Two Cycle Diesel Locomotive

[wholeman]

Someone told me that the older diesel prime movers were two stroke (mixing oil and gas).  Is this true?  If so, when did they switch to four stroke prime movers?

[tomikawaTT]

Fairbanks-Morse locomotives had opposed-piston prime movers (2 pistons in each cylinder, gear-connected crankshafts top and bottom, no cylinder heads, no valve train - the pistons uncovered ports in the cylinder walls at the bottom of their 'away' strokes.)

F-M never switched.  They just got out of the locomotive business.

Chuck

[JamesP]

Not only were Fairbanks Morse Opposed Pistons two-cycle, but EMD is known for their two-cycle prime movers, notably the 567 and 645 series engines.  A two stroke EMD or Detroit diesel isn't like a weed trimmer engine, they don't use the crankcase for aspiration.  The engines have poppet valves in the head for exhaust just like a four-cycle and ports in the side of the cylinder for fresh air intake like any other two cycle.  However, the ports are connected to a manifold that is pressurized by a supercharger (and sometimes use an overrunning clutch setup so an exhaust turbocharger can spin the supercharger faster than the crankshaft can).  The crankcase has oil like a four-cycle.  The engine has a camshafts driven at crankshaft speed to open the exhaust valves every revolution.

 - James

[JamesP]

To answer the other part of your question, I believe that EMD still offers the 2-cycle 710 prime mover in addition to its H Series 4-cycle prime mover, depending on what locomotive is ordered.  Hopefully, somebody more knowledgeable in current EMD products will shed some light on which prime mover is in what locomotive model...

 - James

[creepycrank]

wholeman

Someone told me that the older diesel prime movers were two stroke (mixing oil and gas).  Is this true?  If so, when did they switch to four stroke prime movers?

By "gas" I assume you mean gasoline which is never used in the diesel cycle. EMD's have been and are two stoke uniflow diesels since 1934. Number 2 diesel fuel is very like home heating oil and is what all railroads are runing on. Some times its called "gasoil". The EMD's have run on everything from FP5 navy fuel up to bunker C heavy oil. The diesel engine requires that the air charge is compressed enough that the heat generated is hot enough so that the fuel will ignite when its sprayed in. Diesels are also referred as compression ignition engines-no spark plugs. All the other locomotive builders except Fairanks Morse, lacked the imagination to build anuthing but 4 stroke engines.

[MJChittick]

JamesP

To answer the other part of your question, I believe that EMD still offers the 2-cycle 710 prime mover in addition to its H Series 4-cycle prime mover, depending on what locomotive is ordered.

The only prime mover EMD currently offers is the two-cycle 710.  The 265H-II four-cycle prime mover was offered in the SD90MAC but that model is no longer in production.  However, it is being built under license in China for that market.

[tdmidget]

While I don't doubt that there have been experiments and attempts to use low grade fuels like Bunker C ( also known as  no.6 fuel oil) I am sure that no one has been successful. This "oil" is solid at room temperature or nearly so and very abrasive due to a high solids content. IF you could heat it enough to pass through an injector it would rapidly wear it out. It is a senseless exercise since you would have to flush the fuel system with no 2 or other liquid fuel before shutdown, spend a fortune on apparatus to heat and filter the fuel, and deal with accelerated wear and maintainance IF it worked. To top it off there would be little economic bebefit since modern refining produces very little of it and there not such a price difference as in steam days when it was competitive with coal.

I do know that Alco marine engines fully warmed up and heating the fuel have used oils as heavy as no 3 and 4 but only under ideal conditions.

[silicon212]

wholeman

Someone told me that the older diesel prime movers were two stroke (mixing oil and gas).  Is this true?  If so, when did they switch to four stroke prime movers?

 Wholeman,

The EMD two stroke engine is of a uniflow scavenge design.  This means that, unlike your gasoline two stroke, the crankcase is not involved in the induction/scavenging aspects of the engine's running.  This allows the engine to be lubricated under pressure, like the engine in your car.  Therefore, there is no need to mix oil with fuel.  I'm not going to go into the technical details of either design, but the uniflow design allows charged air entering through ports at the bottom of the cylinder (uncovered by the piston) to push the spent fuel (exhaust) up and out through 4 camshaft operated poppet valves in the cylinder head.

