Class 88 Locomotive I have a question.

[yh00157]

hello. I am a railroad fanatic living in Korea.

While studying mechanics in high school and junior college, I also watch railroad cars.

I am looking at railroad cars and would like to ask a question about the class 88 locomotive.

I know that it is a dual mode locomotive.

What I want to ask here is something I have a question about when driving in diesel mode.

I would like to know if driving at 100 mph (160 km/h) is possible when driving in diesel engine mode.

Wikipedia is not reliable due to the problem of crappy content, so I'm asking a question here.

 

[hexagon789]

In theory, I don't think there is a physical restriction on speed in diesel mode.

In practice, the power of the diesel engine likely means it isn't possible to reach 100mph on diesel with any sustantial load. They have about the same diesel power rating as a single motor car of an Hitachi Class 802 on diesel mode.

By way of a comparison, the other well-known British Electro-Diesel Class, the Class 73 was designed for 90mph (though not all of the class was geared for 90, some were 80). On electric, the continuous output was 1,420hp enough to haul about 10 coaches at 90mph; the diesel engine produced nominally 600bhp but the output after transmission losses was only 420bhp, that was only about enough to maintain ~55/60mph on the level with about 4 coaches.

 

[Nottingham59]

I would expect that the Class 88 would not be able to achieve 100mph in diesel mode, even if the speed under diesel is not limited by the control system. The power of the diesel engine would not be enough to overcome Wind resistance at that speed.

To check this, I note that the record speed on the Intercity 125 HST train was 148mph, driven by two 2250hp engines. Given that wind resistance varies as the cube of the speed, I'd expect the maximum speed of a train driven by a 940hp engine to be around 88mph. This is known as the "balancing" speed of the train.

(If the 940hp quoted here https://www.directrailservices.com/class-88/ is power at the wheel, then the
the equivalent HST power is 2x1770bhp), giving a balancing speed of 96mph. Still less than 100mph though.)

HTH

 

[hexagon789]

I would expect that the Class 88 would not be able to achieve 100mph in diesel mode, even if the speed under diesel is not limited by the control system. The power of the diesel engine would not be enough to overcome Wind resistance at that speed.

If they are permitted 100mph light engine as per 67s and 68s on certain lines, the power in diesel mode should be enough - about 650bhp would accelerate 85 tonnes to 100mph in 5 miles, on an average gradient of 1 in 350.

(If the 940hp quoted here https://www.directrailservices.com/class-88/ is power at the wheel, then the
the equivalent HST power is 2x1770bhp), giving a balancing speed of 96mph. Still less than 100mph though.)

That's the engine power, they are 590kW at rail in diesel iirc.

 

[LRV3004]

As a trainee driver who drives Class 88s I will happily oblige! The locomotive is perfectly capable of reaching 100mph in both electric and diesel modes. However the significant difference is the length of time the locomotive takes to reach 100. The Class 88 is primarily an electric locomotive. When running light engine (the only time permitted to do 100 anyway) in electric mode, 100 will be reached very quickly indeed! In fact, when my instructor demonstrated it on our very first drive, it was accelerating that quickly you could actually feel the force pushing you back in your seat!!
The diesel engine is only small so when in diesel mode, it is possible to reach 100, although it takes considerably longer than when in electric mode. I did manage it once, although we were running downhill as well at the time!

 

[Nottingham59]

The diesel engine is only small so when in diesel mode, it is possible to reach 100, although it takes considerably longer than when in electric mode. I did manage it once, although we were running downhill as well at the time!

Thanks for your insight! How fast do you think it would go on the flat in diesel mode, light engine? I'd be really interested to know how close my guess of 88mph was to the reality.

That's the engine power, they are 590kW at rail in diesel iirc.

Sounds about right. 590kW at rail suggests a balancing speed on the level of 90mph., using the HST equivalent data of 2x1320kW at the rail.

 

[hexagon789]

Sounds about right. 590kW at rail suggests a balancing speed on the level of 90mph., using the HST equivalent data of 2x1320kW at the rail.

Slight ammendment - it's 600kW - ie 85.7% of the engine rating.

 

[LRV3004]

Thanks for your insight! How fast do you think it would go on the flat in diesel mode, light engine? I'd be really interested to know how close my guess of 88mph was to the reality.

During that drive when I did hit 100 on the downhill, I was hitting the mid to high 90s, but it stubbornly refused to hit 100, not helped by the fact I had to slow for cautionary signals!

