Question about EMD prime movers

[silicon212]

So then GE pime movers are just normal 4 strokes then... right

also I read that 2 strokes polute alot more, so how dose EMD get their SD70M-2/ACE to comply with EPA teir 2 that the GEVO(4 stroke) far excedes

Thanks for all your help,

 

To answer your question, one needs to realize that a two stroke diesel is totally unlike a two stroke gasoline, other than in its two stroke operation (by producing a power stroke on each revolution of the crankshaft, vs. every other revolution as in a four stroke).

The problem with pollution on a two stroke gasoline happens under a number of circumstances.  First, a gasoline two stroke uses the upward stroke of the piston to draw an air/fuel mix into the crankcase, and then the downward stroke of the piston pressurizes this air/fuel charge, forcing it into the cylinder intake ports under pressure, to scavenge the engine.  Due to this design, a regular lubrication system is impossible so oil is mixed with the gasoline, where it lubricates everything in the crankcase and then is burned in the cylinder along with the air/fuel mix.  The other problem comes from the scavenging phase, where the spent mix (exhaust) is forced through the exhaust ports, also in the cylinder wall, by the rush of fresh air/fuel mix entering the cylinder.  Some of this fresh mix also scavenges out through the exhaust port, and this is the reason that two stroke gasoline engines pollute.

Diesel engines are direct injected - that is, the injector is intrusive into the combustion chamber and fuel is delivered directly to the combustion chamber under high pressure.  This eliminates two needs of a gasoline two-stroke - namely, the oil/fuel mixture since the crankcase is not pressurized with an air/fuel mix.  This allows the diesel two stroke to be lubricated in a more conventional sense, although the EMD engine uses a 'dry sump' lube oil system where the oil pump is external to the engine and the oil is stored in an external tank as opposed to a sump in the bottom of the engine.  Also, during the scavenging phase, any incoming intake charge lost through the exhaust will be simply air.  These two reasons are why the diesel two stroke does not pollute like a gasoline two stroke.

Also, due to the fact that no raw fuel is lost to scavenging, a two stroke diesel is considerably more fuel efficient, since every drop of fuel consumed is converted into usable power.

The downside to this is that the engine is incapable of breathing air on its own, so air must be pressurized into the intake ports.  This is accomplished by surrounding the cylinder bore with an airbox, which is charged either with a Roots-type blower, or by a hybrid centrifugal blower/turbocharger (turbine is geared to the crank through an overrun clutch), as exhaust pressure at the lower power notches is insufficient to directly drive the turbo.  Once pressure exceeds that threshold, the turbo spins free of the engine.

If you look at an EMD engine assembly, you'll see two sets of 'port holes' in it.  A row above and a row below.  The row below provides access to the individual connecting rods for their power assembly, while the row at the top provides access to the charged airbox.

[J. Edgar]

GE's have a really cool chugging sound,

I guess that depends on your definition of "cool". Personally, I think they sound like a rock crusher gone bad. Give me the old non-turbo EMD's any day. Get 'em in the middle of a rock cut in the 8th notch, now that is the "cool" sound of power!

Cool is a 10 foot flame out the stack of that GE !!!

 ive seen a GE C40-8w blow a turbo under load.....flame was a lil more then 10 feet.....

[Anonymous]

GE's have a really cool chugging sound,

I guess that depends on your definition of "cool". Personally, I think they sound like a rock crusher gone bad. Give me the old non-turbo EMD's any day. Get 'em in the middle of a rock cut in the 8th notch, now that is the "cool" sound of power!

Especially the x-MP four-stack GP38-2s. Those are hands down the loudest locos I have ever heard.

[PBenham]

Would this be practical to model in HO??? No, but it could be fun if you wanted to get rid of your house. Or, your landlord's house !

[mj5890]

Cool is a 10 foot flame out the stack of that GE !!!

That is cool, I wonder if you roasted marshmallows on that flame how would they taste?

Would it be posible to model this in HO?

[Randy Stahl]

GE's have a really cool chugging sound,

I guess that depends on your definition of "cool". Personally, I think they sound like a rock crusher gone bad. Give me the old non-turbo EMD's any day. Get 'em in the middle of a rock cut in the 8th notch, now that is the "cool" sound of power!

Cool is a 10 foot flame out the stack of that GE !!!

[BigJim]

GE's have a really cool chugging sound,

I guess that depends on your definition of "cool". Personally, I think they sound like a rock crusher gone bad. Give me the old non-turbo EMD's any day. Get 'em in the middle of a rock cut in the 8th notch, now that is the "cool" sound of power!

[challenger3980]

This is a EMD power assembly from the outside.  The piston is inside.

The holes in the side are where the air/fuel mixture come in to the cylinder.  EMDs force the air/fuel mix into the cylinder, by a supercharger or a turbocharger. 

The valves on top are exhaust valves. 

Some EMDs do blow a lot of oil out, especially the SD20s that go thru Middleton.

