Copyright: Rainer Radow's Dampf Help V.15e.1 vom 16.02.1999
Citation: Radow's Dampf Help V.15e.1


Einleitung
1.1 TRANSLATOR'S FORWARD and INTRODUCTION

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TRANSLATOR'S FORWARD

I first came across this program in October of 1998, and as I was at that time having difficulty setting the valves of my 3"+ 5" x 4.5" compound, felt it would be of help. I asked Rainer about it and was told that there was not as yet an English translation. I mentioned that I could read the German text. One thing led to another and what you see is my American translation.

This program, because of its great detail both in engine particulars (dimensions, working pressures, etc.) and resident calculation programs, can have broad applications: a simple display of basic engine principles for educational purposes; aid in setting valve timing or angle of advance; detailed and in depth design and evaluation of an engine, to name but a few.

Many concepts -- such as steam expansion and superheat -- are not discussed in adequate depth here. There is not space. I strongly recommend the following books (unfortunately only available at used book stores -- or you might inquire of "Steamboating" at www.steamboating.com):

Audels Engineers and Mechanics Guide, Vol. 1

Frank Graham

Theo. Audel & Co.

Design of Marine Engines and Auxiliaries

E. M. Bragg

D. Van Nostrand Company

Marine Engineers Handbook

F. W. Sterling

McGraw-Hill Book Co.

Any edition of the above books will be fine.

Both Rainer and I welcome constructive criticisms, suggestions, and comments. You may contact me via e-mail at

sl-artemis@worldnet.att.net

Ronald A. Fossum, December,1998

5533 N.E. 30th Avenue

Portland, Oregon 97211-6805 USA

(503) 282-3018

INTRODUCTION

First I have to say Thank You to Ronald Fossum. Without his help the english speaking world would have to wait for this translations many years - and - I would be never ever be able to translate it in this excellent way.

Originally I wanted a quick way to calculate the valve gear action for my "Arkona" steam boat engine. Then I added a "Visualization" subroutine to the program. Pictures and diagrams not only add clarity but -- particularly if they're moving -- also increase interest in the function and performance of steam machinery.

I have provided documentation and an explanation of this program so that not only experienced "steamboaters" can utilize its output, but also "newcomers" can learn something. The Help text can be read as a book -- page-by-page -- with a "click" on the Next Page in the upper right corner of the window.

You can view a descriptive info-text of a given window by using the right mouse button and "clicking" anywhere within the window. It may be somewhat difficult to find specific details, but each info-text starts with the basics and proceeds to details. According to your needs or wishes you can leave, skip over text passages, or go to the next subject.

As this is not a commercially produced program, you may find imperfections (Translators note: I have found non-commercial programs to be more informative and contain less errors than most "professional" programs.). I will always welcome suggestions for improvement, comments, and creative hints.

Rainer Radow, August, 1998

E-mail: radow.rainer@berlin.de

Please have a look at my Homepage at

members.aol.com/steam99/steamboat.html

Here you can find much more information concerning steam boats!


Schritt für Schritt
1.2 READ THE INSTRUCTIONS

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When you use this program for the first time, you should open - in order - each of the windows in the menu and read the attached info-text. By doing this first, you will better understand the way the entire program is inter-related and operates.

You don't need any in-depth knowledge of a steam engine. If, in order to "play around" with the program before reading these instructions, you altered the basic data parameters that appeared when you started the program, DON'T WORRY! You can't mess things up. Just "click" on the Settings Menu Button, and then on Load Basic Data in inches and everything will be reloaded with the resident basic data.

Because of the programming time involved, many of the data entry ports are not protected against invalid data. You can, therefore, cause the program to malfunction through entering information which is too large, too small, or will result in negative values. If you want to seriously work with the program, it is recommended that, from time to time, you make a backup copy or file.


Der Programmaufbau
1.3 PROGRAM OVERVIEW

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This program is written in Microsoft Visual Basic 5. The Main Window contains settings to control -- and counters/registers to display -- basic engine motion. This window also has the Menu Buttons which give access to further display and to settings windows, as well as icons which, in some instances, give more direct access. By "closing" the Main Window, the program is shut down.

Insertion of engine particulars (length, radius, pressure, etc.) is done through the individual windows (more on this will be found in the section 10. Engine Particulars). The basic unit of length or volume measurement throughout the American translation of this program is the inch (You can change to mm whenever you want). I and the program set up the appropriate geometrical mathematics. The essential theoretical data as well as some of the text in the Help-Info portion I found in:

Dampfkolbenmaschinen

Baurat H. Kedenberg, Bremen (1952)

Verlag: Der Betriebs-Okonom GmbH, Verden Aller

with some additions from Ron Fossum, who relied on the books he has mentioned in the Translator's Forward.

