Erik_MagThere's a tradeoff between specific power and specific energy
Until it's near fully charged would be the short and snappy answer. There's a tradeoff between specific power and specific energy, hybrid cars, trucks, commuter locomotives would require high specific power.
Note that the 7MW charge rate would be for less than a minute, with charge rate decreasing as the train slows down. The key question is how many of these rapid charging cycles could be handled by the battery without degrading the battery? My impression is that number varies with with depth of discharge per cycle. I've lso seen many repports on modifications to Li-ion batteries to allow large numbers of high rate cycles.
Erik_MagMy recollection is that LFP batteries are good for repeated 5C charge/discharge rates and with specific energy of say 140w-hrs per tonne, a 10 tonne (11 short ton) battery would be good for 7 MW.
timz oltmannd If I'm a commuter agency, or even short haul intercity, I'd be all about trying to get hybrid locomotive that could keep me at 2 mph/sec or better all the way up to track speed. (And then get a good hunk of the energy back on braking! - with batteries continuing to charge during the station stop.) How possible do you suppose it is?
oltmannd If I'm a commuter agency, or even short haul intercity, I'd be all about trying to get hybrid locomotive that could keep me at 2 mph/sec or better all the way up to track speed. (And then get a good hunk of the energy back on braking! - with batteries continuing to charge during the station stop.)
How possible do you suppose it is?
I think the correct question is how practical it is, as it appears to be possible with existing technology. My recollection is that LFP batteries are good for repeated 5C charge/discharge rates and with specific energy of say 140w-hrs per tonne, a 10 tonne (11 short ton) battery would be good for 7 MW. Coupled with perhaps 3 MW from the prime mover, 10 MW would be good for 50,000 lbf tractive effort at 100 mph, 62,500 lbf at 80 mph and 100,000 lbf at 50 mph. The fastest charging would be during initial deceleration - the question is if the prime mover can make up for the difference between accelerating energy and regenerated braking energy.
I've been wondering about hybrid passenger locomotives since reading about EMD's F69 (12 cyl 710 with AC traction motors) back in the 1990's.
RPS in Fullerton has been saying they can provide that for a number of years.
In my opinion you'd use some combination of on-board KERS and supercapacitor banks for fast regenerative-braking storage in the absence of 'punctuated catenary' or smart third rail. This would then be used for controlled-rate charge and discharge of the actual chemical traction battery between its 20 and 80% or whatever is optimal for its battery chemistry by now -- even with the somewhat cockamamie RPS plan to rebuild cells from BEV batteries en masse to get the necessary capacity, you'd start having trouble if you tried slamming that acceleration and deceleration rate repeatedly across the battery alone with typical peninsula-size loads.
oltmanndIf I'm a commuter agency, or even short haul intercity, I'd be all about trying to get hybrid locomotive that could keep me at 2 mph/sec or better all the way up to track speed. (And then get a good hunk of the energy back on braking! - with batteries continuing to charge during the station stop.)
Backshop At what acceleration rate does it affect the passengers, i.e. those walking down the aisles?
At what acceleration rate does it affect the passengers, i.e. those walking down the aisles?
I'm throwing in with the 2-3 mph/sec acceleration as max for passenger comfort crowd...
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Erik_Mag oltmannd each piece wise linear. As I mentioned a few times, my experience was that the P42's could get up to track speed faster than the F40's when hauling the Surfliners. What would be really interesting is how a hybrid locomotive would work out where the battery was sized to put out 3MW for a short period of time. That is it would be more like an electric locomotive.
oltmannd each piece wise linear.
each piece wise linear.
As I mentioned a few times, my experience was that the P42's could get up to track speed faster than the F40's when hauling the Surfliners.
What would be really interesting is how a hybrid locomotive would work out where the battery was sized to put out 3MW for a short period of time. That is it would be more like an electric locomotive.
If I'm a commuter agency, or even short haul intercity, I'd be all about trying to get hybrid locomotive that could keep me at 2 mph/sec or better all the way up to track speed. (And then get a good hunk of the energy back on braking! - with batteries continuing to charge during the station stop.)
timz oltmannd GE train caught EMD after 0.4 miles. Balance speed for EMD train about 96, 113 for the GE. https://photos.app.goo.gl/cWsPYCVvVde4fC5SA You're misinterpreting your graphs. (And you mislabeled them -- is that easy to fix?) The graph says the F40 and the GE are at the same speed at the 0.4-mile mark, but they don't pass it at the same time. The F40 passes that point at 38 mph, and some time later the GE passes the same point at 38 mph. Remember: the area under the speed-vs-time curve equals distance-vs-time. Looks like the GE catches the F40 about 4.7 minutes from the start -- 4 miles or so.
oltmannd GE train caught EMD after 0.4 miles. Balance speed for EMD train about 96, 113 for the GE. https://photos.app.goo.gl/cWsPYCVvVde4fC5SA
You're misinterpreting your graphs. (And you mislabeled them -- is that easy to fix?)
