Filed under: Hybrids/Alternative
VW says goodbye to TDI, hello to common-rail
VW will be dumping its line of TDI diesels by 2007 and switching to a common-rail design for all of its oil-burners, with annual production of the new engines totaling over 2 million units. This announcement can probably be taken as evidence that mechanical diesel injection has reached its practical limits, despite the relatively high level of refinement that VW has achieved using the technology. Indeed, there will probably be a number of faithful TDI owners who see no reason to give up the system that has brought respectable power and refinement to passenger-car diesels.
Current TDI products sold here in the states uses a four-port radial injection pump, driven off the timing belt, to
achieve the 20,000 PSI or so needed for directly injecting fuel into the cylinder, while VW diesel engines sold
elsewhere are available with an innovative system that uses one pump assembly per cylinder. Both systems rely on
complex electromechanical and electrohydraulic means to control the volume and timing of fuel delivery. Its expensive,
somewhat finicky (a diesel mechanic in a good mood is indeed quite rare), and doesnt offer the exacting control over
the injection sequence thats required to meet upcoming emissions targets and customer expectations.
Common-rail injection systems operate much like standard gasoline port injection systems, with a single pump
pressuring one or more fuel rails (depending on the physical layout of the engine, theres usually one rail per
cylinder bank), and electrically-actuated injectors providing precise control over fuel delivery. The main difference
is the pressures involved - 20,000 PSI and beyond, compared to 40-55 PSI for a typical port injection system.
Obviously, it takes one heck of an electromechanical injector to open and close at such pressures, but the technology
has come a long ways in recent years, and such systems are quickly obsolescing mechanical injection pumps just as EFI
replaced carburetors two decades ago. This system is far less complex from a mechanical standpoint, and things such as
multi-pulse fuel delivery become easy to implement.
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Reader Comments (Page 1 of 1)
W 10:26PM (12/18/2005)
I know of quite a few people who are going to be disappointed about this.
I think that if they are going to change some things, maybe it should be the timing belt, as in not wrapping it around an engine mount to make it easier to change.
VW always seem to hide behind the stigma of fuel emissions. Supposedly they can only bring so many TDI's into the country because of emissions. Instead of chaging the engine to reduce emissions because of the crappy fuel we have here in the states, Why don't we just change the standards that the fuel must meet? That way the Semi's who use 75% of the diesel will be running cleaner as well. You don't hear about Freightliner, CAT or Mack changing their engines to reduce emissions.. Why must the general public be held responsible for for all of the emissions when it is the minority?
Sorry for the RANT.
//
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Stupidly Happy 10:26PM (12/18/2005)
W
Because we, the general public, do not have well paid lobbyists and the politicians in our pockets and therefore will always get screwed.
The US will be going to low sulfur diesel in a few years (I think) but I don't know they exact year. That should help.
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Kirk 10:26PM (12/18/2005)
Actually current VW TDIs sold in the states use Pumpe Duese, or PD, injectors which are electro-mechanical devices driven off the cam shaft which directly inject fuel into the combustion chamber. The radial injection pumps haven't been on TDIs for several years. Finicky? PD injectors are rock solid, actually. I have not heard of anyone experiencing fuel-system related problems in VW TDIs with PD, based on sites like tdiclub.com. I've certainly not had any issues with mine.
The bottom line here is that engineers have reached the limits of what they can accomplish emissions-wise with PD injectors, as fuel injection is limited to when the lobe is depressed. My understanding is you want to be able to slightly retard injection timing to get certain emissions requirements done, and common rail allows you to inject fuel at any time. So common rail with peizoelectric injectors is the way to go. It's not a question of VW TDI owners (I have a TDI Passat) seeing no reason to switch to common rail - quite the contrary, to the extent that it leads to more diesel applications in the states the better.
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Peter W. 10:26PM (12/18/2005)
It seems like a transition from the old to the new. VW's have a very good implementation of a deisel injection system, but have decided to move on to a newer standard. Sort of like how Honda CVCC engines eventually gave way to fuel injected ones, despite being the perfection of carbeuration. Fuel injection just had more potential.
Also, I always thought TDI stood for turbo-deisel. Will the newly rail-injected deisels not be turbocharged? Or are they just going to get a name like CDI to make the distinction?
