How many engines ?

four18

I was waiting on a train and the Maynooth one was there. I was walking along side it and I noticed I could hear an engine running in about every 4 carraiges. Was it a generator running ? How many ''drive'' engines are on a standard train ?

LXFlyer

There is a drive engine under each coach in a railcar.

kc56

29K sets have two engines per carriage - a main engine for traction and a generator.
22K's have a single engine per carriage.

If a train is stopped for a period some of the engines may shut down to save fuel.

four18

Oh ! Every carraige. That must eat the fuel. Why does it need a drive engine per carraige. Whatever happened to the Engine at the front just dragging it along ? Must do a bit of research on this. Thanks

Tarabuses

four18 wrote: »

Oh ! Every carraige. That must eat the fuel. Why does it need a drive engine per carraige. Whatever happened to the Engine at the front just dragging it along ? Must do a bit of research on this. Thanks

They use several small engines rather than one large loco so that they can fit under the carriages.

Carawaystick

four18 wrote: »

Oh ! Every carraige. That must eat the fuel. Why does it need a drive engine per carraige. Whatever happened to the Engine at the front just dragging it along ? Must do a bit of research on this. Thanks

look up DMU and EMU on wikipedia

MU is multiple unit

The high speed trains in Germany are moving to EMU from locomotive hauled

It's about sizing the engine appropriately for the load.

There's also some name for having an engine in front and at the back of a train, like the tgv

Irish Steve

Several advantages to having multiple small engines, or at least one at each end.

Much faster turnround at terminus stations, don't have to worry about freeing up the engine that brought the train in and then connecting to another set of coaches.

If there's several engines, if one fails the train's not dead, it might be a bit slower, but (normally) it will get to it's destination. On high density routes, that's a huge advantage, recovering a broken down train is a nightmare in terms of finding a suitable spare engine, getting it to the disabled train (crew, special escort, back working, extra movement on other tracks that are already busy)

Undermounted engines mean more space for passengers.

Weight issues are less significant, lots of small engines mean that things like bridges are not so stressed by a heavy locomotive.

Less wear on sharp curves, light units don't cause the same wear as heavy units.

Power to weight ratio can be better, so faster acceleration out of stations, so closer densities on mixed routes that have stopper trains and through services without passing loops at stations.

Terrontress

Irish Steve wrote: »

Several advantages to having multiple small engines, or at least one at each end.

Much faster turnround at terminus stations, don't have to worry about freeing up the engine that brought the train in and then connecting to another set of coaches.

If there's several engines, if one fails the train's not dead, it might be a bit slower, but (normally) it will get to it's destination. On high density routes, that's a huge advantage, recovering a broken down train is a nightmare in terms of finding a suitable spare engine, getting it to the disabled train (crew, special escort, back working, extra movement on other tracks that are already busy)

Undermounted engines mean more space for passengers.

Weight issues are less significant, lots of small engines mean that things like bridges are not so stressed by a heavy locomotive.

Less wear on sharp curves, light units don't cause the same wear as heavy units.

Power to weight ratio can be better, so faster acceleration out of stations, so closer densities on mixed routes that have stopper trains and through services without passing loops at stations.

Most of those points defy logic. I am sure they are correct but to a lay person like me, I'd have thought that undermounted engines would result in less space for passengers as the engine has to be accomodated in the same space, rather than having the loco far away from the passengers. Also, power to weight ratio can be altered by sticking a bigger engine on. A coach has no pwr.

Cookie_Monster

Irish Steve wrote: »

Several advantages to having multiple small engines, or at least one at each end.

Much faster turnround at terminus stations, don't have to worry about freeing up the engine that brought the train in and then connecting to another set of coaches.

plenty of EU routes use locos with DVTs, just like the Dublin-Cork route, no run around required

Undermounted engines mean more space for passengers.

how? engine pulling 6 carriages or 6 carriage DMU, how does the DMU have more space?

mikedragon32

Cookie_Monster wrote: »

how? engine pulling 6 carriages or 6 carriage DMU, how does the DMU have more space?

As a layman, I'd assume he means that more of the length of a train goes towards passenger space. So DMU that is six units long, all 6 are for passengers as the engines are under the carriages. A train that's pulled/pushed by an engine unit means that if it's 6 units long at least one of those 6 (if not two) are engines, leaving 5 (or 4) carriages for passengers.

