Exhaust Modifications for #17

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Re: Exhaust Modifications for #17

Post by Low_Water_Odom on Fri Jun 28, 2013 6:19 pm

Robert- I sympathize about the fin comb!  You'll appreciate it that I ALWAYS require hail guards when I specify HVAC equipment.  Smile 

I had forgotten I had found that patent; here's a link for anyone that's interested: http://www.google.com/patents/US2096439

Not having fins would definitely make the things easier to construct and maintain.  I'm reading the patent again...

Hugh

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Re: Exhaust Modifications for #17

Post by Michael Guy on Fri Aug 09, 2013 10:46 am

Gents, I had a very interesting visit to the NHVRy last weekend, thanks to all concerned for their excellent hospitality.

As a new cab denizen of #17 I found the blowback of flame into the cab somewhat alarming, more so when there were at one point five of us aboard and escape from the risk of burning apparel below the knee was near impossible. That aside, everyone assured me that the loco was steaming better than it had prior to the addition of a crossbar to the blast nozzle and a new petticoat pipe.

I have been reviewing this #17 drafting thread and applying some new numbers to my calculator sheet, here is what I have.

If the as-built stack and petticoat is assumed to behave like a lempor mixing chamber/diffuser (I know it probably doesn't but take it as an input assumption), as-built it has an in/out area ratio of 2.64:1.

I took the steam consumption to be 1,355 lb/hr (calculated at 7.5 mph and 50% cut off) no special allowance was made for atomisation steam or air pump and blower usage.

The choke diameter I set at 10" to match the existing and then adjusted the requested vacuum to get a nozzle area that matches the existing one but *with two 1/2" crossbars* (effective area 8.84 sq") rather than just one. The sheet results look acceptable at 9.2 inches of water vacuum. This is playing silly-buggers with the calculator in a sort of semi-reverse engineering way but why not?

Since we have no existing smokebox vacuum numbers with which to compare this exercise means nothing. However, the consensus amongst the #17 crew is that things are much better after the addition of the first crossbar so my recommendations are:

1/ Measure the existing vacuum under load with a train.
2/ If 9.2" is seen as a potential improvement, add a second bar to make it a cross (but please use square bar not round, the corners create useful turbulence), leave everything else alone and measure the resulting vacuum.

An easy way to do this might be to laser-cut a plate, weld it to a pipe to fit over the blast nozzle and add three radial bolts (weld nuts to the tube) to clamp it into place.

Michael.

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Re: Exhaust Modifications for #17

Post by DaveLathrop57 on Fri Aug 09, 2013 10:16 pm

Thanks Michael, wish I could have been there. I'm sorry our volunteer didn't get the manometer installed as planned. You will just have to come back for more.

I hope Robert, who has been chief tinkerer with the front end, will document and post the extent of his work so far and continue to fill us in on what he does, why he decided to do it, and how it is working out.

Dave

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Re: Exhaust Modifications for #17

Post by Nigel Day on Sun Aug 11, 2013 6:17 am

These are constructive educational comments.

The petticoat here is not a mixing chamber as it dose not have the impingement angle of the exhaust steam on the wall.

Cross bars do nothing except increase back pressure. It's true that will increase slightly the velocity up to the terminal back pressure at around 12 psi. Once you active that you will not get more velocity till the nozzles are designed to go super sonic. Even though the back pressure will increase the vacuum will not. You will reduce the cylinder cycle efficiently and then increase the boiler steaming demand for a given rate. If you get to test this loco you will find it will produce about half an inch of vacuum for every pound of back pressure.

Turbulence even caused by round bars is massive and effects the co-efficient of discharge in a negative way. A square bar is even worse. Above describes the results of such bars with respect to back pressure. You want the minimum of turbulence there.

If you want a quick fix do the following. Make your selfs a splitter petticoat like in Chapelon's front ends. It will produce the boundary layer effects you need. You can also make simple delarvel single nozzles to find the optimum size.

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Re: Exhaust Modifications for #17

Post by DaveLathrop57 on Mon Aug 12, 2013 8:05 pm

I keep hoping Robert will pitch in with the details of his work.......

but in the meantime, the stack and petticoat sketches are already posted here - is there a more optimal petticoat we could stick on to the nozzle (with a second bridge or without) that might help us bring more of the fire away from the door?

The burner is below the throat - perhaps a central burner would be less likely to blow out the door vent.

Dave

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Re: Exhaust Modifications for #17

Post by Michael Guy on Mon Aug 12, 2013 9:58 pm

Dave requested I post the link to my video shot in #17 cab last weekend. Here it is: http://youtu.be/Jl1kf9JLNhU The flame blow-back starts at 5:23.

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Re: Exhaust Modifications for #17

Post by JJG Koopmans on Fri Aug 23, 2013 7:54 pm

DaveLathrop57 wrote:... - is there a more optimal petticoat we could stick on to the nozzle (with a second bridge or without) that might help us bring more of the fire away from the door? ....
Dave
Dave,
Over a hundred years ago Goss tested more petticoats than we can imagine. All were deemed awful and a plain petticoatless
system performed best. What about the want for air that the burner system appears to have?
Kind regards
Jos

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Re: Exhaust Modifications for #17

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