4 stroke versus 2 stroke

[Anonymous]

OK, I know, I know, 2 stroke is the modern standard for locomotive power. "Market decision" erc etc

My curiousity is, how and why was that ultimate decision come upon? Strictly "hours of operation/cost", or what?

Just based upon my experiances with smaller engines,..one produces more power per stroke at the crank shaft, and the other sounds like a chainsaw.

The latter tends to out perform the former in "high rev" applications, but I seriously doubt those big dukes in an SD-70 or a Dash-9 are high rev.

Thinking back to my childhood, I can remember when you would feel the "ooomph" of a diesels engine as it went by, the ground would shake, and the exhaust seemed to shake the sky with that power,,,I guess those were Alco's,.... though at the time I was too young to give a darn.

If the current ambitions are towards ever more horse power, why has no one brought a 4 cycle engine into the foray?

[Anonymous]

OK, I know, I know, 2 stroke is the modern standard for locomotive power. "Market decision" erc etc

My curiousity is, how and why was that ultimate decision come upon? Strictly "hours of operation/cost", or what?

Just based upon my experiances with smaller engines,..one produces more power per stroke at the crank shaft, and the other sounds like a chainsaw.

The latter tends to out perform the former in "high rev" applications, but I seriously doubt those big dukes in an SD-70 or a Dash-9 are high rev.

Thinking back to my childhood, I can remember when you would feel the "ooomph" of a diesels engine as it went by, the ground would shake, and the exhaust seemed to shake the sky with that power,,,I guess those were Alco's,.... though at the time I was too young to give a darn.

If the current ambitions are towards ever more horse power, why has no one brought a 4 cycle engine into the foray?

[edblysard]

GE uses 4 cycle engines already. EMD is a 2 cycle fan, because there are less moving parts, less maintainance, and they rev really quick, less stuff to have to drag around the crankshaft. But it involves reed valves, instead of moving intake and exhaust valves, lifters, and rocker arms. The new engine for the SD90MAC is a four cycle. But the old standard EMD will be around for a long time, they are very, very hard to break.
Stay Frosty,
Ed

QUOTE: Originally posted by TheAntiGates

OK, I know, I know, 2 stroke is the modern standard for locomotive power. "Market decision" erc etc

My curiousity is, how and why was that ultimate decision come upon? Strictly "hours of operation/cost", or what?

Just based upon my experiances with smaller engines,..one produces more power per stroke at the crank shaft, and the other sounds like a chainsaw.

The latter tends to out perform the former in "high rev" applications, but I seriously doubt those big dukes in an SD-70 or a Dash-9 are high rev.

Thinking back to my childhood, I can remember when you would feel the "ooomph" of a diesels engine as it went by, the ground would shake, and the exhaust seemed to shake the sky with that power,,,I guess those were Alco's,.... though at the time I was too young to give a darn.

If the current ambitions are towards ever more horse power, why has no one brought a 4 cycle engine into the foray?

[edblysard]

GE uses 4 cycle engines already. EMD is a 2 cycle fan, because there are less moving parts, less maintainance, and they rev really quick, less stuff to have to drag around the crankshaft. But it involves reed valves, instead of moving intake and exhaust valves, lifters, and rocker arms. The new engine for the SD90MAC is a four cycle. But the old standard EMD will be around for a long time, they are very, very hard to break.
Stay Frosty,
Ed

QUOTE: Originally posted by TheAntiGates

OK, I know, I know, 2 stroke is the modern standard for locomotive power. "Market decision" erc etc

My curiousity is, how and why was that ultimate decision come upon? Strictly "hours of operation/cost", or what?

Just based upon my experiances with smaller engines,..one produces more power per stroke at the crank shaft, and the other sounds like a chainsaw.

The latter tends to out perform the former in "high rev" applications, but I seriously doubt those big dukes in an SD-70 or a Dash-9 are high rev.

Thinking back to my childhood, I can remember when you would feel the "ooomph" of a diesels engine as it went by, the ground would shake, and the exhaust seemed to shake the sky with that power,,,I guess those were Alco's,.... though at the time I was too young to give a darn.

If the current ambitions are towards ever more horse power, why has no one brought a 4 cycle engine into the foray?

