All of the 2 cycle Detroits that I'm familiar with never had any glow system. But, they wouldn't start below 32F. without ether unless they were brand spanking new.

I believe the need for glow plugs is mandatory on an IDI diesel due to the very cold environment of the prechamber. A DI diesel has an even chance of starting without glow plugs, but, it's no certainty on any of them when it gets really cold. Ether is the mode of choice to get them going and it doesn't appear to have any negative consequences if used judiciously.

The OM617 type of injection uses a pre-combustion chamber (Indirect Injection).....

The injector does not spray a pattern as most do...instead it "spritzes" a straight stream....

The stream of fuel oil is designed to hit a little ball within the pre-combustion chamber....

This little ball is also designed to retain heat when the engine is running....

The straight shot of fuel oil is vaporized upon contact with the HOT little ball......

The pencil type of glow plug heats this little ball...unsure as to how the older loop style work, for certain....

So when the engine is cold, the glow plug heats the little ball (initially), the fuel is squirted onto the ball, and vaporized.....and combustion occurs when the compression rises to it's ignition point.....after the engine is running the heat of combustion maintains the little ball temperature.....

SB

Note: I think (note think!) that the reason we get the nailing issue is because a piece of carbon (or other trash) causes a portion of the injected fuel to miss the little ball....and to ignite further into the combustion chamber.....and at a slightly later time.....

__________________

Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

In looking at the diagram for the prechamber, glow plug, and ball, you'll notice that the ball is probably 6-9 mm away from the tip of the glow plug. The tip resides in the air space between the bottom of the injector and the ball.

So, with the plugs on for 15 seconds, the capability of getting the ball to anything close to "hot" is non-existant. It's the airspace above the ball that gets most of the benefit from the glow plug. The fuel must pass through this space on its way to the ball. While the ball certainly helps with dispersion, it can't be the main source of heat to light the charge. The steel could never soak up enough heat within the short glow plug cycle.

Knightrider,
Any way you could provide links or any other information on these high compression diesels? I would like to see what they are all about, things like how they are started, fuel used, etc. A search on the internet as well as speaking to some buddies that are mechanics, and a USCG diesel tech have all drawn blanks looking for info on these high compression diesels.....

Thanks, RT

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84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

I don't know of any links to what your asking and I know that these higher compression diesels are not being made anymore due to the extremecost! The 50:1 diesel I told you about was one we engineered for the Dept of the Navy and was an inline 8 cylinder connected to a Carrier refrigerant pump about the size of a large chest freezer. The unit was designed to take an ambient temperature of a comfortable 75 degrees Farenheit and turn it into a 105 or lower deep flash freeze in less than 5 minutes! We never knew what the Navy wanted this for and we didn't ask but I believe since the Navy was doing some climate survival studies on the effect of humans and the environment that this was it's purpose. The goal of getting it cold ASAP was because it was not efficient and even with a boost pressure of 50:1, it sucked fuel like flushing a toilet! It cooled, er froze a room of about 400 square feet in size! The engine had an electric motor of 2.5 HP driving the lubrication pump constantly whether the engine was running or not. The engine drove none of it's necessary accessories, coolant pump, oil pump, fuel pump etc. except for it's DI pump and a 400 CPS Dynamo. This design was later used by fisheries in Alaska to flash freeze the catch of the day, although not to these exact specs because of cost, but smaller and simillar. I've worked on power generating systems that had higher compression ratios in Alaska. These were the only power station for smaller towns some years ago. The size of the starter motor was designed to turn them over at a high RPM to get them started! Machinery made for an intolerable climate would not be anything you would see here in the lower 48.
I should also point out that after reading your questions, I think you think I meant that these engines were 50:1 at a normal startup. Not so and I didn't mean to confuse anyone, but sometimes I get lost in my little engineering details, heh heh! A 50:1 diesel will first light up at about 25:1. I'm not sure if I'll do a good job of explaining this one but here goes. When an engine begins to gyro, that is turn and run on it's own, the metal are stressed in a totally different way than you would think on a engine designed to run at a constant speed. A 50:1 diesel in your car or truck in stop and go driving with varying engine speeds would not last the entire month under those conditions! Balancing is crutial to high compression and high RPM constant speed diesels. When a diesel engine, or any engine for that matter begins to gyro, the metals stress not from up and down or side to side, but in a spherical pattern. When the engine is running at high RPM and turning over to the left, the casing will want to turn and gyro to the right. If your engine design was to have a center point of balance, like the crank, turning to the left while the engine casing rotated to the right, you could run it at very high ratios and counteract the destructive force behind having one part immobile and the other part at a fast velocity. In essence, your engine block and internals become a total part of the driving force,see? Two opposing forces counteract each other! I didn't believe it when I saw this either and it all sounds very star trek but it has been done. I guess that the closest thing we would see today would be a jet turbine. Multiple cylinders in a rotating casing running on lubricating oil has been tried and was a test pilot project powerplant in large heavy trucks, but it was all very hush-hush, trade secret and all that. When these truck specialty motors were taken "out of service" they were destroyed so as to protect our corporate interests, but it sure was fun and some of the research technologies are being used today. Variable compression and volumetric efficiency are more commonplace now. As far as I know, there are not many people lucky enough to say they saw, much less worked on a counter-rotating force diesel with a CR of 50:1 and 14,400 RPM! Guys, I really miss my days at Chrysler and this is why it was some of the best times of my life!