LLU

Terrontress wrote: »

Most of those points defy logic. I am sure they are correct but to a lay person like me, I'd have thought that undermounted engines would result in less space for passengers as the engine has to be accomodated in the same space, rather than having the loco far away from the passengers. Also, power to weight ratio can be altered by sticking a bigger engine on. A coach has no pwr.

But as the name suggests, the undermounted engine is under the passengers, beneath the floor. There is no encroachment on passenger space by this engine and, as someone else has mentioned, it enables the train to be one or two units shorter. This is simply good use of space.

corktina

Cookie_Monster wrote: »

plenty of EU routes use locos with DVTs, just like the Dublin-Cork route, no run around required


how? engine pulling 6 carriages or 6 carriage DMU, how does the DMU have more space?

dmu has seven carriages in this analogy not 6 ....simples.

Carawaystick

Terrontress wrote: »

Most of those points defy logic. I am sure they are correct but to a lay person like me, I'd have thought that undermounted engines would result in less space for passengers as the engine has to be accomodated in the same space, rather than having the loco far away from the passengers. Also, power to weight ratio can be altered by sticking a bigger engine on. A coach has no pwr.

If you look at ordinary coaches, they have bogies and space under the floor. Putting engines here is using unused space

Plus the lack of a loco

Run_to_da_hills

Loco hauled trains look and sound more like real a train.

DMU = Railcar. :pac:

Victor

Irish Steve wrote: »

Power to weight ratio can be better, so faster acceleration out of stations, so closer densities on mixed routes that have stopper trains and through services without passing loops at stations.

More important is having multiple driving axles which radically improves acceleration as there is better grip on the rail.

Terrontress wrote: »

Also, power to weight ratio can be altered by sticking a bigger engine on.

While that may increase raw available power, it might not increase usable power. There will also be limitations on just how big an engine you can put on a locomotive.

Marcusm

corktina wrote: »

dmu has seven carriages in this analogy not 6 ....simples.

That wouldn't be a DMU; those would be loco hauled coaches.

Jehuty42

Marcusm wrote: »

That wouldn't be a DMU; those would be loco hauled coaches.

I think i got a headache just reading your post.

The choices were "engine pulling 6 carriages or 6 carriage DMU"

An engine pulling 6 carriages is a 7-unit configuration, 7 things coupled together to form a train. One of those things, the loco, is not providing any passenger accomodation. 6 are.

In a DMU, an equivalent 7-unit configuration carries passengers in each and every unit, which is possible because it has multiple engines mounted underfloor. So for the same train length, you have 1 extra passenger carrying car. There might be slightly less capacity in a DMU carriage than loco hauled due to extra electronics and exhausts, though, yes.

It really is simples.

Terrontress

LLU wrote: »

Terrontress wrote: »

Most of those points defy logic. I am sure they are correct but to a lay person like me, I'd have thought that undermounted engines would result in less space for passengers as the engine has to be accomodated in the same space, rather than having the loco far away from the passengers. Also, power to weight ratio can be altered by sticking a bigger engine on. A coach has no pwr.

But as the name suggests, the undermounted engine is under the passengers, beneath the floor. There is no encroachment on passenger space by this engine and, as someone else has mentioned, it enables the train to be one or two units shorter. This is simply good use of space.

Did you ever see the Deutsche Bahn coaches where the space between the bogies is utilized, there are low down seating areas and above those is an upper saloon as well. Over the bogies there are staircases and some seating as well. I think that with good design locomotive hauled coaches must have more useable space than MUs.

And of course, a MU doesn't necessarily have underfloor engines. The old NIR 80 class have the engine in between the driver and the passengers and it is a DEMU. These are great trains in terms of space, light and comfort.

I have been on the Virgin Voyager DEMUs on a number of occasions with the underfloor engines and they would drive you half mad with the vibrations and revving noise by the time you reach your destination. Nearly as bad as an IE 29k.

Terrontress

Victor wrote: »

Terrontress wrote: »

Also, power to weight ratio can be altered by sticking a bigger engine on.

While that may increase raw available power, it might not increase usable power. There will also be limitations on just how big an engine you can put on a locomotive.

