4 stroke versus 2 stroke

[sooblue]

QUOTE: Originally posted by drailed1999

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

Hi drailed,
The EMD 2 strokers must be designed to run at that RPM. (obviously) but Generaly speaking 2 strokers run at higher RPMs. Loco engines and marine prime movers may be the exception to the rule.
Smaller GM 2 strokers run 1800-2500 vs Mack 1200-2100 vs cummins 1600-2200
I'll say though if an engine puts out 4500 hp at 905 RPM I am in awe. That is IMPRESSIVE
Sooblue

[sooblue]

QUOTE: Originally posted by drailed1999

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

Hi drailed,
The EMD 2 strokers must be designed to run at that RPM. (obviously) but Generaly speaking 2 strokers run at higher RPMs. Loco engines and marine prime movers may be the exception to the rule.
Smaller GM 2 strokers run 1800-2500 vs Mack 1200-2100 vs cummins 1600-2200
I'll say though if an engine puts out 4500 hp at 905 RPM I am in awe. That is IMPRESSIVE
Sooblue

[Anonymous]

beleve it or not the Detroit Diesel 2 stroke truck engine was an offshoot of the EMD 567

[Anonymous]

beleve it or not the Detroit Diesel 2 stroke truck engine was an offshoot of the EMD 567

[Anonymous]

Hi there

I think that GM got into two cycle mode back in the late 1920's and early 1930's when big diesel engines were found mostly in Submarines. The distalate engines proved very unreliable in Gas electric car service because of the long maintenace intervals and temperatures they were exposed to while the German diesels used in there U boats provided the required technology that is an engine driving a generator in a severe service environment GM cloned existing technology . The main benefit of the 2 cycle is the droop which is the change in the engine RPM when the load changes . With mechanical governors an engine with a power stroke on each crank revolution has lower droop. The major draw back is that you have pressureize the crank case to get air into the cylinder . This makes the crankcvase oil part of the air cleaner and it gets real dirty real fast and the intake air is polluted by exposure to the oil. You also have some limitiations on how much air you can put in the cylinder hence the engine horse power. GM went to the four cycle engines to meet the EPA air polution standards and to get to 6000 Hp. When you use 2 cycle engines on medium sized generator sets they also get poor fuel economy compared to a four cycle with the same Hp I don't know if big engines have this problem or not.
With electronic fuel injection controls and the possibility of even controlling the intake and exhaust valve timing electronically the benifits of the two cycle design have been severly diminished The railroads obviously havea lot of two cycle engines and parts and employ training are a problem when you go to a different technology but if you operate it in California you may not have a choice of what technology you use

Engine controls guy

[Anonymous]

Hi there

I think that GM got into two cycle mode back in the late 1920's and early 1930's when big diesel engines were found mostly in Submarines. The distalate engines proved very unreliable in Gas electric car service because of the long maintenace intervals and temperatures they were exposed to while the German diesels used in there U boats provided the required technology that is an engine driving a generator in a severe service environment GM cloned existing technology . The main benefit of the 2 cycle is the droop which is the change in the engine RPM when the load changes . With mechanical governors an engine with a power stroke on each crank revolution has lower droop. The major draw back is that you have pressureize the crank case to get air into the cylinder . This makes the crankcvase oil part of the air cleaner and it gets real dirty real fast and the intake air is polluted by exposure to the oil. You also have some limitiations on how much air you can put in the cylinder hence the engine horse power. GM went to the four cycle engines to meet the EPA air polution standards and to get to 6000 Hp. When you use 2 cycle engines on medium sized generator sets they also get poor fuel economy compared to a four cycle with the same Hp I don't know if big engines have this problem or not.
With electronic fuel injection controls and the possibility of even controlling the intake and exhaust valve timing electronically the benifits of the two cycle design have been severly diminished The railroads obviously havea lot of two cycle engines and parts and employ training are a problem when you go to a different technology but if you operate it in California you may not have a choice of what technology you use

Engine controls guy

[Anonymous]

Another querkie difference between EMD/GE 4 strokes and EMD 2 strokes is that on a 4 stroke engine you change the lube oil every 45 days and the 2 strokes burn so much oil that you just keep adding until they are due for a filter change. The average EMD 645 will burn about 30 to 50 gallons of oil to 3500 gallons of fuel. The only time they get their oil changed is when they get all of the power assemblies changed or a main bearing change
[;)][:D][8D]

sorry Ed I forgot about you. PTRA's big Cats get their oil changed too[:D]

[Anonymous]

Another querkie difference between EMD/GE 4 strokes and EMD 2 strokes is that on a 4 stroke engine you change the lube oil every 45 days and the 2 strokes burn so much oil that you just keep adding until they are due for a filter change. The average EMD 645 will burn about 30 to 50 gallons of oil to 3500 gallons of fuel. The only time they get their oil changed is when they get all of the power assemblies changed or a main bearing change
[;)][:D][8D]

sorry Ed I forgot about you. PTRA's big Cats get their oil changed too[:D]

[Anonymous]

In general, I think that G.E.s are rattling pieces of crap. My cup will vibrate off of the desk, and that is on a new -9. I caught a new AC6000 last trip and was impressed. It was almost as nice as a MAC. WOW!

