Maximum Power of Railroad Diesels.

According to FM on their PA6B, "This engine has been expanded to include the longstroke “B” version, which is 25 percent more powerful than the PA6." Perhaps this is the difference. FM lists the engine width as 240 mm (7.87') but this includes the twin turbochargers.

http://www.fairbanksmorsenuclear.com/en ... ckPA6B.php

Engineer Spike wrote:Horsepower is only half of the equation in locomotive performance. Tractive effort is also very important. One of the last posts talked about the HHP8 electric motors having 8,000 hp. That is fine for a high speed locomotive, pulling 12 or so coaches maximum.
In freight service, we have seen an increase in both horsepower and tractive effort. A railroad which ran 4 units sets of SD40-2s, then upgraded to 3 unit sets of SD60s. now 2 SD70MAC units. You will note that the 3 60s have about the same hp as the 4 40s. When the ac units are used, 1/3 horsepower is lost. The ac units can pull the same train, but slower. The AC6000, and SD90MAC were intended for trains where speed counts. I don't know if the absolute number of cars which can be started would differ between the AC4400/SD70MAC, vs. AC6000?SD90MAC. The AC6000/90MAC can just move them faster.
Since the first generation diesels, as power increased, so did the capabilities of the wheel slip controls, and reliability. Eventually the builders will reach the maximum adhesion factors set by the laws of physics, based on their weight for a C-C wheel arrangement unit. If GE and EMD can build a reliable, and powerful enough to replace 2 present ac traction design units, they may have to go for D-D or B-B-B-B wheel arrangements. The present units are at the practical limit for size and weight. We will have to see what the builders can do.

BNSF's new fleet of ES44C4's are,by all reports, reliably operating at 1100HP per motored axle (they have A-1-A trucks with the middle axle unpowered) so 6600 HP for a 6 axle unit should be do-able..
Way back when the SD90MAC-H and AC6000CW were being developed there were some GE and EMD engineering staff quoted about the next step being 7,000-7,250 HP for 6 axle freight units. GE even had an prototype 18 cylinder HDL engine they tested at over 7,000 BHP but it never was installed in a locomotive..

If I'm not mistaken, the three main problems with 6,000 Hp+ prime movers:

1. Air pollution.
2. Reliability.
3. Getting that power to the rail.

Denver Dude wrote:If I'm not mistaken, the three main problems with 6,000 Hp+ prime movers:

1. Air pollution.
2. Reliability.
3. Getting that power to the rail.

What's your basis for items 1 &3. Item 2, ties in with what I wrote in one of my ealrier psots about performsance and reliability of past large diesels, although that might be overcome. What makes you say that larger engines can't be made compliant with mandated emission requirements, or are more polluting than several smaller engines. As to item 3 - what would be the problem in getting the power to the rails, when straight electric locomotives have 4 or 6 axles delivering rather massive power to the track?

To the best of my (rather limited) understanding, the limiting factor seems to be the traction motors. Each motor can only absorb a limited amount of power. If the prime mover can generate more output than the motors can absorb, the answer is to either add more motors or develop more robust ones.

The last locomotive I drove was a BNSF ES44C4. This is mechanically a four motor unit, with an adjustable idler axle on each truck to spread weight. An automatic system lifts the center (idler) axle incrementally to transfer weight to the driving axles. Coupled with a state-of-the-art wheel slip control system, it performed like a conventional ES44. This was as lead unit in a consist including ES44's and Dash 9-44CW's. These ES44C4's were the only A-1-A-A-1-A units I ever ran.

The ES44C4's should effect a maintenance savings, with four motors instead of six.

Les

railfan365 wrote:

Denver Dude wrote:If I'm not mistaken, the three main problems with 6,000 Hp+ prime movers:

1. Air pollution.
2. Reliability.
3. Getting that power to the rail.

What's your basis for items 1 &3. Item 2, ties in with what I wrote in one of my ealrier psots about performsance and reliability of past large diesels, although that might be overcome. What makes you say that larger engines can't be made compliant with mandated emission requirements, or are more polluting than several smaller engines. As to item 3 - what would be the problem in getting the power to the rails, when straight electric locomotives have 4 or 6 axles delivering rather massive power to the track?

I'm no expert, but I have read abput air pollution compliance concerns and problem with the 6000+ hp prime movers. I don't know why pollution levels couldn't be improved.
As Desertdweller said, traction motors seem to be a limiting factor. If you can't make efficient use of all that extra power, what's the point in having it?

GE's AC6000CWs had their share of "issues" in the beginning, but as far as I know, the traction motors were not among those issues.

CSX has re-engined many of their AC6000CWs with GEVO-16 engines rated at 6000 HP, and they seem to be performing fine based on what I've heard.

The only issue I can think of in regards to emissions is that you'd need a fairly massive cooling system. Look at the radiators on an SD70ACe... they're the same size as the radiators on an SD90MAC-H. The radiators on an SD70MAC are much smaller; EMD had to make them bigger in the SD70ACe in order to meet Tier 2. It stands to reason, therefore, that if EMD or GE wanted to build a Tier 2 or Tier 3 compliant 6000 HP locomotive, they'd have to make the radiators even bigger. And when Tier 4 comes into play, one or both builders may need to add additional equipment such as particulate filters or urea injection. Finding space for that stuff in an SD70ACe or ES44AC will be a challenge. It would be an even bigger challenge if you tried to do it to a bigger locomotive, without making the locomotive longer or taller or both.

