Exhaust Passage Design

[GWRdriver]

Today's question concerns exhaust, specifically the blast pipe. I am about to draw up a design for the blast pipe for my 7.5"ga TICH and after reading something written in an old ME on the benefits of keeping the exhausts from each side separated until the last moment, actually making the blastpipe stand dual chambered. I wonder how much effect this really has in model practice? I'm in the position of being able to design almost anything and have the room to do something like this, if it makes a hill of beans in the final wash. What do you think? At the very least I would fabricate a generously radiused Y-tube manifold, but I wonder how far to take it.
Cheers,
Harry

[steam4ian]

G'day Harry.
I googled "blast pipe" and "Porta" and come up with an article on the application of a Lempore ejector. It was a gentleman called Kordina who proposed a system like you are considering.
BTW; to suck eggs you first get a grandmother.......!
If you can do it why not? It would be great to see how it works out.

Regards,
Ian

[baggo]

Hi Harry,
It would probably be difficult to say whether the swept exhaust gives any vast improvement over the basic T design without doing some practical experiments. However, I've always thought the straight T design is pretty poor and unless the passageways are very generous is bound to restrict the escape of the exhaust steam which should be as free as possible. Too generous passageways will probably make the exhaust very soft. I would always go for a swept design if it's possible to fit it in as this is bound to give a smoother flow to the blast nozzle and probably a sharper blast.
Keeping the two (or more) exhausts separate as far as possible will help to reduce any back pressure in the pipes caused by steam from one cylinder flowing back into the others. I think the advantage of the multi chambered blast pipe is that it acts a little like an ejector and the exhaust from one cylinder creates a lower pressure in the others.

John

[havoc]

If you have the space then why not? Those little engines can use all little bits to help them out. I must be honest that I see no reason to keep 100+ year old designs to the last detail just for the sake of it.

[GWRdriver]

Baggo & Havoc,
My thinking also. Why not! And Ian, very interesting diagrams in that article, but interesting and intimidating maths also.