The graph says the F40 and the GE are at the same speed at the 0.4-mile mark, but they don't pass it at the same time. The F40 passes that point at 38 mph, and some time later the GE passes the same point at 38 mph.
Remember: the area under the speed-vs-time curve equals distance-vs-time. Looks like the GE catches the F40 about 4.7 minutes from the start -- 4 miles or so.
Damn it! Of course, you're right! Here's the charts you're looking for...
https://photos.app.goo.gl/a1CmBUVWp65k9BUi6
GE catches up after 4:46 and 4.04 miles.
timz The graph says the F40 and the GE are at the same speed at the 0.4-mile mark, but they don't pass it at the same time. The F40 passes that point at 38 mph, and some time later the GE passes the same point at 38 mph. Remember: the area under the speed-vs-time curve equals distance-vs-time. Looks like the GE catches the F40 about 4.7 minutes from the start -- 4 miles or so.
For a 15 to 25 mile run, the GE will obviously be faster than the F40. The chart does reflect my experience with P42 powered trains going noticeably faster over most of the route.
I'm assuming Don was calculating speeds for level track, and I would expect that the GE would show up better on an ascending grade such as northbound out of San Juan Capistrano. Another thing that hasn't been discussed is accelerating from some sort of restricted speed, where the P42 would already be partially loaded.
Erik_MagFWIW, the acceleration rate for the original BART cars was 3 mphps from 0 to 30mph
I haven't been on new Silverliners, but fifteen years ago the DC-motor (?) cars took maybe 70 seconds to reach 80 mph. In the first ten seconds, maybe 100 feet.
FWIW, the acceleration rate for the original BART cars was 3 mphps from 0 to 30mph, and 3 mphps is roughly 4.5 fpsps. The traction control system took a couple of seconds to go from standing still to max acceleration. I remember walking in BART cars when starting and I had time to adjust between walking on level and hill climbing. The PCC research indicated that a high rate of acceleration was tolerable as long as the change from no acceleration was done smoothly. FWIW, the PCC cars could do 5 mphps.
My recollection was that the Metroliners were set up to accelerate at 1.1 mphps (~1.6 fpsps) from 0 to 100 mph. I suspect the 2.5 fpsps figure came from the Silverliners, where short distances between stops prioritized higher initial acceleration, while the longer distances between stops for the Metroliners priotitized sustained acceleration.
BackshopAt what acceleration rate does it affect the passengers, i.e. those walking down the aisles?
There were reports in Trains (I think in Pennypacker's story on the Metroliners circa 1967) that mentioned the higher figure for those trains. The lower figure was for 'transit' vehicles -- could have been BART, could have been Silverliners, I find I don't remember precisely enough.
I do not know offhand either what the various figures for the higher-speed Shin Kansen, TGV, Chinese HSR, and various maglev systems are, but they should be relatively easy to find for comparison discussion.
If you could guarantee all passengers firmly in their seats and belted in, you could get remarkable acceleration out of modern AC drive. But I don't think that's practical.
oltmanndGE train caught EMD after 0.4 miles. Balance speed for EMD train about 96, 113 for the GE. https://photos.app.goo.gl/cWsPYCVvVde4fC5SA
Overmod Undortunately, I don't see any use for acceleration above about 2.5fpsps (the old transit 'norm' I recall was about 1.5) so zero to 79 in under a trainlength might not be customer-desired. But it would be fun to watch, and probably to hear...
Undortunately, I don't see any use for acceleration above about 2.5fpsps (the old transit 'norm' I recall was about 1.5) so zero to 79 in under a trainlength might not be customer-desired. But it would be fun to watch, and probably to hear...
With a locomotive hauled train, the advantages of the extra accelerating power will come from raising the speed where acceleration is limited by adhesion. 1.5 ft/sec sustained to 60mph will get you to 60 mph in 1/2 mile. To get a higher acceleration rate would require motors on the trailing car axles with batteries or supercaps on each car. The advantage in the latter case is that more of the braking energy could be re-used for acceleration - a potential win-win with faster schedules and lower fuel consumption.
Erik_MagWhat would be really interesting is how a hybrid locomotive would work out where the battery was sized to put out 3MW for a short period of time. That is it would be more like an electric locomotive.
Keep in mind that you would retain the GE-style excitation that loads the diesel engine comparatively slowly for emissions, and the diesel engine would not be kept at full synchronous RPM for HEP as on the U-34s (or the F40s set up to take it off the main or dedicated generator). Naturally, if you could pre-accelerate the engine against only its own pumping resistance plus nominal small excitation, and then ramp up the alternator excitation quickly in sync with the battery excitation, you could get any desired AC starting current that the motors could use. If you were using even the current generation of hydrogen fuel cells, there might be comparatively little lag to bring the cells on in parallel with the battery drain once you got the train over about 10mph and could start using the higher horsepower to maintain acceleration rate...