Just to compare:

Here's an SD-24 diagram from EMD by way of IRM: 60' 8 1/2" L x 10' 8" W x 15' 0 3/16" H

Here's a SD-70MAC diagram from a 3d party: 73' 1 3/16" x 10' 7" W x 16' 0 1/2" H

How much more can a unit grow as it has to move not just the tonnage of the train, but the tonnage of itself, and still have a single power plant?

The reason the railroads haven't gone with 6000hp is the limiting factor of 200k Tractive Effort. The only advantage of more horsepower is for more speed or faster acceleration. Both mean higher fuel consumption. The higher fuel consumption means the railroad has to price the service higher. But there is another problem, on busy railroad networks great speed differentials between trains means you have to assign priorities to trains, normally the faster ones. This means that the other trains will run slower than they can because they must move out of the way to allow the faster train to pass. This is the reason BNSF said no to UPS when they requested a higher speed Intermodal between Chicago and Los Angeles. As busy as BNSF's Transcon is and was adding a high speed Intermodal to Amtrak's SW Chief would have meant delays of up to two hours for other Intermodals on the route. The additional costs to BNSF's other trains would more than wipeout any profit that could have been made running that train for UPS. Overtaking meets on a railroad consume great amounts of track capacity. This is why BNSF minimizes the amount of coal trains that run on the Transcon, and it is also why the few manifest trains that run on the route have higher power to weight ratios than those that run elsewhere on BNSF, trying to minimize speed differentials.

When it comes to fuel consumptin,where would it figure in that, generally, one 6,000 hp engine would use less fuel than 2 3,000 hp engines?

Also, since hp has a force compnent and a speed component, wouldn't additional hp mean having either greater speed, greater tractive effort, or some of each, depending on the nature of the operation? Much the way that a passnger or freight train has need for raw tractive efort and spped - but with a speed bias for passangers and a TE bias for freight?

railfan365 wrote:When it comes to fuel consumptin,where would it figure in that, generally, one 6,000 hp engine would use less fuel than 2 3,000 hp engines?

the single 6000hp diesel might use less fuel or it might use more, there are too many factors that affect fuel consumption beyond raw horsepower produced, things like piston ring tension, stroke length, emission controls, auxiliary equipment, turbocharger efficiency, etc.

Also, since hp has a force compnent and a speed component, wouldn't additional hp mean having either greater speed, greater tractive effort, or some of each, depending on the nature of the operation? Much the way that a passnger or freight train has need for raw tractive efort and spped - but with a speed bias for passangers and a TE bias for freight?

The force component is the drawbar pull needed to overcome the current drag from the train being pulled (or pushed). Passenger trains are normally light (low drag) so the corresponding "Force" component is small allowing the "Speed" component to be large. With Freight trains you have the opposite situation.

v8interceptor wrote:

Engineer Spike wrote:Horsepower is only half of the equation in locomotive performance. Tractive effort is also very important. One of the last posts talked about the HHP8 electric motors having 8,000 hp. That is fine for a high speed locomotive, pulling 12 or so coaches maximum.
In freight service, we have seen an increase in both horsepower and tractive effort. A railroad which ran 4 units sets of SD40-2s, then upgraded to 3 unit sets of SD60s. now 2 SD70MAC units. You will note that the 3 60s have about the same hp as the 4 40s. When the ac units are used, 1/3 horsepower is lost. The ac units can pull the same train, but slower. The AC6000, and SD90MAC were intended for trains where speed counts. I don't know if the absolute number of cars which can be started would differ between the AC4400/SD70MAC, vs. AC6000?SD90MAC. The AC6000/90MAC can just move them faster.
Since the first generation diesels, as power increased, so did the capabilities of the wheel slip controls, and reliability. Eventually the builders will reach the maximum adhesion factors set by the laws of physics, based on their weight for a C-C wheel arrangement unit. If GE and EMD can build a reliable, and powerful enough to replace 2 present ac traction design units, they may have to go for D-D or B-B-B-B wheel arrangements. The present units are at the practical limit for size and weight. We will have to see what the builders can do.

BNSF's new fleet of ES44C4's are,by all reports, reliably operating at 1100HP per motored axle (they have A-1-A trucks with the middle axle unpowered) so 6600 HP for a 6 axle unit should be do-able..
Way back when the SD90MAC-H and AC6000CW were being developed there were some GE and EMD engineering staff quoted about the next step being 7,000-7,250 HP for 6 axle freight units. GE even had an prototype 18 cylinder HDL engine they tested at over 7,000 BHP but it never was installed in a locomotive..

Is 1100 hp a theoretical number? The prime mover can generate 4400 hp, but then there's the other equipment it's running, loss of efficiency, etc.

Denver Dude wrote: Is 1100 hp a theoretical number? The prime mover can generate 4400 hp, but then there's the other equipment it's running, loss of efficiency, etc.

Railroad diesel engines in North American service are rated based on the output of the main generator/alternator which is after most parasitic loses. So a late model 7FDL-16 as used in a AC4400CW was rated at 4400hp (actually 4390hp but rounded up) and so when you put it on a load test box at full throttle you would want to see a reading on the meter of about 3284 kW, give or take a few percent. If you weren't getting that much, something was wrong.