 Unlike the crossflow two stroke (your chainsaw, dirt bike etc), the uniflow engine isn't necessarily a simpler design than a 4 stroke, it just allows the engine to make more power with less use of space than a comparably powerful 4 stroke.

[CSSHEGEWISCH]

Some of the very large marine diesels  http://people.bath.ac.uk/ccsshb/12cyl/  use a lower grade of fuel oil that's closer to Bunker C than No. 2 diesel oil. 

[Paul_D_North_Jr]

Let's review and list the functions/ events that occur during each stroke as follows, as I understand it:

For a 4-stroke:

Up 1 = Compress to ignite

Down 1 = Power by expanding

Up 2 = Exhaust push out

Down 2 = Intake fresh air

REPEAT . . .

For a 2-stroke:

Up = Exhaust push out - valves close - Compress to ignite

Down = Power by expanding - valves open - Intake fresh air

REPEAT . . .

Any additions/ corrections/ clarifications ?

- Paul North.

[The Butler]

wholeman

Someone told me that the older diesel prime movers were two stroke (mixing oil and gas).  Is this true?  If so, when did they switch to four stroke prime movers?

Thanks for asking that question!  I always assumed "two-stroke" meant fuel/oil mixture and wondered how EMD pull that off. 

[wholeman]

I also found this information.  http://science.howstuffworks.com/diesel-locomotive4.htm  It could use some clarification to avoid confusing the general public.

[tleary01]

I agree with wholeman It could use some (a lot of) clarification to avoid confusing the general public.  The statement that a 4 stroke cycle engine of the same size as the EMD 2 stroke cycle engine cannot produce comparible power is dead wrong. The General Motors (actually Winton)originated 2 stroke cycle engine has a long history of excellent performance in locomotive service but it is not the only show in town.  A Fairbanks Morse engine though of the opposed piston type is also a 2 stroke cycle port scavengd engine.  And in particular the GE 7 FDL 4 stroke cycle engines since the 1980's have proven their performance is equally as good with higher HP ratings compared to competitve EMD engines.   

[silicon212]

tleary01

I agree with wholeman It could use some (a lot of) clarification to avoid confusing the general public.  The statement that a 4 stroke cycle engine of the same size as the EMD 2 stroke cycle engine cannot produce comparible power is dead wrong. The General Motors (actually Winton)originated 2 stroke cycle engine has a long history of excellent performance in locomotive service but it is not the only show in town.  A Fairbanks Morse engine though of the opposed piston type is also a 2 stroke cycle port scavengd engine.  And in particular the GE 7 FDL 4 stroke cycle engines since the 1980's have proven their performance is equally as good with higher HP ratings compared to competitve EMD engines.   

 The 7FDL is 15.7 liters / cylinder while the 710 is 11.7 liters / cyl.  Not the same size.  Another thing to consider is that top speed of the 710 is 900 RPM, top speed of the 7FDL is 1050 RPM.

[tleary01]

But also consider that a 2 stroke cycle engine produces a power stroke each revolution whereas the 4 stroke cycle produces a power stroke every 2 revolutions.

[creepycrank]

The difference between 2 stroke and 4 stroke engines of comparable size is that the peak firing pressure of the 2 stroke is half that of the 4 stroke but it does it every stroke whereas the 4 stoke gets around to it every other stroke. The result is the same horsepower output. All the components of the 4 stroke have to be built up to take the extra stress. The result is a substantially heavier engine. If the 4 stroke did not have a turbo it would develop about half the power. That's why it seems that every 4 stroke diesel over 40 hp has a turbo. (I was surprised to see that a 40 foot Beneteau sailboat auxiliary engine had a turbo on it.)

[silicon212]

This is very true, and is the reason why the two stroke is generally a smaller, slower engine than it's equivalent powered 4-stroke.

 Remember, with the RPM difference between the two stroke (900) and the four stroke (1050) means that the power stroke delta is something less than 2:1.

[erikem]

 Yet another advantage of the four stroke over the two stroke is better scavenging pf the exhaust (though scavenging may not be the correct term here). This allows for more oxygen in the cylinder, which should further reduce the delta.

[chutton01]

Since we are discussing 2cycle vs 4cycle, I have read that the 4cycle engined locomotives don't 'load' as fast as an equivalent 2cycled one, so that acceleration is consequently poorer.
Is this, as a rule, true (or was it at one time)?