What I meant Victor was that the loco can be changed. I often use the words locomotive and engine interchangeably.

As I said before, I am no expert but surely it is not an absolute fact that a DMU has a better power to weight ratio than a loco hauled set because the engines in the DMU are fixed. With a set of carriages, presuming resources are unlimited, you just put a more powerful loco on the front and your power to weight ratio is now better than the DMU.
Or is there some barrier that I am not considering?

dowlingm

Terrontress - the limited height of IE railways (due to never needing to move double height containers) virtually precludes the use of bilevel coaches such as operated by DB.

As for re-engining locos - you have to take wheelslip into account. Also, many modern DMUs are modular and therefore can accommodate more powerful powerpacks - the size chosen is likely to reflect the design speed requirement. No need to put a 200km/h powerpack in a 120km/h unit like a 2700 class.

Cookie_Monster

Bear in mind a DMU will have less space per carriage of a given length due to driver compartments, that 6 unit DMU may well have 4 driver compartments in it...

Victor wrote: »

More important is having multiple driving axles which radically improves acceleration as there is better grip on the rail.

There was a thread on here a while ago stating that the 22ks neither accelerate faster or use less fuel in the real world than 201 hauled stock did
I can't find it though

The old 2600 and 2700 DMUs are also incredibly noisy due to the underfloor engines and transmissions IMO

Victor

Terrontress wrote: »

Or is there some barrier that I am not considering?

While that may increase raw available power, it might not increase usable power.

If you put a million horse power engine on the front of a train, less than 1% would be usable as the wheels would just spin on the rails.

8 axles delivering 1,000hp each is better than 1-2 axles delivering 8,000hp.

kc56

Another factor is power for the carriages for heat, light and air-con. With loco hauled trains a separate generator is required; on the Cork service this is the DVT; with the Mk3's there was a separate EGV (engine generator van). Therefore these loco hauled trains has 2 additional non-passenger units (loco and egv/dvt). Exceptions were the Mk3 push-pulls which as a generator under the DVT but had no air-con and the Enterprise where the loco supplies the power which has been a cause of the high unreliability of that service.

DMU carry their own power sources either driven from the main engine (22000) or by a separate engine (29000). Like the main engines, power is shared between carriages in a set to that if one generator fails, power is still available from the other carriages.

For small trains, 6 cars or less, a DMU is more efficient in terms of fuel consumption. For short trains - 2,3 or 4 carriages, DMUs win hands down.

DMUs are also more effective with handling, no shunting or changing of locos, and flexible in that it is easy to combine units together to form longer trains. To do this with loco hauled either use excessively large locos or changing the loco when trains are lengthened (this rarely happened). Having short trains enables more off peak services to be run where a longer loco train would not be viable and this has happened since the 22Ks arrived.

The exhaust on the 22000's is between the carriages so no space conceded there.

dowlingm

When you don't have enough DMUs (or double end locos)... you get something like this:

https://www.youtube.com/watch?v=yRBjzKhqk6g

Three 3,000hp locos which between them pulled 30 *doubledeck* coaches as lead locos in commuter service now hired out to pull four coaches between them, because on one of the two branches the turntable is busted :rolleyes:

Jehuty42

kc56 wrote: »

The exhaust on the 22000's is between the carriages so no space conceded there.

True, but on 29000s and 2800s it takes up a pillar next to one of the doors.

Marcusm

Jehuty42 wrote: »

I think i got a headache just reading your post.

The choices were "engine pulling 6 carriages or 6 carriage DMU"

An engine pulling 6 carriages is a 7-unit configuration, 7 things coupled together to form a train. One of those things, the loco, is not providing any passenger accomodation. 6 are.

In a DMU, an equivalent 7-unit configuration carries passengers in each and every unit, which is possible because it has multiple engines mounted underfloor. So for the same train length, you have 1 extra passenger carrying car. There might be slightly less capacity in a DMU carriage than loco hauled due to extra electronics and exhausts, though, yes.

It really is simples.

Let me blow your mind further

An engine pulling 6 coaches (probably plus a DVT) would be referred to as a "rake".

In DMU (or indeed DEMU or EMU)-world, there is only one UNIT; that is the point. Each railcar has its own function, the end ones ay have driver cabs, some of those in-between may be powered or they may not. However, the point is that (in your example) all 7 form one unit as they all wok together. (You could couple a number of units together but unlikely ever to get up to 7!)

