Direct Injection heads?

[Blaine Hufnagle]

Has anyone seen or heard of any direct injection work for the 6.2/6.5?

Just wondering if it's been done, or if it's been done and considered a failure, or what....

-blaine

[Dieselboy]

Word was that GM gave them a try for an interum solution until the Dmax came out. They were deemed too noisy, and so the project was scrapped.

More Power would have better info.

[britannic]

Noisier, but should provide more power one would hope :D - be kind of a fun (costly and time consuming of course!) retro project.

[NH2112]

Noise? If I cared about noise I'd drive a gasser :D

[Blaine Hufnagle]

Well, since I'm more or less bench racing at this point, noise really isn't an issue. :D

(and I doubt they'd be louder than a Detroit S60)

I'm guessing they made new castings?

I'd be interested in doing a retro project if I could find 1) a truck/engine to start with, and 2) a set of the heads to play with. :D

I've toyed with a few ideas on how to cobble a set of DI heads, but I've got no ideas on how difficult it'd be.

[Dieselboy]

As far as I know, the engines never made if off the test stand, and only a few heads were produced.

[C.K. Piquup]

I think GM has been overly concerned with diesel"noise"since the 350diesel.Diesels were a new concept in America in light duty vehicles.They did cars too,remember?I heard more comments about the"bad knock".Then,in short time,the motor proved to be a bad product.This just reinforced people`s concerns.GM`s been trying to live that one down eversince.

[dieselhumvee]

seems like a machinist could make custom prechambers that put the injector closer to the piston, without redesigning the entire head

[Dieselboy]

It's likely that a different injector or new calibration would be required as well. The current setup is designed to shoot fuel into the confined area of the prechamber while a DI engine needs to have the injector fire in such a way that produces the right swirl pattern in the cylinder during expansion. There's a number of engineering problems to take into account, and this is just the first one that came to mind.

I'd be interested to learn how GM accomplished direct injection with merely a new set of heads, and how much of the fuel system had to be altered to accomodate the change.

EDIT: Grammar :D

[ 03-24-2004, 06:49 AM: Message edited by: Dieselboy ]

[NH2112]

I believe that the pre-combustion chambers in a DI engine are actually turbulence chambers, and provide the swirl or turbulence needed for the fuel charge to properly mix with the air. Pop pressure is also much higher with a DI engine, which helps a lot with creating the required turbulence. Specs for my Volvo TD60 call for opening pressures of 3900-4000psi, as opposed to the 1800-2000psi for 6.2L/6.5L injectors. I believe the DB2/DS4 pump can provide those pressures, though.

[britannic]

DI engines don't have pre-combustion chambers, but instead inject fuel directly onto the pistons.

In the Cummins 6BT that I have, the pistons have a recessed "chinese hat" shape on top and the injector sprays in the center of them. Although the injectors are angled in the 12V 5.9L, the nozzles are designed to give a vertical spray to compensate.

Your point is exactly correct for the IDI engine and there's a lot of factors that are considered when designing the pre-combustion chamber, of which swirling is one of them.

The DB pump can definitely provide enough pop pressure for a DI and in fact I know that some John Deere and Cummins engines use a DB2 for their 4 bangers.


Originally posted by NH2112:
I believe that the pre-combustion chambers in a DI engine are actually turbulence chambers, and provide the swirl or turbulence needed for the fuel charge to properly mix with the air. Pop pressure is also much higher with a DI engine, which helps a lot with creating the required turbulence. Specs for my Volvo TD60 call for opening pressures of 3900-4000psi, as opposed to the 1800-2000psi for 6.2L/6.5L injectors. I believe the DB2/DS4 pump can provide those pressures, though.

[CleviteKid]

You guys are all correct that the Comet Mark V prechamber and piston top configuration in the 6.2L and 6.5L generates the swirl (not turbulence) necessary to mix the fuel droplets and the air. Swirl in DI engines is generated via the angular momentum of the incoming air and is magnified when the piston compresses the charge and the angular momentum is conserved. The fuel, in essence, is injected across a veritible windstorm of swirling air, exposing the burning drop to fresh oxygen as it burns. Quite an accomplishment in those engines that do it well ! ! !

Dr. Lee :cool:

[NH2112]

I was just looking through the Volvo TD60 shop manual I got from Peter J Bierman and it shows an oddly-shaped combustion chamber on the piston top. Picture a heart-shaped cutter, pointed end up, used to create the combustion chamber. There's a conical projection in the middle, with a donut-shaped chamber around it, 57mm wide and 21.8mm deep at its deepest point. I can just imagine the air currents created as the piston is coming up to TDC on the compression stroke.

[britannic]

Technically that Volvo TD60 is a DI and now I see where you were coming from. For me the classification of an IDI is the injector sitting in a combustion chamber in the head and indirectly feeding pressure into the cylinder.

[NH2112]

I knew the TD60 was a DI engine, but guess I was thinking of the combustion chamber as being a part of the head, like on a gasser, and doing the same job (swirling the air, directing the burn and expansion, etc.) It does the same thing but is in the piston crown instead.

[Blaine Hufnagle]

Yeowza... Took me a while to get back to this. Such is life on the road. smile.gif

Again, bench racing here. I'm not intimately familiar with the 6.2/6.5 heads. I'm assuming the prechambers are removable; given that, would an engine even run (i.e. idle) if one were to basically machine off the bottom half of the prechamber so that the injector fired directly onto the piston crown?

Note that this is still a thought experiment. Power output at this point is a secondary concern; I'm just wondering if the engine would even start.

(I have lots of time to think, but nothing to experiment on yet. smile.gif )

-blaine

[britannic]

It would run, but I'll bet efficiency would be way down, unless the injector was redesigned. IMHO, the pre-chamber would need to be removed, the void filled in flush with the bottom of the cylinder head and then the injector port drilled into it so that a long injector would be positioned to inject on top of the piston crown.

The pistons would need to be a different design with either the sort of chamber nh2112 described or some other diesel design.

Glowplugs would be a problem, but the Cummins only uses intake grid heaters below freezing with 17.5:1 cr.

When's all said and done, it's probably a whole lot easier to install a purpose built DI like a Dmax or Cummins and enjoy :D !

[dieseldummy]

I beleive that the Duramax and the 6.5 have the same bore, and I think that the stroke is only 3mm different. do you suppose that pistons from the Duramax could be fitted to a 6.5? It would provide the correct type of piston crown for DI combustion.