Class 88 UKDual & EuroDual

[rebmcr]

Back of an envelope calculations:
Wikipedia has the 88's power output of 4 MW electric / 0.7 MW diesel, or a 5.7:1 ratio.
Compared to that 1960s bimode, the Class 73, at 1600hp/600hp, or a 2.6:1 ratio.

0.7MW comes in at ~939hp, and 4MW at 5364hp.

None of that is comparable, we need the at-rail figures to know for sure.

 

[thecrofter]

Word on the street is that the first 88 (002) is due in the U.K. around 24 Jan. Any advance on that?


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[eastwestdivide]

None of that is comparable, we need the at-rail figures to know for sure.

I did say back of an envelope!

 

[Sunbird24]

88001 fairly romped away with the 1580 ton test train on the level circuit at Velim so no issues there. On the less visible inner loop which has sharper curves and a 1:37 gradient it was tested with the same train from a standing start while the track was being sprayed with a soapy liquid. Apparently the performance was equally impressive but no figures have been released yet.
Starting tractive effort on diesel power is considerable more than a class 20, as is continuous, also the traction motors are way more powerful than those on a class 20, and the modern traction efficiency is way better than 60 year old technology.
It has been pre-geared for 100MPH operation under full power instead of the original Eurolight design specification of 75MPH.
Not sure where people get "full bi-mode" from, its not in the official glossary which merely states "bi-mode" = "electro diesel" with no mention of power capability. "Last-mile" relates to a small diesel engine, nominally 3-600HP with sufficient fuel to operate into and out of unwired yards at each end of a journey, normally 3-500 litres. The 88 has a 950HP diesel and 1800 litre fuel tank so can work at a higher speed and for longer distances than last-mile only subject to limitations on loading. One requirement of DRS is that is should be capable of hauling a dead class 390 in diesel mode while still supplying full electrical power to said train from its on-board generator.
I think some readers here may be pleasantly surprised by its performance.
Now to an update from this morning. Most locos appear to have been re-united with their bogies now. This morning 88003, 88006, 88009 and 88010 were all visible in the yard but with no visible names. 88005 went for a jaunt in the country by running out to the end of the test track, effectively out in the middle of nowhere. The only one I have not seen there this week is 88004. Nothing but trams visible at Sagunto port.

 

[thecrofter]

Deliveries delayed by Pantograph mods?


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[59CosG95]

88001 fairly romped away with the 1580 ton test train on the level circuit at Velim so no issues there. On the less visible inner loop which has sharper curves and a 1:37 gradient it was tested with the same train from a standing start while the track was being sprayed with a soapy liquid. Apparently the performance was equally impressive but no figures have been released yet.
Starting tractive effort on diesel power is considerable more than a class 20, as is continuous, also the traction motors are way more powerful than those on a class 20, and the modern traction efficiency is way better than 60 year old technology.
It has been pre-geared for 100MPH operation under full power instead of the original Eurolight design specification of 75MPH.
Not sure where people get "full bi-mode" from, its not in the official glossary which merely states "bi-mode" = "electro diesel" with no mention of power capability. "Last-mile" relates to a small diesel engine, nominally 3-600HP with sufficient fuel to operate into and out of unwired yards at each end of a journey, normally 3-500 litres. The 88 has a 950HP diesel and 1800 litre fuel tank so can work at a higher speed and for longer distances than last-mile only subject to limitations on loading. One requirement of DRS is that is should be capable of hauling a dead class 390 in diesel mode while still supplying full electrical power to said train from its on-board generator.
I think some readers here may be pleasantly surprised by its performance.
Now to an update from this morning. Most locos appear to have been re-united with their bogies now. This morning 88003, 88006, 88009 and 88010 were all visible in the yard but with no visible names. 88005 went for a jaunt in the country by running out to the end of the test track, effectively out in the middle of nowhere. The only one I have not seen there this week is 88004. Nothing but trams visible at Sagunto port.

What about 007? Haven't heard much about that one.

 

[Sunbird24]

What about 007? Haven't heard much about that one.

Been sitting on accommodation bogies for months with 88006 but both have been moved so its probably inside with the others.
88003 is the only one with Beacon Rail logos which it appears to have acquired at Innotrans.