This is the fundamental point, loco and coaches can have varied configurations during service (maybe have a buffet car then swapped out for a cargo car etc). The DMU/EMU/DEMU however, without massive engineering changes, will not change its configuration.

bk

Marcusm wrote: »

This is the fundamental point, loco and coaches can have varied configurations during service (maybe have a buffet car then swapped out for a cargo car etc). The DMU/EMU/DEMU however, without massive engineering changes, will not change its configuration.

Except they can and do. For instance Irish Rails 22k's normally come in other three car sets or six car sets and can be configured in

combinations of two 3-car sets, three 3-car sets, two 6-car sets and a 3-car set + a 6-car set are possible. In case of emergency, they can operate in formations of up to 18 cars

!!!

The reality of high frequency operations mean that in reality you would never have the time to swap out a dining coach for a cargo coach!!

The reality in Ireland anyway is that rail freight is dead and you only have a few types of coaches, the 22k DMU's can certainly be configured for the different realistic scenarios that we face in Ireland and without major engineering effort:

http://en.wikipedia.org/wiki/IE_22000_Class#Unit_types

Basically in Ireland we either have intercity with dining car in short or long lengths or higher capacity commuter without dining car.

Marcusm

bk wrote: »

Except they can and do. For instance Irish Rails 22k's normally come in other three car sets or six car sets and can be configured in !!!.

Completely agree with you here and I had mentioned running combinations of units in my note but maybe I wasn't clear. In fact for 6 years, I travelled to work on an EMU comprising 2 units each of 4 cars which were coupled together 3 stations below mine in the morning (having come from different starting pints) and when I got them in the evening would have been decoupled three stations after I got off (front 4 cars for Caterham (1x4 car EMU), rear 4 cars (other 4 car EMU) for Tattenham Corner).

It's also the case that some units have been broken up - the Class 222 Meridian DEMU (similar but better than the Virgin Voyager Class 220 mentioned above) were configured for longer distance operations at design and build stage (including dining facilities) at 9 car configurations and were subsequently redesigned with some of the cars removed to increase the size of other smaller units.

Before this was done, the owner tried to provide them to IE/NIR for use on Enterprise!! The reconfiguration to Irish gauge would have been easier than splitting and reconfiguring the units.

four18

Oh dear, look what I started ! How do they get all the engines to run at exactly the same rpm ? I would imagine if one of the engines was running slightly slower would the wheels of that carraige not just drag ?
And my other Q, Is there one fuel tank feeding all the engines ?

Victor

Marcusm wrote: »

Let me blow your mind further

An engine pulling 6 coaches (probably plus a DVT) would be referred to as a "rake".

No need to be sharp about it.

---

four18 wrote: »

How do they get all the engines to run at exactly the same rpm ?

Computer control.

I would imagine if one of the engines was running slightly slower would the wheels of that carraige not just drag ?

Given that they are working against a few hundred tonnes of train, it all gets evened out.

And my other Q, Is there one fuel tank feeding all the engines ?

I imagine its one tank per powered vehicle.

Losty Dublin

four18 wrote: »

Oh dear, look what I started ! How do they get all the engines to run at exactly the same rpm ? I would imagine if one of the engines was running slightly slower would the wheels of that carraige not just drag ?
And my other Q, Is there one fuel tank feeding all the engines ?

One bogie per carriage is powered from the engine via a crankshaft with the other one unpowered. The engines themselves are controlled from a drivers cab via cabling, gearboxes control the distribution between the engine and traction bogie on each unit. As a rule, each carriage unit can be in different gears at different times to aid climbing and deceleration and yes, there typically is one fuel tank per engine.

Carawaystick

four18 wrote: »

Oh dear, look what I started ! How do they get all the engines to run at exactly the same rpm ? I would imagine if one of the engines was running slightly slower would the wheels of that carraige not just drag ?
And my other Q, Is there one fuel tank feeding all the engines ?

Diesel engines don't have a choke, so have much less engine breaking than a petrol engine. All the engines would run at the same revs if they were in the same gear and there was no wheelslip. If the train was accelerating, then if an engine was weaker, it'd just not be adding as much accelerating effort as the rest. It'd be like the difference between flooring the accelerator and only pressing it to accelerate slowly

There'd be one (or two) tank per carriage, there's no fuel passed between them afaik.

