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Old 11th January 2008, 10:34   #31
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Guys PD(or unit injector) has been in use for many years in heavy European/US trucks. Back in the day before Common rail was invented PD was the only system able to produce super high pressures. Back then there were either IDIs or VW's TDI. Then VW adapted PD with electronics for light duty car diesels with pilot injection, whereas the others went the common rail route. (dont ask why... VW simply likes eccentric engineering) The advantage was that PD was still producing higher pressure at the cost of refinement.

Well PD stagnated and by the time 2nd gen common rail was introduced, they had caught up with injection pressures. Time to bury the PD for high refinement cars but trucks still swear by them.

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Old 11th January 2008, 10:44   #32
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Old 11th January 2008, 11:12   #33
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Quote:
Originally Posted by mail4ajo View Post
. I also learned that Pumpe-Duse engines produces better torque than its common rail counterpart. Any info?
I think Pumpe Duise Engines have minimal turbo lag though the same cannot be said about outright power. Am not sure about this.
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Old 11th January 2008, 11:25   #34
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Originally Posted by akshay1234 View Post
fiestas and dicors have crdi tech.
absolutely correct. only the acronyms change with every manufacturer.

Eg: DICOR stands for "Direct Injection Common Rail", which is essentially a CRDi.
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Old 11th January 2008, 11:37   #35
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The technical situation is somewhat confusing. In PD you have an indpendent injector for each cylinder. The Injection is at very high pressure using 'I am quite sure' Piezo pumps. In the cRDI you have a common high pressure line (not as high as PD injection) where you open and shut the valve to the injector (once again quite likely Piezoelectric). It is difficult to say which is better.

While the whole world is working on CR only the VW group is on PD. A technology need not be better to succeed - see VHS vx Betamax. It looks like that CR is moving faster than PD and hence the latter is likely to become a footnote in history or be confined to trucks and the like, where the engine speeds are lower, and NVH is not such an issue. Returning to the Video analogy Betamax became the preferred system in studio equipment.
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Old 11th January 2008, 13:05   #36
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Quote:
Originally Posted by sgiitk View Post
The technical situation is somewhat confusing. In PD you have an indpendent injector for each cylinder. The Injection is at very high pressure using 'I am quite sure' Piezo pumps. In the cRDI you have a common high pressure line (not as high as PD injection) where you open and shut the valve to the injector (once again quite likely Piezoelectric). It is difficult to say which is better.

While the whole world is working on CR only the VW group is on PD. A technology need not be better to succeed - see VHS vx Betamax. It looks like that CR is moving faster than PD and hence the latter is likely to become a footnote in history or be confined to trucks and the like, where the engine speeds are lower, and NVH is not such an issue. Returning to the Video analogy Betamax became the preferred system in studio equipment.
In all injection systems (other than the old injector-in-throttlebody/manifold petrol injection), there is always 1 injector per cylinder.

The comparison of PD systems (as in Skoda's ads) is with the older in-line-pump- or distributor-pump-based systems with electrically controlled injectors. Between ILP and DP systems, DP had better control over emissions (OK, injection profile of each spritz). The pump is cam driven, the injector is piezo-actuator controlled.

Common Rail, for which FIAT had originally held patents, has been in development since '30s, but due to lack of consistently controllable injectors, it wasn't productionized till Bosch managed to make good electrically controlled injectors ('90s).

PD is also Bosch technology, came in as a replacement for the DP systems for cars in the 90's, at the same time as CR was in final proto stage. Most Indian diesels have had DP from Bosch or Lucas, even the just-phased-out old Endeavour. After that, everyone jumped straight to CR - Bosch, Hitachi, Denso, Delphi, ..., bypassing the PD systems altogether.

There are no clear advantages of one over the other, since they have comparable injection profiles. Production PD systems are slightly costlier than CR. All other 'features' are software control implementation dependent, which takes advantage of the fine controllability of the quantity of diesel injected per firing.
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Old 11th January 2008, 19:04   #37
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Originally Posted by ajmat View Post
In a CRDi, the tolerances are so fine that the petrol with dissolve the lubracity provided by the diesel oil
Never knew that CRDi engines require closer tolerances, when compared to PD engines. Always thought that it is the newer engines which are manufactured to closer tolerances.

Any idea why the CRDi engines require closer tolerances, whereas the PD engines are manufactured to "looser" tolerances?
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Old 11th January 2008, 22:00   #38
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Quote:
Originally Posted by DerAlte View Post

Common Rail, for which FIAT had originally held patents, has been in development since '30s, but due to lack of consistently controllable injectors, it wasn't productionized till Bosch managed to make good electrically controlled injectors ('90s).