 

[CosherB]

At least DRS are planning for life after the 57/3s for VTWC Thunderbird duties, although this maybe a very long time away (and a lot can change in that time!). I guess this is feasible with an 88, assuming it has the same ETS as a Class 68 of 96.

 

[captainbigun]

At least DRS are planning for life after the 57/3s for VTWC Thunderbird duties, although this maybe a very long time away (and a lot can change in that time!). I guess this is feasible with an 88, assuming it has the same ETS as a Class 68 of 96.

That's 500kW, which would be most of the engine output, so no. Pendos have very specific requirements for being hauled.

 

[43096]

That's 500kW, which would be most of the engine output, so no. Pendos have very specific requirements for being hauled.

Well, quite.

There seem to be be attempts to re-write Newtonian physics in this thread. I'm particularly liking the implication that an 88 having bigger traction motors than a 20 will somehow magically mean more power...

 

[Sunbird24]

That's 500kW, which would be most of the engine output, so no. Pendos have very specific requirements for being hauled.

Seems it was my misreading of the document which is headlined as Class 88 but actually says a lot about the class 68 in its preamble, which is where I saw the bit about having to be rated at 500KW for the class 390.

As for those who don't appear to understand the physics of a traction system as a whole, the ciass 20 has DC traction motors and the system efficiency is about 18% so that what they deliver at the wheel rim to rail is relatively small. An AC traction motor system is nearer 38% efficient so for the same input power it will give just over twice the power at the wheel rim to rail. You also need to take into account the power losses between the diesel engine and the traction motors, there are lots of other parts of the system which all contribute to losses to a greater or lesser degree. At the end of the chain it is the power at rail which matters more than anything else and this is shown more clearly by the tractive effort figures, HP is only a small part of the equation.
Put bluntly, its not the number horses which come out of the engine stable, its the number which get their feet on the track doing the work of moving.

 

[furnessvale]

As for those who don't appear to understand the physics of a traction system as a whole, the ciass 20 has DC traction motors and the system efficiency is about 18% so that what they deliver at the wheel rim to rail is relatively small. An AC traction motor system is nearer 38% efficient so for the same input power it will give just over twice the power at the wheel rim to rail. You also need to take into account the power losses between the diesel engine and the traction motors, there are lots of other parts of the system which all contribute to losses to a greater or lesser degree. At the end of the chain it is the power at rail which matters more than anything else and this is shown more clearly by the tractive effort figures, HP is only a small part of the equation.
Put bluntly, its not the number horses which come out of the engine stable, its the number which get their feet on the track doing the work of moving.

Fully agree with all that but surely the main point is the difference in horses on the rail between electric and diesel mode. Perhaps the loco can move a 1500t train but if it cannot move that train at a reasonable speed in diesel mode it makes the loco last mile (or perhaps last 10 miles on a lightly used branch) or emergency recovery in case of wires down etc.

 

[Billy A]

As for those who don't appear to understand the physics of a traction system as a whole, the class 20 has DC traction motors and the system efficiency is about 18% so that what they deliver at the wheel rim to rail is relatively small. An AC traction motor system is nearer 38% efficient so for the same input power it will give just over twice the power at the wheel rim to rail. You also need to take into account the power losses between the diesel engine and the traction motors, there are lots of other parts of the system which all contribute to losses to a greater or lesser degree. At the end of the chain it is the power at rail which matters more than anything else and this is shown more clearly by the tractive effort figures, HP is only a small part of the equation.
Put bluntly, its not the number horses which come out of the engine stable, its the number which get their feet on the track doing the work of moving.

18% efficiency is an impressively dreadful figure. So you're saying that ignoring other power losses along the way a 1,000 bhp engine will only get 180 bhp to the wheels in a DC diesel electric? Why does anyone make the things if they're that bad?

 

[CosherB]

18% efficiency is an impressively dreadful figure. So you're saying that ignoring other power losses along the way a 1,000 bhp engine will only get 180 bhp to the wheels in a DC diesel electric? Why does anyone make the things if they're that bad?

You do realise we're referring to a 1950's design?

 

[Billy A]

Indeed, but the nearly 38% efficiency of AC motors is described as being something of a good thing. That's still dreadful.

 

[sprinterguy]

18% efficiency is an impressively dreadful figure. So you're saying that ignoring other power losses along the way a 1,000 bhp engine will only get 180 bhp to the wheels in a DC diesel electric?

