Diesel Coasting

[wellhouse]

I'm aware there are circumstances when coasting is normal with electric traction, but I recent experienced it for the first time with diesel traction.

A Class 150 arriving in Sheffield from Huddersfield completely shut down the engines as it entered Platform 1. I was in the second coach of three and I certainly heard no engine sound from the other two coaches as we coasted to a halt in the correct position, and there was none as I left the train.

How normal or exceptional is this?

 

[king_walnut]

Doesn't matter what source is powering it, a train will coast frequently depending on track gradients and upcoming speed changes.

If you get a train to 70mph on an even gradient it will coast for a long long time, it's not like a car which will come to a stop very quickly. You get it to line speed and then shut off, then re-apply power once you need to get it back to line speed.

Aside from that, all trains coast into a station. Taking power is the last thing you'd want to do when you're stopping.

 

[skyhigh]

I'm aware there are circumstances when coasting is normal with electric traction, but I recent experienced it for the first time with diesel traction.

A Class 150 arriving in Sheffield from Huddersfield completely shut down the engines as it entered Platform 1. I was in the second coach of three and I certainly heard no engine sound from the other two coaches as we coasted to a halt in the correct position, and there was none as I left the train.

How normal or exceptional is this?

I can guess which driver it was as one does it quite a lot. If you have enough air and momentum to get where you want to go then there's not really any need for the engines to be running on a 150.

 

[wellhouse]

You get it to line speed and then shut off, then re-apply power once you need to get it back to line speed.

Aside from that, all trains coast into a station. Taking power is the last thing you'd want to do when you're stopping.

My point is that the engines were completely shut down.

I'm not sure how confidently and quickly engines can be restarted and power re-applied with diesel traction as compared with electric traction.

 

[Irascible]

- ( misread as a 158, oy my eyes today ).

Some time ago I had to read a bunch of tech manuals for various sprinters, and I don't remember any guidelines about shutting down & restarting as routine - but that's not to say it's not a TOC choice. Given the era of tech involved I would be surprised if it was voluntary...

 

[E27007]

On a short coast described, probably not a problem, but coasting for a long distance with the diesel engine not turning and the torque convertor impellor "stalled" , can damage a torque convertor, The momentum is converted to heat in the transmission oil , i have seen the consequences of Tampers with torque convertors which have been incorrectly towed "dead engine" with drive still engaged, the paint blistering on the transmission case due to extreme heat of the transmission oil, The old fitters claim the gearbox oil can catch fire on long tows.

 

[craigybagel]

I'm aware there are circumstances when coasting is normal with electric traction, but I recent experienced it for the first time with diesel traction.

A Class 150 arriving in Sheffield from Huddersfield completely shut down the engines as it entered Platform 1. I was in the second coach of three and I certainly heard no engine sound from the other two coaches as we coasted to a halt in the correct position, and there was none as I left the train.

How normal or exceptional is this?

In practical terms, you can only really do it in scenarios like the one described above, where a unit is terminating and probably not being used again for a few minutes. On most, maybe even all DMUs, you can't switch on the engines whilst the train is on the move - you need to have the direction switch in neutral and doing that on the move applies the emergency brakes.

Without the engines running, if the compressor is driven by the engine (as it is on a 150) then eventually the emergency brakes will apply if the air pressure in the main res pipe drops below a certain point.

Doesn't matter what source is powering it, a train will coast frequently depending on track gradients and upcoming speed changes.

If you get a train to 70mph on an even gradient it will coast for a long long time, it's not like a car which will come to a stop very quickly. You get it to line speed and then shut off, then re-apply power once you need to get it back to line speed.

Aside from that, all trains coast into a station. Taking power is the last thing you'd want to do when you're stopping.

One disadvantage of the 6 speed ZF transmission fitted to 172s and 195/6/7s is the much greater resistance when coasting. There is much less opportunities for coasting with these units (although there are some gradients where they're actually easier to drive as the resistance holds the train at line speed, you don't need to apply the brakes constantly to avoid speeding). They only coast like any other DMU below about 20mph.

 

[12LDA28C]

My point is that the engines were completely shut down.

I'm not sure how confidently and quickly engines can be restarted and power re-applied with diesel traction as compared with electric traction.

Some TOCs instruct drivers to shut down the engines as part of the Terminate Cab process, or if the unit is likely to be stabled for a certain period of time. In which case it matters little if the driver does that coming into a terminating station, or after coming to a stand. Either way the engines need to be shut down and restarted.

 

[Halish Railway]

I’ve had this sort of situation the OP describes at Birmingham International on a TfW Class 158, with the engines being turned off as the lead carriage entered the platform.

 

[william.martin]

I’ve had this sort of situation the OP describes at Birmingham International on a TfW Class 158, with the engines being turned off as the lead carriage entered the platform.

I've had it loads with TFW 158's, specifically arriving into Shrewsbury and Pwhelli.

 

[driver9000]

My point is that the engines were completely shut down.

I'm not sure how confidently and quickly engines can be restarted and power re-applied with diesel traction as compared with electric traction.

On any diesel traction I've driven including 15x Sprinter units shutting down engines on the move is frowned upon and restarting on the move shouldn't be done. The Driver won't be able to apply traction power anyway until the train is stopped and Forward is selected.

 

[E27007]

On any diesel traction I've driven including 15x Sprinter units shutting down engines on the move is frowned upon and restarting on the move shouldn't be done. The Driver won't be able to apply traction power anyway until the train is stopped and Forward is selected.