Measured or calculated data -- such as valve events -- and tables and graphs are accessed and displayed through Windows on the Main Window. A "click" with the right mouse button anywhere in many of the windows gives one the option of altering the window configuration or creating a printout of the displayed graph.

Anyone who has worked with the Muller-Reuleaux or Bilgram diagrams for valve design and timing knows how difficult it is to achieve the ultimate valve design for an engine. This could not be avoided until the recent advent of the computer. Now it is much easier.

Through the various individual, but inter-related, calculations performed in this program, certain theoretical values can be determined. It is possible to bring them fairly close to reality but, it should be remembered, they are still only hypothetical.


Die Installation
1.4 INSTALLATION

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At the same time as you install the program, you choose the installation version, and in the installation version you will find all the necessary files. It should contain:

Dampf.exe	Execute program

Dampf.hlp	Help file

Dampf.ctn	Index/Table of Contents for Help

Bild.ico	Icon Building file

Infotext.rtf	Programs history

Dampftafel.txt	Steam table for calculating steam volume etc.

(Some of the file names may have a number with them, for example: Dampf33.exe, which indicates the version of the Dampf.exe file.)

Visual Basic has its own way of program storage. In Windows, all the standard elements in *.dll and *.ocx are located near the actual *.exe file. Once you have loaded these in your computer all you need to load future updates is the *.exe. Sometimes one has already installed one or more of the *.ocx or *.dll files with another Visual Basic program. In that case all you need do is bring in the missing pieces. (Translator's note: The entire program only takes about 2.5 megs of hard drive, so I suggest you load it all if you have the room.)

After installation, the file Dampf.exe sets a file name:

Radow.reg

itself and links to the contents of the registered files in your computer. Through this, the files with the ending *.rdd (Radow's Dampf Dateien) are identified and, through the file manager, build a small steam engine. In the *.rdd files all the geometric and settings particulars are stored and later called up. For instance, simply "click" at the "Explore" on the corresponding file and the Dampf.exe program opens with the selected settings.


Beschreibung des Hauptfensters
2.1 MAIN WINDOW

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In the Main Window are controls which immediately affect the computations and influence the valve gear simulation. This is, as it were, the control station of the engine. This is where certain data computations are displayed in counters or registers.

The valve, along with the adjustment of the valve gear, is the central element here. By using the mouse to move the Reversing Lever, and thereby shift the link position, you can alter the valve events and the engine rotation. Through the Motion Increments slide bar you set the increments of crank position in degrees (used in later information displays). The Motion Delay slide bar slows the crank rotation (for easier viewing in later information displays). From here you can also go to the configuration windows for the engine geometry as well as the output display windows (see next page).

For additional information about individual elements of this window, point the mouse and "click" the right button.


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2.2 MENU HEADINGS

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In the upper bar of the Main Window you will find the menu lists. Briefly, the functions of these are:

File -- Allows the selection and/or creation of the data load files, viewing of printer parameters, or ending of the program. (Translator's note: If you have entered new data in the engine particulars -- say a simulation of your own engine -- and you wish to save this for future use, then go to File, click on Save As and when the standard Windows file window is displayed, create a name for it, hit the Save, and in the future when you open Dampf33 you go to File, then Open, select your engine, and that is what will be displayed. You are only limited by your computer's capacity.)

Windows -- Opens and closes all of the engine parameter insertion and display windows.

Settings -- Leads to three selection buttons which you turn either "on" or "off". A "click" on the Load Basic Data in inches button will set all of the engine's particulars to the resident basic data originally loaded with the program. (Translator's note: The resident basic data supplied with the American translation is for a 3" x 4" engine closely patterned after the one offered by Tiny Power. I felt that this engine was a good "compromise" in representing proportions, etc. of the average 5hp steam launch engine.)

Start Next Time With Currently Loaded Data button will load the actual data contained in the file name displayed in the Main Window when the Start button is next "clicked". By deactivating this button, at the next Start the basic data will be loaded.

Don't Remember The Window Positions After Closing means what it says. You can alter the size and position of the various windows in this program and they will be held over to the next "Start" unless this button is activated.

English or Deutsch -- The language listed in this space is NOT the language being used (i.e.: if English is what the program text is using, Deutsch will be displayed in this space and "clicking" on the button will then cause German text to be used and the word English will appear in this space.).

? -- Takes you to the help and info-texts. You can also find the version of Dampf that you are using through here.


