Reply To: Kylchap Exhaust Systems
I agree with you about the jet ejector pump being an inefficient device, but under the environment in which it is operating it’s difficult to see a comparable alternative.
As I understand it the jet has a minimum length to ensure complete mixing, and this is the reason why larger locomotives have multiple jets, however, I struggling to see the purpose of the cowls in a Kylchap if the gas leaves the intermediate nozzle at the same velocity that it entered it. One possible explanation is that the momentum of the smokebox gas hitting the side of the jet will cause the four jets to merge into one.
I agree that a slightly convergent jet will give a limited amount of back pressure, but this may help in preventing the nozzles reaching sonic velocities. I’m thinking of the Kylchap being rather like a steam turbine with the pressure drop divided by a number of stages.
For a conventional single stage jet the gas which merged at the bottom of the jet will help to entrain more gas as it travels to the top, so it will act in the same way that you have described above.