[creepycrank]

chutton01

Since we are discussing 2cycle vs 4cycle, I have read that the 4cycle engined locomotives don't 'load' as fast as an equivalent 2cycled one, so that acceleration is consequently poorer.
Is this, as a rule, true (or was it at one time)?

Its called turbo lag. EMD unique scavenging system uses an over running clutch and an 18 to step up gear train to turn the impeller at start up and lower speeds an loads where there isn't enough exhaust flow and energy to turn the turbine fast enough to give enough combustion air. Both 4 stroke and 2 stroke diesel are more properly called compression ignition engine where a charge of air is compressed enough to heat it to the point where diesel fuel at the top dead center is sprayed in and ignites. The resultant increase in pressure on the piston is extracted a torque by the crankshaft as the piston descends. Getting air and exhaust out of the cylinder is called scavenging. The piston on the 4 stroke substitutes as an part time air pump where as 2 strokes use a separate blower or the gear drive turbo combination that EMD uses. Positive displacement blowers like root blowers are more efficient at moving air in high volumes and low pressure than centrical blowers and both are better than piston pumps. Thats the reason just about every 4 stroke engine above 40 hp size uses a turbo to get a decent specific horsepower. Now back to turbo lag. EMD generators running at synchronous speed no load have the turbo at 16200 rpm an closing the breaker it quickly goes to full power with the turbo off the gear train at about 18000 rpm for full air box pressure. A 4 stroke at synchronous speed no load has a turbo being dragged around by to low energy exhaust flow and has to gain a great more rotational speed to pick up the full load. Typically 4 stroke can only manage to pick up 35% load without stalling but the EMD can pickup 100%. For locomotives as well as generators the load has to be fed in slowly to avoid smoking which makes them even slower.

[aut1rml]

When I was a kid the Detroit truck engine used both a blower and a turbo. Scavenging of a cylinders exhaust was not good from an emissions point of view. How did they clean up the 710.

[oltmannd]

creepycrank

All the other locomotive builders except Fairanks Morse, lacked the imagination to build anuthing but 4 stroke engines.

You win! That's my laugh for the day! (EMD people were always some of my favorites....)

[creepycrank]

aut1rml

When I was a kid the Detroit truck engine used both a blower and a turbo. Scavenging of a cylinders exhaust was not good from an emissions point of view. How did they clean up the 710.

Although EMD and Detroit Diesel Allision were part of GM together the engineer departments never coordinated on anything. The only exception is that Allison made all the engine bearings and I suppose had a lot to do with the turbo design. I know EMD started using CAD fairly early and had enough computer capacity to run prototype designs on the computer rather than build the parts and run the equivalent of several years in the field on test engines. Possibly all this was done on a GM mainframe. I don't know what happened to DDA but I think they just went along with the conventional wisdom rather than have any confidence in there own abilities. Somehow they still offer 2 stroke engines probably for the export market. Everybody and their brother has a different scheme to improve the basic 710. The first thing was to develop new piston rings which at this point reduce lube oil consumption by about 50%. You can get away with this because of the very great improvement in oil additive packages in the last 30 years. For locomotive EMD has electronic unit fuel injectors, 18:1 compression pistons, and a separate cooling system for the after coolers to control the temperature at 120 deg F. There was an experiment done at Southwest Research on a Ingram Barge 12-710-GA engine that include an injector of a patented design o an f after treatment catalyst. It made T2 but with a penalty of raising the bnsf from 0.325lb/hp-hr to about 0.350lb-lb-hr. They didn't replace the original 2 pass aftercoolers or the original 16:1 pistons.

[M636C]

Creepycrank I'm sure you didn't mean:

"The first thing was to develop new piston rings which at this point reduce lube oil consumption by about 50airbox temperature at about 120deg."

There must be something missing between "50" and "airbox".

Also

" It made T2 but with a penalty of raising the bnsf from 0.325 to about 0.350."

Did you mean BSFC (Brake Specific Fuel Consumption) in pounds per horsepower hour?

Detroit Diesel's problem was that with the blowers running at full power, they couldn't get anywhere near the fuel consumption of the competing four strokes, which EMD achieved with the overrunning clutch on their turbo and blower. That was too expensive for the small engines, so they just changed over to four strokes.