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3.1 ENGINE ANIMATION

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This window displays the engine geometry and construction of the valve gear. The geometry and relative size of the individual parts is as a result of data entered through the Main Window and various engine parameter windows. You can enlarge or shrink the size of this window. Place your cursor on the frame with the mouse and move the right and top edges. The engine display will automatically proportion itself.

A popup window ("click" anywhere with the right mouse button) gives entrance to: Settings window; Print window; and a window to select background color.

The Settings window permits adjustments of the general layout and placement within the window to enable better viewing.

The left half of the window contains the crank assembly, and the right, the valve gear. The crank assembly is composed of the crank circle (bottom, left), the crank itself, the connecting rod, the wrist pin (symbolic of the crosshead), the piston rod, and the piston. The cylinder surrounds the piston with top and bottom clearances drawn in.

Upper and lower steam passages connect the cylinder to the valve seat face in the valve chest and, thereby, to the valve action. Within the valve chest, the valve moves up and down on the valve seat. Live steam pushes against the valve and holds it upon the seat. Between the two steam passage ports you will find a third port and passage which exhausts the spent steam either to the atmosphere or to the condenser. Although a "D" slide valve is drawn, the events of a piston valve will be the same.

For the purposes of clarity the valve gear eccentrics -- to which are connected the eccentric rods and thereby the associated valve gear -- have been offset to the right half of the window. It is the same crankshaft -- only now it shows the eccentrics and valve gear separate from the crank assembly.

The valve timing of a given engine is determined by two variables: the angle between each eccentric and the piston crank (90° + angle of advance) -- entered after other engine variables are fixed -- and the position of the reach rod(s) which, through the Reversing Lever, determine not only the direction of the engine, but also the admission and exhaust cutoff.


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3.2 SETTINGS -- ENGINE ANIMATION

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Adjustments in this animation window only affect the visual representation. The true simulation is not influenced through here.

The picture border (given in percent) represent that proportional spacing, in percent, of an edge from the crank assembly. The top, bottom, and left edges can be adjusted. The right edge is automatically reconciled based on the left.

The line thickness of the individual window elements is given in number of pixels. The joint diameter (diameter of pivot point) is also given in pixels.

The X-Distance to crank (horizontal measurement of the "eccentric crankshaft" from the cylinder assembly crankshaft -- see: 3.1) should be chosen so that the elements of the two actions do not overlay each other.

From the check boxes you can blank out the valve seat face, as well as the steam passages, and also turn "on" or "off" show steam conditions (a color representation of the steam activity in the cylinder, valve chest, and passages). The colors indicate:

Solid Red	steam admission

Dotted Red 	steam expansion

Solid Blue	exhaust

Dotted Blue	compression


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3.3 ENGINE ANIMATION -- PRINT

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From here you can order a printout of the engine animation display. The program, operating through Windows, automatically establishes contact with your printer. The Print button causes the display to be loaded to the printer.

You can select a vertical or horizontal print format by "clicking" on the appropriate button. Below it you can alter line thickness and pivot point diameter.

The picture size on the printout is proportional to the image as displayed in the window.


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4. ENGINE MOVEMENT -- TABLE

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This table allows an analysis of the major moving engine parts, while in motion. The degree separations are determined by the Motion increments setting in the Main Window.

In the first column, a moving red cursor indicates the crank position (while in motion). The second column, Position of crank, is self-explanatory, as are the other columns.

It requires a revolution of the engine in animation to fill the table ("click" the Start button in the Main Window). If you alter anything in the engine geometry or particulars, a complete revolution is necessary to insert the new values in the table.


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5.1 VALVE MOVEMENT BY CRANK ANGLE  --  GRAPH

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This window graphically shows valve movement by angle of crank (0° is taken at 12 o'clock and the degrees are numbered in a clockwise rotation. In America, direction of rotation in marine engines is as viewed from the after end of the engine, but you will have to look at the geometry of the engine--location of reversing lever, movement of link, etc.--to decide if this is right for you.).

The four heavy horizontal black lines represent the edges of the valve face ports. The upper two represent the port/passage to the top of the cylinder and the bottom two, to the bottom of the cylinder.

The crank angle positions are noted in the horizontal plane. Here, vertical lines denote the crank angle; from left to right: TDC (top dead center), 90°, BDC (bottom dead center), 270°, and again top dead center.

The sine curves represent the position of the valve edges. Through these sine curves one can easily see the amount a valve port is open at any crank position. The red area represents steam admission and the blue, steam exhaust.

Here you can see, graphically, the resultant changes in steam flow -- and therefore engine performance -- caused by variations in valve gear geometry, angle of advance, and valve lap.

