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Re: The Need for HEP and DPUs
Author: theconductor
Date: 07-03-2011 - 23:14
Marty Bernard Wrote:
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> OK, why do they save fuel on flatlands? I don't
> see the reason. So what's the physics on
> flatlands of all up front vs. DPUs that causes
> fuel savings? The things that cause fuel
> consumption are train weight, rolling resistance,
> aerodynamic drag, and rates of acceleration.
> (Speed is a factor in rolling resistance and
> aerodynamic drag.) Mr. theconductor, how do DPUs
> change any of these variables? What am I missing?
Marty,
I wish I could explain the physics, but I can't. I can tell you that I was in the Directors office in Portland while he was on the phone with the locomotive superintendent (or his equivalent) in Omaha asking this same question. We wanted to know why we needed to run our APDWG as a 2x1 instead of just putting all three on the head end. He said in no uncertain terms that the company had spent a vast amount of money testing this theory and found it saves around 6%.
If I had to take a guess, I would say it's from the reduced drag. With the entire weight of the train exerting draw on the head end (in non-dpu) the engines are constantly pulling. With power on the rear most of the drag an draw forces are eliminated.
-Kyle
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> OK, why do they save fuel on flatlands? I don't
> see the reason. So what's the physics on
> flatlands of all up front vs. DPUs that causes
> fuel savings? The things that cause fuel
> consumption are train weight, rolling resistance,
> aerodynamic drag, and rates of acceleration.
> (Speed is a factor in rolling resistance and
> aerodynamic drag.) Mr. theconductor, how do DPUs
> change any of these variables? What am I missing?
Marty,
I wish I could explain the physics, but I can't. I can tell you that I was in the Directors office in Portland while he was on the phone with the locomotive superintendent (or his equivalent) in Omaha asking this same question. We wanted to know why we needed to run our APDWG as a 2x1 instead of just putting all three on the head end. He said in no uncertain terms that the company had spent a vast amount of money testing this theory and found it saves around 6%.
If I had to take a guess, I would say it's from the reduced drag. With the entire weight of the train exerting draw on the head end (in non-dpu) the engines are constantly pulling. With power on the rear most of the drag an draw forces are eliminated.
-Kyle
