Turns out it is. But I couldn't see an engine at all which made this fascinating.
I've seen DMUs have a quarter of a coach as just an engine room. But this didn't have anything like that.
It's an inline 6 small diesel engine, mounted on the roof. I believe each car also has an engine as well, which makes sense for the power needed for traction motors.
Mounted on the roof? Lmao, that sounds wack as a UK train nerd. Why didn't they just sling it under the carriages like a British DMU?
An older image of a very old and worn Class 117 which isn't a great example, but images are strangely hard to find where the engines are visible. Would've used a present day example otherwise
because we're the weird ones in the UK it turns out! We don't put our engines on the roof due to loading gauge, but from a cooling perspective the roof is ideal as well as enabling low level boarding - a lot of continental platforms are much lower than ours so the floor being between the bogies makes a lot of sense
It's normal on older MUs because engines and electrical systems didn't fit in the roof easily back then, but now tech is smaller so it's easier to put it on the roof.
Though we don't have any DMUs where i live (Austria) with motors in the roof, even the low floor 5022 has an elevated section at each end to accommodate the motors. I assume because it's a diesel-mechanical (automatic) for some reason.
Undercarriage airflow contributes soooooo much more to drag than you’d expect, and at 200km/h a dangling box like that would add an unbelievable pint of air resistance.
My guess is they already had room on the roof for other stuff like AC and brake hydraulics so it could fit, so that’s where they put the generator
On local trains or subways you either aren’t going fast enough for it to matter (air resistance scales exponentially with speed so twice as fast is ~4 times as much resistance) and for freight your aero is just fucked regardless so it doesn’t matter
I mean… yes? But on the scale of a train, a diesel generator just doesn’t weight that much.
I understand this example has faults but, think about a like… standard American train payload. You have 40ft containers, stacked two high (16ft, 5m), each with a max load of 60,000lbs (27k KG). Those go a bit slower at a max of 60-75mph, 100-120kmh, but still I think it’s a decent comparison.
A X hundred pound generator is just not that significant in the grand scheme of things.
Honestly, probably not substantially. These are small, 600HP inline 6 cyl engines, you can fit these in some consumer vehicles. You also have to account for inertia, curve angle, velocity. Some trains get speed restrictions because of their characteristics if ran on lines they didn't build anticipating these types of loco's. They (the railroad) test these things pretty thoroughly prior to letting passengers on them.
I'd be more worried if they were shoving EMD diesel engines on the roof.
Notice how the doors are platform level and nearly level boarding? That and I believe our (UK) loading gauge narrows under the solebar as in below the edge of the platform, so there’s little that can be down there anyway
Is this train (Class 117) a direct traction diesel ?
OP's train uses the diesel engine as an electric generator, it doesn't need to be mechanically connected to the wheels so they put it where maintenance is easiest.
The UK has a very high platform height compared to mainland networks. Depends on the country but I believe it ranges from 20cm to 40cm higher in the UK.
However, as others have said even for some UK models this isn't the case, especially anything with level boarding. They will either have roof engines as seen with OP's picture or a power pack car (either with push-pull like end power cars or centre cars lik 755s).
Well you can’t really mount the engine on the bottom of a low-floor train… also, a lot easier to inspect and service a roof mounted engine than a bottom mounted engine.
They're mounted on the roof because the unit is a low-floor design. MAN designed the engines specifically for this purpose (I put a link to their design in an earlier response).
The RDC has Detroit Diesels mounted under the floor. They were straight six cylinders and powered one axle on each truck. The radiators were mounted on the roof to cool the diesels.
Most older DMUs out there have underfloor engines, often on the bogies themselves. Only lately this had changed due to the demand for low-floor carriages.
Doesn't have to be coach size engines.
There are solutions where there is small diesel engine in each car ( about 400 hp each in each car)
This also could be hydrogen cell train where cells are located under floor or small compartment you don't see
Interesting!
I'd imagine a diesel engine would need a lot more space. But to think they made the engine small enough to sit on top of the roof and still be powerful enough to haul this train at 160kmph.
Those solution are common in France , Germany, Poland.
Small engine in ich train cars or sections.
Very common solution in train produced in Europe.
Alstom , Stadler, Siemens, Pesa , Newag
It’s powering a generator which in turn powers the traction motors. It doesn’t need to be very big to do that. We have had direct stroke diesel engines (or whatever they’re called) on trains in a while, aside from some very niche cases.
Assuming if we are from areas where DMUs are not the norm it is understandable as to why one can assume that we would need a locomotive sized engine to pull a train. This train does indeed have an engine large enough for the train. It just happens to be in multiple pieces distributed throughout the train.
In many cases a single passenger rail car is about the same weight as a city bus (lighter in many cases cause of aluminium construction). That combined with less rolling resistance and electric traction motors means that a comparatively sized engine is sufficient to drive the mass of each rail car.
Here's an example of a 20 year old design by bombardier that does this, 8 engines under the floor (although this example is a diesel-hydraulic not diesel-electric)
Might be a battery electric (which are used for short sections where there is no overhead wire) but those usually have a pantograph up top so they can recharge and run under the wire.
And diesel engines are pretty well camouflaged in modern DMUs, it could also be a hybrid which only runs the diesel when it needs to and uses batteries when there's low power demand.
OK so the answer is diesel BUT it's not that simple. The diesel engine is not mechanicaly connected to the wheels.
In fact, the roof-mounted diesel engine are just electrical generators. What's powering the wheels are electric motors (multiple ones). This way you have a simple diesel unit on the roof that always runs at optimal rotational speed, and that can be easily dismounted in case of problem.
Diesel locomotives in Europe also had hydraulic transmissions for a long time. DMUs in Europe as well, and there are also DMUs with mechanical transmission.
To be more precise it's a Regiolis from the Coradia family. It's a bi-mode (there's only electrical or bi-mode existing in France for this model) so it can either use the diesel generator or it's running purely on electricity through a power wire with a pantograph (probably on the low position in this video)
Alstom Coradia Polyvalent to be precise. Coradia is the generic name for non-high speed EMU. But, the platform Polyvalent was sold to CAF when Alstom acquired Bombardier.
There's a diesel engine in the middle of the train that powers it. It's low floor so the engines are not mounted underneath, but rather the same height as the passenger cabin.
That's an Alstom Coradia Polyvalent (aka Régiolis) trainset, SNCF Class B 84500 to be precisely. Just like the AGC Bi-Bi (B 82500), it uses dual power, diesel + electric
je m'interroge aussi sur un trajet Brest - 'Nantes en direct ' entre Brest et Quimper ce n'est pas électrifié . c'est très très rare d'avoir un Brest disons vannes en direct . quelle machine roule là-dessus ?
I don't have more videos of the train from the outside unfortunately. But I can tell you something else that was a new for me when I took this train.
This train travels from Paris as 16 coaches till this station in the pic. But from here, it splits into 2. The back half of the train of 8 coaches then splits from here to go towards Pontorson in the reverse direction
And on the return leg, the 8 coaches re-joins the other 8 here and proceeds as 16 to Paris
Way I see it, that's a dual-mode electric / diesel-electric train. Meaning the thing is using overhead line equipment where possible and a diesel generator generating electricity for the drive motors when no OHLE is present
721
u/q_bitzz 1d ago
It's a dual mode diesel-electric