That can't be right. Stated power at rail for a class 20 is 770hp. There's no UK loco design that I know of that delivers less than a fifth of it's engine output at the railhead, unless I'm missing something critical here.

 

[hwl]

That can't be right. Stated power at rail for a class 20 is 770hp. There's no UK loco design that I know of that delivers less than a fifth of it's engine output at the railhead, unless I'm missing something critical here.

Sunbird's figures refer to total system efficiency starting slightly futher upstream from the energy contained in the fuel. 18% sounds about right on that basis for Cl.20
--- old post above --- --- new post below ---

18% efficiency is an impressively dreadful figure. So you're saying that ignoring other power losses along the way a 1,000 bhp engine will only get 180 bhp to the wheels in a DC diesel electric? Why does anyone make the things if they're that bad?

Input power is based on energy contained in fuel basis. Look at the size of the cooler system on the 20s...

The engine is an old inefficient design AND the electric transmission is an old inefficient design, big improvements to both aspects could reasonably double performance.

 

[sprinterguy]

Sunbird's figures refer to total system efficiency starting slightly futher upstream from the energy contained in the fuel. 18% sounds about right on that basis for Cl.20.

Ah, right. I think I get it now.

 

[Sunbird24]

Indeed, but the nearly 38% efficiency of AC motors is described as being something of a good thing. That's still dreadful.

Its not the efficiciency of the AC motors but of the whole system used to drive the AC motors, including the diesel engine itself, the generators and alternators, the power converters and all the other bits and pieces in the entire chain.
Just to put things into perspective, the human heart, designed and developed by nature over thousands of years is at best little more than 70% efficient.
Losses go out of the exhaust in the form of emissions, out of the body in the form of heat, which is a loss on generators, alternators and motors also. DC has lots of moving and wearing parts, AC a lot fewer bit still some. There will be continued improvements over the next 50 or so years but there is a theoretical maximum which may never be reached and it is likely to be between 50-60% so now, looking back, 18% 60 years ago, 38% now, perhaps 48% in another 60 years. Earlier if there is another radical design which does away with lots of the extras between the crankshaft and the wheels.
If we look back 130 years to when horse trams were in fashion, while researching such a system in central Java I discovered that losses were just as drastic then, even though all the horses power was on the track. The attrition rate was sometimes as high as 100 horses per month and within 20 years they were all replaced by two steam locomotives, at a great saving in horses lives. Both steam locomotives are still extant having remained in use until the 1970s!

 

[squizzler]

Seems it was my misreading of the document which is headlined as Class 88 but actually says a lot about the class 68 in its preamble, which is where I saw the bit about having to be rated at 500KW for the class 390.

As for those who don't appear to understand the physics of a traction system as a whole, the ciass 20 has DC traction motors and the system efficiency is about 18% so that what they deliver at the wheel rim to rail is relatively small. An AC traction motor system is nearer 38% efficient so for the same input power it will give just over twice the power at the wheel rim to rail. You also need to take into account the power losses between the diesel engine and the traction motors, there are lots of other parts of the system which all contribute to losses to a greater or lesser degree. At the end of the chain it is the power at rail which matters more than anything else and this is shown more clearly by the tractive effort figures, HP is only a small part of the equation.
Put bluntly, its not the number horses which come out of the engine stable, its the number which get their feet on the track doing the work of moving.

I note you get these figures from a page you linked earlier. The 18% and 38% are the ratio of adhesion against loco weight for heritage dc and modern ac drive respectively. This is absolutely different to efficiency, as used by engineers. I agree that the energy efficiency of the electronics and motors will be substantially better than heritage traction (but certainly not double - I seem to recall 1st gen diesel electric transmissions are something like 75-80%). I have however learnt that the starting tractive effort (the puling force at 0 mph) can be expected to be double that of a heritage loco of the same weight.

 

[CosherB]

Sounds like we need a Top Gear-type race to put this on to bed!

 

[captainbigun]

I have however learnt that the starting tractive effort (the puling force at 0 mph) can be expected to be double that of a heritage loco of the same weight.

....provided you don't run out of sand.