M636C

[creepycrank]

Yes, thank you. I discovered that I can edit after the fact. I think the point I wanted to make was that revising the design to get to Tier 2 isn't all that difficult and but you can rapidly get bogged done in the details, the reports on this subject can run to 50 pages. Of the other 2 stroke manufactures only Fairbanks Morse seems to be building for the new engine market as they announced that they sold some fast start emergency generators to a customer in Australia. Without researching, Bergen Diesel, owned by Rolls Royce, still makes 2 stroke engines.

[monon99]

 The EMD products are nearly all two strokes which wind up very fast on acceleration, but GE's product is a 4 stroke which is quite delayed in response. Old heads tell me that Monon RS-2's and C-420's would load up faster and kick better than an EMD by a long shot - probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke! As usual the better, longer lasting product was muscled out of the market by the ones with better financial arms. Must be why they still build new ALCos in India and France.

NYC guys swear by Baldwin S-12's being the absolute best quick-load kicking engine - don't know if the 606 or deLavergne was a two or 4 stroke.

On a practical level in todays railroading a two stroke is the best  on a light intermodal train for maintaining a schedule but on a heavy drag freight in hilly terrain with tough grades I'll take a GE every time - pulls like a bear and won't let you down - the EMDs will be a constant fight with sand and independant brake to get them to quit slipping and lose so much speed that you stall.

 

[tdmidget]

monon99

probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke!

monon99

 The EMD products are nearly all two strokes which wind up very fast on acceleration, but GE's product is a 4 stroke which is quite delayed in response. Old heads tell me that Monon RS-2's and C-420's would load up faster and kick better than an EMD by a long shot - probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke! As usual the better, longer lasting product was muscled out of the market by the ones with better financial arms. Must be why they still build new ALCos in India and France.

NYC guys swear by Baldwin S-12's being the absolute best quick-load kicking engine - don't know if the 606 or deLavergne was a two or 4 stroke.

On a practical level in todays railroading a two stroke is the best  on a light intermodal train for maintaining a schedule but on a heavy drag freight in hilly terrain with tough grades I'll take a GE every time - pulls like a bear and won't let you down - the EMDs will be a constant fight with sand and independant brake to get them to quit slipping and lose so much speed that you stall.

 

monon99

 The EMD products are nearly all two strokes which wind up very fast on acceleration, but GE's product is a 4 stroke which is quite delayed in response. Old heads tell me that Monon RS-2's and C-420's would load up faster and kick better than an EMD by a long shot - probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke! As usual the better, longer lasting product was muscled out of the market by the ones with better financial arms. Must be why they still build new ALCos in India and France.

NYC guys swear by Baldwin S-12's being the absolute best quick-load kicking engine - don't know if the 606 or deLavergne was a two or 4 stroke.

On a practical level in todays railroading a two stroke is the best  on a light intermodal train for maintaining a schedule but on a heavy drag freight in hilly terrain with tough grades I'll take a GE every time - pulls like a bear and won't let you down - the EMDs will be a constant fight with sand and independant brake to get them to quit slipping and lose so much speed that you stall.

 

monon99

  - probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke!

 WHAT have you been smoking?

 

[tdmidget]

 Now I find that I can't edit because I use firefox. So:

1.If the fuel is not injected directly into the cylinder, it is not a Diesel engine

2. IF it ran it would destroy itself due to preignition

3.It would not produce usable power

[erikem]

tdmidget

 Now I find that I can't edit because I use firefox. So:

 

That's strange, I have no problem editing with firefox (version 3.5.5 running on Solaris 10u8 (SPARC)) but have had problems with paragraph formatting on Safari running on MacOS 10.5 (x86).

[Tugboat Tony]

Older Caterpillar and many small bore high speed engines inject the fuel into a precombustion chamber where the fuel is ingited and then the flame burns into the main cylinder. A Diesel cycle engine simply means that the fuel charge is ignited by the heat from compression only.

 

as far as why EMD's can load faster then a GE, it's simply how the switch gear works, as stated earlier,  if you want to kick cars, grab an old FM, or alco, my in my expierance an S-2 alco will speed up before the P-contactors kick in to feed current to the motors, (the *** thing would take off like a rocket) a GE C44AC loads much faster then a SD9043MAC. its all in the wiring.