[sooblue]

One of the drawbacks of a GM two stroke is the tendency to run backward durring a stall condition. I've had that happen twice. The first time I didn't know what was going on and couldn't figure what happend to my power and why forward was reverse. I got out and looked at the engine. Smoke was comming out of the intake. What made me stop the engine was when I saw oil pumping out of the dipstick.
One of the plusses of the two stroke is that they are very fast. Quick responders.
They are better in stationary service or as prime movers in a loco. though.
They can not take low rpms. Lugg them and you'll lose the cylinder sleave (crack). I've seen that a few times too.
A two stroke likes to be started and run at a constant speed and not shut off.
Sooblue

[sooblue]

One of the drawbacks of a GM two stroke is the tendency to run backward durring a stall condition. I've had that happen twice. The first time I didn't know what was going on and couldn't figure what happend to my power and why forward was reverse. I got out and looked at the engine. Smoke was comming out of the intake. What made me stop the engine was when I saw oil pumping out of the dipstick.
One of the plusses of the two stroke is that they are very fast. Quick responders.
They are better in stationary service or as prime movers in a loco. though.
They can not take low rpms. Lugg them and you'll lose the cylinder sleave (crack). I've seen that a few times too.
A two stroke likes to be started and run at a constant speed and not shut off.
Sooblue

[Anonymous]

OK ED. Time for machinist 101. a 4 stroke cycle GE or EMD prime mover has 4 valves in the cyl. head, 2 intake & 2 exhaust. In a 2 stroke cycle ( EMD 567,645,710 )there are 4 valves also but they're all exhaust valves. at the bottom of the piston stroke there is a ring of holes that open into an airbox that is supplied by the roots blowers or the turbo. then the cylinder fires every time the piston comes up.

don't get snake bit,

no reed valves. this ain't no chainsaw

PS, EMD 2 strokes turn 905 RPM and EMD & GE 4 strokes 1050 RPM [:p]

[Anonymous]

OK ED. Time for machinist 101. a 4 stroke cycle GE or EMD prime mover has 4 valves in the cyl. head, 2 intake & 2 exhaust. In a 2 stroke cycle ( EMD 567,645,710 )there are 4 valves also but they're all exhaust valves. at the bottom of the piston stroke there is a ring of holes that open into an airbox that is supplied by the roots blowers or the turbo. then the cylinder fires every time the piston comes up.

don't get snake bit,

no reed valves. this ain't no chainsaw

PS, EMD 2 strokes turn 905 RPM and EMD & GE 4 strokes 1050 RPM [:p]

[adrianspeeder]

Thanks drailed, I always wondered how a 2 stroke diesel works, but I have some questions. When the piston is at top dead center, does the piston block the intake "holes" like a reed valve? And is the injection system on a 2 stroke diesel different than a 4 stroke?

Thanks, adrianspeeder

[adrianspeeder]

Thanks drailed, I always wondered how a 2 stroke diesel works, but I have some questions. When the piston is at top dead center, does the piston block the intake "holes" like a reed valve? And is the injection system on a 2 stroke diesel different than a 4 stroke?

Thanks, adrianspeeder

[Anonymous]

the injector fires every other time (4cyc) as opposed to every time ( 2cyc ) . yes the piston covers the holes.

[Anonymous]

the injector fires every other time (4cyc) as opposed to every time ( 2cyc ) . yes the piston covers the holes.

[Anonymous]

EMDs newest diesel is a four stroke. i think they call it their H block.

[Anonymous]

EMDs newest diesel is a four stroke. i think they call it their H block.

[Anonymous]

QUOTE: Originally posted by drailed1999

OK ED. Time for machinist 101. a 4 stroke cycle GE or EMD prime mover has 4 valves in the cyl. head, 2 intake & 2 exhaust. In a 2 stroke cycle ( EMD 567,645,710 )there are 4 valves also but they're all exhaust valves. at the bottom of the piston stroke there is a ring of holes that open into an airbox that is supplied by the roots blowers or the turbo. then the cylinder fires every time the piston comes up.

don't get snake bit,

no reed valves. this ain't no chainsaw

PS, EMD 2 strokes turn 905 RPM and EMD & GE 4 strokes 1050 RPM [:p]

Derailed,...Nice to have an authority!!

If I can take advantage of your knowledge?

Applying a 4 stroke mentality to 2 stroke theory, it always seemed a little odd thatt the intake and power stroke were one in the same with a 2 cycle engine, while the exhaust is (i guess just taken for granted that it will happen at the bottom of the power stroke) a scavenger action ... is that all correct up to this point?