The dots upon the valve edge line represent the degree increments of the crank, as determined in the Main Window. The red dot represents the actual crank position. If the animation is in motion, it will move along the sine curve in time to the crank position.

A "click" with the right mouse button in the window brings the usual popup window (see 5.2).


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5.2 VALVE MOVEMENT BY CRANK ANGLE -- SETTINGS

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In this window you can alter the display of the Valve Movement by Crank Angle and the Valve Movement by Piston Position windows.

Period number, initially set at "1", controls the number of complete crank revolutions that the graph simultaneously displays. (Translator's note: I find "1", a single revolution, to be adequate. "2" compresses things too much to gain useable information, although it might be useful as an instructional tool.)

Circle Diameter is the diameter, in pixels, of the dot on the sine curve that indicates the crank increments and position (Translator's note: I find a 30 pixel setting to be less intrusive and actually clearer than the 40 pixel that is loaded in the basic data.).

Timing Line allows one to turn "on" or "off" a vertical line which marks the actual crankshaft position, and which moves in time to the red dot when the engine is in animation mode.

Input causes any alterations made here to be entered in the window.


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6.1 VALVE MOVEMENT BY PISTON POSTION -- GRAPH

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The representation of valve movement in this window is similar to that in the previous 5.1 Valve Movement by Crank Angle. The main difference here is that the horizontal axis is measured in units of actual piston travel in the cylinder. Here the vertical lines represent, from left to right: TDC (top dead center), 1/2 downstroke, BDC (bottom dead center), 1/2 upstroke, and again TDC.

The piston position is derived from the combination of the crank angle AND connecting rod length, thus taking into account the angle of obliqueness -- a sometimes substantial factor. The valve timing is therefore displayed with great accuracy no matter what the ratio of crank diameter to connecting rod length.

A "click" with the right mouse button brings the same popup as seen in 5.2.


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6.2 VALVE MOVEMENT BY PISTON POSITION -- SETTINGS

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In this window you can alter the display of the Valve Movement by Crank Angle and the Valve Movement by Piston Position windows.

Period number, initially set at "1", controls the number of crank revolutions which the graph simultaneously displays. (Translator's note: I find "1", a single revolution, to be adequate. "2" compresses things to much to gain useable information, although it might be useful as an instructional tool.)

Circle Diameter is the diameter, in pixels, of the dot on the sine curve that indicates the crank position (Translator's note: I find a 30 pixel setting to be less intrusive and actually clearer than the 40 pixel that is loaded in basic data.).

Timing Line allows one to turn "on" or "off" a vertical line which marks the actual crankshaft position, and which moves in time to the red dot when the engine is in animation mode..

Input causes any alterations made here to be entered in the window.


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7.1 VALVE TIMING -- GRAPH

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This graph is derived from the previous window: 6.1 Valve Movement by Piston Position. However, the important valve events are indicated in both inches (in.) and percent (%) of piston travel (The red and blue shading is omitted in order to better read these values).

open (steam admission or exhaust) means the point at which the valve edge uncovers the valve port.

close (steam cutoff or exhaust cutoff--co) means the point at which the valve edge closes the valve port.

The red colored line indicates the period of steam admission and the blue, that of exhaust.

The valve timing values are determined through program calculations which involve all engine particulars. The valve position is calculated for every 0.25° of crank position from 0° to 360° After the point at which a valve port opens or closes is fixed, the corresponding crank angle is computed.


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7.2 VALVE TIMING -- TABLE

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This window contains the information from the 7.1 Valve Timing -- Graph, but displayed in a easier to use table format.

The degree column indicates the crank angle in degrees.

The inch column, that of piston travel in inches.

The percent column, that of piston travel in percent.


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8.1 STEAM DIAGRAM -- GENERAL

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The Steam Diagram defines the potential output and efficiency of the engine. It displays measured and computed values and a theoretical card.

The values and the card are theoretical only. The actual (working) values are affected by many factors including (but, certainly, not limited to) the size of the engine. For example, if an engine is very small (like a model steamship engine) the proportionally large steam passages necessary for the model to work create clearance volumes well beyond acceptable practice.

However, program calculated values given here, as well as the theoretical card, are a good starting point.


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8.2 STEAM DIAGRAM -- PRESSURE UNITS

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Translator's note: The text here is entirely mine, and is to a large degree so in the following sections through 9. Working Parameters. Rainer's original text at this point was based on the current International System in use on the Continent and dealt with definitions particular to that system, but having no bearing on the system in use in the United States.