 

[yh00157]

As a trainee driver who drives Class 88s I will happily oblige! The locomotive is perfectly capable of reaching 100mph in both electric and diesel modes. However the significant difference is the length of time the locomotive takes to reach 100. The Class 88 is primarily an electric locomotive. When running light engine (the only time permitted to do 100 anyway) in electric mode, 100 will be reached very quickly indeed! In fact, when my instructor demonstrated it on our very first drive, it was accelerating that quickly you could actually feel the force pushing you back in your seat!!
The diesel engine is only small so when in diesel mode, it is possible to reach 100, although it takes considerably longer than when in electric mode. I did manage it once, although we were running downhill as well at the time!

Okay. Wikipedia's content is unreliable.

 

[martin2345uk]

As a trainee driver who drives Class 88s I will happily oblige! The locomotive is perfectly capable of reaching 100mph in both electric and diesel modes. However the significant difference is the length of time the locomotive takes to reach 100. The Class 88 is primarily an electric locomotive. When running light engine (the only time permitted to do 100 anyway) in electric mode, 100 will be reached very quickly indeed! In fact, when my instructor demonstrated it on our very first drive, it was accelerating that quickly you could actually feel the force pushing you back in your seat!!
The diesel engine is only small so when in diesel mode, it is possible to reach 100, although it takes considerably longer than when in electric mode. I did manage it once, although we were running downhill as well at the time!

I assume that 88s are one of the classes of loco authorised to go at more than 75mph when running light then?

 

[hexagon789]

I assume that 88s are one of the classes of loco authorised to go at more than 75mph when running light then?

Yes, as per 67s, 68s and (previously) certain HST power cars (ie not ex-FGW/GWR that had brake mods).

 

[ac6000cw]

Re. getting to 100mph running light - an 88 on diesel is about 11 hp/tonne (940hp/86t). For a close comparison, a 3-car 755 on diesel is about 9.8 hp/tonne (1290hp/132t) and has been reported to take about 4-5 minutes to reach 100mph. Both the 88 and the 755 use modern diesel engines and AC traction drives with 4 driven axles.

On that basis, in theory an 88 on diesel should easily reach 100mph, given enough time.

11 hp/tonne is somewhat more than a (100mph capable) Deltic hauling normal length passenger trains had back in the day... e.g. Deltic + 8 coaches was a 280t timing load + loco weight, so around 8.5 hp/tonne (assuming no ETS load).

 

[Richard Scott]

Re. getting to 100mph running light - an 88 on diesel is about 11 hp/tonne (940hp/86t). For a close comparison, a 3-car 755 on diesel is about 9.8 hp/tonne (1290hp/132t) and has been reported to take about 4-5 minutes to reach 100mph. Both the 88 and the 755 use modern diesel engines and AC traction drives with 4 driven axles.

On that basis, in theory an 88 on diesel should easily reach 100mph, given enough time.

11 hp/tonne is somewhat more than a (100mph capable) Deltic hauling normal length passenger trains had back in the day... e.g. Deltic + 8 coaches was a 280t timing load + loco weight, so around 8.5 hp/tonne (assuming no ETS load).

Don't forget wind resistance and rolling resistance is a big factor, comparatively it'll be greater for a single loco with lower power than a loco and trailing load with greater power.

 

[XAM2175]

Okay. Wikipedia's content is unreliable.

Which bit in the Class 88 article is wrong? I'll take a look at fixing it.

 

[hexagon789]

Re. getting to 100mph running light - an 88 on diesel is about 11 hp/tonne (940hp/86t). For a close comparison, a 3-car 755 on diesel is about 9.8 hp/tonne (1290hp/132t) and has been reported to take about 4-5 minutes to reach 100mph. Both the 88 and the 755 use modern diesel engines and AC traction drives with 4 driven axles.

On that basis, in theory an 88 on diesel should easily reach 100mph, given enough time.

11 hp/tonne is somewhat more than a (100mph capable) Deltic hauling normal length passenger trains had back in the day... e.g. Deltic + 8 coaches was a 280t timing load + loco weight, so around 8.5 hp/tonne (assuming no ETS load).

The 950hp (708kW) figure is the engine output though, the actual amount available for traction in diesel mode across the speed range (the continuous output) is 600kW (805hp).

Admittedly that only brings the figure down to about 9.36hp per tonne, which is still more than sufficient for 100mph.

 

[ac6000cw]

Don't forget wind resistance and rolling resistance is a big factor, comparatively it'll be greater for a single loco with lower power than a loco and trailing load with greater power.

Which in my comparison of 88 versus 3-car 755 won't that favour the 88 a little (fewer axles and shorter, but with power in the same ballpark)?

The 940hp (700kW) figure is the engine output though, the actual amount available for traction in diesel mode across the speed range (the continuous output) is 590kW (790hp).

Admittedly that only brings the figure down to about 9.2hp per tonne, which is still more than sufficient for 100mph.

As far as I know, the power-on-diesel is quoted the same way for 88 and 755 - it's power at the crankshaft, as is normal in Europe - so for comparison purposes it doesn't matter assuming similar transmission efficiency. The 'hotel' loads will lower the 'power available for traction' on the 755 as well.