It used to be in the Rule Book, Coasting is not permitted, coasting defined as the switch in neutral position while train on the move, on SR slam door stock the power handle had to held down at all times in forward or reverse,( or the brakes apply) in neutral the power handle could be released without the brakes applying, drivers would coast in neutral to give their tired aching arm a respite

 

[12LDA28C]

It used to be in the Rule Book, Coasting is not permitted, coasting defined as the switch in neutral position while train on the move, on SR slam door stock the power handle had to held down at all times in forward or reverse,( or the brakes apply) in neutral the power handle could be released without the brakes applying, drivers would coast in neutral to give their tired aching arm a respite

Assume you're referring to SR EMUs there which isn't really relevant to this discussion. A usual definition of 'coasting' would mean a DMU is moving whilst not under power which happens all the time, shutting down the engines on the move (whilst in forward direction) is more unusual but should not cause any issues if it's only for the final approach to a terminal station, no different to an engine shutting down on the move which can easily happen.

On any diesel traction I've driven including 15x Sprinter units shutting down engines on the move is frowned upon and restarting on the move shouldn't be done. The Driver won't be able to apply traction power anyway until the train is stopped and Forward is selected.

What do you mean exactly by 'frowned upon'? Is there an instruction issued that expressly forbids it? Shutting down the engines on the final approach to a terminal station would have no negative impact on the train and as others have said, it's not possible on many (any?) DMUs to restart engines whilst in forward direction (on the move or otherwise) anyway.

 

[edwin_m]

Assume you're referring to SR EMUs there which isn't really relevant to this discussion. A usual definition of 'coasting' would mean a DMU is moving whilst not under power which happens all the time, shutting down the engines on the move (whilst in forward direction) is more unusual but should not cause any issues if it's only for the final approach to a terminal station, no different to an engine shutting down on the move which can easily happen.

As often happens we are being confused by ambiguous use of jargon. The definition I would use is moving without applying either traction or braking.

At one time it was possible to put the direction selector of some (all?) diesel locomotives into neutral and release the deadman's handle without any brake application. They were modified to prevent this, late 1980s I think.

 

[TurboMan]

What do you mean exactly by 'frowned upon'? Is there an instruction issued that expressly forbids it? Shutting down the engines on the final approach to a terminal station would have no negative impact on the train and as others have said, it's not possible on many (any?) DMUs to restart engines whilst in forward direction (on the move or otherwise) anyway.

Not very easy to recover from a stop short if you've shut the engines down. Also, on most diesel traction, interior lighting will go to emergency levels only as soon as the engines shut down (as only the emergency lights are fed from the batteries) so you could be plunging your passengers into semi-darkness just as everyone's getting up and getting their belongings together.

 

[Tomnick]

I'm aware there are circumstances when coasting is normal with electric traction, but I recent experienced it for the first time with diesel traction.

A Class 150 arriving in Sheffield from Huddersfield completely shut down the engines as it entered Platform 1. I was in the second coach of three and I certainly heard no engine sound from the other two coaches as we coasted to a halt in the correct position, and there was none as I left the train.

How normal or exceptional is this?

On 15x traction, whether the engines are running or not makes no difference to how it coasts – at least until you run out of main res air. Once you shut the power controller off, the transmission is drained of its oil and thus the engine is effectively disconnected from the final drive. It's quite routine for DMUs to coast, sometimes for quite long distances, with the engines left running.

 

[skyhigh]

Also, on most diesel traction, interior lighting will go to emergency levels only as soon as the engines shut down (as only the emergency lights are fed from the batteries)

Not on 15x. Main lighting is from the auxiliary battery, emergency is from the starter battery if I remember correctly. Regardless the main lighting will stay on until the low voltage protection kicks in so unless the batteries are shot you should keep full lighting for a reasonable length of time.

 

[dk1]

Obviously it isn’t possible to start 15X engines on the move as I seem to recall you’d need to be in neutral. I always shut engines down running into shed roads at the depot to save filling them with fumes. Occasionally I was a bit heavy on the brake so had to restart which was embarrassing.

These days with bimodal traction we regularly stop/start diesel engines on the move.

 

[Tomnick]

Not on 15x. Main lighting is from the auxiliary battery, emergency is from the starter battery if I remember correctly. Regardless the main lighting will stay on until the low voltage protection kicks in so unless the batteries are shot you should keep full lighting for a reasonable length of time.

It's all off the auxiliary batteries, but as you say you should keep the main lighting for quite a while. I'd understood that it was until the battery volts dropped below a certain level that it dropped to emergency lighting (which, in turn, you keep until the low voltage protection knocks that and everything else off too), but I've just dug out an original 156 traction manual and that says that it's timed – 30 minutes – from when the driver's key is removed!

 

[The Lad]

1st Generation DMU's will coast and the vacuum exhausters will be driven through the final drive so in theory could go some distance.
I was told a tale of Croft to Darlington after the fuel ran out.

 

[dk1]

1st Generation DMU's will coast and the vacuum exhausters will be driven through the final drive so in theory could go some distance.
I was told a tale of Croft to Darlington after the fuel ran out.

I’ve lost an engine before and had to ring the box asking for a clear run in expecting the other to go as possibly running on fumes. All good fun.

 

[Taunton]

1st Generation DMU's will coast and the vacuum exhausters will be driven through the final drive so in theory could go some distance.
I was told a tale of Croft to Darlington after the fuel ran out.

1st gen dmus could also start slowly with just one engine running because of a failed starter or starter battery, and when at adequate speed jump-start the other, like pushing a car. I didn't think such was possible with just one gear control until I experienced it.

I always thought their vacuum exhausters were engine driven, which was why they would sometimes have their engines raced in neutral after starting, to get the vacuum up to the line.