[Anonymous]

In general, I think that G.E.s are rattling pieces of crap. My cup will vibrate off of the desk, and that is on a new -9. I caught a new AC6000 last trip and was impressed. It was almost as nice as a MAC. WOW!

[Mookie]

QUOTE: Originally posted by ironken

In general, I think that G.E.s are rattling pieces of crap. My cup will vibrate off of the desk, and that is on a new -9. I caught a new AC6000 last trip and was impressed. It was almost as nice as a MAC. WOW!

Ken, we have had one coming up from the south on Saturday morning pretty regularly. Why don't you catch it around either KC or Brownsville NE and come on up. Get off at 1st and J!

Jen

[Mookie]

QUOTE: Originally posted by ironken

In general, I think that G.E.s are rattling pieces of crap. My cup will vibrate off of the desk, and that is on a new -9. I caught a new AC6000 last trip and was impressed. It was almost as nice as a MAC. WOW!

Ken, we have had one coming up from the south on Saturday morning pretty regularly. Why don't you catch it around either KC or Brownsville NE and come on up. Get off at 1st and J!

Jen

[Anonymous]

I can't Mook, I don't run North. Wish I could though. When I was going to Lincoln, I spent a little time at a place called Brewski's. Ever been there?
Ken

[Anonymous]

I can't Mook, I don't run North. Wish I could though. When I was going to Lincoln, I spent a little time at a place called Brewski's. Ever been there?
Ken

[Mookie]

World's Best Hamburgers! In fact we have one about 6 blocks from our house!

Yum!

Jen

[Mookie]

World's Best Hamburgers! In fact we have one about 6 blocks from our house!

Yum!

Jen

[Anonymous]

Oh, yeah, speaking of food. I also like the new AC6000 because I can wedge a burger or McMuffin in between the cylinders for reheating. Works perfectly!
Ken

[Anonymous]

Oh, yeah, speaking of food. I also like the new AC6000 because I can wedge a burger or McMuffin in between the cylinders for reheating. Works perfectly!
Ken

[rrbrewer]

Folk

If you want more details [explained well with good illustration] about two stroke vs. four stroke, suggest you check out

http://www.howstuffworks.com/

There is a lot of information on this site about the workings of a great variety of "things."

[rrbrewer]

Folk

If you want more details [explained well with good illustration] about two stroke vs. four stroke, suggest you check out

http://www.howstuffworks.com/

There is a lot of information on this site about the workings of a great variety of "things."

[sooblue]

QUOTE: Originally posted by jgoose1

Hi there
The major draw back is that you have pressureize the crank case to get air into the cylinder . This makes the crankcvase oil part of the air cleaner and it gets real dirty real fast and the intake air is polluted by exposure to the oil. You also have some limitiations on how much air you can put in the cylinder hence the engine horse power.

Engine controls guy

I think there is some confusion here.
The detroit 6-71, 8V-71, 8V-92 etc. Are blown engines. They have air chests that are separate from the crank case. The pressurized air enters through ports in the skirt of the cylinder sleeve. If engine oil is getting into the combustion chamber there is some other problem. The most common problem with the GM Detroit diesels has been cracking of the skirt at the intake ports which allows cooling fluid to enter the combustion chamber. I can't imagin that the Detroit prime movers are much diffrent, but they could be.
If you boosted through the crank case you'd toss all the oil out through the dipstick on the first crank of the engine.
The "how things work" web site is good but "Rudimentary"
If you want to you can blow the heads off with the super charger.[:p]
I suspect that EMD ran into problems with air volume. With the short "window" the 2 stroke couldn't get the volume of air needed to produce 6000 Hp. The 4 stroke has a bigger window built into it.
Sooblue

[sooblue]

QUOTE: Originally posted by jgoose1

Hi there
The major draw back is that you have pressureize the crank case to get air into the cylinder . This makes the crankcvase oil part of the air cleaner and it gets real dirty real fast and the intake air is polluted by exposure to the oil. You also have some limitiations on how much air you can put in the cylinder hence the engine horse power.

