Locomotives

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?

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

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

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

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?

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.

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.

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.

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. 

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 . . .

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. 

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

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.   

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.

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.