In the American system of pressure measurement (Once upon a time, we called it the English system -- but they don't do it this way anymore.), the basic unit is pounds per square inch expressed as psi. In dealing with steam machinery, however, the various formulas use pounds per square inch-absolute or psia.

The pressure you see displayed on the steam gauge on your boiler, for example, is measured from the atmosphere, which is set as 0 psi. Anything below this atmospheric pressure is considered to be a vacuum and is generally expressed in "inches of Mercury" or Hg.in.. Now a perfect vacuum is approximately (at sea level) 0 Hg.in.. Try and use these two in the same formula, particularly since vacuum in Hg.in. is regressive, unlike psi which is progressive.

Since traditional large steam equipment uses vacuum for efficiency (in fact, early steam engines were vacuum engines), it was soon determined that a uniform system was needed. For the purpose of ease of calculation, most steam measurements, as used in formulas, are determined from a point of absolute (attainable only in theory) vacuum.

Since absolute vacuum is approximately a minus 15 psi, you can readily determine the pounds per square inch-absolute, or psia, by simply adding 15 psi to the pressure registered on your pressure gauge (Note: some pressure gauges are calibrated for psia and will have "psia" printed on the dial face. If this is not present, you have a common psi gauge.).

So, follow instructions and look for psi and psia. Remember, there is a difference.


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8.3 STEAM DIAGRAM -- DESCRIPTION

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The vertical (Y) axis, here called P for pressure, denotes the pressure expressed in psia.

The horizontal (X) axis, here called V for Volume, represents the piston position in the cylinder -- and therefore the volume -- and is expressed in cubic inches and %. Additionally, the volume at certain points, most importantly that of steam cutoff, is given in both cubic inches and %. At the end of the V  line, the total piston stroke volume of the cylinder is given.

To illustrate, by way of example, the information you can receive here: go to the Settings button on the Main Window and through it Load the basic data in inches. Move the engine through a couple of revolutions (You should do this every time you alter any data to be recalculated) so all the data is set in the tables, etc., and then open the Steam Diagram -- Theoretical window.

You will see the steam card drawn. The left edge of the card delineates the pressure parameters from the vacuum of 5 psia (approximately 20 Hg.in.) -- normal for our small engines when run condensing -- to pressure at the valve chest of 165 psia (150 psi) -- again, a normal working pressure. The number 130 psia, with a blue horizontal line to the right edge of the card, notes the pressure in the cylinder when the exhaust opens. Now, starting at the upper left corner of the card, one moves to the right (and, you'll notice, stays at a constant pressure) until admission cutoff occurs at a volume of 77.7% and 21.96 cubic inches. A red vertical line marks this point. Now the steam pressure drops off as the volume continues to increase. The steam is still working, but to a lesser degree, until at the end of the stroke it is at 130 psia.

So what, you say. Ah, but go to the next page for a revelation.


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8.4 MEAN EFFECTIVE PRESSURE

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The mean effective pressure (MEP) is automatically calculated by the program. It is found at the right side of the card and is given in psi.

The mean effective pressure is the average pressure applied to the piston area during the entire stroke. This is very important and the easiest way to explain it is by example: With the basic data loaded you'll notice the cutoff is at 77.7% (21.96 cu.in). From the card the MEP is 156 psi. The steam pressure in the cylinder from start through 77.7% is 160 psi (165 psia - 5 psia). But, because of the peculiar expansive properties of steam, the average work performed is at 156 psi. Now go to the Main Window and move the Reversing Lever from 14° to 0°. Run the engine briefly and look again at the Steam Diagram -- Theoretical. The cutoff is now at 47.4% (13.41 cu.in.) -- we've used 49% less volume of steam -- but the MEP (work) is at 134 psi -- a decrease of only 14%. And the steam pressure at the exhaust has fallen from 130 psia to 83 psia -- a 36% reduction in otherwise wasted steam. Since the volume of steam is created by fire in the firebox, a small decrease in work (energy output) is offset by a much larger decrease in fuel consumed (energy input). For those who have experience in this area, I know this is a very simplistic explanation and there are a lot of other variables involved, but it is easily understood by a beginner.

The MEP is used to calculate the Indicated (theoretical) Horsepower (IHP) of the engine. This is done with the formula:

P x L x A x N / 33,000 = IHP

Where:

P = MEP in psi

L = Piston Stroke in feet (not inches, and usually expressed as a decimal part thereof)

A = Piston Area ( pi x r^2) in square inches

N = Number of Revolutions per Minute (rpm)

33,000 = A constant: the number of pounds a horse can move one (1) foot in one (1) minute

If the engine is double-acting (steam is alternately applied to each end of the piston) the answer is multiplied by two (2). Remember this is theoretical horsepower and does not take into account friction, losses due to cylinder condensation, valve passage constriction, and many other variables. A rough approximation of shaft horsepower will be found by multiplying by 0.75.

