Difference between Turbo diesel and CDI engine - Mercedes-Benz Forum

 
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post #1 of 10 (permalink) Old 03-26-2009, 02:35 PM Thread Starter
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Difference between Turbo diesel and CDI engine

Is there difference or it's only a modern name for the same engine? If there is difference would you mind explaining, please?
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post #2 of 10 (permalink) Old 03-26-2009, 02:56 PM
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CDI has a turbo, but it just uses a common rail electrically-triggered injection system, not unlike a modern gas engine. Older turbodiesels used a centrally located mechanical pump.
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post #3 of 10 (permalink) Old 03-26-2009, 02:57 PM
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How about Turbo Tax?
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post #4 of 10 (permalink) Old 03-26-2009, 03:07 PM
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To complicate matters, the '05 CDI was the wonderful straight six diesel. Then they went to the V6 diesel engine, and called it the Bluetec for a year. But it wasn't. Then, they really went with the true Bluetec with urea injection (piss in the tank) last year.

I don't really know if any of this is true, I started drinking early today.
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post #5 of 10 (permalink) Old 03-26-2009, 03:15 PM
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post #6 of 10 (permalink) Old 03-26-2009, 03:18 PM
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How about Turbo Tax?
It's ready to get supercharged.
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post #7 of 10 (permalink) Old 03-26-2009, 06:20 PM
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CDI has a turbo, but it just uses a common rail electrically-triggered injection system, not unlike a modern gas engine. Older turbodiesels used a centrally located mechanical pump.
.
That is basically true. With the 606 engine, when it was turbocharged it was also intercooled. This is now also the standard configuration for the CDI series of Diesels.

The direct injection system is a significant advance over the previous technology, as MB and VW have implemented it. Older Diesels injected the fuel through what is commonly called a relief valve, into a prechamber, above the piston, in the cylinder head. The prechamber included a few bizarre solutions to noise and rate of combustion challenges. It is also where the glow plug heating element is located.

The 606 engine has a more sophisticated injector that, as it opens, gives a little presquirt of Diesel, stops, and then lets loose the rest of the wad in a single shot. The idea was the presquirt lit up quickly (lots of oxygen, heat and little fuel) and the main wad shot goes directly into the flame front from the first shot. Much better combustion, lower noise and less soot. More NOx at off throttle. Greater efficiency though.

The new injectors are truly controllable fuel injectors - little electronic actuators buzz the injector for up to 5 or 7 separate injection events per combustion stroke. Much cleaner burning. Much lower noise. Better mileage.

The emissions standards are tighter though and the higher efficiency produced more NOx. To address that they added a LOT of exhaust gas recirculation at low throttle positions. Less O2 available to make NOx. So, the idea is to try to achieve the gas engine's stoichiometric fuel and oxygen mixture, while still filling the combustion chamber with compressible gasses so you can do the Diesel ignition thing. This only works to a point. Diesels are normally very lean burning, and when they don't blow any smoke they are very lean burning. Lean means NOx. So they added catalysts. And particulate traps again, and the Bluetech urea injection to maintain the catalysts.

At present a "CDI" and "Bluetech" means you have the new common rail (fuel header maintained at ~1800 or more psi) fuel distribution to those highly controllable injectors that inject directly into the combustion chamber above the piston, and the engine is fed air through a turbocharger at elevated pressure, after it has passed through an air to air heat exchanger called an intercooler, that is mixed with recirculated exhaust just before the intake manifold, which is tapped off the exhaust header before the exhaust passes through the emissions cleaning catalysts and particulate filters.

The 1980's vintage turbocharged Diesels were much simpler and did not have intercoolers. As far as I know the intercoolers were introduced on the 606 engines. (the 1998 and 1999 E300D TurboDiesels in the US in the W210 chassis).

Hope all this helps.

Jim
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post #8 of 10 (permalink) Old 03-26-2009, 07:34 PM
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My earlier post was brief 'cause I typed it on my iPhone.

It's true about the intercoolers starting with the OM606 turbos. I had one custom made for my current OM603. I'm presently in the process of installing an OM606 from a '99 E300D in my wagon. That's the first I've heard that the OM606 had multiple injection stages, which is something I've only previously associated with modern direct injection engines, like the VW TDI and MB CDI. Since the OM606 is still an indirect injection engine with pre-chambers, I'm not sure that multiple stages of injection would be as beneficial--dunno for sure.
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post #9 of 10 (permalink) Old 03-26-2009, 07:47 PM
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Hope all this helps.
Appreciated it here actually; I even understood some of it. Now why can't/won't they clean up the diesel exhaust from large trucks??

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stoichiometric
Woohoo! Triple Word Score!
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post #10 of 10 (permalink) Old 03-27-2009, 12:51 AM
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My earlier post was brief 'cause I typed it on my iPhone.

It's true about the intercoolers starting with the OM606 turbos. I had one custom made for my current OM603. I'm presently in the process of installing an OM606 from a '99 E300D in my wagon. That's the first I've heard that the OM606 had multiple injection stages, which is something I've only previously associated with modern direct injection engines, like the VW TDI and MB CDI. Since the OM606 is still an indirect injection engine with pre-chambers, I'm not sure that multiple stages of injection would be as beneficial--dunno for sure.
On the OM606 engine this is achieved by having the pintel shaped vaguely like the ideal female form. As the little relief valve lifts due to building fuel pressure from the variable displacement, positive displacement pump, the pintel lets a small amount of fuel squirt as the "waist" passes by the nozzle. As the pintel continues to lift and the "hips" pass by the nozzle, it acts like a "normal" injector opening and the rest of the stroke of fuel from the pump is squirted into the prechamber based on your throttle setting with your right foot. The difference is the greater volume squirt is directed into the flame front from the prior mini-squirt that was very thoroughly atomized. Properly working these things reduce the knocking (my OM606 hardly knocks even at start up when it is cold, provided all the glow plugs work), reduce the smoking and sooting and give a better fuel economy than the regular old injectors of the past. I believe they require the electronic controls on the injection pump to work properly (idle could be a challenge), but that is a guess.

As for trucks, new trucks do a lot better with the low sulphur fuel and similar injector technology. I believe they are all direct injection machines. When new ones smoke excessively the problem is maintenance. Properly running they leave mostly only a heat plume now, even hauling up a slope at altitude in the Rockies (just spent a week skiing at Wolf Creek, Colorado and there were plenty of clean burning trucks hauling loads over the pass without the usual twin streams of black smoke). But there are lots of older units on the road still, and likely will be for some time to come.

Jim

Last edited by JimSmith; 03-27-2009 at 12:56 AM.
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