triple expansion engine for sale

[steamboatjack]

There is a Triple expansion engine on e.bay, ex Ribbledale one of a pair said to be rated at 50 IHP each. Infact with a quick calculation you would have to run this at 600rpm to develop 50 IHP rather than the 200 quoted in the SBA register for the boat.
Regards Jack

http://www.ebay.co.uk/itm/290650342380? ... 1423.l2649

[Lopez Mike]

It is interesting how the numbers do creep. I have dynamometer tested a lot of different I.C. motorcycle engines over the years and the vast majority develop about two thirds of the advertised ratings. The advertising department clearly has great influence.

Another amusing fact is that I developed several race winning engines before I had any proper test facilities and one of the modifications I did was to work on the intake and exhaust ports. I then acquired a flow testing machine and was able to test several of those wonderful cylinder heads. Without exception, every one of them was equal or slight worse than a stock unit. Humbling.

I then started building racing exhaust systems and found that it was very, very difficult to come up with anything that produced more output that the stock system. Lighter, yes. But not more powerful. The Japanese know what they are doing.

Very off topic. Sorry.

Mike

[Maltelec]

I suppose you could calculate an exhaust system for a steam engine so it produces a lower pressure on the exhaust port due to resonance and steam momentum.

[Lopez Mike]

Theoretically, yes. But compared to a typical I.C. engine, there are some significant practical issues.

The first one that comes to mind is that most I.C. engines run at such a high r.p.m. The resonant lengths for a steamer would be really something! Like perhaps a hundred feet long at 500 r.p.m.

Another limitation would be that the exhaust opening rate on our steam engines is fairly slow. In fact, one of the more noticeable differences between late nineteenth century locomotives and the ones fifty years later is how much less bark there is to the exhaust note. Less wasted energy with modern valve gear.

With a Corliss or a uniflow design, there might be more acoustic energy to use.

I don't even want to think about the complications and ramifications of condensation and temperature reductions in such a long tube and with such relatively low velocities. With I.C. engines, the pipe cross sectional areas can be reduced by a factor of four or more between the exhaust port and the tail pipe due to the cooling and shrinkage of the gas.

And one last drawback would be that resonance effects only work properly at the design r.p.m. The really successful I.C. racing engines practically have to be spun up to r.p.m. to start them and then kept there with multi speed gear boxes.

Just thinking about all of this makes me smile fondly at my boat engine. Incredibly flexible, low stress and reliable. If I want high tech and efficiency I will steal my neighbor's Prius power plant and bolt it into a boat. Boring.

Mike