To demonstrate the formula, reset to program to the basic data. From the Steam Diagram -- Theoretical, MEP = 156. From engine data: L = 0.3333 feet (4" divided by 12); A = 7.069 sq. in. ( 3.1415 x 1.5²). A small engine like this is happiest at a maximum of rpm = 500. Substituting in the formula:

(156 x 0.3333 x 7.068 x 500 / 33,000) x 2 = 11.14 IHP

Now try it with the cutoff at 47.4% (Reversing lever set at 0).


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8.5 EXHAUST

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The purpose of this program is not only to have some fun, but to show how to improve the efficiency of our engines. An oft neglected area is the engine exhaust.

You've already located where the cylinder pressure at exhaust is displayed -- left side, at blue line. You've noted what happens to cylinder pressure at exhaust when you vary the cutoff. In the Operating  Parameters window set the Vaccum at 15 psia (atmospheric pressure). Run the engine with the Reversing lever set at 14° and 0°. Here are the results for atmospheric and 5 psia vacuum.

Exhaust                 15 psia                           5 psia

Cutoff 77.7%        MEP 146, Exh. 130     MEP 156, Exh 130

Cutoff 47.4%        MEP 124, Exh.   83     MEP  134, Exh   83

Note that an increase in exhaust pressure does not alter the cylinder pressure exhaust, but does reduce the MEP, and thereby the work. At 47.4% cutoff it is almost 8%.

Therefore the use of a condenser and pump to remove the condensate will result in an increase in efficiency. Couple with this the recycling of the water to the boiler, thus eliminating carrying large supplies of water on board, and there is a significant gain.


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8.6 OVER-EXPANSION

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As with everything in life, one can have too much of a good thing. The same is true with expansion, particularly if exhausting to atmosphere.

Once again, Load the basic data in inches. Move the Reversing Lever to 0° (47.4% cutoff). Go to Operating Parameters and set the Vacuum entry at 15 psia (exhausting to atmosphere). Now let's assume you have "throttled" (reduced the steam pressure at the valve chest) so that the engine will run very slowly. Set the Valve chest pressure at 25 psia. Turn the engine over a few times and look at the Steam Diagram -- Theoretical.

Surprise. The steam expansion curve drops below the exhaust pressure before the piston completes its stroke. While this will probably not stop the engine, but it will slow it and cause it to run roughly (in the case of a compound engine, however, it will most certainly stop).

This is another argument for running condensing, particularly if you want to use boiler pressures below 100 psi (It's been less than 100 years since pressures over 100 psi became common, and many steam launches were operated at 70 psi to 80 psi well into this century.).


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8.7 STEAM TABLE

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For this description you will need to have ready access to the real Steam Table. Shrink this window [-]. Go to the Main Window and "click" on the Windows bar. From there to go Steam Table. You will find a table with the properties of steam, and they can be very useful to you in designing the complete plant for your dream (or present) steamboat.

Across the top of the Steam Table you will see alphabetical characters heading each column. These mean:

t.....temperature:	in degrees Farenheit

hf...heat in fluid:	in Btu per pound

hfg.heat fluid to gas:	the heat needed, in Btu per pound to move from water at this temperature to steam

hg..heat in gas:	the total heat , in Btu per pound, to bring the water
from 32° F to the steam at this pressure

v.....volume:	of the steam in cubic feet per pound

w....weight:	of the steam in pounds per cubic foot of volume

sf....saturated fluid entropy:

sfg..saturated fluid to gas entropy:

Definition: Btu, as used here, is the amount of heat required to raise one (1) pound of water one (1) degree Farenheit.  There are more sophisticated definitions, but this will do for our purposes.

Here are some problems you can solve with this table:

How big a boiler do I need?

Go to the Main Window and Settings and Load basic data in inches. Now go to the Steam Diagram Theoretical through the icon on the Main Window. You will note that at the 77.7% cutoff, the volume of steam admitted to the cylinder in one stroke (1/2 a revolution) is 21.96 cubic inches. Since you want a boiler big enough for the maximum use of the engine, we'll assume revolutions per minute as 500. Steam usage of any steam engine is figured in pounds per hour so we'll multiply the number of rpm by 60. And we need the answer in cubic feet because that's how   v  and  w  in the Steam Table are given. Remember we need to multiple the stroke volume by 2.

