So, I've been having a discussion with someone on another forum about whether or not the EMD 2 Cycle Turbo with overrunning clutch is a "true" turbo charger.
My argument was that it was, because any turbocharger without the clutch wouldn't provide a power boost until some critical RPM (exhaust volume) was achieved. And that point in an EMD was ~run 6 where the clutch disengages. The fact that the clutch exists and therefore the turbo is ALSO a supercharger doesn't change this. So the device is a "true" turbo charger...and also a mechanically driven compressor
My compatriot suggested that no, the mere existence of this secondary feature made it not a true turbo, but some sort of other thing.
Not a true turbo...like a GE FDL has. So we've been having a nomenclature fight which is irritating and if someone here has a thought, I'd welcome it. Wikipedia in their lack of wisdom calls the EMD turbo a Turbo-compressor which is dumb, because a turbo charger is already a type of compressor. Technically, it's a type of supercharger although nobody uses the term that way.
Anyway, Mr. Language person questions aside,
Well this begged a question for me. Obviously the FDL (or 244/251 from Alco) has a turbo and that turbo must provide boost pressure at some point when RPM/Exhause volume hits a critical value.
Would it be fair to suggest that that critical value is also somewhere in the run 6 area as in the EMD? Or is it different in the FDL and Alco series locomotives
The next question I have is, How is the efficiency of the overruning clutch+Turbo below run 6? In other words, I think it would be a fair hypothosis that the Turbo when in mechanical mode is less efficient than a purpose built Roots Blower based supercharger...And I further would suggest that that implies that a GP38 (as an example) Should produce more HP below run 6 than a GP40...or, at least they should be equivalent..but i'd guess less. Then at run 6, the GP40 should produce significantly more HP.
I don't have the Horse Power Curves to review nor did Google seem to understand what I was asking about.
I'm assuming the parasitic loss due to the mechanical drive of the Roots blowers and the clutch are roughly equivalent.
anyone have any thoughts on the topic? Am I totally off base? Pure foamer fanwank here?
Nomenclature and terminology can be funny and confusing sometimes, and differ between sources.
To muddy the waters further, on occasion one will find the roots-blown (non-turbocharged) EMD and Detroit Diesel engines described as "naturally-aspirated two-stroke diesels", which is of course an oxymoron.
Greetings from Alberta
-an Articulate Malcontent
Firstly, the GP40 isn't jus a GP38AC that someone bolted the turbocharger onto.
The power output at each notch should be the same proportion of the notch 8 power for both blower and turbo engines. So the GP40 is more powerful than the GP38 at each notch above idle, whether or not the turbo is operating.
The GP40 has a centrifugal compressor which operates differently than the roots blower. The roots blower is basically two interlocking paddle wheels compressing the air and is regarded as a positive displacement compressor. The centrifugal compressor isn't as linear in its operation but has to pump around fifty percent more air at notch 8.
When the clutch releases, the hundreds of horsepower that were being used to drive the centrifugal blower becomes available to the alternator. The effect of this is to reduce the specific fuel consumption, down to that of a turbocharged four stroke engine, and significantly less per unit power develped than that of a blower engine.
A useful comparison is between a GP38 and a GP39, which is slightly more powerful but significantly more economical as far as fuel consumption is concerned.
But the 645E3 engine in the GP40 should produce the same proportion of its maximum power at any particular notch as the GP38.
Below notch 6, the fuel consumption per unit horsepower should be roughly the same for both GP38 and GP40.
Above notch 6, the GP40 uses significantly less fuel per unit hosepower than a GP38.
Peter
The GP40 is more efficient in every notch than a GP38 because the turbine is always supplying some of the energy needed to run the compressor. The gear drive and clutch just supply the difference.
If you look at the fuel curves for a GP40, the increment of fuel and HP from notch to notch is nearly dead-on linear. On a GP38, it the efficiency drops as the air box pressure drops from notch to notch toward the higher notches. The roots-blower just can't keep up.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
It costs about 300 horsepower just to run the turbo on the clutch. Perhaps SHP is linear but I do not believe that KWHP is linear. It may be close....
Randy
OK, I guess that makes sense. So there is less parasitic loss in the Turbo below notch 6, because the Exhaust flow is still helping drive the turbine even if it isn't sufficient to drive it alone. I'm not sure I understand how a GP40 isn't just a GP38 with the turbo bolted on...and bigger Radiators. I thought that was the point. The 645E is the 645E...adding the 3 turbo to make a 645E3 doesn't change the block or the Power assemblies does it? A GP39 is a V12 and so I would imagine it is more fuel efficient.
If the turbo is eating up 300HP below notch 6, what power does the roots blower eat up?
What's the mythical HP curve of a 645E where the Roots blowers are driven by an external motor and are not a parasitic loss on the engine?
...adding the 3 turbo to make a 645E3 doesn't change the block or the Power assemblies does it? A GP39 is a V12 and so I would imagine it is more fuel efficient.
The compression ratio for the turbo engine is lower than that for the blower engine.
