Are hybrid trains a thing? If not, why not?

[swaldman]

I don't know a lot about rail engineering, so this may be silly - but if so, I'd like to know why. It seems to me that diesel trains spend most of their time either (a) at full power, accelerating or climbing a hill; or (b) coasting, decelerating or stationary, at or close to idling revs.

This feels like it would be the perfect place for a hybrid drivetrain: where a smaller diesel engine spends most of its time at its most efficient speed, and a battery is used to smooth out the peaks and troughs.

That feels like it ought to be worthwhile even before one factors in the benefits of regenerative braking.

Has it been tried? Is there a reason why it wouldn't work?

 

[TRAX]

That’s basically the principle of diesel-electric trains (without the batteries though), which for some reason has never been a favourite of British railways.

 

[swt_passenger]

I don't know a lot about rail engineering, so this may be silly - but if so, I'd like to know why. It seems to me that diesel trains spend most of their time either (a) at full power, accelerating or climbing a hill; or (b) coasting, decelerating or stationary, at or close to idling revs.

This feels like it would be the perfect place for a hybrid drivetrain: where a smaller diesel engine spends most of its time at its most efficient speed, and a battery is used to smooth out the peaks and troughs.

That feels like it ought to be worthwhile even before one factors in the benefits of regenerative braking.

Has it been tried? Is there a reason why it wouldn't work?

Yes it was trialled. An HST was used, “hayabusa HST” is the search term you need.

“Hybrid” is also also often confusingly used as a synonym for bi-mode diesel or electric traction, so a search for hybrid will often find that as well.

 

[Bletchleyite]

I don't know a lot about rail engineering, so this may be silly - but if so, I'd like to know why. It seems to me that diesel trains spend most of their time either (a) at full power, accelerating or climbing a hill; or (b) coasting, decelerating or stationary, at or close to idling revs.

This feels like it would be the perfect place for a hybrid drivetrain: where a smaller diesel engine spends most of its time at its most efficient speed, and a battery is used to smooth out the peaks and troughs.

That feels like it ought to be worthwhile even before one factors in the benefits of regenerative braking.

Has it been tried? Is there a reason why it wouldn't work?

I believe Vivarail are toying with the idea. Regen of course is used on electric trains.

 

[swaldman]

Yes it was trialled. An HST was used, “hayabusa HST” is the search term you need.

Ah, thanks. So... the project ended quietly and nothing more was done about it? Sad.
Having said that, it was a while ago with old battery tech - the 48kWh of the battery is no bigger than an electric car might have nowadays, is only equivalent to about two minutes of a Class 43's generator output. I think that revisiting it today, with today's energy densities, would be an entirely different proposition. It surprises me that it isn't in use in new DMUs.

 

[swt_passenger]

Ah, thanks. So... the project ended quietly and nothing more was done about it? Sad.
Having said that, it was a while ago with old battery tech - the 48kWh of the battery is no bigger than an electric car might have nowadays, is only equivalent to about two minutes of a Class 43's generator output. I think that revisiting it today, with today's energy densities, would be an entirely different proposition. It surprises me that it isn't in use in new DMUs.

It might well come with some future new DMUs, there haven’t been many recently.

 

[boxy321]

I have travelled on hybrid buses and they can be both great and terrible.

Off the mark they're great but on a sustained incline they reduce to a crawl (There's a hill in Meriden, West Mids where the 82 bus reduces to walking pace with the engine going flat out). I believe they use super capacitors, not batteries though. The diesel Mercedes models they use on the same route can keep up with cars.

The advantage of a hybrid train pulling off with wheels spinning is not great (!), and the likes of 172s use mechanical gearboxes due to their efficiency.

 

[swaldman]

It might well come with some future new DMUs, there haven’t been many recently.

Ah, fair point

I have travelled on hybrid buses and they can be both great and terrible.

Off the mark they're great but on a sustained incline they reduce to a crawl (There's a hill in Meriden, West Mids where the 82 bus reduces to walking pace with the engine going flat out).

*nod* This would happen, in the train context, if the batteries didn't have enough capacity to keep full power available all the way up an incline (they'd actually need to be bigger than this, to account for maybe not being full at the start of the incline). Data on what capacity is needed should be easily obtainable, simply by looking at existing trains and measuring how long they spend at what power setting.