     2 x 21.96 x 500 x 60 / 1728 = 762. 5 cubic feet of steam per hour

Divide this answer by 2.753, the number of cubic feet of steam in a pound of steam at 165psia:

     762. 5 / 2.753 = 277 pounds of steam per hour (rounded off)

A pound of water and a pound of steam are the same thing for weight purposes; the volume is different.

An average water tube boiler will evaporate 5 pounds of water per square foot of heating surface. Again, this is an oversimplification, but close enough for our little steamboats.

     277 / 5 = 55. 4 square feet

But we all like to do whistle blowing, etc. and you may want to add some other steam machinery down the road, so let's make it   65 square feet.

How much water do I need?

We'll continue with this example. Usually the boiler feedwater pump is driven off the engine.  Sometimes it is stepped down in speed, but for now we'll use engine speed,  500rpm.  A pound of water occupies approximately 28 cubic inches.  A good rule of thumb is to have a pump which will provide twice the amount of water needed.  Pounds of steam per hour, divided by 60 (for minutes), divided by 500 (to get one revolution), times 28, times 2:

     [277 / (60 x 500)] x 28 x 2 = 5.17 cubic inches of water per revolution

I leave it to you to come up with a pump to do this.

How much fuel will I burn?

From the Steam Table go to the column hg, and down this column to 165psia.      1194.6 Btu is required to create steam from 32F to 165psia.  But our condensed water is returned at, say, 70F.  A savings of 38 Btu per pound.  So Btu per pound at 32F,  minus 38 Btu per pound, times number of pounds per hour:

     (1194.6 - 38) x 277 = 322,040.2 Btu per hour

But our boilers are only about 75% efficient, so we  will need to divide this figure by 0.75:

     322,040.2 / 0.75 = 429, 387 Btu per hour--Almost three times what your home furnace puts out.

A gallon of furnace oil (no. 2 diesel) provides about 135,000Btu per gallon.  Therefore:

     429,387 / 135,000 = 3.18 gallons per hour

How can I reduce this?

One easy way is to preheat the feedwater to the boiler.  This can be done in a number of ways: a coil of pipe in the area above the boiler (to scavenge otherwise wasted heat); a jacket around the exhaust pipe from the engine before it goes to the condenser; raising the temperature of the water in the hotwell (where the condensate is returned); and any combination of these.  Whatever you use, the feedwater going to the boiler can be brought to 212° F with little difficulty.  Originally we said the temperature of the feedwater was  70F, and we have now raised this--with no additional fuel--to 212F, a savings of 142 Btu per pound.  So if we multiply this figure by 277 pounds per hour, subtract it from 322,040.2 Btu per hour, divide by 0.75, and finally divide by 135,000 we will get the gallons per hour of fuel.

     [ 322,040.2 - (142 x 277) / 0.75] / 135,000 = 2.8 gallons per hour

A savings of one (1) gallon of fuel for every three hours of fun, and it doesn't take any more work and only a little money for some pipe and fittings!

This still sounds like a lot.  What else can I do?  First of all, remember that we set the cutoff at 77.7%.  Go back to the Main Window, check to make sure you have basic data inches loaded, move the Reversing lever to 0°, this will give approximately 47.6%.  Earlier in this text at 8.4 Mean Effective Pressure  you were supposed to work this setting out for the IHP.  If you didn't, do so now!  Compare the two different IHP values and note the decrease in work performed at the 47.6% cutoff setting.  Now, using the new Steam Diagram  Theoretical values (you did remember to run the engine a full revolution after changing the Reversing lever setting didn't you?) and the Steam Table, go through the calculations above to find out how much altering the cutoff will truly save.

I don't want to burn oil--what about coal or wood?  The Btu values are as follows:                                                                Wood: about 8,000 Btu per pound

       Coal: about 12,000 Btu per pound

Why didn't you go into entropy?

I probably won't live long enough to make this comprehensible. Unless you have a good background on a college level in chemistry and physics, it's hard to explain. For those who do have this background, the values are in the table.

This very brief guide to using the Steam Table only skims the surface of its value. I'm sure you will now find many other applications.


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9 OPERATING PARAMETERS

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In the window Operating Parameters one inserts information about pressures and temperatures of the steam supplied to the engine -- and thereby directly affects the Steam Diagram -- Theoretical.

Valve chest  is the pressure provided to the engine at he valve chest and is expressed in pounds per square inch-absolute (see: 8.2 Steam Diagram -- Pressure Units).

Exhaust indicates back pressure, or exhaust (see: 8. 5 Exhaust and 8. 6 Over expansion). It may be above 15 psia ( if the high pressure cylinder of a compound engine is being calculated); at 15 psia if exhausting to atmosphere; or below 15 psia if exhausting to a condenser.

