Two stroke diesels

[HillCountrykid]

Does anyone know how the power of a two stroke diesel compares to a four stroke? The CFI drag truck on the ddra site has a two stoke Detriot, and it's runnin' 110 mph (hauling a$$ for a huge aerodynamically challenged box). I've been around two stroke dirt bikes most of my life, mainly a 465cc Suzuki, and in this application I would'nt trade my two stroke for anything. I know I'm comparing apples to oranges here.



Brian

 

[illflem]

Don't know how the power compares, but have seen 2-stoke diesels in smaller boats. One thing I always thought was cool about them was that to go in reverse the engine stops then restarts turning the other direction.

 

[emarsh]

Yeah, I had this happen to me on a motorcycle, I stalled the engine on a hill and it rolled backwards while I pulled in the clutch; I coasted down the hill while the engine was still running and shifting into neutral, then on flat ground I let out the clutch and it went backwards! This is true. a Hodaka 90 cc that must have had retarded ignition timing.

 

[Cummins Corvette]

UMMMMM... ... Illflem... ... ... . If a two stroke diesel runs in reverse it will pull exhaust into the supercharger, out the air filter, and total the thing. It wouldn't really even work because the expanding exhaust gases would counter the effort of the supercharger and no air would be moving thus no combustion would take place. But, if it did move enough air, the supercharger moving hot exhaust is going to ruin the seals, plus it would be sucking unfiltered air in though the exhaust which couldn't be good. And you said that this was a marine application right? That wouldn't be air going into the engine, would it? The exhaust exits below water in every boat I have been in. No real expert here, but I have taken apart a 6-71 detriot, and from what I have learned, that really wouldn't work well. Oh ya, the injectors aren't going to work right either. The timing in reverse would be so off that the thing would inject the fuel when the piston was half way up.

 

[Joe G.]

The 71 series diesels will run backward for a short time. They make a big mess when they do. The supercharger turns backward too so it's trying to suck from the engine. All the fish boats I've had anything to do with have exhaust stacks so water in the exhaust is not a problem. Usually they will start right back up in the normal direction and the only damage is the mess. It's kind of a rare event. Some large 4 stroke diesels were made to run backwards instead of haveing a reverse gear. I think that is a thing of the past now.

 

[illflem]

The ones I've seen definitely aren't six cylinder Detroits, they're a one very large cylinder Lister. Don't ask me how, but they run in reverse. Very common in fishing dories in Norway.

 

[Joe G.]

The six cylinder Stirling (sp?) diesel in WW II tug boats would run either way. To reverse it the engineer would stop the engine and turn a brass wheel to do something with the cam shaft and start it. It used air start so it started instantly. BIG engine. The floor (that's correct, not deck) was even with the center of rotation of the crank, and the top of the head was taller than a man.

 

[Rcpilotlv]

Brian, in diesel engines I dont believe you have any power advantage with a two stroke. From what i here most truckers prefer 4 stroke ie, Cummins and Cat... Also you probably would have more fuel consumption... This is considering the engines are the same size... Now in dirt bikes and atvs it takes about 150 cc more displacement for a four stroke to compare to a two stroke. However the gap is narrowing. The new four strokes are big bore,short stroke quick reving engines just like the old two strokes. . Ever ride a YZ 426... . I saw one pull a YZ 250 in every gear and top speed... Also they are more reliable then there two stroke cousins... . Some have DOHC, 5 valves and even Fuel Injection... Four stroke Technology is advancing every day because of emissions... . One day there will be no two strokes left... emissions emissions emissions..... OOPS this is a diesel fourm

 

[DieselB59]

Unfortunately, the info on that site was wrong. The CFI drag truck uses two Cummins N14 engines with a total of three turbos on both engines. The CFI Pikes Peak truck uses a Caterpillar and, as well does the CFI Flat Out salt racer. None of them use Detroit two strokes. The Smith Racing Team, in their Tornado and Tornado II trucks use the Detroit two strokes. They boast about them being quad turbo and supercharged. The quad turbo is for power, but the supercharger is there by design only to provide the cylinders with air. Without one, the engine would not function. On the cylinder head there are only exhaust valves. The intake vents provide the intake air. The engines are God awful loud, and are described by the industry as "road oilers". A Detroit mechanic once said to me that the engines leaking oil is a good sign..... a sign that there is still oil in the engine.

 

[HillCountrykid]

Thanks for the information guys. Two stroke gas engines are different enough, but it looks like the two stroke diesels are totally different.



Chris, thanks for the correction. Two N14's, 6 turbos, no wonder it's scooting that fast. Think I could shoehorn that into my truck. Or maybe we could put that engine in the project truck that runs 11's in my truck. Then we could roast marshmellows on my clutch.

 

[illflem]

Click here for a good explanation of 2 vs. 4 stroke diesels.

 

[KB0OU]

STROCKIN X 2

Yes there is a power advantage to the two stroke engines, but an economy disadvantage.

I have seen some run in reverse, most are not designed to and it is really not good for them.

