pressure rise and resulting knock. The large single injection event also caused some fuel to go unburned increasing emissions greatly.

Aside from that, the Piezo injectors are much simpler and reduce the complexity greatly. Another side benefit is along with the software that drives the fuel system they are able to provide much tighter control of the fuel injection process again translating into higher efficiency and lower emissions AND increasing the component life of the fuel system.

DB
 
#9 ·
How clean is your fuel?

The wear items are the nozzles, these can be replaced at far less than the cost of a whole injector. However MB in the US will not permit any of the dealerships to perform this function since they do not have the training or equipment.

The best advice, replace the fuel filter as specified every 26K using the best quality filters you can get (OEM, or MANN-Hummel).

Use good quality fuel that is rated at 400HFFR or lower for lubricity. Most US fuels don't meet this spec, so small amount of fuel additives may be needed to comply with this spec. In most cases 2%-5% Biodiesel will improve the lubricity of the worst fuels (520HFFR) and reduce it to the mid 300 range.

At 24,500psi any amount of dirt will act like a hydraulic cutting jet, it will slice thru any metal or in the case of a fuel system, erode the .117 micron nozzles holes (7 in total on each injector). Also high amount of dirt larger than 2 microns will oval the holes and destroy the spray pattern and ruin the characteristics of the fuel patterns...

Fuel filtering and fuel quality is the holy grail of injection system component life.

DB
 
#11 ·
Huh?

The V-6 CDI is Piezo actuated. The I-6 is selenoid (Still capable of 5 injections per combustion stroke).

The seals should be copper, one time use. The copper deforms and forms a high pressure seal against the aluminum and the steel of the injector. This type of seal is extremely effective as long as the contact surfaces are clean and free from oil or residue (Yes kind of like an oxygen fitting). Oil trapped between the contact surfaces can create channels that gasses may eventually leak from.

My point, the Piezo actuators have nothing to do with the injector seal.

Below is a Piezo next to a selenoid injector

DB
 

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#14 ·
Drivbiwire:
Do you know the voltage the pizeos need to actuate? Is it 11-15V or hundreds of volts? I know the pizeo stack is a series arrangement designed to add the motions of each crystal to get the required linear opening, but I have never seen what voltage is required in the real world to make the crystals deflect.
Thanks:cool:
 
#15 · (Edited)
“As the valve is actuated more quickly with piezo-actuators, very precise intervals are possible between pre- and main injection, which significantly reduces the emissions. Developments so far mean that peak pressures of up to 2500 bar can certainly be implemented,” observes Dr. Klaus Egger, management board member of Siemens VDO Automotive.

“The basis for the success of piezo-technology was the reduction of the required drive voltage to a range of below 200 volts,” adds Dr. Reinhard Gabl, Head of Piezo-Technology Product Development at EPCOS. This can be done because the piezo-actuator – like a ceramic multilayer capacitor – is built up of many individual ceramic and electrode layers. A modern actuator for diesel injection consists of around 350 active piezo layers. At a length of 30 millimeters, it can produce a stroke of 40 micrometers. Forces of up to 2500 N are then released. “That is sufficient to open the valve needle against a future pressure of up to 2000 bar,” he continues. It should be added that whereas the stroke was fixed in the previous electromagnetic injection systems, piezo-actuators allow it to be varied by the magnitude of the applied
voltage.
Injector lift measured in fractions of a millimeter Since the mid-nineties, and with
immense financial effort – Bosch alone has invested 5 billion euros in high-pressure diesel injection systems in the year 2000 – both companies have been developing piezo injectors to the point of large-series production maturity. The new injectors, which have been available to the auto industry
since 2003, exploit the effect of piezoelectricity, which is the ability of certain crystals to generate a voltage in response to mechanical stress. The piezoelectric effect is reversible in that piezoelectric crystals, when subjected to an externally applied voltage, can change shape by a small amount.
Piezo injectors make use of the change in the crystal's length that occurs as a part of the effect.

The discovery of the piezoelectric effect in 1880 places it in the era that
gave rise to the first gasoline and diesel engines. Harnessing the power of the piezo in our day included the realization that the change in length caused by the piezoelectric effect ranges within a thousandth of a millimeter. This minute dimension therefore falls far short from the lift required for the switching valve. For this reason, the actuator of a piezo injector consists of 350 stacked layers of piezo crystals whose combined expansion at 150 volts adds up to roughly 40 μm. This is sufficient to effect reliable injector valve switching.

More leeway for injection strategies The major reason for the development of piezo injectors was the promise of the short switching intervals, which permit a more accurately measured injection. In its search for uncompromising performance, Bosch exploits this benefit in its piezo inline injectors,
which were first introduced in 2003 with the third-generation common-rail injection technology. In this injector, the piezo actuator transfers its expansion lift directly to the switching valve inside the injector.
Compared to conventional electromagnetic injectors, the piezo injector is four to five times faster.

Because the fuel injector's opening or closing interval has shrunk to a mere 100 μs, up to seven injections
per cycle are feasible at an injection pressure of 1800 bar (26,107 psi) (planning for 2000 bar is underway). Even very small fuel volumes of only 1 mm3 per lift are easily accomplished with piezo injectors.

The piezo inline injectors in current automotive use allow for improved combustion as a consequence of the increased accuracy of metered postinjections. Compared with conventional injectors, this reduces emissions by up to 20 percent. At the same time, diesel engines using piezo injectors not only run cleaner, but they are audibly quieter. The required smooth progression of the pressure increase is accomplished through precision pre-injection of minute fuel volumes.

In the history of diesel technology that has lasted well over 110 years, piezo inline injectors represent the cutting edge of technology with regard to ecological and economical diesel fuel injection.
That's from several papers that I have.

Varying the voltage and duration permits complete control over the opening of the respective nozzle with Piezo injectors.

DB
 
#17 ·
High voltage low amperage. Ever get hit by a spark plug wire? 50,000 volts hasn't killed me yet (Damn lawnmowers)...

Hybrids are another animal since there are thousands of amps behind the high voltage battery banks, dead is your word of the day if you grab a hold of those wires!

DB
 
#21 · (Edited)
I dose with B20 (Diluted to less than 5%) on occasion.

Locally we have RME which there is a story about why it was chosen to power state owned vehicles. Idaho when they looked into Biofuels went to Germany and discussed with various diesel engine component makers (Bosch) topics related to the type of fuel they should support. Rapeseed as you probably know is the fuel of choice in Europe due to specific burn characteristics. Anyway, long story short RME is produced locally and multiple fuel suppliers blend it into the fuels in 20% ratios.

Given my background and experience in diesel systems, I opted to respect the limit for RME I use to 5% (give or take) since this is the ratio that provides the best bang for the buck.

Biodiesel (1st gen) is a dead end road, the next generation fuels (GTL followed by Bio-GTL) will become the true alternative to Petroleum and 1st Generation biofuels such as plant oil based biodiesel.

There are occasions where I don't dose my fuel, I don't lose sleep over it. My other diesel has run just fine over hundreds of thousands of miles without any fuel system component being damaged or worn out.

You can say that the Bosch recomendation of 400 HFFR may be overkill compared to the US spec of 520. But a little dosing (2-5% Bio) here and there easily makes up the difference and allows just about any fuel to meet those optimum lubricity requirements.

Lastly, another option is PowerService, Not as effective but it does increase cetane for quieter running and has emulsifiers to prevent free water (which in my opinion is the best way to go).

DB
 
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