PD is also Bosch technology, came in as a replacement for the DP systems for cars in the 90's, at the same time as CR was in final proto stage. Most Indian diesels have had DP from Bosch or Lucas, even the just-phased-out old Endeavour. After that, everyone jumped straight to CR - Bosch, Hitachi, Denso, Delphi, ..., bypassing the PD systems altogether.
Small correction. Common Rail came first when PD was in prototype stage. Mercedes (the venerable OM611) and Alfa launched common rail in 1997 and people went ga-ga over the smoothness and torque of these engines. VW which until then was known as the pioneer in diesels (they went DI in 1988 much much before everyone else) wanted to do something better and also did not want to pay royalty to FIAT and so went the PD route with Bosch touting the high injection pressure of 2050 bar (CR was 1350 bar)and launched the first car only in year 2000. The torque was fantastic but the engine was gruff and noisy because it did not have the fine control to generate the several pilot injections. Eventually they gave up and hooked up with Siemens to develop a CR system with piezo injector.

PD was never offered with a piezo injector AFAIK.


Quote:
Originally Posted by DerAlte View Post
I
There are no clear advantages of one over the other, since they have comparable injection profiles. Production PD systems are slightly costlier than CR. All other 'features' are software control implementation dependent, which takes advantage of the fine controllability of the quantity of diesel injected per firing.
Till date, PD can still generate high pressures compared to 3nd gen common rail. That is why trucks use them. But for cars the fine control is more important for emission and NVH. PD of course is also more expensive because it needs 1 pump per cylinder and the lack of volumes of scale.

Last edited by Mpower : 12th January 2008 at 10:21.
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Old 11th January 2008, 22:43   #39
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Another factor to consider. Maintenance cost- PD spares should be really expensive. The pump in CRDI costs 30k plus 15k for each injector. I wonder what is the cost of replacing all the injectors on a PD engine. it must cost a bomb as each injector has an integrated pump too.
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Old 12th January 2008, 21:05   #40
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Quote:
Originally Posted by Mpower View Post
Small correction. Common Rail came first when PD was in prototype stage. Mercedes (the venerable OM611) and Alfa launched common rail in 1997 and people went ga-ga over the smoothness and torque of these engines...
Well, well, well, nice to hear someone who has kept track.

You have seen / heard AFTER they got mounted in cars / trucks. I've been on the other side - ideas to test track!

Quote:
Originally Posted by Mpower View Post
Eventually they gave up and hooked up with Siemens to develop a CR system with piezo injector.
Way after Bosch. Siemens was lower cost - strategically. They were nowhere in the picture before 1995, when they came up with 8051 (derivative) ECUs.

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Originally Posted by Mpower View Post
PD was never offered with a piezo injector AFAIK.
The piezo was good tech improvement - quite some time back. Check Ford ads.
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Old 13th January 2008, 18:26   #41
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Diff btwn PD and CR are

PD is a unit injector and each unit has its own pump and nozzle built into it . since the pump and the injector is integrated ,it offers higher pressure compared to a CRDI as a crdi pump is connected to the inectors via a high pressure pipe which in turn reduces the effective pressure to the injectors .

Pump duese is simpler compared to crdi as no electronics are needed ,they can be built with simple mechanical injectors ,just like on the lombardini focs series of engines .

PD system works with the engine camshaft. PD system has been discontinued by VV mainly due to emission regulations and VV has incorporated CRDI as well
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Old 14th January 2008, 18:13   #42
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CR being an older technology compared to PD, it also did not have any electronics.

The main reason for makers prefering CR because, in this, the pumping and injection is more or less independant of each other. Therefore, a more flexible injection program can be incorporated into the system. The combined units like PD, the injection is locked with pumping and there it is difficult to control injection. (Makers have experimented with tandem pumps and dual injectors but it has not been popular). Therefore CR can give a higher RPM bandwith and more even distribution of torque. Also the pollution control can be better over the entire rpm range.
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Old 1st February 2009, 17:36   #43
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A quick recap on the thread to brush up my knowledge - hoping I've got my tech stuff right, please correct me wherever I'm wrong - I'm assuming a 4-cyl engine for the purpose of my own understanding:

A. Petrol MPFi - has a pump which feeds petrol to all 4 cylinders. The old carb engine mixed air & petrol in the manifold and then sucked it in. MPFi just sucks in air and the injector opens on the command of a computer chip when each piston is at BDC (bottom dead centre), spraying a very atomised petrol into the cyl. Piston moves up to TDC (top dead centre) and spark plug fires. Boom. We've got power. The injector is both a port for entry of petrol into the cylinder, as also a valve (a 2-in-1 affair).

