The Steamboating Forum

And by the way.

If you use Rainer's simulation program, and I don't know if he ever released the multi expansion version of it, or he just let me play with it, but you can balance your cylinder powers via a very simple expedient while using the simple engine program

Run the simple engine program, but analyze two different engines.

One is your HP engine

One is the LP engine.

Match the mass flow by adjusting the cut off in the LP engine to suit the mass flow of the HP engine.

You HP exhaust and incoming LP pressures can be estimated by your cylinder ratio.

Make your receiver volume equal to the LP swept volume as a minimum. You'll be in good shape.

Dave

Hi Dave

I just discussed this theme with Lars Hansen, another SBA steamboat fellow here in DK, the other day.

I have myself made an excel based calculation program for a compound, and if the cut offs are identically at HP and LP, the receiver pressure must be stabilise at exactly that pressure giving the same mass flow at the two cylinders.

He argued that this balance results in quite a difference in power output for the two cylinders.

The question is: Should the cut off adjustment, and thereby the receiver pressure, actually be used to give the same power output at the two cylinders, for a given condenser pressure, or do we just accept the different power outputs ?

Best regards
And a pleasant Easter to everyone
Jørgen Hansen

The power levels should be balanced ( balanced for power output , not cut off) or you will have unequal wear and lots of vibration..

Increasing the LP cut off will decrease the power output of the LP and increase the power output to the HP.

That seems a contradiction, but your program should prove that out..

I;ll type later if you like.

Dave

If your spreadsheet computes the PV diagrams, the area's under the curves will equal the work done by the engine during one complete cycle. If you know the speed of the engine, you can determine the power from there.

But you are looking for equal power.

The cut off for each cylinder will be a function of initial steam pressure, terminal steam pressure, cylinder ratio ( D squared / d squared), and to a significant extent receiver volume.

A small receiver causes quite a bit of pressure variation in the LP.

I'll post my PV diagram and method as this weekend progresses....thank you for your patience.

Out of curiousity, are you using a lookup table for the steam properties?, or an equation of state.....?

Dave

Hello Piet,

Here is a scan of my calculations.

The reference is Cecil H. Peabody's "The Thermodynamics of the Steam Engine"

Pages 169 forward.

The volumes are normalized to the HP volume which for the calculation has a qauntity of 1.0

All other volumes are relative to the HP volume.

Steam in real engines behaves somewhat like an ideal gas with a polytropic constant of approximately 1.1 or 1.2.

For simplicity, if the constant is set to 1.0, the equations simplify dramatically resulting in what is generally a isothermal gas. PV = Constant.

The equations are based on that.

This text dates to July 21st 1920 and was used at the Massachusetts Institute of Technology as a text book. I know this because in the book I found copies of the final exam for the course with that date on it. ( with some crib notes too..... )

All in all, the effort is 6 equations and 6 unknowns solved Simultaneously.

The resulting PV diagram is integrated with a planimeter or by counting squares as I did about 15 years ago. The result is multiplied by a coefficient varying between .6 and .9.
.6 for high speed engines, and .9 for low speed engines......I think low speed engines are the class we are in...if you look at piston speed.

The volumes are normalized volumes of the given cylinder with respect to the HP cylinder

The HP cylinder has a volume of 1. In my case,the Lp cylinder has a volume of 4, and the receiver has a volume of 3.

I am running 75% cut off on both cylinders on my engine. I have no exhaust lap. I am running inside admission on the HP cylinder to keep high pressure steam away from the valve rod glands and outside admission on the LP cylinder to keep vacuum away from the valve rod gland.

My diagrams show more power is generated in the LP than the HP. I did this on purpose, rightly or wrongly, as I was concerned about the LP having more condensation losses than the HP. My engine runs smoothly, so I'll state its not wrong, though it could be argued it is not necessarily right either.

Piston valves on both cylinders.

If there are any questions or comments, please contact me.

Piet, if you wish, I am sure the moderator can move this to the technical section. I have no problem with that. I have much respect for your efforts to date Piet. I know how much work your boat was...trust me.

Dave

Hi all
Well thats a lot of information.
I have ordered the book, but not received it jet.
Thank you all for comments, This is a lot to read Dave,You'll warned me.
Nice, first thing to do is to try to understand all the comments. Ahh well I've the hole summer.
If I have questions I wil contact you Dave, on the forum or direct.
I've no probleme if the moderetor wants to put this in the technical, its where it belongs.

Thank you guys..........Piet

The christening ceremony of Panatela
http://www.flickr.com/photos/wsvbinnenm ... 766297514/
Is that the right word?

Regards Piet

Piet,

Nice pictures. Looks as though it all went very smooth. She looks good and fast on the water.

Thanks, Ron

Such a beautiful boat.

Congratulations on your successful maiden voyage.

You've done what we all dream about! You've taken a dream and created a dream machine! Well done!! Den