The Deltic DC-DC transmission is less efficient than AC-AC so need to factor that in for a more accurate comparison, but chucking in the 1960's stuff was just for a bit of fun really

 

[hexagon789]

Which in my comparison of 88 versus 3-car 755 won't that favour the 88 a little (fewer axles and shorter, but with power in the same ballpark)?


As far as I know, the power-on-diesel is quoted the same way for 88 and 755 - it's power at the crankshaft, as is normal in Europe - so for comparison purposes it doesn't matter assuming similar transmission efficiency. The 'hotel' loads will lower the 'power available for traction' on the 755 as well.

The Deltic DC-DC transmission is less efficient than AC-AC so need to factor that in for a more accurate comparison, but chucking in the 1960's stuff was just for a bit of fun really

It absolutely does matter. The 68 for instance can only produce 2400kW of its 2800kW engine power at rail.

Even with modern transmission you cannot get 100% efficiency. Even for modern locos with AC motors 85% efficency is about usual.

 

[LRV3004]

I assume that 88s are one of the classes of loco authorised to go at more than 75mph when running light then?

Yes, along with 68s, and as mentioned elsewhere, 67s!

 

[ac6000cw]

It absolutely does matter. The 68 for instance can only produce 2400kW of its 2800kW engine power at rail.

Even with modern transmission you cannot get 100% efficiency. Even for modern locos with AC motors 85% efficency is about usual.

I'm well aware of both of those points. I deliberately chose the 755 as a comparator because it has similar power output from its diesel engines and a similar modern AC-AC traction system, primarily because I thought the efficiency between engine and wheels would be similar. For a simple 'rule of thumb' comparison I thought that would suffice. Without any hard information on 'power at rail' for an 88 and 755/3 in diesel mode I can't check my assumptions - do you have access to diesel 'power at rail' values for the 88 and 755/3?

 

[Richard Scott]

Which in my comparison of 88 versus 3-car 755 won't that favour the 88 a little (fewer axles and shorter, but with power in the same ballpark)?

Tends to favour longer train if has more installed power so more likely to swing in favour of 755.

 

[hexagon789]

I'm well aware of both of those points. I deliberately chose the 755 as a comparator because it has similar power output from its diesel engines and a similar modern AC-AC traction system, primarily because I thought the efficiency between engine and wheels would be similar. For a simple 'rule of thumb' comparison I thought that would suffice. Without any hard information on 'power at rail' for an 88 and 755/3 in diesel mode I can't check my assumptions - do you have access to diesel 'power at rail' values for the 88 and 755/3?

I've stated the 88 figure previously above - 600kW.

I've seen the 755 figure as well somewhere, give half-a-tick and I'll try where I think I've seen it.

 

[yh00157]

Which bit in the Class 88 article is wrong? I'll take a look at fixing it.

I saw the wikipedia class 93 locomotive.

There are class 88 locomotive contents, but there are crappy contents.

"While the Class 88 has only limited power when operating in diesel mode, equivalent to that of a single Class 20 locomotive, thus being limited to ‘last mile’ operations in sidings or slow-speed operation on freight-only branches, the Class 93 is to have a far more powerful self-operating capability, allowing for high speed mainline operations on non-electrified lines. To achieve this, a more powerful 900 kW (1,200 hp) diesel engine has been adopted, along with a series of batteries, which can generate up to double the power of the Class 88 when in diesel mode."

 

[D365]

The Class 93 is an upgraded version of the Class 88 that has been ordered by ROGS (Rail Operations Group).

What part about the Class 88 is confusing?

 

[yh00157]

The Class 93 is an upgraded version of the Class 88 that has been ordered by ROGS (Rail Operations Group).

What part about the Class 88 is confusing?

The description of the diesel mode was somewhat lacking, so I was confused.

"While the Class 88 has only limited power when operating in diesel mode, equivalent to that of a single Class 20 locomotive, thus being limited to ‘last mile’ operations in sidings or slow-speed operation on freight-only branches, the Class 93 is to have a far more powerful self-operating capability, allowing for high speed mainline operations on non-electrified lines. To achieve this, a more powerful 900 kW (1,200 hp) diesel engine has been adopted, along with a series of batteries, which can generate up to double the power of the Class 88 when in diesel mode."

For reference, while looking at this content, I wanted to know if a class 88 locomotive could run 100 mph (161 km/h) on the mainline.

 

[Future]

For reference, while looking at this content, I wanted to know if a class 88 locomotive could run 100 mph (161 km/h) on the mainline.

They can run 100mph light loco (ie on their own without any wagons/coaches) on certain routes but when hauling freight they will be limited by the speed of the freight train (normally 60-75mph)