B. Rotary/inline pump diesels - Rotary or inline pumps have built-in valve systems with 4 pipes leading out from the pump (from each valve opening). Rotary - the pipes come out from a cylindrical body like spokes of a hub); Inline - the pipes come out from one side of a flatter block, like an inflated rubber glove). The pipes into the 4 injectors (a not-so-complicated piece of metal with very fine holes in it, with no electronics to control it's opening/shutting) - as the pump turns, it is synchronised with the crankshaft via a belt or chain or camshaft, so that at the point that a cylinder comes to it's compression TDC, a metered dose of diesel spray under moderate pressure is released into the pipe, and through the injector into the cylinder. Pressure: 3,000 - 6,000 psi.

C. DI/IDI - Based on where the injector (in the cylinder head) is located vis-a-vis the main cylinder in a diesel. If the tip of the injector "stares out" towards the head of the piston, that's DI. If the injector remains in "purdah" like the Maharanis of Jodhpur in their own anterooms/cubbyholes (aka a precombustion chamber), that's IDI.

D. CDi/CRDi/CRDe/DICOR/TDCi/TCDi - The inline / rotary pump stopped having 4 pipes leading to the engine - it's now got a single pipe running there carrying liquid diesel at very high pressure, and smaller & shorter pipes lead from the main pipe into the 4 injectors. These injectors are more like the petrol MPFi injector-cum-valves - they can also open and shut on electronic command from a computer chip, which also keeps track of where the cylinders are - cyl comes to comp TDC, injector opens, and the high-pressure liquid diesel comes out as a much finer atomised spray. Pressure: 14,000 - 20,000 psi.

E. PD (Pumpe Duse - literally, Pump Injectors in German) - VW/Skoda's exclusive copyright, I believe. No high-pressure diesel pump. Only a low-pressure diesel pump where the CDi's single high pressure pump sat. Feeds to all cyls. Instead, there are now FOUR high-pressure pumps sitting on the engine's cylinder head - the injector-cum-valve has evolved to be an injector-cum-valve-cum-high-pressure-pump. Like any old pump, the pressure drops in some mathematical relation to the distance away from the pump (is it the square of the distance? my maths was bad - members, your inputs please). So, get the pump closer to the piston, get better pressure, hence better atomisation. Voila - more power. Pressure: 30,000 psi.
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Old 1st February 2009, 20:53   #44
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Thank you SS-Traveller for having encapsulated the whole thing very well. Let me just clarify here that the injection pressures that can be maintained in Pumpe Duse can be as high as 30,000 PSI. The CDI (the original acronym given by its developers Mercedes Benz and Bosch) engines maintain about 14,000 to 16,000 PSI under normal conditions and can tolerate upto 20,000 PSI under peak load conditions. Therefore the PD engine maintains 100% more perssure as against a CDI engine at normal load and 50% more pressure as against a CDI engine at peak load.

The advantages of PD are: Finer atomisation of the fuel; high torque; high power; low emissions; high FE.

As Mpower has pointed out, PD or Unit Injector, has been in use for many decades in heavy vehicles and has been adapted for use in light duty car engines only now, perhaps, due to technical developments affording finer control via electronics.

CRDi, CRDe, DICOR, etc. etc. are all the self-same CDI introduced by Mercedes Benz and Bosch. The only new advance in Diesel engines is the 'MultiJet' introduced by Fiat, the Maruti-Swift engine is manufactured by Fiat.

Incidentally there is a similar thread on briskoda (BRISKODA - The Skoda Forum and Community) which started in 2005 and discusses the supposed or perceived move of VAG group (VW) away from PD. Which goes on to conclude that VW has not moved away from PD but uses both CDI and PD in their range.

The PD engines are not known to be very refined but are acknowledged to be extremely frugal and, everyone knows that FE is the presiding deity of the Indian car customer.

Cheers,

Last edited by Ravveendrra : 1st February 2009 at 21:06.
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Old 1st February 2009, 21:47   #45
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Originally Posted by SS-Traveller View Post
A. Petrol MPFi - has a pump which feeds petrol to all 4 cylinders. The old carb engine mixed air & petrol in the manifold and then sucked it in. MPFi just sucks in air and the injector opens on the command of a computer chip when each piston is at BDC (bottom dead centre), spraying a very atomised petrol into the cyl. Piston moves up to TDC (top dead centre) and spark plug fires. Boom. We've got power. The injector is both a port for entry of petrol into the cylinder, as also a valve (a 2-in-1 affair).
A small correction. Injecting petrol right into the cylinder is not MPFI, but it's GDI (Gasoline Direct Injection) which is the next level in petrol fuel injection.

In an MPFI (multi point fi) engine the injector is placed outside the cylinder, just before the intake valve. The fuel is injected into the airstream that's going into the cylinder. Each intake runner has it's own injector. There's another older FI system for petrol engines, they're called single point fuel injection or throttle body injection. In this system the injector is placed at the entry to the intake runners and all the cylinders are fed by a single injector. The first Opel Astra sold here came with this type of fuel injection system.
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