But beyond that, the analogy with hybrid buses stops. I believe they use a parallel hybrid system, like a Toyota Prius - they're still basically diesel-driven, with a mechanical transmission, so the diesel engine revs according to the vehicle speed, but they use their electric motor for a boost - most obviously when pulling away - and to allow them to stop the engine when it isn't needed. Because of this boost they are probably provided with a less powerful engine, and hence they run out of juice on a sustained incline.

What I'm envisaging is a series hybrid. In a diesel-electric train we already have electrical transmission, and we already have traction motors that can supply the full power needed. But because there's no energy storage, the engine still has to throttle up and down according to how much power is needed by the motors. This is inefficient.
In a series hybrid you reduce the size of the diesel engine (or even keep it and throttle it back, which would have less benefit but also lower risk) and it is always either (a) idling*, or (b) running at its most efficient rpm. You keep the same *average* power output, but you use the battery to smooth out as much as possible of the inefficient peaks and troughs.

Because our aim is to smooth out the power requirements of the motors, not to provide greater peak power, there's no reason that it should cause more wheelspin.



* Potentially stopped in a DMU scenario, with engines small enough to do stop/start.

 

[gazthomas]

In some respects the Parry People Mover follows the principle with its smaller engine, albiet with power being first stored in, then applied from the flywheel

 

[Ken H]

All this is very well until you get a sustained gradient. imagine trying to so settle-Ais gill with reduced power. Same reason i wont have a hybrid car - i go up 1:3 gradients quite a lot and I need the oompf.

 

[WideRanger]

Ah, thanks. So... the project ended quietly and nothing more was done about it? Sad.

If I remember correctly, Hitachi used a lot of the experience from Hayabusa (Japanese for Perigrine Falcon) for the development of Hybrid trains in use in Japan.

 

[swaldman]

All this is very well until you get a sustained gradient. imagine trying to so settle-Ais gill with reduced power. Same reason i wont have a hybrid car - i go up 1:3 gradients quite a lot and I need the oompf.

The gradients on the UK rail system are known. You size the battery to be sufficient for the longest one that the train will encounter.

If it's not feasible to do that for weight, or cost, or space reasons, then you use a bigger engine. You lose some of the efficiency gains, but you still benefit from being able to smooth out *most* of the peaks and troughs in power demand, so it should still be worth it.

 

[swaldman]

If I remember correctly, Hitachi used a lot of the experience from Hayabusa (Japanese for Perigrine Falcon) for the development of Hybrid trains in use in Japan.

Oh, they have them in Japan? Nice

 

[swaldman]

For any others who are curious, they do seem to be rolling out in Japan.

Here's a bimode + battery hybrid multiple unit:
https://asia.nikkei.com/Business/Japan-rail-car-builders-rolling-out-next-gen-diesel-trains
https://en.wikipedia.org/wiki/HB-E210_series

Here's a hybrid shunting loco:
https://en.wikipedia.org/wiki/JR_Freight_Class_HD300

According to wikipedia, in 2009 Hitachi announced that the diesel versions of the IEP would be hybrids. Not sure what happened to that!

 

[Greybeard33]

A key difference between diesel road and rail vehicles is that the latter have a much lower power to weight ratio. Consequently a rail diesel engine spends much more of its time at or near maximum power output, either during acceleration or maintaining maximum speed.

In a hybrid road vehicle, the battery supplies short bursts of power during acceleration and hill climbing, enabling the diesel engine to be downsized substantially and operate more efficiently. Whereas in a hybrid diesel-electric rail vehicle, the diesel generator would need to be nearly as powerful as in a conventional diesel-electric, in order to sustain prolonged periods of accleration and high speed running. There would be efficiency savings from regenerative braking, but these must be traded against the additional weight of the batteries and control electronics.

The Vivarail Class 230, Porterbrook Class 769 and Stadler Class 755 FLIRT are all recent projects that potentially could have made use of hybrid drive trains, but the designers evidently concluded that the drawbacks outweighed the advantages.

 

[Chris125]

Diesel/Battery hybrids are on the way: Rolls-Royce and Porterbrook launch first hybrid rail project in the UK

"Rolls-Royce and Porterbrook, the UK’s largest owner of passenger rolling stock, have agreed the delivery of MTU Hybrid PowerPacks that can convert Class 168 and Class 170 ‘Turbostar’ DMUs from diesel-only to hybrid-electric operation"​

Vivarail's 5 class 230s for Transport for Wales will also be diesel hybrids: Vivarail announce new order for Wales and Borders

“Our aim has always been to provide innovative solutions for operators and to that end I’m delighted to announce that our trains will be built as battery/diesel hybrids to cut down on emissions and make use of the exciting new technology we have developed over the past two years.