So yes, the power assemblies are different. I seem to recall hearing that the power assemblies were changed on the GP40s being converted to GP38. I imagine the same would apply to adding a turbo.
The block can be different. When the GP39 was introduced, a stronger crankcase was required compared to that in the SW1500. All later twelve cylinder crankcases were built to the new design. This resulted in the Queensland Railways raiding some withdrawn G22C locomotives to find crankcases suitable for conversion to 12-645E3, but many couldn't be used.
I expect that all new-build 16-645 crankcases were to the stronger design, but I'm hapy to be corrected on that.
Engines with the Rootes blower are called naturally aspirated because the incoming charge is not above atmospheric pressure. The blower is geared to the crankshaft and does not turn fast enough to "supercharge" the engine at above atmospheric pressure. Speed does not matter because it is a positive displacement pump. The centrifugal blower on the other hand becomes more effective with greater speed. You can't flatly say that it overrides the clutch at a particular throttle notch because changes in elevation affect air density and the point where it becomes supercharged.
I think some miss the point when they say clutch . What EMD turbo two strokes use is actually a type off free wheel that allows the turbocharger to turn faster than the gear train but not slower . It sort of makes the best of both worlds ie the gear train drives the turbochargers rotating assembly at engines revs below where there is sufficient exhaust energy to drive the turbos turbine faster than the gear train .
I should also add that a piston engines exhaust energy increases more so in proportion to load than engine revs - or in this case throttle notches .
Also pumping efficiencies vary greatly when comparing roots blowers to EMDs turbochargers . Roots blowers are nortiorious for adding more heat to the charge or inlet air than turbochargers .
Anyway you can argue all day about blowers vs turbos but at the end of the day EMD did what they did and the next factory roots blown 710 will be the first .
Also moot point because the future appears to be turbocharged four strokes - in North America anyway .
tdmidget Engines with the Rootes blower are called naturally aspirated because the incoming charge is not above atmospheric pressure. The blower is geared to the crankshaft and does not turn fast enough to "supercharge" the engine at above atmospheric pressure. Speed does not matter because it is a positive displacement pump. The centrifugal blower on the other hand becomes more effective with greater speed. You can't flatly say that it overrides the clutch at a particular throttle notch because changes in elevation affect air density and the point where it becomes supercharged.
Your wrong on that one according to our shop foreman. He has rebuilt many old 6-71 Detroits in his time as a mechanic. All of them are 2 strokes with a roots style blower. In order to scavange the engine during the time they had the blower has to produce about 5 pounds of boost to drive the exhaust out of the cylinder at BDC of each stroke.
Air box pressure. It must be slightly higher or their would be no flow into the cylinder .
EMD blowers are exhaust scavenging also ,4-5 psi. An EMD and a Detroit share a lot in common.
On 2 stage EMD turbo's the parts manual describes a clutch.
Randy Stahl EMD blowers are exhaust scavenging also, 4-5 psi. An EMD and a Detroit share a lot in common. On 2 stage EMD turbo's the parts manual describes a clutch.
EMD blowers are exhaust scavenging also, 4-5 psi. An EMD and a Detroit share a lot in common.
To some extent, the 71 was a half scale 567, with 1/8 the displacement as a result. Of course the construction was entirely different also due to the size, but initially, there were only inline 71s and only vee-type 567s.
But in this context, Detroit two stroke engines all had roots blowers for scavenging, whether or not they were turbocharged. One result of this was that the blower power was required at full engine power and this had an impact on fuel economy, compared to the EMD solution.
The Detroit two stroke disappeared fairly quickly at least partly on the basis of fuel consumption, while the EMD two stroke remained competitive on this score and has only been sidelined from new domestic locomotive constuction by emission regulations.
The drive for the EMD locomotive turbocharger has always been called an "overrunning clutch" to my recollection. I think the marine engines have a different design, due to the different duty cycle, but it is still called a clutch.
M636C Randy Stahl EMD blowers are exhaust scavenging also, 4-5 psi. An EMD and a Detroit share a lot in common. On 2 stage EMD turbo's the parts manual describes a clutch. To some extent, the 71 was a half scale 567, with 1/8 the displacement as a result. Of course the construction was entirely different also due to the size, but initially, there were only inline 71s and only vee-type 567s. But in this context, Detroit two stroke engines all had roots blowers for scavenging, whether or not they were turbocharged. One result of this was that the blower power was required at full engine power and this had an impact on fuel economy, compared to the EMD solution. The Detroit two stroke disappeared fairly quickly at least partly on the basis of fuel consumption, while the EMD two stroke remained competitive on this score and has only been sidelined from new domestic locomotive constuction by emission regulations. The drive for the EMD locomotive turbocharger has always been called an "overrunning clutch" to my recollection. I think the marine engines have a different design, due to the different duty cycle, but it is still called a clutch. Peter
I guess you might have never heard of the 12-71 it was a V-12 configuration and could also be turbocharged. All Detroit's could be turbocharged it's just that instead of being part of the supercharger they were the standard exhaust driven setup.