If so it sure looks like they are bleeding a lot of power by compromising the power stroke's total potential.

I can see how a driven input such as a turbo or a blower helps ventilate the combustion chamber by helping to force out the combustion byproducts of the previous cycle, but at what points, in terms of top dead center of piston travel, is the intake portion of the cycle made, and at what point in the piston cycle is the fuel injected?

Just curious, thanks in advance for your input

[Anonymous]

QUOTE: Originally posted by drailed1999

OK ED. Time for machinist 101. a 4 stroke cycle GE or EMD prime mover has 4 valves in the cyl. head, 2 intake & 2 exhaust. In a 2 stroke cycle ( EMD 567,645,710 )there are 4 valves also but they're all exhaust valves. at the bottom of the piston stroke there is a ring of holes that open into an airbox that is supplied by the roots blowers or the turbo. then the cylinder fires every time the piston comes up.

don't get snake bit,

no reed valves. this ain't no chainsaw

PS, EMD 2 strokes turn 905 RPM and EMD & GE 4 strokes 1050 RPM [:p]

Derailed,...Nice to have an authority!!

If I can take advantage of your knowledge?

Applying a 4 stroke mentality to 2 stroke theory, it always seemed a little odd thatt the intake and power stroke were one in the same with a 2 cycle engine, while the exhaust is (i guess just taken for granted that it will happen at the bottom of the power stroke) a scavenger action ... is that all correct up to this point?

If so it sure looks like they are bleeding a lot of power by compromising the power stroke's total potential.

I can see how a driven input such as a turbo or a blower helps ventilate the combustion chamber by helping to force out the combustion byproducts of the previous cycle, but at what points, in terms of top dead center of piston travel, is the intake portion of the cycle made, and at what point in the piston cycle is the fuel injected?

Just curious, thanks in advance for your input

[Anonymous]

QUOTE: Originally posted by edblysard

GE uses 4 cycle engines already. EMD is a 2 cycle fan, because there are less moving parts, less maintainance, and they rev really quick, less stuff to have to drag around the crankshaft. But it involves reed valves, instead of moving intake and exhaust valves, lifters, and rocker arms. The new engine for the SD90MAC is a four cycle. But the old standard EMD will be around for a long time, they are very, very hard to break.
Stay Frosty,
Ed

Thanks Ed. Foe some reason I got the mistaken impression that the 4 stroke died with Alco.

Could be because the magazine seems to rely heavily on the opinion of *** Dilworth, and from the in print examples I've read to date, that former EMD employee is somewhat less than objective, in terms of both GE as well as those German HYDRO units tried by SP and Rio Grande.

As far as being an operator yourself, where does your opinion on 2 stroke vs 4 stroke fall?

[Anonymous]

QUOTE: Originally posted by edblysard

GE uses 4 cycle engines already. EMD is a 2 cycle fan, because there are less moving parts, less maintainance, and they rev really quick, less stuff to have to drag around the crankshaft. But it involves reed valves, instead of moving intake and exhaust valves, lifters, and rocker arms. The new engine for the SD90MAC is a four cycle. But the old standard EMD will be around for a long time, they are very, very hard to break.
Stay Frosty,
Ed

Thanks Ed. Foe some reason I got the mistaken impression that the 4 stroke died with Alco.

Could be because the magazine seems to rely heavily on the opinion of *** Dilworth, and from the in print examples I've read to date, that former EMD employee is somewhat less than objective, in terms of both GE as well as those German HYDRO units tried by SP and Rio Grande.

As far as being an operator yourself, where does your opinion on 2 stroke vs 4 stroke fall?

[Anonymous]

4 strokers, 2 strokers[:p][:p][:p][:p][:p] wellllllll, lets don't there[;)][;)]

[Anonymous]

4 strokers, 2 strokers[:p][:p][:p][:p][:p] wellllllll, lets don't there[;)][;)]

[Anonymous]

QUOTE: Originally posted by emeraldisle

4 strokers, 2 strokers[:p][:p][:p][:p][:p] wellllllll, lets don't there[;)][;)]

Ya,...the slacker errr' I mean Wankel will be next

[Anonymous]

QUOTE: Originally posted by emeraldisle

4 strokers, 2 strokers[:p][:p][:p][:p][:p] wellllllll, lets don't there[;)][;)]

Ya,...the slacker errr' I mean Wankel will be next

[Anonymous]

AntiGates: the start of injection occurs 28 - 30 degrees BTDC (before top dead center). This is happening every time the piston comes up. And yes, what Sooblue says is true, it's very rare.