​

 

[swaldman]

A key difference between diesel road and rail vehicles is that the latter have a much lower power to weight ratio. Consequently a rail diesel engine spends much more of its time at or near maximum power output, either during acceleration or maintaining maximum speed.

In a hybrid road vehicle, the battery supplies short bursts of power during acceleration and hill climbing, enabling the diesel engine to be downsized substantially and operate more efficiently. Whereas in a hybrid diesel-electric rail vehicle, the diesel generator would need to be nearly as powerful as in a conventional diesel-electric, in order to sustain prolonged periods of accleration and high speed running.

Hmmm. For suburban DMUs that are stopping/starting all the time, with a significant proportion of their time idling at stations, I don't think this is the case - and given the new Japanese DMU designs, it seems that they agree. I guess an intercity train that is maintaining top speed for hours on end would be using a lot of engine power for a long period, but surely not maximum output? Given sufficient battery capacity the engine only needs to be sized for (a little more than) that sustained output, rather than for acceleration or hill climbing.

Let's try some very rough maths. I think I read somewhere on this forum that it takes an HST about six minutes to reach 125mph. An HST has somewhere in the region of 3MW of electrical output (both power cars together). So then electrical energy required to reach top speed from a standing start is roughly 3000 x (6/60) = 300kWh. If we assume that half of that is provided by engines, and half from batteries, then we need 150kWh of batteries for that maneuver, which is less than two Tesla cars. Now, Tesla batteries can't output their energy that fast, and something that could would certainly be larger, and heavier, and have greater cooling needs. But I should think that ought to be achievable on a train.

Obviously that's incredibly rough, and yes, the engine would need to be able to provide the sustained output that's needed to keep full speed on the flat, but it seems to me that the order of magnitude of battery size that's needed for acceleration is entirely within the range of what's feasible.

The Vivarail Class 230, Porterbrook Class 769 and Stadler Class 755 FLIRT are all recent projects that potentially could have made use of hybrid drive trains, but the designers evidently concluded that the drawbacks outweighed the advantages.

Interesting. Do you know that it was considered and rejected, or just that they are recent diesel-electric designs that didn't incorporate batteries?

 

[100andthirty]

Greybeard...Some at least of the Transport for Wales FLIRTs will be electric/diesel/battery hybrids. Class 769 would not have benefited much from having a battery in series with the hybrid system as the class 319's don't have any regenerative braking to help keep the batteries charged. But one never knows, perhaps a class 455 diesel/battery hybrid might be possible, as the soon to be ex-SWR Porterbrook units do have regenerative brake.

 

[Billy A]

That’s basically the principle of diesel-electric trains (without the batteries though), which for some reason has never been a favourite of British railways.

They used to be though, as diesel electric DMUs were very much a thing once until Voith hydrodynamic gearboxes were introduced. DE fell out of favour for the same reasons as you don't have it in your car - it's heavy, expensive and inefficient. Having so said more modern AC equipment is rather better.

 

[robbeech]

Hmmm. For suburban DMUs that are stopping/starting all the time, with a significant proportion of their time idling at stations, I don't think this is the case - and given the new Japanese DMU designs, it seems that they agree. I guess an intercity train that is maintaining top speed for hours on end would be using a lot of engine power for a long period, but surely not maximum output? Given sufficient battery capacity the engine only needs to be sized for (a little more than) that sustained output, rather than for acceleration or hill climbing.

Let's try some very rough maths. I think I read somewhere on this forum that it takes an HST about six minutes to reach 125mph. An HST has somewhere in the region of 3MW of electrical output (both power cars together). So then electrical energy required to reach top speed from a standing start is roughly 3000 x (6/60) = 300kWh. If we assume that half of that is provided by engines, and half from batteries, then we need 150kWh of batteries for that maneuver, which is less than two Tesla cars. Now, Tesla batteries can't output their energy that fast, and something that could would certainly be larger, and heavier, and have greater cooling needs. But I should think that ought to be achievable on a train.

Obviously that's incredibly rough, and yes, the engine would need to be able to provide the sustained output that's needed to keep full speed on the flat, but it seems to me that the order of magnitude of battery size that's needed for acceleration is entirely within the range of what's feasible.



Interesting. Do you know that it was considered and rejected, or just that they are recent diesel-electric designs that didn't incorporate batteries?

