Reply To: Jos Koopman Conundrum

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Martin Johnson

    Hi Chris,
    Well yes, that might be so. But an offbeat engine means the valve events are not as they should be, so more energy is going up the stack and less into turning the wheels. Therefore, more energy is being expended in the blast pipe, meaning more energy to draw the fire, to make more steam to feed that hungry off-beat engine.

    As to the relative merits of a Jube Vs. a Black 5, I do not really know enough detail of the two designs to comment.

    I remain un-convinced that peak flow through the blast is a good thing. The more “peaky” the flow, the more likely you are to be running part of the cycle in the sonic regime. However, if you can smooth things out, you should be able to run the whole cycle sub-sonic. The attraction of sub-sonic is that a basic contracting nozzle will work well across the whole flow range. Once you start putting DeLaval nozzles on, it will be great if you get sonic velocity at the throat, the expanding section will INCREASE exit velocity. However, if you do not get sonic velocity, the expanding section simply re-expands the steam and you DECREASE exit velocity. So at anything below design point, you are making things worse, not better – unless somebody can explain how they have matched a DeLaval nozzle to the draught requirement ACROSS THE WHOLE OPERATING ENVELOPE then I maintain it is not the way to go. Porta certainly does not touch on this subject, nor E.G. Young. Any suggested reading for me?