"Spool-up" sound on trains?

Question

I live close to railroad tracks. Every now and then, I'll hear one coming through, usually at a low speed, and hear something sound like it's winding up or spooling up. It only lasts about 1/2 - 1 second. What is this sound?

Answer 1

That "spool-up" sound you hear is from the diesel engines turbocharger. Most of the newer road diesels have very large 12 to 16 cylinder diesel engines and they are turbocharged.

Answer 2

could be the air compressor

Answer 3

Here in the USA, virtually ALL Diesel locomotives are "Diesel-Electric"... the diesel engine drives a generator that provides ELECTRICAL power to the "traction-motors" built into the "trucks" (wheel-structure).

The diesel engine will have an idle-speed, and an RPM that is most efficient to generate the electrical power...

Now I am GUESSING that you hear it at an idle as the train is "coasting", and then you hear it spool-up to it's best RPM to provide traction due to a tiny grade nearby ??

I used to hunt Diesel-Electric Submarines... and would often hear them idling... then spool up when they needed to apply the power to their electric MOTOR to get moving.

OH !! My BEST analogy would be a hybrid-car... the engine is idle until that point that extra power is demanded !!

Answer 4

The sound you are hearing is the air compressor.

For clarity, the dynamic brake is used on flat land as well for speed reductions.  Most train handling guidelines established by the carrier suggest this method for fuel conservation purposes, as less is consumed when using the dynamic brake as opposed to power braking, where the power is applied as the brakes are applied.  This is done to keep the slack stretched.

Most engineers prefer the power braking method because the configuration of the slack needn't be changed, as with dynamic braking, where the slack will start stretched, bunch up as the brake is used, and then stretched out again after the speed reduction is completed.

Keep in mind, when changes to the configuration of the slack are made, the likelihood of a train separation increases.

The whine of the turbo-charger is an EMD affectation.  The turbos used on their prime movers are different than a conventional turbo charger, which is driven by a motor's exhaust.  The Turbos on EMD prime movers are a hybrid, in that they are gear driven up through run #5, as is a blower, then a clutch disengages and they operate as a true turbo charger in run #'s 6, 7 and 8.

Answer 5

David,

The dynamic brakes are only used when locomotives are going down grade, which usually sounds like a whining noise as they are basically coasting and using braking to regulate their speed.    I'm certainly no diesel locomotive expert, and others here with more knowledge can likely give better answers, but my guess is that it is likely the engineer slightly throttling up.

Answer 6

If it's less than a second, it's the air compressor.  On newer locos, they are elecrically driven, and that's the electric motor coming up to speed - the engineer probably is releasing his brakes at that point and needs the air to recharge the train brakes, but the compressor switches on automatically every so often to keep the main reservoir charged.

If it takes a few seconds for the "spool up," it could be the dynamic brakes coming on, or perhaps the turbo (if the engine revs up at the same time as the spool up, it's the turbo, and if the engine is already going strong when it spools up, it's the dynamic brakes).

Answer 7

Because they are using what is essentially a jet engine for power.

Answer 8

It's probably the diesel generator spinning up.  It can spin up pretty quickly since it's not directly connected to the wheels.  It has to spin up to produce enough electricity to accellerate the train.