I think whilst you admit the calculations are generic that it should be feasible for certain applications, I guess one point to consider is that, by today’s standards it’s painful to say hst are a bit steady and we are thriving to achieve better acceleration levels for these kinds of trains. Things like the 220/1/2 are all considerably better in that department, as are the (DMU rather than DEMU) 180s when they’re not having a diesel bath.

 

[broadgage]

A true hybrid multiple unit, fitted with both diesel engines and batteries would have a lot of advantages.
Consider as an illustrative example a train that needs 500KW to maintain line speed on level track, it would need at last 1000Kw of engine power in order to ascend inclines and to accelerate.
A lot of the time those heavy and expensive engines will not be fully utilised.

Instead consider a similar train with 500Kw of engine power and another 500Kw available for perhaps 10 minutes from batteries.
Acceleration and performance on inclines would be the same, and fuel would be saved by the engines running more efficiently for a larger proportion of the working day.
The engines would recharge the batteries when coasting, proceeding slowly, or stopped.
All this presumes electric drive, trying to add battery power to a unit with direct mechanical drive sounds very complex.

It would be relatively simple to integrate the diesel and battery power under common control so that the driver operates a single power control.
Notch 5--------full battery power and full diesel power, 1000Kw
Notch 4--------half battery power, full diesel power, 750 Kw.
Notch 3 -------battery idle, full diesel power, 500Kw.
Notch 2--------battery on slow charge, net power for traction 350KW.
Notch 1--------battery on fast charge, net power for traction 200Kw.
Stopped-------Shuts down one engine once battery is say 70% full.

Or some similar scheme.

 

[Indigo Soup]

I think whilst you admit the calculations are generic that it should be feasible for certain applications, I guess one point to consider is that, by today’s standards it’s painful to say hst are a bit steady and we are thriving to achieve better acceleration levels for these kinds of trains. Things like the 220/1/2 are all considerably better in that department, as are the (DMU rather than DEMU) 180s when they’re not having a diesel bath.

In big handfuls, it doesn't really matter how fast the train accelerates. That will impact the battery discharge rate, but not the total energy required to get a 400 tonne train from stationary to 125 mph. There'll be some fiddling depending on losses, which will probably reduce with improving acceleration.

 

[robbeech]

A true hybrid multiple unit, fitted with both diesel engines and batteries would have a lot of advantages.
Consider as an illustrative example a train that needs 500KW to maintain line speed on level track, it would need at last 1000Kw of engine power in order to ascend inclines and to accelerate.
A lot of the time those heavy and expensive engines will not be fully utilised.

Instead consider a similar train with 500Kw of engine power and another 500Kw available for perhaps 10 minutes from batteries.
Acceleration and performance on inclines would be the same, and fuel would be saved by the engines running more efficiently for a larger proportion of the working day.
The engines would recharge the batteries when coasting, proceeding slowly, or stopped.
All this presumes electric drive, trying to add battery power to a unit with direct mechanical drive sounds very complex.

It would be relatively simple to integrate the diesel and battery power under common control so that the driver operates a single power control.
Notch 5--------full battery power and full diesel power, 1000Kw
Notch 4--------half battery power, full diesel power, 750 Kw.
Notch 3 -------battery idle, full diesel power, 500Kw.
Notch 2--------battery on slow charge, net power for traction 350KW.
Notch 1--------battery on fast charge, net power for traction 200Kw.
Stopped-------Shuts down one engine once battery is say 70% full.

Or some similar scheme.

As a general question, what is the charge rate? A battery that discharges in 10 minutes at full power takes how long to charge if given its maximum charging chances, say when the train is in notch 1 or idle? Whilst I appreciate the figures were just given as an example I would hope that a battery would be able to be charged at a sufficiently high rate at the same time the train sustains maximum line speed. If we don’t get this then an acceleration from stationary to maximum line speed is going to see the batteries drained and not replenished.

 

[broadgage]

Modern batteries as used in electric road vehicles can be charged very quickly, 10 minutes for a 50% charge has been quoted.
In the illustrative example above, I would propose a battery that can supply 500Kw for 10 minutes and be 50% discharged in so doing.
To replace this charge would take about 10 minutes with the train stopped and both engines charging the battery.
Whilst few schedules have 10 minute station stops except at the ends of the route, it must also be remembered that slow charging would be achieved whenever running at less than line speed on level track, and whilst decelerating prior to a stop, and when running down a gradient.