 

I am not familiar with the EMD prime movers in particular, but the air/fuel mixture in a diesel engine does not happen outside the cylinder. A Diesel engine receives a charge of fresh air into the cylinder, and then compresses nothing but fresh air on the compression stroke of the cycle. the compression of the air increases the temp to a high level, then at the appropriate time for ignition, the injectors, inject the fuel into the cylinder, which is then ignited. A Diesel engine has no spark plugs (not to be confused with glow plugs) the air/fuel mixture ratio is not critical in a Diesel engine as it is in a gasoline engine. With a diesel the more air that can be compressed into the cylinder the more power it can produce. the same amount of air in the cylinder will effectively burn any amount of fuel, from a small amount to as large an amount as there is adequate oxygen to combust properly.

                                                                             Doug

[greyhounds]

but when ever I flushed the toiled(alot), within 2 seconds I would hear the whoop sound of the air compressors, but since the toilet uses a vacum i dont see how these are related

Maybe you should see a doctor?

[mj5890]

GE's are indeed 4 cycle hence the sound difference....dual overhead cams with 4 vavles per cylinder?.......sounds like a racecar......drag racing anyone?

yes the sound difrece is very noticeble, GE's have a really cool chugging sound,

When we took the City Of New Orleans last summer and I stood in the doorway of the first supliner right behind the engine and just listened to the chugging sound of the exhaust and the whoop of the air compressors, I could have stood there all night but some exhaust fumes started to come through the door so I left

but when ever I flushed the toiled(alot), within 2 seconds I would hear the whoop sound of the air compressors, but since the toilet uses a vacum i dont see how these are related

[J. Edgar]

GE's are indeed 4 cycle hence the sound difference....dual overhead cams with 4 vavles per cylinder?.......sounds like a racecar......drag racing anyone?

[mj5890]

So then GE pime movers are just normal 4 strokes then... right

also I read that 2 strokes polute alot more, so how dose EMD get their SD70M-2/ACE to comply with EPA teir 2 that the GEVO(4 stroke) far excedes

Thanks for all your help,

 

[M636C]

This is a EMD power assembly from the outside.  The piston is inside.

The holes in the side are where the air/fuel mixture come in to the cylinder.  EMDs force the air/fuel mix into the cylinder, by a supercharger or a turbocharger. 

The valves on top are exhaust valves. 

Some EMDs do blow a lot of oil out, especially the SD20s that go thru Middleton.

 i stand corrected.....

 so one would assume that they have 2 exhaust valves????....hence the dual rocker shafts??

Four exhaust valves! (driven by one overhead cam per bank of cylinders). All EMD two strokes from the 567 onward are all Vee engines.

M636C

[J. Edgar]

This is a EMD power assembly from the outside.  The piston is inside.

The holes in the side are where the air/fuel mixture come in to the cylinder.  EMDs force the air/fuel mix into the cylinder, by a supercharger or a turbocharger. 

The valves on top are exhaust valves. 

Some EMDs do blow a lot of oil out, especially the SD20s that go thru Middleton.

 i stand corrected.....

 so one would assume that they have 2 exhaust valves????....hence the dual rocker shafts??

[M636C]

The link worked for me: perhaps you should try it again.

The EMD engine draws air in through "ports" (holes in the cylinder wall, just above the piston at bottom dead centre) but unlike small petrol engines, the gas is exhausted through four valves located in the clynder head, like those in four stroke engines (except there are no intake valves).

The EMD 567, 645 and 710 engines have normal lubricating oil systems with oil held in a sump under the crankshaft, but do have one different feature: lubricating oil is sprayed from a pipe to the underside of the piston (when at bottom dead centre) to cool the piston.

The crankcase of the EMD diesel engines is not pressurised as it is in a small petrol engine, which allows conventional lubrication.

M636C

[WSOR 3801]

This is a EMD power assembly from the outside.  The piston is inside.

The holes in the side are where the air/fuel mixture come in to the cylinder.  EMDs force the air/fuel mix into the cylinder, by a supercharger or a turbocharger. 

The valves on top are exhaust valves. 

Some EMDs do blow a lot of oil out, especially the SD20s that go thru Middleton.

[J. Edgar]

 

 

http://www.marinediesels.info/Basics/the_2_stroke_engine_explanation.htm

 

I tried the link but it said "error 404 not found"

 link worked for me.....great lil site there......

[J. Edgar]

another note.......turbo'ing a diesel increases the pressure even more hence the valve train in the engine

[J. Edgar]

 EMD prime movers are 2 cycle in operation but they operate as a 4 cycle.....I.E. they have intake and exhaust valves.....the pressures in the combustion chamber in a diesel are to high to operate with reed valves like a dirtbike or chainsaw......

[mj5890]

 

 

http://www.marinediesels.info/Basics/the_2_stroke_engine_explanation.htm

 

I tried the link but it said "error 404 not found"

[CAZEPHYR]

 

 

http://www.marinediesels.info/Basics/the_2_stroke_engine_explanation.htm

 

[mj5890]

I have heard that EMD's engines(except for the SD90MAC) use 2 stroke engines, but I am in a class at school where we work on lawn mowere and other small engines and a 2 stroke engine has holes in the side of the cylinder where the gas comes in and exhaust gose out but your sposed to mix the oil with the gas because where the air/fuel mixture comes in is where the oil would be on a 4 stroke.  So unless they do mix their gas and oil together then how do these engines differ from a chain saw or weed wacker in terms of where the oil goes and where the holes are in the cylinder and where they come from and go out, but if there is oil then it couldnt go throug the crank case where the oil would be??? I am really confused

 Thanks, Joe