251 turbo speeds

My son is home on leave from the US Coast Guard, where he is stationed on a cutter propelled by a pair of 18-251s. He was curious about how fast the turbos typically spin. I thought I had the answer in some of my TPs, but they all refer me to various MIs (which I don't have) for turbo information.

Also, do the 244 and 539 turbos run at similar speeds?

I can't give you an exact response, but I can give a bit of info on the 12-cylinder 251. The blades create a frequency of around 6300 Hz in the recordings I have, so multiply that by 60 and divide by the number of blades and you get the speed of the turbo. The only problem is that I don't know how many blades there are on the turbo rotor. I think the rotating speed would be in the 30000 rpm range. I would think most turbos run at a similar speed, but my expertise is lacking to explain any more!

Rotating speed most turbos have is between 25.000 and 35.000 rpm so Alco would not made big differences; this range comprimises pressure, achievement line and life span.
The acoustic frequency the 251 produces must be higher, when the engine runs over notch 7 the turbo noise can hardly been heard so the frequency leaves the audibile range which is about 15.000 Hz.

I took a keyboard and matched notes with the turbo whistle in a recording, and it's five F#'s above middle C--which is around 6000 Hz. If the rotor has 12 blades (just a guess) that would translate to a rotating speed of 30000 rpm.
http://trainiax.net/recordings/sample-mlw-turbo.wav

On EMD locomotives, there's both a high-pitched whistle and sometimes--varying from one unit to the next--a whine from the rotor itself. The whine in the sample below is about 330 Hz, which translates to a rotating speed of about 20000 rpm.
http://trainiax.net/recordings/sample-emd-turbo2.wav

It seems that my frequency range ends at this point, i think i´m getting old...........

Bringing this subject back from the dead, I picked up a copy of Army TM 55-271 on eBay last week, and it had an excellent write-up on the turbo used in the 539s. I never did find anything with turbo speeds in my Alco manual collection, which admittedly has a few holes in it

That particular turbo idles at 2,200 RPM, the full load speed is 10,300 RPM, and the max. speed is 13,000 RPM. The boost is 5 PSI, and the inlet air flow is 3000 CFM. I would imagine a 244 or 251 turbo wouild run at similar speeds, as they are not appreciably larger in overall size.

A cutaway drawing shows many small blades on the exhaust side. I would think 80 to 100 blades would be a good estimate, as opposed to Trainiac's speculation of 12. This would throw the math, based on frequencies, way off.

A cutaway drawing shows many small blades on the exhaust side. I would think 80 to 100 blades would be a good estimate, as opposed to Trainiac's speculation of 12. This would throw the math, based on frequencies, way off.

It certainly would! I've done a little more searching, though, and it's the impeller (on the input side, not the exhaust side) that causes the whistle (I'm only just learning about the internals of turbochargers ). The sound created by 80 to 100 blades at 20,000 rpm would be far above the range of hearing. I found a cutaway view of an EMD turbocharger, and the impeller appears to have 16 blades--which coincides precisely with the actual turbo sound (the blade whistle is 16 times the frequency of the impeller whine--four octaves higher). http://www.epowerrail.com/images%20prd/ ... 0view3.jpg

I still don't know how many blades are on ALCO turbo impellers, but if it is 16, then the turbo would be spinning at about 22,000 rpm (given a 6,000 Hz blade whistle). The figure of 12 was just based on a 30,000 rpm speed, which I had heard from other people.

trainiac wrote:

I still don't know how many blades are on ALCO turbo impellers, but if it is 16, then the turbo would be spinning at about 22,000 rpm (given a 6,000 Hz blade whistle). The figure of 12 was just based on a 30,000 rpm speed, which I had heard from other people.

trainiac - Here’s a photo of a cutaway turbocharger on an Alco 244 display at the Rochester (NY) Museum of Transportation:http://albums.photo.epson.com/j/ViewPho ... p=74408410

It’s tough to count 'em in the photo, but it looks like there’s about 120 blades on the exhaust turbine. Means then the turbine spins somewhere in the 3,000 – 3,500 RPM range based on the observed full load frequency. (This assumes of course the turbos generating the sounds others have recorded are similarly constructed.) ...FB

It’s tough to count 'em in the photo, but it looks like there’s about 120 blades on the exhaust turbine. Means then the turbine spins somewhere in the 3,000 – 3,500 RPM range based on the observed full load frequency. (This assumes of course the turbos generating the sounds others have recorded are similarly constructed.) ...FB

That's assuming it's the blades on the exhaust turbine that make the whistling sound. However, I was referring to the impeller , which is for incoming air. With EMD locomotives it's indeed the impeller blades (16) that make the whistling sound, and an imbalanced impeller will make a whining sound (330 Hz or so) that translates to about 20,000 rpm. I've heard the same whine at a slightly higher frequency from a GE Dash-9 with an imbalanced impeller. 3000-3500 rpm just sounds way too slow for a turbocharger--some smaller turbochargers will spin in excess of 100,000 rpm. In the cutaway photo you mentioned, it looks like two blades of the impeller are visible in the yellow area behind the exhaust rotor.

In US patent #5544486, which is for application of the GE 7S1716 twin discharge turbocharger to the Alco 251 engine, it lists a maximum speed of 18000 rpm for the prior art Alco 165 turbocharger. I have the MIs for the Alco 131 and 165 turbochargers. Neither of them give any operational type information but from the photographs of the inlet impeller I can count 23 blades.

Using these numbers and doing the math would give a frequency of 6900Hz. This is very close to trainiac's 6300Hz measurement from his recordings. Since the 18000 rpm is probably for an engine running at it's maximum rpm the locomotives were most likely not running at full throttle when the recordings were made.

JohnR

In US patent #5544486, which is for application of the GE 7S1716 twin discharge turbocharger to the Alco 251 engine, it lists a maximum speed of 18000 rpm for the prior art Alco 165 turbocharger. I have the MIs for the Alco 131 and 165 turbochargers. Neither of them give any operational type information but from the photographs of the inlet impeller I can count 23 blades.

Using these numbers and doing the math would give a frequency of 6900Hz. This is very close to trainiac's 6300Hz measurement from his recordings. Since the 18000 rpm is probably for an engine running at it's maximum rpm the locomotives were most likely not running at full throttle when the recordings were made.

That's really, really interesting! So that means that if the units in the recording had 23 impeller blades, the turbos were spinning at a little over 16,000 rpm. Keep in mind that this was from two 25 year-old M420W's that weren't necessarily in their prime. There were two EMD's in the consist as well, and they were in run-8. (I can't tell the throttle position from 4-cycle units alone). I wonder if the turbo speed varies between 12- and 16-cylinder engines?