[Anonymous]

AntiGates: the start of injection occurs 28 - 30 degrees BTDC (before top dead center). This is happening every time the piston comes up. And yes, what Sooblue says is true, it's very rare.

[Anonymous]

QUOTE: Originally posted by drailed1999

AntiGates: the start of injection occurs 28 - 30 degrees BTDC (before top dead center). This is happening every time the piston comes up. And yes, what Sooblue says is true, it's very rare.

Derailed,

Thanks! One last bonehead question?, At what stage of the piston cycle are the air intake valves opened and closed? before/after the bottom of the power stroke,.. (or before TDC /after TDC if thats more conveniant for you to use.

The point I'm tripping on is, yeah I guess with a 'driven' air intake , it would be possible to perform intake as the piston is progressing into it's compression stroke,..but (in contrast) a normally aspirated 2 cycle couldn't (could it?) it would have to rely on a portion of the pistons downward stroke, which is the power stroke, meaning combustion/exhaust/intake all have to occur on the pistons downward stroke, without a turbo or blower?

[Anonymous]

QUOTE: Originally posted by drailed1999

AntiGates: the start of injection occurs 28 - 30 degrees BTDC (before top dead center). This is happening every time the piston comes up. And yes, what Sooblue says is true, it's very rare.

Derailed,

Thanks! One last bonehead question?, At what stage of the piston cycle are the air intake valves opened and closed? before/after the bottom of the power stroke,.. (or before TDC /after TDC if thats more conveniant for you to use.

The point I'm tripping on is, yeah I guess with a 'driven' air intake , it would be possible to perform intake as the piston is progressing into it's compression stroke,..but (in contrast) a normally aspirated 2 cycle couldn't (could it?) it would have to rely on a portion of the pistons downward stroke, which is the power stroke, meaning combustion/exhaust/intake all have to occur on the pistons downward stroke, without a turbo or blower?

[sooblue]

QUOTE: Originally posted by drailed1999

AntiGates: the start of injection occurs 28 - 30 degrees BTDC (before top dead center). This is happening every time the piston comes up. And yes, what Sooblue says is true, it's very rare.

It's not very rare if your Polish like me[:D]
actually I only had it happen to me twice when I was a newbe.
With over head exhaust valves and a blown intake 2 strokers can be very fast reacters. One thing, I never heard of a 2 stroke with a lower rpm then a 4 stroke.
Usually the rpm range is higher on a 2 stroke. Because of the tendency to kick backward their not lugged like a 4 stroke can be.
But ??? I don't know it all [;)]
Sooblue

[sooblue]

QUOTE: Originally posted by drailed1999

AntiGates: the start of injection occurs 28 - 30 degrees BTDC (before top dead center). This is happening every time the piston comes up. And yes, what Sooblue says is true, it's very rare.

It's not very rare if your Polish like me[:D]
actually I only had it happen to me twice when I was a newbe.
With over head exhaust valves and a blown intake 2 strokers can be very fast reacters. One thing, I never heard of a 2 stroke with a lower rpm then a 4 stroke.
Usually the rpm range is higher on a 2 stroke. Because of the tendency to kick backward their not lugged like a 4 stroke can be.
But ??? I don't know it all [;)]
Sooblue

[Anonymous]

AntiGates: the air holes are opened about 20 degrees before the exhaust valves open. with that higher pressure it forces the gases out. then the exhaust valves close about 20 degrees before the air holes to allow boost pressure to build up. then it starts all over again.

sooblue: if you look at the onboard computer of a GE you'll see that at full throttle it turns approx.1050RPM. An EMD SD70 for example the computer will show 905RPM
The EMD just sounds like its turning faster because it has twice the power strokes

[Anonymous]

AntiGates: the air holes are opened about 20 degrees before the exhaust valves open. with that higher pressure it forces the gases out. then the exhaust valves close about 20 degrees before the air holes to allow boost pressure to build up. then it starts all over again.

sooblue: if you look at the onboard computer of a GE you'll see that at full throttle it turns approx.1050RPM. An EMD SD70 for example the computer will show 905RPM
The EMD just sounds like its turning faster because it has twice the power strokes