On some submarines we had 6 cylinder Fairbanks Morris with 12 pistons, two cycle. They had a top crank and a lower crank with a joiner shaft on one end. Ran good til the joiner shaft joint slipped!!

By the way, no head, injectors etc. in the middle of the cylinder where the two pistons per cylinder came together on the compression stroke, the injector fired about 7. 5 deg before the middle dead center (MDC).



That engine is bigger than my truck!!

 

[HillCountrykid]

Thanks illflem, that answers all my questions.



Brian

 

[David Oxland]

Many, maybe most, large (over 5000 HP) two and four stroke Marine Diesels use what's called direct reversing. The engine is started and runs backwards rather than have a reversing gearbox. I spent a couple of fun years running two 3000HP "Mirlees" direct reversing engines on a ship.



There are several ways of doing this but all involve changing the inspiration, exhaust, and fuel timing. The Mirlees had two sets of cams on the same shaft ,side by side, with followers that could slide back and forth to respond to one cam or it's differently positioned mate and transmit motion to the push rod. The same applied for all cams intake, exhaust, and fuel. Some makes of engines have a shaft with two complete sets of cams rigidly mounted in diferent positions and to prepare the engine for reverse one slides the whole cam bodily until the new cams are in position to do their job. These engines are very robust and generally run on heavy fuels which used to be called Bunker A,B,and C. Bunker C's viscosity was comparitive to very heavy molasses. They're made by companies like MAN/B&W, Sulzer and Mitsubishi It couldn't be handled, pumped or transfered tank to tank unless heated to about 100F. To be prepared for injection temps are brought up to in excess of 200F. Largest engines produced, I believe, approach 100,000 HP and run at 95 to 100 RPM. with 12 cylinders in line.



Notably, for the oil change freaks, they never change lubricating oil.



If it still exists, I started a thread about "large engines" it might have been called. There was a picture and a little demo file there I think I found the thread it was "A Marine or Stationary Engine" not sure if I can get it as an attachment for you but a search will find it

David

 

[Joe G.]

KB0OU,



I was on a diesel sub once when it came to Eureka. I noticed that when it came up to the dock it was really pumping the water thru the cooling system. So when I was BSing with the chief guiding the tour I asked him how long it takes to pump the Pacific Ocean thru those engines. Cracked him up. I guess nobody asked that one before. I'm not sure but I think it had two FM rockcrushers, might have been four. My memory may be failing but I think they were laying on their side in that boat so the cylinders were horizontal. Two cranks and no head. I believe it also had a plastic window on one end so the engineer could see that the prelube pump had oil thru the engine before it was started. I did notice the rack of ear protectors right outside the engine room and the warning sign about wearing them. One of those engines would have crushed my truck flat to the ground.



I helped a friend overhaul a big Cat in a fish boat once. Mostly unskilled labor from me. The parts were heavy. Red line was 900 RPM on that thing.

 

[HillCountrykid]

I allready found it David. That's a big engine. I've seen specs for large engines, but that is probably the biggest one I've seen in a picture, except maybe for a generator at a 3M plant here in Austin. The biggest engine I've found specs for so far (I only remember the weight) was 711,000 lbs.



I was looking around and found one a little bigger. No pictures, but here are some specs.



Sulzer RTA96C-14

Length-85 ft

Width-14ft 4in

Height-44ft 4in

Weight-5,070,632 lbs

Cylinders-14(not sure of configuration)

Bore-37. 8 in

Stroke-98. 4 in

HP-107,389@102 rpm



Brian

 

[KB0OU]

LARGE ENGINE THREAD

I can't find it where is it???

If ya want to see some big ones Carthage, Missouri still has some at the power plant, I will see if I can get some pictures sometime and post them.

John

 

[SOOT]

CFI

I went to the pikes peak race this year it was awsome I watched the CFI truck with the 1450HP C16 Cat and the 12 in diameter turbo and about 14 in's of a 6 in diameter exhaust pipe I was standing next to it when he started it all I can say is SWEEEEEEEEEEETTT and no smoke!

 

[roadranger]

2 stroke diesels

Back in the 70's I drove for an outfit that had several similar trucks outfitted with either 350 hp Detroit Diesels (2-stroke) or 350 hp Cummins.

We had many trips running together at max GVW.



The Detroits could have their governors turned up to turn 2900 rpm, so could run faster over the road in high gear.



The Cummins did not get turned up more than 2100 rpm, or they would live up to their nickname at the time of "come-apart".



The Detroits would fall flat on their face on any hill, as they had 1/3 less torque than the Cummins.



So, running two of these trucks on a trip together would be like the Rabbit and the Turtle story.

The Detroit would run like hell to hit the hills, only to have the Cummins pass it on the hill. They would both get to the destination within 15 minutes of the same travel time, though.

 

[David Oxland]

Sure I'd like to see the photos. Also I mentioned on another post there's a site

www.prime-mover.com that's worth a check out for engine lovers. There's lots of stuff in there to dig around.