So... spreadsheet. Those who guess that the P42's HP would catch the F40 in less than a mile were good seat of the pants estimaters. I used one locomotive, 500 HEP HP, 8, 55 ton coaches.
EMD to full load in 20 seconds, linear. GE to full load, 10% after 30 seconds, 50% at 60 seconds, full load at 90 seconds - each piece linear.
GE train caught EMD after 0.4 miles. Balance speed for EMD train about 96, 113 for the GE.
https://photos.app.goo.gl/cWsPYCVvVde4fC5SA
Oops. Sentry was wheelcreep. CHEC was excitation. In the late Dash 7s. Micro version in Dash 8s.
oltmannd Overmod timz An F40 with Cummins-or-whatever-it-is HEP will do a standing-start mile faster than any GE. If the train is shortish, any F40 will beat the GE. But that has nothing whatsoever to do with locomotive power; it only reflects GE's preoccupation with slow electrical loading. Eliminate the pollution fakery and you will see what Erik indicated. It was my impression observing the last days of the U34CHs that they would out-accelerate any EMD operating in NJT service then. In part that was due to the way their prime movers were governed at station stops -- held at 725rpm for HEP frequency compatibility, and excited in passenger service only slightly behind the governor feeding additional fuel at constant rpm for the start. A typical consist starting from North Hackensack with the locomotive opposite the MdDonald's at River Edge Road would have the cab car end crossing the street at a good percentage of track speed... the subsequent passage and echoes being very much 'honorary steam engine' as the prime-mover chugging did not change cadence with acceleration. I think the eix vs. four traction motors and the relatively rudimentary state of effective traction-control 'electronics' may have had something to do with this, more than the additional horsepower difference (which IIRC is between 3400 traction hp and about 2200 for the GE and EMD respectively when producing HEP to the consist...) My experience load testing quite a few EMD Dash 2s and GEs with Sentry Excitation is the EMD would crush a GE in commuter service. Time to full load from idle for the EMD was about 20 seconds and pretty linear. GE uses a three-slope curve for loading. Wipe the throttle from idle to 8 and it take 80 seconds to get to full load. The first slope is shallow. about 30 seconds to get to a few hundred HP. The second slope is steeper. Another 30 seconds and you're at about 1/3 load. The last slope is steep, with the last 2/3 coming on like gangbusters in the last 20 seconds. Both get to full engine speed pretty quickly. Getting to full load is where the EMD shines. I have a friend who worked at nuclear plant. The back up diesels there had to be a full load in 20 seconds. They used ALCO 251s. How? By using compressed air to spin up the turbo to get the intake manifold pressure up, fast. You could do this with an FDL, I suppose...
Overmod timz An F40 with Cummins-or-whatever-it-is HEP will do a standing-start mile faster than any GE. If the train is shortish, any F40 will beat the GE. But that has nothing whatsoever to do with locomotive power; it only reflects GE's preoccupation with slow electrical loading. Eliminate the pollution fakery and you will see what Erik indicated. It was my impression observing the last days of the U34CHs that they would out-accelerate any EMD operating in NJT service then. In part that was due to the way their prime movers were governed at station stops -- held at 725rpm for HEP frequency compatibility, and excited in passenger service only slightly behind the governor feeding additional fuel at constant rpm for the start. A typical consist starting from North Hackensack with the locomotive opposite the MdDonald's at River Edge Road would have the cab car end crossing the street at a good percentage of track speed... the subsequent passage and echoes being very much 'honorary steam engine' as the prime-mover chugging did not change cadence with acceleration. I think the eix vs. four traction motors and the relatively rudimentary state of effective traction-control 'electronics' may have had something to do with this, more than the additional horsepower difference (which IIRC is between 3400 traction hp and about 2200 for the GE and EMD respectively when producing HEP to the consist...)
timz An F40 with Cummins-or-whatever-it-is HEP will do a standing-start mile faster than any GE. If the train is shortish, any F40 will beat the GE.
But that has nothing whatsoever to do with locomotive power; it only reflects GE's preoccupation with slow electrical loading. Eliminate the pollution fakery and you will see what Erik indicated.
It was my impression observing the last days of the U34CHs that they would out-accelerate any EMD operating in NJT service then. In part that was due to the way their prime movers were governed at station stops -- held at 725rpm for HEP frequency compatibility, and excited in passenger service only slightly behind the governor feeding additional fuel at constant rpm for the start. A typical consist starting from North Hackensack with the locomotive opposite the MdDonald's at River Edge Road would have the cab car end crossing the street at a good percentage of track speed... the subsequent passage and echoes being very much 'honorary steam engine' as the prime-mover chugging did not change cadence with acceleration.