Engine controls guy

I think there is some confusion here.
The detroit 6-71, 8V-71, 8V-92 etc. Are blown engines. They have air chests that are separate from the crank case. The pressurized air enters through ports in the skirt of the cylinder sleeve. If engine oil is getting into the combustion chamber there is some other problem. The most common problem with the GM Detroit diesels has been cracking of the skirt at the intake ports which allows cooling fluid to enter the combustion chamber. I can't imagin that the Detroit prime movers are much diffrent, but they could be.
If you boosted through the crank case you'd toss all the oil out through the dipstick on the first crank of the engine.
The "how things work" web site is good but "Rudimentary"
If you want to you can blow the heads off with the super charger.[:p]
I suspect that EMD ran into problems with air volume. With the short "window" the 2 stroke couldn't get the volume of air needed to produce 6000 Hp. The 4 stroke has a bigger window built into it.
Sooblue

[Mookie]

I am going to add this subject to my others on power vs traction and the braking system, traction motors and spindle bearings and we are going to have a big party with all kinds of food, drawings and everyone explaining all these things to me so I am not

Clueless in Lincoln

Mook!

[Mookie]

I am going to add this subject to my others on power vs traction and the braking system, traction motors and spindle bearings and we are going to have a big party with all kinds of food, drawings and everyone explaining all these things to me so I am not

Clueless in Lincoln

Mook!

[Anonymous]

Lets try the explanation again. There is an air box as SooBlue said that distributes combustion air from the engine blower to all the cylinders. The inlet for the air is near the bottom of the cylinder. and the engine oil rings have to move past the intake port which wipes lube oil off the rings and combines it with the intake air thus explaining the oil consumption. In big engines they can not hold the tollerances fine enough so some of the compressed intake air as well as combustion blow by escapes arround the piston into the crankcase which makes the crankcase moderately pressurized. This air and oil vapors are then vented to the atmosphere in older engines or put into the engine exhaust . GM was not willing to cobel the design to meet the EPA guide lines for 2005. The other point mentioned by SooBlue is that in a two cycle you only have a short time at moderate speeds to charge the cylinder. To get more air into the cylinder you have to increase the boost which at some point proves to be impracticle. In a 4 cycle you have most of the intake stroke to do this so you can create a higher cylinder pressure.

[Anonymous]

Lets try the explanation again. There is an air box as SooBlue said that distributes combustion air from the engine blower to all the cylinders. The inlet for the air is near the bottom of the cylinder. and the engine oil rings have to move past the intake port which wipes lube oil off the rings and combines it with the intake air thus explaining the oil consumption. In big engines they can not hold the tollerances fine enough so some of the compressed intake air as well as combustion blow by escapes arround the piston into the crankcase which makes the crankcase moderately pressurized. This air and oil vapors are then vented to the atmosphere in older engines or put into the engine exhaust . GM was not willing to cobel the design to meet the EPA guide lines for 2005. The other point mentioned by SooBlue is that in a two cycle you only have a short time at moderate speeds to charge the cylinder. To get more air into the cylinder you have to increase the boost which at some point proves to be impracticle. In a 4 cycle you have most of the intake stroke to do this so you can create a higher cylinder pressure.

[Anonymous]

sooblue:
while i was still at the roseville loco shop i talked to an EMD tech rep. and he said that some of the Conrail SD80's had their 20 cyls. turned up to almost 6000hp.
Also the Detroit Diesel and EMD's have air boxes. they do not pressurize the crankcase. And as for the oil, it is brought up to the air box by the piston rings. It's unavoidable.

[Anonymous]

sooblue:
while i was still at the roseville loco shop i talked to an EMD tech rep. and he said that some of the Conrail SD80's had their 20 cyls. turned up to almost 6000hp.
Also the Detroit Diesel and EMD's have air boxes. they do not pressurize the crankcase. And as for the oil, it is brought up to the air box by the piston rings. It's unavoidable.

[sooblue]

Reply to jgoose1 and derailed,

What you have said makes sense to me. Yet I seem to remember that there was a seal on the piston that matched the sleave just below the intake ports that would seal the crank case off but would not seal on the way down because of the taper of the sleave. thus allowing the oil rings to pickup lube for the cylinder.

Anyway, the amount of the oil in the oil rings shouldn't be any more than that found in the 4 stroker. There is always some oil use but minimal for sure unless there is a problem.

Again "anyway", thanks for your input on this issue. I'm sure that the prime movers
vs the smaller diesels are like compairing apples and oranges so I must defer to you experts.
Sooblue

[sooblue]

Reply to jgoose1 and derailed,

What you have said makes sense to me. Yet I seem to remember that there was a seal on the piston that matched the sleave just below the intake ports that would seal the crank case off but would not seal on the way down because of the taper of the sleave. thus allowing the oil rings to pickup lube for the cylinder.

Anyway, the amount of the oil in the oil rings shouldn't be any more than that found in the 4 stroker. There is always some oil use but minimal for sure unless there is a problem.

Again "anyway", thanks for your input on this issue. I'm sure that the prime movers
vs the smaller diesels are like compairing apples and oranges so I must defer to you experts.
Sooblue