What to use as CRD fuel rail Material?

[PapaG]

Hi all.
I have been reading and lurking for awhile and nust say that this is a great forum..

I am in the planing-design stage of a hybrid CRD EFI system for retro fit to older IDI diesels. I am mostly doing this for myself, but some others may tag along for the ride.

This will be on a 5.7l GM diesel (yes the olds diesel) but the basic design could be used on 6.2l, 6.5l and 6.5T diesels.

I would expect pressure could be as high as 1600 bar, but I really expect them to be in the 1100-1300 bar range. VW Style TDI injectors will be my choose, with a lot more volume (3x) for the differance in engine size. 5.7l vs 1.9l.

What can I use to make some fuel rails out of. I don't think I need too large a size as a lot of gasoline V8's in excess of 1000hp do not use overly large id bores.

I am going to make adapters to fit the Bosch style injectors to fit the hole in the head. I am looking at using a aftermarket sequential EFI controller, with a crank trigger. Of course no one says the have a diesel system. I have a few issues to work out with that but they do not seem to be mayor issues. Like MAP, TPS, and a couple others...


Thanks
Richard Green
New Ulm, TX

 

[tbuelna]

PapaG,

When selecting a material for your fuel rail, you should consider the following:

Strength: will the material provide an adequate margin of safety, with regards to stress and fatigue, for your particular design, over the life of the vehicle.

Corrosion: will the fuel/environment cause the material to fail due to corrosion.

Machineability: usually, the most corrosion resistant materials are also the most difficult to machine.

Safety: you mention you will be working with pressures as high as 1600 bar. A leak in a 1600 bar fuel system can be quite dangerous, especially in a confined area like under the hood of a car. A leak in a high pressure fuel rail will instantly create a cloud of fuel vapor, that when ignited, will produce a massive explosion.

Serviceability: I have worked with high pressure (1800 bar) common rail fuel systems. These fuel systems require metal-to-metal seals at every joint in the system. To get those metal-to-metal joints to seal properly, they must be perfectly aligned, have a perfect machine finish on the mating surfaces, and be surgically clean at assembly.

Good luck.

 

[PapaG]

Pressure should be lower than 1600bar. Most of what I plan on using will be Bosch based, using VW TDI peaces or others that are compatable.

 

[PapaG]

Just checked my faq's again, and 900bar is what the TDI is using.

 

[PapaG]

Opps I got my high pressure from here on CRD as a general
CRD fact.

Dynamic simulation of electromechanical systems: from Maxwell's theory to common-rail diesel injection.

Kurz S, Becker U, Maisch H.

Robert Bosch GmbH Stuttgart, Germany.
Stefan.Kurz2@de.bosch.com
==============================================================The CRD difference

In conventional diesels, the engine had to build and generate pressure every time the fuel was injected into the cylinders. That did not give it much flexibility in terms of the intensity of pressure that could be built-up or the variation in pressure and fuel injected that may be required for responding to the vehicle's needs. So, in the older diesel engines, the amount of fuel injected rarely changed in accordance with the demands of the driver.

However, the CRD engine achieved the set goals by isolating the two functions — generating pressure and maintaining a real-time check on the amount of fuel injected. Under the CRD system, a common rail or pipe (also called a central accumulator) fitted alongside electronically controlled injectors acts as a shared reservoir of fuel.

Diesel is stored in the common rail at a constant pressure ranging from about 1,350 bar up to about 1,600 bar (approximately 24,000 pounds per square inch). The fuel available constantly at such high pressure eliminates the need for a build-up of pressure individually at each injector.

Connectors from the common rail deliver diesel already at a high pressure to each injector. At the end of the injector, a solenoid valve (a peizo valve in some of the newer ones) regulates the injection timing and the amount of fuel injected based on inputs from a microprocessor or an electronic control unit (ECU).

In the CRD system, as diesel is permanently available at very high pressure even when the engine rpm is low, the injection pressure is independent of the engine operating conditions.

This is what makes CRD engines more fuel efficient than the diesels with the older technology.

Once the fuel is injected into the cylinder at high pressure, the compression heats up the air to temperatures above the ignition point of diesel. As the fuel is being sprayed at high pressure, it ignites and a form of controlled, yet fierce, explosion takes place in the combustion chamber. This is what happens in a conventional diesel engine, too, and that is the reason for the signature rattling noise of many modern diesels even when the car is cruising.

However, there are two features that are different in a CRD engine. The pressurised spray of diesel is so fine in a common rail engine that it gets atomised when mixing with air in the combustion chamber.

So, there is complete combustion of fuel in a CRD engine, thereby boosting power output, even while eliminating wastage, keeping emissions down and improving the fuel economy.

To eliminate the noise and the vibration caused by the inevitable violent explosion accompanying the combustion process in diesel injection, most CRD engines employ what is known as a `pilot injection or pilot burn'. Seconds before the main fuel load is injected into the cylinders, a small amount of diesel is injected.

This pilot injection and ignition starts the combustion process even before the main load is injected, thus containing its explosive force. The rise in temperature and pressure is staggered and thereby less noisy.

Common rail diesel engines are a major breakthrough not just for meeting more stringent emission standards, but also for improving the level of refinement inside the vehicle.

Extremely efficient CRD engines can improve fuel efficiency by as much as 15 per cent compared to similar-sized turbo intercooler diesel engines.

============================================================
Since mine is a hybrid system it won't use as much pressure.