As an example, consider approaching and then leaving Totness. At the summit approaching Totness, the battery would be about 80% full. Descending into the station, the battery would charge since little if any traction power would be needed downhill, this might charge the battery from 80% to 90% (estimate 2 minutes downhill running, charging battery at 5% per minute) A station stop of 2 minutes would fully charge the battery. Ascending the incline away from Totness might take 8 minutes of full battery power, during which the battery charge would decline from 100% to 60% (discharge at 5% a minute)
On arrival at Penzance or other terminus, the driver would shut down one engine if the lay over was to exceed perhaps 20 minutes, since the single engine would still fully charge the battery before departure. Preferably the running engine would be the one in, or nearest to, the open air so as to minimise nuisance.

Such a unit would not be the optimum choice for a route with prolonged and fast inclines as the battery would be become discharged and the performance limited to what could be achieved with only the rather limited diesel power.

For a route with many stops, many short inclines, or a very variable line speed, it would be ideal. Perhaps 2 engines to purchase and maintain instead of 4, less fuel used, and less pollution.
For example for in the south west, the unit would have to be able to do say 100MPH and the engines would be specified to just achieve that speed. No extra engine power for inclines or acceleration need be supplied, this coming from the batteries.

 

[D365]

The Class 230 for Wales essentially operates as a Prius: battery power for acceleration and low speed, diesel power for long distance and higher speeds.

 

[Ken H]

Mentions of power output, but what about 'hotel power' which can be quite a lot on hot or cold days?
Class 47 drivers used to cut ETH when accelerating so all the generator/alternator output went to the wheels.

 

[broadgage]

In the interests of simplicity and approximation, I considered only traction power.
To supply say 100Kw hotel power in addition would require either 600Kw of diesel power rather than the indicative 500Kw suggested, or provision of 100Kw less for traction than my indicative suggestion.

Exact figures would vary according to detailed design criteria, my approximations are intended to be an indication of the possibilities of equipping a train with approximately equal diesel and battery power, the diesel power sufficient for the average demand, and the total of diesel and battery power being sufficient for acceleration and ascending inclines.

 

[Japan0913]

For any others who are curious, they do seem to be rolling out in Japan.
Here's a bimode + battery hybrid multiple unit:
https://asia.nikkei.com/Business/Japan-rail-car-builders-rolling-out-next-gen-diesel-trains
https://en.wikipedia.org/wiki/HB-E210_series

Here's a hybrid shunting loco:
https://en.wikipedia.org/wiki/JR_Freight_Class_HD300

According to wikipedia, in 2009 Hitachi announced that the diesel versions of the IEP would be hybrids. Not sure what happened to that!

Will be helpful to you?

Hitachi　Hybrid Propulsion

◆Energy-saving hybrid propulsion system using storage–battery technology
http://www.hitachi-rail.com/products/on-board/propulsion/hybrid/index.html

◆◆Characteristics of Hybrid Propulsion System
http://www.hitachi-rail.com/products/on-board/propulsion/hybrid/feature01.html


◆◆Hybrid propulsion system control
http://www.hitachi-rail.com/products/on-board/propulsion/hybrid/feature02.html

▼HAYABUSA　
Evaluating our energy saving technology in the UK
The V-Train 2 was a demonstration train designed in order to demonstrate our skills and expertise while bidding for the Intercity Express Programme project.
http://www.hitachirail-eu.com/products/research-development/v-train-2

 

[Neen Sollars]

I don't know a lot about rail engineering, so this may be silly - but if so, I'd like to know why. It seems to me that diesel trains spend most of their time either (a) at full power, accelerating or climbing a hill; or (b) coasting, decelerating or stationary, at or close to idling revs.

This feels like it would be the perfect place for a hybrid drivetrain: where a smaller diesel engine spends most of its time at its most efficient speed, and a battery is used to smooth out the peaks and troughs.

That feels like it ought to be worthwhile even before one factors in the benefits of regenerative braking.

Has it been tried? Is there a reason why it wouldn't work?

Hi swaldman, check out this episode from "Fullypowered" on you tube.

Then do your research on Vivarail for class 230 DEMU and BEMU. Vivarail appear also to want to run a train with Hydrogen so I guess that would be a HEMU? Lots of videos on you tube about Vivarail and Class 230 trains that will answer all your questions and confirm your observations/conclusions

 

[Neen Sollars]

Hi swaldman, check out this episode from "Fullypowered" on you tube.

Then do your research on Vivarail for class 230 DEMU and BEMU. Vivarail appear also to want to run a train with Hydrogen so I guess that would be a HEMU? Lots of videos on you tube about Vivarail and Class 230 trains that will answer all your questions and confirm your observations/conclusions

Ooops wrong video Try