As FI mentioned above, when we refer to compression ratio, we're talking about static compression ratio. Simply take the volume of the cylinder with the piston at BDC and compare it to the volume of the cylinder at TDC. That's your ratio.

If you then manage a higher effective ratio via the use of additional boost pressure, that's another condition altogether and it's got nothing to do with the static compression ratio.

Even 25:1 is significant for a diesel when looking at static compression ratio. Clearance for the valves becomes a significant problem. Were these DI engines?

Yes. A piece of thin paper would be the only thing you could fit inside the cylinder for instance. At first, we wanted to be behind an explosion barrier when at first start!

I would think that the surface of the ball would pick up a bit of radiant heat in a small space.......and as you pointed out the air within the pre-combustion chamber would be warm/hot.......

Perhaps I am missing something, but that's how I thought this type of pre-combustion chamber works....perhaps I am mistaken, would you care to enlighten me???

SB

__________________

Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

Don't know what the little ball does. Other IDI diesels I have looked at, GM and VW, IIRC don't have the little ball. The precombustion chambers don't protrude into the combustion chambers in the GM either. The MB has 5 little holes that all that hot gas has to pass through. The GM has an oval port.... I'd like to know what the difference is. RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

I believe the ball definitely picks up radiant heat from the tip of the plug. But, being that it's steel, I can't heat up to anything close to ignition temperatures in the short period that the plugs are on.

You can easily duplicate this with a glow plug and a battery. Put a piece of steel about 1/4" away from the red hot glow plug. In 15 seconds, I'll bet that you can still touch that piece of steel without burning yourself. If so, then the ball cannot be the ignition source.

The air surrounding the tip of the plug will probably climb up to 200 degrees or so within 15 seconds. Couple this with the added heat of compression and you've got the temperature you need to light off.

The temperature of the ball won't climb 5 degrees during the compression stroke........the temperature of the air will climb hundreds of degrees.

This is getting to be an interesting thread. I still don't understand why the need for glowplugs in some and not other diesels. It isn't the compression ratio apparently.
My CAT 3208 is in a Bluebird Wanderlodge. It came from the factory with a block heater but no ether injection system, so it seems there was a fair amount of optimism about its ability to start in cold weather unaided, although it does have a Perkins glow-plugged diesel generator which can be used to operate the block heater. I believe the 4 cycle Detroit 8.2 diesel also did not have glow plugs. I've seen an ether injection system on one of those. How about the Cummins 555?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

My buddy has two Detroit 8-71TI's in a Hatteras. Old engines but way cool with two turbos intercooled and feeding the blower. 425hp and ridiculous torque. No glowplugs and no cold starting system. Dunno if they even have block heaters. They are very cold-blooded and smoke enough to kill every mosquito in the state for a few minutes until warm. They take a good bit of cranking to get them to light off. I know its old tech but the noise they make is great. RT

__________________
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

Yes, very interesting. Apparently the explanation isn't as simple as one would think.

Brian, your idea of a test wouldn't work unless it was made within the same small space as the precumbustion chamber. Doing it in open air wouldn't be conclusive.
I bet the results of this test would be interesting.

I would imagine the answer lies somewhere between Shorebilly and Brians explanation.

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1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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Please note that I never said that the little ball was a source of ignition.....I said....

"So when the engine is cold, the glow plug heats the little ball (initially), the fuel is squirted onto the ball, and vaporized.....and combustion occurs when the compression rises to it's ignition point.....after the engine is running the heat of combustion maintains the little ball temperature....."

....try dripping a a few drops of diesel onto a hot soldering iron.....it will produce a white smoke like vapor....this is what I was referring to when I said vaporized.....this fuel vapor is easily ignited......

I had not intended to begin an in depth discussion of the process....I was doing my best to simplify the operation of the pre-combustion chamber, to a point where most could understand what was going on inside of the pre-combustion chamber......and the fact that the initial heat supplied by the glow plug was maintained by the heat of combustion.....

SB

__________________

Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

http://en.wikipedia.org/wiki/Diesel_engine#Fuel_injection_in_diesel_engines

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Scott C.

2006 E320 CDI (120k miles)
FOR SALE: 1998 E300 Turbo Diesel - Black w/Tan Leather - Euro delivery (236k miles)