 

[MikeHalloran]

Nine hundred bar is still a damn high pressure. Even if it doesn't ignite, a leak from a system like that can instantly sever an electrical cable, a brake hose, or a probing finger. It deserves your respect.



Mike Halloran
Pembroke Pines, FL, USA

 

[jejtopgun]

Hi,

The actual common rail runs on 1600 bar, the new generation is 1800 and the future product ( coming 2006/7) will run on 2500 bar.

The common rails are normally made out of steel with some special surface finishing. Personally, I used stainless steel for some customized common rails that we made. Stainless steel is really strong, do not rust in the vehicle, it is fairly heavy but you need less material as other type of steel. The only problem you an have is the machining, just make sure that you have tool that can be used for stainless steel machining ( ask your local dealer).

With the engine size you have, to reduce the pressure fluctuation and therefore the pressure regulation problem I will recommand something in the region of 5 to 8 cc volume ( total ). If you have a V engine, use 2 common rail, that is easier to regulate as only one.

Theoretically, you can use a EFI ECU to control the Diesel injection system. The programming is not that far away I should be roughly working. It may be later on a problem with pre and post injections but you can have a look a this later on. Just make sure that the ECU can handle the large amount of energy required by the common rail injectors. I already burned out an ECU in a project because the injector was using far too much energy.

There is no ECU available on the market for Diesel. We are currently developping one. If you have any other sources, please let me know !

Hope I help, if you have any other question, feel free to ask !

Have fun with your engine

Jerome Douay
Team74.com

Jerome Douay
Team74

http://www.team74.com

 

[PapaG]

I will be working V8 engines, of around 6l - 6.5l
I should be using a external driver board on the injection system to isolate the ECU from high current loads. That way all I should loose is the driver board.

I am in SE Texas where we have a lot of oil field equipment, and there should be a machine shop able to handle SS material.

Pressure may ba lower as 900bar, but I may have to go higher, thats why I would feel better over designing-building the protype fuel system. Since I will be starting with mostly VW TDI parts, I will be using this as my working model.

Also since this will a retro fit system for existing IDI engines. I am not think of pilot injection, or multi injection events. It will start as a one shot event.

I have worked with sever MegaSquirt units, which is a DYI EFI system, but it is a batch system for gas engines.

I may see if I can adapt a Stanadyne DB2 head or something if i need to. I have not given it any thought at all.

Thanks
Richard Green
Dodging hurricane Rita.

 

[MikeHalloran]

Richard, if you are not going to just copy someone else's fuel rail, you need to get an engineer involved in sizing it.

Jerome, common stainless steel is difficult to machine because it work-hardens easily. It is not particularly strong. It is quite a bit less strong than common structural steel.



Mike Halloran
Pembroke Pines, FL, USA

 

[PapaG]

I have been looking for information on the DuraMax fuel system but I have not found anything.

I have been busy with Hurricane Rita, while it missed me, we did move back into our house which we are selling, but living in a 36 ft 5th wheel TT. We are back home after going to help some friends out that did get hit by the storm.

I have worked with a lot of older simi-truck diesels, high pressure hydraulics, Pneumatics, high output RF, high pressure vacumm, acids including Hydrofluoric acid, deionized, hydrogen gas, fluorine, Chlorine, Arsine, Phosphine, hydrogen sulfide, silane and others.

I have a great respect for dangerous things.

 

[thundair]

15-5 Stainless Applications Aircraft components, fabricated parts in high pressure corrosive environments including valves, shafts, fasteners, fittings and gears


This is Heat Treatable and Machining is ok as long as you keep your speeds low and always pull a chip. if you burnish over the top of a cut; your done. That goes for threads too.

Regards

 

[PapaG]

Mike Halloran

I could copy the DuraMax fuel rail. It is the basic size engine of 6.6l if I remember correctly. This is larger then my 5.7l but would be closer to the 6.2l and 6.5l engines.

I was also thinking of trying to use steel mechnical IP line but I will need to check the pressure. I think the VW TDI uses steel (or something like steel tubing) tubing with electronic control of the firing of the injector. I think this is more of a simi EFI system in actual design. I will need to check my information.

I don't thing use of the spark control on gas EFI systems will give the control the PWM on the injectors, where I can control the amount of fuel delivered to the engine under boost conditions.

I was going to use a MAP sensor but a MAS sensor might be better.

Jerome
What is the projected finish of your company's diesel EFI system?

Well that's it for now.

Richard
Diesel IDI EFI Hybrid Project

 

[jejtopgun]

Hi Mike,

You are right the Stainless steel is not higher than the steel but it is still fairly strong.

I recommend no to use any parts in aluminium or copper based. We have found a few years back that copper and alumium are "dissolved" by the fuel under pressure and landing in the nozzle as really fine particle. It seems to be that unprotected steel seems to rust failry quickly in contact with the fuel and also create this really funny fine particle.

As I mentionned earlier, I will just buy a few standard V6 common rail 6 to 8 cc and build 2 or 3 in the engine, it is the cheapest solution I guess.

Have fun

Jerome Douay

http://www.Team74.com

Jerome Douay
Team74

http://www.team74.com

 

[PapaG]

I found a good site with very good informatin and pipe-tube size, burst pressure, wall thickness, inside diameter. Using Barlows Formual:

theoretical bluging pressure= 2(yeld strenth)t/2
theoretical bursting pressure= 2(tensile strenth)t/d

t=Wall thickness
d=outside diameter.

I did not book mark it and have been trying to find it again, without any luck.

Richard