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amp 10:26PM (12/18/2005)
W,
The U.S. will be implementing new low-sulfur diesel fuel requirements starting next year (see the link below). Im not sure of all of the details, but it looks like starting June 1, 2006, refiners will have to start producing fuel with a 15 parts per million (ppm) sulfur content or less. This is in contrast to todays standard, which is more like 500 ppm. This new fuel will be of similar purity to what theyre selling across the pond right now. As a result, you should start seeing more of those diesels making their way over to America in the coming years. Currently, our fuel is to dirty to allow them to meet emissions requirement. Ive also heard that sulfur content of our fuel can also foul their high-precision fuel systems, although I dont know if theres any truth in that.
http://www.epa.gov/fedrgstr/EPA-AIR/2001/January/Day-18/a01a.htm
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Kirk 10:26PM (12/18/2005)
TDI stands for "turbo direct injection". SInce turbo charging and compression combustion go together like pizza and beer, I'm sure they will continue to incorporate boost.
(Mercedes label their common rail motors CDI, so perhaps they would object.)
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Peter W. 10:26PM (12/18/2005)
Ahhh, that's why CDI's are in Jeep... Liberties... *shakes head*
I guess VW will have VDI or TDI-c or somethin..
In the meantime, why hasn't any company made a two stroke deisel for a passenger car yet? It seems like most companies have gotten the costs of diesel hardware and turbochargers low enough that a VW or a Mercedes (smart!) could drop in a two-stroke, two-cylinder pumping out something impressive...
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sparc 10:26PM (12/18/2005)
W,
Diesel regulations are constantly getting tighter, even for commercial trucks. Having formerly worked as an engineer for CAT engines, I saw first hand how much work went into emissions. Meeting the latest EPA requirements was generally first priority for every new design, since you can't make money on an engine that you aren't allowed to sell.
The most recent standards update occured in 2004 and required all manufacturers to come out with new engines. At this time CAT introduced a whole new technology branded as ACERT which is essentially some very sophisticated controls for fuel delivery and engine management. See here
http://www.dieselnet.com/news/2003/01cat.php
or maybe here
http://www.cat.com/cda/layout?m=48920&x=7
The emissions requirements tighten again in 2007 and will require even more innovation to meet.
Not only are emissions getting tighter for on-road engines but off-road engines (such as those used in construction/mining equipment) are getting cleaner as well. Granted these standards usually lag behind at least a couple years, but it is certainly not being ignored.
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Eric Bryant 10:26PM (12/18/2005)
Kirk,
Thanks for the clarification. I was under the incorrect impression that the domestic-market TDIs still used the radial pump.
Peter W.,
I can't imagine that a two-stroke diesel would be acceptable nowadays for a passenger-car application, although Detroit Diesel sure had a hell of a run with them for OTR and off-highway applications. Maybe the application of modern engine controls would make a two-stroke the way to go for diesels; it'd sure be cool to see someone try.
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sparc 10:26PM (12/18/2005)
It seems to me that TDI would still be a valid acronym since the engine is still turbocharged and the fuel is still being directly injected into the cylinder. It's just the delivery method that's a little different.
If they change it to anything I'd expect it to go to Diesel Stratified Injection (DSI) to match with their new gasoline FSI power plants.
Peter, you probably don't see two-stroke diesel cars for the same reason you don't see two-stroke gas cars, emissions.
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Big 10:26PM (12/18/2005)
Just for clarity, why? Is this meant to increase fuel effeciency, lower cost, or increase power.
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jamie 10:26PM (12/18/2005)
#1 - "You don't hear about Freightliner, CAT or Mack changing their engines to reduce emissions.."
Apparently the government is already meddling in their pants and wants them to comply with more stricter regulations in 2008. Ho-hum, so what else is new?
I am disappointed that the TDI is going to be dropped, but I believe VW made a wise decision. The new engine will be less complex and therefore less prone to mechanical failure which has been one of the main complaints levelled against the TDI. Ah, the price of progress!
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sirAQUAMAN64 10:26PM (12/18/2005)
To my knowledge, Bosch makes both the VW Group-specific TDI individual-cylinder injection pumps as well as the common-rail systems. I think the VW injectors are incredibly expensive, and thousands to replace should water get into the system and render them inoperable.
I am sad to see this system go away.
I heard VW was developing an entirely new range of TDI's, and I guess this is them.
What's in the EcoRacer concept?