I actually said
initially, there were only inline 71s and only vee-type 567s.
The vee-type 71s were a post WWII development. During the war, many landing craft used gear coupled pairs of 6/71s since no larger version was available. These were called "Twin 71s". One later landing craft drawing still had the description "Twin 71" on a ship with two 12V-71s, presumably because the draftsman copied the wording from the older drawing without understanding what it meant.
I was fairly familiar with the larger Detroit engines, including the 16-149TI which had two roots blowers fed by four turbochargers. The roots blower sat down on the vee of those engines and was fed from a separate turbocharger on each bank of each half of the engine. I think all the big vee type Detroit engines had the block cast in two pieces, so a 12-71 was two 6V-71s bolted together, the V-8 being the biggest single block.
Actually I have run the 16 cyl 7 fdl without a turbo connected. We removed all the airtubes in order to observe the valve action in notch one. There wasn't a noticeable increase in smoke so its safe to assume that the turbo does nothing in notch one.
RSS
There is certainly a lot of misinformation here. When we talk about locomotive horsepower for diesel electric locomotives, what we are talking about is how much horsepower the engine is producing. If you take a EMD 3,000 horsepower, 645E3 engine and put it into a tugboat it's a 3,000 HP tugboat. If you put it in a power plant it is a 3,000 HP stationary generator. If you put it in a locomotive it's a 3,000 HP locomotive. You can remove a 2,000 HP, roots driven, EMD 645 from a GP38-2 (rated at 2,000 HP). Replace that with a 3,000 HP, turbocharged EMD 645, and now the locomotive is 3,000 HP. What ever engine you put into that locomotive is what that locomotives horsepower will be. If you took the DD40X and put in two blower driven 645's then it would be a 4,000 HP locomotive.
With regards to the clutch issue. In mechanical terms when the turbo is run by the gear train, I think we could say that the engine is super charged since this is run by mechanical. After the pressure is high enough it is run by the exhaust gases and becomes a true turbo charger. As a former locomotive mechanic I would defiantly say it's a true turbo charger because the exhaust gases are always turning it. True it needs help at lower RPM's with the clutch, but the exhaust is always contributing.
Turbo chargers are obviously superior to blowers which is why you have a 1,000 plus horsepower increase for the same engine. The majority of locomotives out there are turbo charged. The only problem with turbo chargers (especially with EMD locomotives) is they load up quickly. This is problematic in yards as you don't want locomotives accelerating too quickly. Non turbo charged locomotives are ideal for yard duty as they are load up slowly
I do not see a significant difference concerning resistance between roots blowers and turbochargers at lower RPM's. If anything they should be almost equal. If I had to guess, I would estimate it probably takes around 23 horsepower to run either. They would have to be engineered very similarly since they are both running on identical engines which need to load up at around the same time.
Thomas 9011The only problem with turbo chargers (especially with EMD locomotives) is they load up quickly. This is problematic in yards as you don't want locomotives accelerating too quickly. Non turbo charged locomotives are ideal for yard duty as they are load up slowly
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I've seen an EMD GP 30 load up quickly. Quickly enough to run itself through the N Fond Du Lac rear roundhouse wall.
I just repaired the fast start feature, I didn't tell anyone..
Thomas 9011Non turbo charged locomotives are ideal for yard duty as they are load up slowly
Depends on the resistors on the rate card. RC.
Trying to kick with a slow loading engine sucks.
"Give me a kick"
"Yeah.. it's coming. Might as well get soemthing to drink and use the bathroom while you're waiting."
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.
zugmann Trying to kick with a slow loading engine sucks. "Give me a kick" "Yeah.. it's coming. Might as well get soemthing to drink and use the bathroom while you're waiting."
I used to work with a engineer who told me "general electric locomotives are so slow that you could read a novel by the time they load up". I would have to agree. That is probably why you rarely see any GE locomotives doing yard duty for any class 1 railroads.
Thomas 9011That is probably why you rarely see any GE locomotives doing yard duty for any class 1 railroads.
I've done it. Also on locals. They weren't bad on the local - but you had to have patience. Give it a notch or two and it will eventually start pulling. Guys used to running 4 axles had a hard time using them.
I don't see any difference in loading with the GP38 or the GP40. The 50's and 60's are excellent locomotives and more powerful. I do remember them loading up slightly quicker than the GP38-2's. We didn't use them too often, usually when there was power shortages. Most had comfort cabs which is not good for yard duty. We had one of the last active SD45T-2's come to our UP yard one day. I talked the engineer into using that instead of our usual dual GP38-2's. That locomotive is a absolute beast! Pull 40 loads like it was nothing. We got done probably 2 hours early. Kicking cars was a bit difficult though. Turbos do have a slight lag when starting. So when it does kick in, cars start to move pretty quickly after it loads up. More work for the engineer when you are only dealing with say less than 20 cars especially if they are empty. Pretty hard to find a balance in the yard. Something that would probably be ideal would be a six axle, blower driven, locomotive. I always felt like the SD-9 was the perfect yard switcher.
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