Kylchap Exhaust Systems

[Chris Corney]

And now for my next question!
Given the advantage of the Kylchap on the “efficiency curve” principle described above, and if I’ve understood the explanation in Wardale’s book “Red Devil” correctly, the basis of the Lempor exhaust is the de Laval nozzle. These oscillate between supersonic flow/high back pressure during the “chuffs” and subsonic flow/low back pressure between the chuffs. Since the high back pressure more or less co-incides with the dead-centre position of the piston, it gives an improvement in efficiency.
I’m just mulling over what would happen if you combined de Laval nozzles with a Kylchap chimney.

Chris

[Chris Corney]

On page 140 of “The fire burns much better…” at the end of section 7.6.3, Koopmans says “It is conceivable that a properly designed petticoat could act as a sequential ejector. However, this approach does not appear to have been the subject of any investigation.” Does anyone have any more information on sequential ejectors?

[Chris Corney]

There is another question that I’ve been mulling over.
Assuming the smokebox gas impinges on the steam jet at an angle, it will be possible the resolve the velocity into two vectors, one parallel with the steam jet, and the other one perpendicular.
Now the Kinetic Energy (KE) of each component can be calculate from the equation KE = ½ mv2
And as the two values of KE are proportional to the square of velocity and the vectors are at right angles to one another, Pythagoras tells us that summing the two together will give the KE of the resultant flow (which is what you would expect).
Now considering the KE of the perpendicular flow in isolation, it would be straight forward to obtain a value of velocity by dividing the volume flow by the surface area of the steam jet.
The question is whether this is a significant quantity. The KE has to be generated by the exhaust acting as an ejector pump, and then the energy is just lost as heat, which will have further detrimental effects.
Basically I’m wondering what the advantage of the Kylchap was, or in other words why Chapelon, Gresley and others went to the trouble of using it.
I’m thinking that the design of the Kylchap, with the various cowls and mixing areas would have maximised the effective surface area of the steam jet, and therefore minimised the “lost” KE of the perpendicular moment of flow. Does this make sense?

[Chris Corney]

Further to the above post, I came across some data for a Class 6 locomotive, and at the maximum boiler output this quantity would be of the order of 50kW. This is a significant amount of power and is worthy of further consideration, however, it is calculated on the basis of steady flows. If you take the pulsing effects into account it could easily be double this value.

[Martin Johnson]

Hi Chris,
Have been out of circulation for a while, and then locked myself out of my account one here!

Anyway, to pick up on your recent posts:
Koopmans says “It is conceivable that a properly designed petticoat could act as a sequential ejector.” – Is that not a Kylchap, which we were discussing right at the top of this thread?

I’m thinking that the design of the Kylchap, with the various cowls and mixing areas would have maximised the effective surface area of the steam jet, and therefore minimised the “lost” KE of the perpendicular moment of flow. – Maybe. I come at it from the ESDU graph, which shows that as the steam / gas mass ratio moves lower, the area ratio increases and the peak efficiency will increase – which seems to be the question you are posing. Whether or not the efficiency increase is due to the mechanism you postulate I can’t say for sure, but it looks reasonable.

Further to the above post, I came across some data for a Class 6 locomotive, and at the maximum boiler output this quantity would be of the order of 50kW. – Yes, quite a lot of power and when you factor in the jet pump efficiency, thats at least 150 kw off the DBHP!

If you take the pulsing effects into account it could easily be double this value. I think that is a very valid point. The “oft quoted received knowledge” is that the pulsation does not have a measurable effect. However, I think that is mis-leading. The pulsations affect the nozzle peak Mach number, the kinetic energy loss, the porosity of the firebed, and IMHO the tendency of the fire to lift, the loss of unburnt fuel.

Martin

[Chris Corney]

Hi Martin, Regarding the “sequential ejector”, for a long time I thought that the various cowls of the Kylchap were slightly convergent, so that the pressure energy in the blastpipe is converted to velocity in a number of small steps. A similar idea to a multi-stage turbine. Looking at drawings and photographs, as far as I can tell, they are parallel, which makes analysis of the deviice a lot easier!
It’s an interesting point about the nozzle peak mach number. According to Wardale’s “Red Devil”, Porta held the view that in some cases it was advantageous to use de laval nozzles. Peak velocity occur at exhaust release which is close to the piston dead centre position, where back pressure doesn’t matter. At mid stroke the nozzles would be operating with subsonic flow conditions imposing a low back pressure on the pistons. This would make best use of the residual exhaust steam pressure.
Chris

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