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Peter W. 10:26PM (12/18/2005)
Sparc:
http://auto.howstuffworks.com/diesel-two-stroke1.htm
"you can see the big difference between a diesel two-stroke engine and a gasoline two-stroke engine: In the diesel version, only air fills the cylinder, rather than gas and air mixed together. This means that a diesel two-stroke engine suffers from none of the environmental problems that plague a gasoline two-stroke engine. On the other hand, a diesel two-stroke engine must have a turbocharger or a supercharger, and this means that you will never find a diesel two-stroke on a chain saw -- it would simply be too expensive."
But would a two stroke deisel be too expensive in a car? Twice the power in half the space seems like something car companies wouldn't mind wrapping a test mule around...
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sparc 10:26PM (12/18/2005)
Thanks for the link Peter, cleared it up a bit for me. I'm still not convinced that they are equal from an emissions standpoint though. Looks like you would still get an unknown quantity of oil in the intake, and you would have a much harder time predicting how much exhaust gas is left in the cylinder after the valves close. This affects the combustibility of the air and limits how much fuel you can put in, so it's really a good thing to know.
Other drawbacks I can see include an engine that is necessarily taller (to accomodate that taller piston) resulting in greater size and more weight. The piston and rods would be even heavier, limiting top RPM more than it already is. You would also need a cooling system that can deal with twice the amount of heat per cylinder, which may not be feasable in high horsepower (relative to size) applications.
Not to say these hurdles couln't be overcome, but if two-strokes were really as good as they look on paper, one would expect at least one automaker to be using them.
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Peter W. 10:26PM (12/18/2005)
Big: Yes
It's basically all the benefits of disconnecting fuel injection from the engine timing mechanically.
Moving to Common-rail with piezo as opposed to a radial pump or PD is like moving to electronic ignition module from distributors... There is now a lot more freedom to time the injections based on engine speed and throttle input, which should allow for hikes in emissions, power, and economy depending on how they play with it.
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66coronet 10:26PM (12/18/2005)
I wonder if VW is making these changes to meet chrysler specs too. Since the VW 2.0L diesel will be used in the dodge caliber and most likely the jeep patriot and compass and some mitsubishi's.
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PG 10:26PM (12/18/2005)
TDI and CDI are marketing terms and don't really stand for anything apart from identifying it as a diesel.
Common rail technology uses a pressurised fuel tube (the rail) to feed a number of electronically controlled injectors.
The unit injector technology that VW have termed PD (Pump Duse, loosely translated as Pump Injector), has a pump integrated into each electronically controlled injector. Each pump is driven of a lobe on the camshaft.
I don't believe that there is much performance difference between the two. The decision (if true) is more likely to be due to a packaging issue with the slightly taller injector/pump becoming an issue with tall engines reducing the space available for bonnet crumple zones for pedestrian impact regs. That along with the economies of scale with most other manufacturers sticking with common rail.
PG.
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Hooonza 10:26PM (12/18/2005)
Hi there,
Pumpe-D?is being abandoned because of what Kirk said. CR can inject the fuel at any time and you need this ability to regenerate the particle filter (fuel injection into the exhaust).
Actually, the filter can be also regenerated by using an iron-based additive fluid, but that would mean you have to refill the additive tank approx. every 80 000 - 120 000 km ( ~50 000 - 75 000 miles). This process is also known as "maintenance" and the customer wants everything maintenance-free... This can only be realised via common-rail / HADI.
The PD-injectors (~500 per unit) are not that expensive for small engines because you do not need an additional high-pressure pump (~1000).
I am very sad too that PD is not going to be further developed. A like my PD-engine very much.
Greetings from Central Europe
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Bert Graef 10:26PM (12/18/2005)
Its time the public got enraged over the increasingly silly and outrageous environmental standards to which the diesel engine is held hostage to.
It seems evident that as soon as manufacurers meet the new standards, these environmental kooks come along and raise the bar even higher just to prove what complete A-holes they really are.
Just ask these morons what vehicle actually is "greener"; a Prius driven 30000 miles a year getting 60 miles to the gallon, or a SUV owner driving his "hateful, terrorism causing,global warming creating, evil" vehicle driving only 10,000 miles a year and getting 20 mpg.
Simple arithmetic will tell anyone but the dogmatic environmental boneheads that in this scenario, both vehicles actually use the same amount of fuel in a year.
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