 

[Sunbird24]

I note you get these figures from a page you linked earlier. The 18% and 38% are the ratio of adhesion against loco weight for heritage dc and modern ac drive respectively. This is absolutely different to efficiency, as used by engineers. I agree that the energy efficiency of the electronics and motors will be substantially better than heritage traction (but certainly not double - I seem to recall 1st gen diesel electric transmissions are something like 75-80%). I have however learnt that the starting tractive effort (the puling force at 0 mph) can be expected to be double that of a heritage loco of the same weight.

You need to take the whole power chain into consideration, not just traction motors.
First the diesel engine itself is only about 50-60%
DC generators are 60-80%*
Alternators can be up to 90% but are often less, say 70%.
DC motors 60-80%
AC motors 90%
Rough calculations, there is a lot more to factor in.
Worst case DC 50% x 60% x 60% = 18%
Best DC 60% x 80% x 80% = 38.4%
Worst AC 50% x 70% x 90% = 31.5%
Best AC 60% x 90% x 90% = 48.6%
*Depends whether the DC motors/generators use brushes or not, brushes being very inefficient.

 

[captainbigun]

You need to take the whole power chain into consideration, not just traction motors.
First the diesel engine itself is only about 50-60%
DC generators are 60-80%*
Alternators can be up to 90% but are often less, say 70%.
DC motors 60-80%
AC motors 90%
Rough calculations, there is a lot more to factor in.
Worst case DC 50% x 60% x 60% = 18%
Best DC 60% x 80% x 80% = 38.4%
Worst AC 50% x 70% x 90% = 31.5%
Best AC 60% x 90% x 90% = 48.6%
*Depends whether the DC motors/generators use brushes or not, brushes being very inefficient.

I'm yet to see a brushless DC machine!

 

[Sunbird24]

I'm yet to see a brushless DC machine!

That was my thought also, I think brushless DC motors/generators may be a recent innovation. It only makes the figures for the older machines even worse. Not found any efficiency figures for the actual diesel engines in question but I suspect the new Cat is better.

 

[Domh245]

That was my thought also, I think brushless DC motors/generators may be a recent innovation. It only makes the figures for the older machines even worse. Not found any efficiency figures for the actual diesel engines in question but I suspect the new Cat is better.

The thermal efficiency of an internal combustion engine is pretty dire, indeed the news that Mercedes AMG HPP are approaching 50% thermal efficiency in their massively complex power unit was regarded as a massive achievement. Whilst diesel is inherently more efficient than petrol, an old diesel engine would probably be nearer 30% efficient, a newer CAT might be around 40%

 

[Billy A]

You need to take the whole power chain into consideration, not just traction motors.
First the diesel engine itself is only about 50-60%
.

A diesel with 50-60% efficiency would be a wonderful thing to have! Huge two stroke marine diesels achieve a little over 50% but road and rail going ones would do well to get into the mid 40s.

 

[43096]

That was my thought also, I think brushless DC motors/generators may be a recent innovation. It only makes the figures for the older machines even worse. Not found any efficiency figures for the actual diesel engines in question but I suspect the new Cat is better.

I rather think you are seeking to convince people of your argument by throwing out lots of random statistics and often switching terminology around (e.g. using adhesion and efficiency interchangeably).

The point is that, yes, AC traction is better than DC, but that to get anything like decent performance on diesel the 88 needs more horsepower. The AC motors are particularly beneficial in providing the tractive effort to start the train, but as speed increases it is power that is beneficial. If it wasn't why (for example) did ÖBB go for a rating of over 6MW on their AC-motored Taurus locos?

You seem to be using the same argument the idiots at DfT did when they claimed that a rating of 2MW on an IEP would provide the same performance as an HST because they had more traction motors. Roger Ford exposed that one for the fraud that it is.

 

[Sunbird24]

Interestingly, the same Caterpillar C27 engine as already seen service in Poland, fitted into the Newag rebuilds of SM-42 Bo-Bo locomotives, now designated as Newag 6Dg. These rebuilds have the original bogies and traction motors but an AC generator. They are used on passenger trains, light freight trains and shunting work.
Maximum speed 90 km/h (56 mph)
Weight 70 t (69 long tons; 77 short tons)
Power output 708 kW (949 hp)
Tractive effort 219 Kn (c50,000 lbs)
Link here: https://en.wikipedia.org/wiki/Newag_6Dg
The 88 should perform somewhat better than this.

 

[captainbigun]

An AC generator? You mean alternator, which is brushless....