Cookie_Monster

Do MUs have dynamic braking or is that even possible with the direct drive transmissions on them?

kc56

Cookie_Monster wrote: »

Do MUs have dynamic braking or is that even possible with the direct drive transmissions on them?

The DMUs have dynamic retarders fitted to each engine to give 'engine' braking. When braking is required, they are filled with hydraulic fluid when provides resistance. The excess heat is dissipated by the engine cooling system.

kc56

Carawaystick wrote: »

Diesel engines don't have a choke, so have much less engine breaking than a petrol engine. All the engines would run at the same revs if they were in the same gear and there was no wheelslip. If the train was accelerating, then if an engine was weaker, it'd just not be adding as much accelerating effort as the rest. It'd be like the difference between flooring the accelerator and only pressing it to accelerate slowly

There'd be one (or two) tank per carriage, there's no fuel passed between them afaik.

The transmission on DMU is essentially an automatic gear box with 1 speed. From zero to about 70mph (22K) and 50mph(Others) the engines more or run at constant RPM with the torque converter providing the gearing. Above these speeds, the transmission goes direct drive. The transition point varies with the load.

Captain Chaos

As far as I can recall the 29k DMUs have had their dynamic braking disabled in recent years. They did use them when they were first in service but I think it was stopped around 2007/8.

kc56

Captain Chaos wrote: »

As far as I can recall the 29k DMUs have had their dynamic braking disabled in recent years. They did use them when they were first in service but I think it was stopped around 2007/8.

There was an issue with 'blended braking' where dynamic and air brakes over braked the motor axles. The solution was to disable blended braking. Don't know if dynamic was disabled but the mixed use of dynamic and air brakes was disabled.

22Ks do use dynamic braking. You can hear the engines rev-up during higher speed braking.

corktina

Carawaystick wrote: »

Diesel engines don't have a choke, so have much less engine breaking than a petrol engine. All the engines would run at the same revs if they were in the same gear and there was no wheelslip. If the train was accelerating, then if an engine was weaker, it'd just not be adding as much accelerating effort as the rest. It'd be like the difference between flooring the accelerator and only pressing it to accelerate slowly

There'd be one (or two) tank per carriage, there's no fuel passed between them afaik.

do you mean clutch rather than choke? I can't see thats right, put then I only know about car engines.

four18

I was googling this but have got more info on this thread than google. I remember when I was young the Irish railway record soceity used to hold their meetings in the closed down Drumcondra station, It reopened about 15 years ago. They would not let me join because I was only 10 !

Terrontress

corktina wrote: »

Carawaystick wrote: »

Diesel engines don't have a choke, so have much less engine breaking than a petrol engine. All the engines would run at the same revs if they were in the same gear and there was no wheelslip. If the train was accelerating, then if an engine was weaker, it'd just not be adding as much accelerating effort as the rest. It'd be like the difference between flooring the accelerator and only pressing it to accelerate slowly

There'd be one (or two) tank per carriage, there's no fuel passed between them afaik.

do you mean clutch rather than choke? I can't see thats right, put then I only know about car engines.

yeah, I used to drive a car with a choke. I think it restricts the air flow to the engine, resulting in more petrol being combusted. When the engine would warm up, you'd turn it off.

As far as I am aware diesel engines, diesel cars anyway, did not have chokes but I can't see what that would have to do with engine braking. I presume there is a clutch of some description to allow the train to sit at the station with the engine running.

kc56

Terrontress wrote: »

yeah, I used to drive a car with a choke. I think it restricts the air flow to the engine, resulting in more petrol being combusted. When the engine would warm up, you'd turn it off.

As far as I am aware diesel engines, diesel cars anyway, did not have chokes but I can't see what that would have to do with engine braking. I presume there is a clutch of some description to allow the train to sit at the station with the engine running.

It not the choke, it's the throttle. A petrol engine has a throttle, a metal flap, which controls the flow of air into the engine - even with fuel injection. When the throttle is closed, it creates a suction in the inlet manifold which results in engine braking. A diesel engine does not have a throttle. Power is controlled by direct injection. Without a throttle there is no suction and no engine braking. This applies to car, trucks, buses and trains with diesel engines.

