common rail Help me

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common rail Help me

Postby wojtasfans » Sat Nov 26, 2016 12:41 pm

describe operation of common rail medium speed engines
Additionally advantages and disandvantages Help ME please :) !!!!

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The Dieselduck
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Re: common rail Help me

Postby The Dieselduck » Sat Nov 26, 2016 3:13 pm

consistent high pressure fuel injection maximizing combustion cycle = lower smoke, better fuel consumption, more precise control of injection and timing.
Cons, cost, precision equipment, electronics.

Medium speed, high speed, slow speed, the principles are the same, you can read about common rail on large two strokes here ... Update.pdf
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Re: common rail Help me

Postby Merlyn » Sun Nov 27, 2016 4:46 am

My personal experience with medium speed common rail engines started back in the early eighties and I have to say that in a way it was like starting out all over again in many ways.
We thought fuel delivery pressures were high in the old days but common rail pressures of sometimes in excess of 20,000 psi showed otherwise.
So different all round.
As well as fuel economy emissions seemed to play a very large part of it all.
No manual injection timing, the death of spill timing, no injectors upside down on pipes to see spray patterns, dangers of any leaks increased dramatically compared to the now termed " old days "
Told on courses that ideally no fuelpipes to be re used, all renewed ( which of course we never do ) and being told of any LFO contamination by substances containing no lube properties and everything from the fuel tank up to the last port of call (the injectors ) should be changed.
Seeing CR injectors with solenoid and then ceramic stacks operating them thousands of times a minute and naturally stripping same to see what makes them "tick" ( I couldn't do anything with them unlike the old days when being taught how many to overhaul them, resetting pressures, regrinding pintles with Merlin grinders etc etc. )
Some engines require replacement injectors to be programmed to the ECU when fitted.
Wish I had a pound for every injector I have overhauled sinc 1960 .

Learning about ECU /ECM electronics, searching for dry joints on boards and letting in new IC's etc into the boards using our new purpose built special soldering station built especially for the job.
Learning common faults with Bosch for example, the first time despite having all the million pound electronic kits taking a couple of days to isolate the fault.
A miniature green O ring in the fuel regulator valve having a small nick in the ring, hard to see with the naked eye but causing a intermittent collapse of pressure in the fuel rail thus cutting out the engine which in this case requires 300 bar for the ECU to lift the pintles to enable a start up.
Engine may well restart and run for several days, here we are thinking ECU/ HP pump problems etc etc when all the time it's a fourpenny hapeny O ring, but it's a special thickness one and not in your big boxes of O ring kits you carry.
Next time you have a similar problem you check/replace the O ring first before delving further into the problem.
Other one to be learnt back in the eighties was yet again a collapse of pressure in the fuel rail causing an intermittent shut down.
Once again testing (among other items) injectors.
Scoping the injectors with a four channel scope kit.
Or removing and Function testing on the bench with special kit.
Or the cheap way out ( which often shows up straight away ) the Hampster bottle kit.
Calibrated plastic bottles attached to the spill returns and looking for an excess of 10% fuel return flow rate.
Once learnt you carry spares but the initial learning curve here causes a lot of the old hands to throw up their hands in the air saying bring back the old days, we all knew what we were doing then, all theses electronics, it's ridiculous.
Where I am some of the old hands can't ( or won't ) take it all onboard and yet on the old " mechanical installations " they were top of their game but find the new electronic world difficult to understand.
Now we have LNG engines Common Rail.
So basically the common rail engine has a series of sensors all over the engine reporting to a programmed ECU who instructs sets of actuators again all over the engine to run at the most efficient way it can, throught rev ranges, temp. ranges and of course load ranges.
I am still totally amazed at some of the changes brought about by Common Rail Management systems.
We do a lot of DPF ( diesel particulate filters ) regenerations whereby you program the ECU and it retards the injection timing which of course causes the engine to run a controlled overheat temperature and lifts and holds the RPM for maybe 20 minutes and burns off all the excess carbon in the exhaust uptakes and into atmosphere .
God help an engine with a lazy stat. or early headgasket failure problem although of course all the temp. Sensors will monitor this and hopefully not allow an overheat situation to cause any damage.
Some diagnostics can be a pain in more ways than one.
Diagnostic equipment is expensive and every year you have to have it updated to keep up with the latest technology .
Parts such as injectors/HP pumps ECUs etc can approach the value of an older/higher houred engine and when you have tested parts approaching the makers top limits you have to decide whether to renew/replace them although they are ok for further use.
That all said there can be (like the Anzipods ) no doubts that they are here to stay as they are much more efficient, squirt much much less into atmosphere and require less running costs all round.
There is so much further to this subject that one can fill several pages talking about it and when you crack a problem on an engine that has been elsewhere for an attempted unsuccessful repair by renewing expensive parts unecesssarily it does bring back the old "Buzz " which I guess drives us all onwards.
In passing have a look at Caterpillars HEUI interpretation of CR, done a few of them, very clever whoever designed it.
No injector pipes here!
However if you wish to remain in the trade you have little option other than to try and take CR onboard to avoid being " left behind " in the ever changing world of CR.
Onwards and Upwards with CR!
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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D Winsor
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Re: common rail Help me

Postby D Winsor » Sun Nov 27, 2016 5:41 am

In reference to Merlyn's "Miniature Green O rings" and how some sort of unseen defect can cause major issues with this type of precision system.
This could lead to another lesson hard learned when one is expected to use less expensive after market parts such as O rings by those counting the pennies. Such parts, especially those made by others other that those supplied to the OEM Supplier, are less expensive for a reason, but could cost much more in the long run.
Troubleshooting 101 "Don't over think it - K.I.S.S. it"

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Re: common rail Help me

Postby Merlyn » Sun Nov 27, 2016 6:26 am

It's true what you say Dave but the twist here is that it was on several engines that this failure occurred and the O rings were made by Mr Bosch himself ( probably in China )
The large O ring boxes did not contain that size cross section for that diameter.
You could ( using those older kits ) cut those straight lengths in that Vee block supplied in the kit with Mr Loctite.
I have used them a lot in the past and as long as you cut and butt the faces up square they have worked well for fuel, air and hydraulics systems.
Get you out of trouble jobby methinks.
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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Re: common rail Help me

Postby popeye62 » Mon Dec 05, 2016 9:09 am

Dear Wojtasfans
Medium speed CR engines differ from slow speeds in that a MS cannot be 'camshaftless' a MS engine needs a camshaft to operate the valves. A slow speed uses ports for inlet and a hydraulically operated exhaust valve, or loop scavenged. While the camshaft still drives the pumps on 2S and MS, they are not timed and the three lobed cams continuously operate the fuel pumps which discharge to an accumulator, the accumulators supply the common pressurised fuel rail. A signal is sent from the phase angle sensor (the sensor that determines where in the four stroke cycle the particular unit is) to the injection control unit which uses 200 b control oil (main engine oil) to open the injector valves and let fuel into the unit.
In the mid noughties I served on a cruise ship with some of the first generation Wartsilla CR engines using the WECS software. They were a scary nightmare. The phase angle sensors would fail intermittently when the engine was at full chat and start bouncing around. The only option was to stop it, quickly before it went out of the side of the ship (they did have robust vibration monitors which would shut it down if it went on for too long). The phase angle sensor is the most important component and they are provided with two for redundancy. Most of the issues disappeared when Wartsilla introduced the UNIC 3 software and since then have been a preferred choice.
They are a preferred choice because of their low load operation. Emissions are much reduced and will comply with IMO tier III if it is ever ratified outside of current ECA and US regs.
Common rail is nothing new (check out Doxford) but it has become much more reliable.

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