I think the eix vs. four traction motors and the relatively rudimentary state of effective traction-control 'electronics' may have had something to do with this, more than the additional horsepower difference (which IIRC is between 3400 traction hp and about 2200 for the GE and EMD respectively when producing HEP to the consist...)
My experience load testing quite a few EMD Dash 2s and GEs with Sentry Excitation is the EMD would crush a GE in commuter service.
Time to full load from idle for the EMD was about 20 seconds and pretty linear. GE uses a three-slope curve for loading. Wipe the throttle from idle to 8 and it take 80 seconds to get to full load. The first slope is shallow. about 30 seconds to get to a few hundred HP. The second slope is steeper. Another 30 seconds and you're at about 1/3 load. The last slope is steep, with the last 2/3 coming on like gangbusters in the last 20 seconds.
Both get to full engine speed pretty quickly. Getting to full load is where the EMD shines.
I have a friend who worked at nuclear plant. The back up diesels there had to be a full load in 20 seconds. They used ALCO 251s. How? By using compressed air to spin up the turbo to get the intake manifold pressure up, fast. You could do this with an FDL, I suppose...
GE FDLs had crappy exhaust mainfolds - alway cracking. So, in the 90s, GE redesigned and result was reduced volume, which promised to reduce turbo lag some. I don't know if they ever took advantage of it with micro-Sentry excitation rates.
timz oltmannd We can simulate on a spreadsheet. Someone should do it. Maybe you can do it (lotsa luck!) but none of us knows how much tractive effort any engine has X seconds after it starts, having reached speed Y by that time, since the TE depends on both X and Y. I remember walking along the high platform at Summit (DL&W), alongside the cab of a GP40P. I think the amp needle was at 1200 before the train was too fast for me -- but maybe I misread it. Does that sound reasonable?
oltmannd We can simulate on a spreadsheet. Someone should do it.
Maybe you can do it (lotsa luck!) but none of us knows how much tractive effort any engine has X seconds after it starts, having reached speed Y by that time, since the TE depends on both X and Y.
I remember walking along the high platform at Summit (DL&W), alongside the cab of a GP40P. I think the amp needle was at 1200 before the train was too fast for me -- but maybe I misread it. Does that sound reasonable?
BaltACD oltmannd timz Yes, if they start side by side the GE might well catch up to the F40 after a few miles. We can simulate on a spreadsheet. Someone should do it. There are way too many people that think spreadsheeting is railroading. IT IS NOT. Railroading is done in the real world, with real weather and real varying condiditons.
oltmannd timz Yes, if they start side by side the GE might well catch up to the F40 after a few miles. We can simulate on a spreadsheet. Someone should do it.
timz Yes, if they start side by side the GE might well catch up to the F40 after a few miles.
Yes, if they start side by side the GE might well catch up to the F40 after a few miles.
We can simulate on a spreadsheet. Someone should do it.
There are way too many people that think spreadsheeting is railroading.
IT IS NOT.
Railroading is done in the real world, with real weather and real varying condiditons.
Of course. But the physics can be done on a spreadsheet. It's simple stuff.
And I've been involved in enough, real world, over the road, locomotive performance testing to know the limits of what you can and shouldn't do on a spreadsheet.
This GE vs EMD train acceleration question is answerable on a spreadsheet.
The slower a train moves with the locomotives a full throttle - the higher the reading of the amp meter. The 'short time' ratings that are used with DC traction motor engines represent this fact.
Amperes through traction motors generate heat - more amps, more heat. Heat that is capable, in the extreme, of basically melting its electrical parts down.
AC traction motors, through electrical processes I don't have enough knowledge to explain do not have this same kind of failure mode.
Never too old to have a happy childhood!
oltmanndWe can simulate on a spreadsheet. Someone should do it.
oltmannd My experience load testing quite a few EMD Dash 2s and GEs with Sentry Excitation is the EMD would crush a GE in commuter service. Time to full load from idle for the EMD was about 20 seconds and pretty linear. GE uses a three-slope curve for loading. Wipe the throttle from idle to 8 and it take 80 seconds to get to full load. The first slope is shallow. about 30 seconds to get to a few hundred HP. The second slope is steeper. Another 30 seconds and you're at about 1/3 load. The last slope is steep, with the last 2/3 coming on like gangbusters in the last 20 seconds.
My experience with F40's vs Genesis was on Amtrak where the shortest start to stop was on the order of 15 miles. The extra 1000HP in the Genesis had plenty of time to make their presence known.
Battery technology has progressed to where a hybrid commuter locomotive would make sense, where tractive effort could be adhesion limited to a much higher fraction of track speed than with a standard diesel-electric.
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