Trains have a clutch but it's not like a car's clutch. It's a fluid coupler that can be emptied of liquid to disengage and filled to engage.

Cookie_Monster

kc56 wrote: »

It not the choke, it's the throttle. A petrol engine has a throttle, a metal flap, which controls the flow of air into the engine - even with fuel injection. When the throttle is closed, it creates a suction in the inlet manifold which results in engine braking. A diesel engine does not have a throttle. Power is controlled by direct injection. Without a throttle there is no suction and no engine braking. This applies to car, trucks, buses and trains with diesel engines.

so haw come you can engine brake with both a deisel and petrol, I really don't understand what you are trying to say here. Engine braking is just the mechanical resistance when no fuel is injected and burnt...

Marcusm

Do IE MUs have regenerative braking?

kc56

Cookie_Monster wrote: »

so haw come you can engine brake with both a deisel and petrol, I really don't understand what you are trying to say here. Engine braking is just the mechanical resistance when no fuel is injected and burnt...

have a look at this this article on Wikipedia (once the 24hr blackout is over).

Basically only petrol engines have engine braking. Diesels achieve engine braking by other means as explained in the article. Most cars have turbos these days and they provide some braking.

goingnowhere

All DART units have both regenerative and rheostatic brakes enabled.

Direct drive engagement on the 22k is 56mph I think, 29k its about 50mph. there is a very noticeable change in engine noise when the torque converter locks up. Other units use more traditional 3 stage gearboxes with automatic gear shifting

The retarder brake has a slight issue in that it is not as responsive as the electro pneumatic system so under leaf fall conditions its not able adapt quickly enough.

The 201 class is also fitted with blended dynamic brakes, aka rheostatic brakes

corktina

kc56 wrote: »

have a look at this this article on Wikipedia (once the 24hr blackout is over).

Basically only petrol engines have engine braking. Diesels achieve engine braking by other means as explained in the article. Most cars have turbos these days and they provide some braking.

Im sure you arent right there. Engine braking is to do with the gears and whatever clutch arrangement it has, thus an auto ,which doesnt have a clutch, does not provide engine braking but a diesel with manual gearbox does...its to do with the engine not revving under power whilst coasting and the power train thus has a retarding effect...ie if the engine is only doing (lets say) 1000 rpm going down a hill with the throttle shut ,it doesnt want to allow the gearbox and the propshaft and therefore the roadwheels to turn any faster proportionatly than that.

Cookie_Monster

corktina wrote: »

Im sure you arent right there. Engine braking is to do with the gears and whatever clutch arrangement it has, thus an auto ,which doesnt have a clutch, does not provide engine braking but a diesel with manual gearbox does...its to do with the engine not revving under power whilst coasting and the power train thus has a retarding effect...ie if the engine is only doing (lets say) 1000 rpm going down a hill with the throttle shut ,it doesnt want to allow the gearbox and the propshaft and therefore the roadwheels to turn any faster proportionatly than that.

exactly, though I'm sure some nitpicker will point out that that is drivetrain braking or something

In advance of every town over here there are signs that state "Trucks and heavy vehicles, no engine braking for the next Xkm. Thank you"

Seems kinda pointless if deisel trucks don't actually have it doesn't it:rolleyes:

foggy_lad

Cookie_Monster wrote: »

exactly, though I'm sure some nitpicker will point out that that is drivetrain braking or something

In advance of every town over here there are signs that state "Trucks and heavy vehicles, no engine braking for the next Xkm. Thank you"

Seems kinda pointless if deisel trucks don't actually have it doesn't it:rolleyes:

Trucks often have an exhaust/compression braking system which can be quite noisy.

Compression brakes, a form of engine brakes, produce excess amounts of noise pollution in comparison to exhaust brakes. For this reason, some vehicle original equipment manufacturers prefer to use exhaust brakes, even when the performance is not as good, due to the noise issues. However, combining exhaust brakes and compression braking increases their effectiveness while significantly cutting back on noise pollution.
Numerous cities, municipalities, states, and provinces ban the use of unmuffled compression brakes.

http://en.wikipedia.org/wiki/Exhaust_brake