The valve chest and exhaust pressures determine, respectively, the upper and lower boundaries of the theoretical card.

The factor of Superheat ranges from 1 for no superheat, through 1.2 for moderate superheat, to 1.3 for high superheat. The term Superheat means the increase in temperature (sometimes also called drying) of the steam above that temperature at which it is created.  Remember, heat is energy waiting to happen!

In our example, at a pressure of 165 psia, the steam (at this point said to be saturated -- i.e. containing as much water vapor as it can and still be completely steam) has a temperature of 366° Farenheit (see: Steam Table within the Windows bar on the Main Window).

If one changes the grade of superheat, say from 1 to 1.3, one will observe a more rapid dropoff in pressure during the expansion part of the steam card. This is brought about by a peculiarity of steam: that by raising the superheat, the mass (weight) will decrease while the volume remains constant. The figures 1 thru 1.3 become the power to which the  V (volume of the steam at that pressure) is raised for superheat: V^n = Vs (volume at superheat).  At 165 psia the volume of one pound of steam (from the Steam Table) is 2.753 cubic feet and the temperature is 366°.  Substituting in the formula: 2.753^1. 3 = 3.7298.  The steam has about 35% more volume per pound than at saturated temperature.

A good illustration of this is given by using the Steam Diagram -- Theoretical. Make sure to Load basic data in inches and set the Reversing lever  at 14°. (77.7% cutoff). Run the engine a few revolutions. Now go to the Steam Diagram -- Theoretical and note the MEP and the pressure at exhaust. Then go to Opeerating Parameters and set Superheat at 1.3, "click" on the Input; run the engine; and go again to the Steam Diagram -- Theoretical and observe the same pressures. Repeat the above two Superheat settings with the Reversing lever set a 0°.(47.4% cutoff). Note the results:

Superheat                 1                                       1.3

Cutoff 77.7%            MEP 156, Exh 130        MEP 155, Exh 121

Cutoff 47.4%            MEP 134, Exh   83         MEP 128, Exh   67

With a late cutoff (77.7%) we lose only 1 psi in the MEP, while lowering the pressure at exhaust by 9 psi. And with an early cutoff (47.4%) we lose 6 psi in the MEP while lowering the pressure at exhaust by 16 psi. The ratio of MEP to Exhaust at a late cutoff is much greater than that of MEP to Exhaust at an early cutoff.

This demonstrates the efficiency gained by the use of superheat in a compound engine -- where it is accepted practice to set the cutoff for the HP (high pressure) cylinder as late as 75% to 85% -- and yet reduce the pressure at exhaust to a point where the balance of work performed between the HP (high pressure) and LP (low pressure) cylinders is nearly equal.

But nothing in this world comes free.  The price here is mechanical wear on the engine.  Our little engines should not be operated above 550° F. unless especially designed to do so.  And even then lubrication in the form of cylinder oil must be injected into the steam just before it enters the valve chest.  If the engine is run condensing (something desireable, as we have seen) then this oil must be removed from the condensate before it is pumped back to the boiler as feedwater--otherwise it will coat the inside of the boiler tubes and decrease heat conductivity,

resulting in tube failure.  Taking the volume determined from the above calculations and looking up the temperature of steam at this volume of  3.7298 cubic feet and at the pressure of 165 psia from superheat tables (they are not included here) we find the temperature of the superheated steam to be approximately 600° F.--far too high for our engine!

In order to keep the temperature within a reasonable range, the value of 1.1 for Superheat is used.  This will give a steam temperature of about 430° F, about 64° F. of superheat--not enough to cause lubrication problems, but sufficient to insure the steam reaching the engine will be dry.

Work out the calculations for the MEP and exhaust at both the Reversing lever settings, and then compare to determine what the percentages of gain and loss are--as we did above.


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10 ENGINE PARTICULARS -- GENERAL

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The engine measurement values (particulars) determine the geometry and function of the engine. Because of the number of variables involved, more than one window to enter and display them is required. The variables are grouped by function.

It is possible, through entering of improper values, that the engine will not operate. A message to this effect will appear in the Main Window when you activate the Start button.

This may be caused by one, or both, of two things:

1. The valve does not open the valve ports, or the valve events are incorrect. The engine will be drawn correctly, but will not operate:

2. The measurement values are incorrect. That is to say, some values are beyond operating range or, in combination with other values, are meaningless. The engine will not be drawn properly and, of course, will not operate.


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10.1 CRANK ASSEMBLY

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All units are to be expressed in inches and decimal parts thereof.

 Legend for drawing:
1 --- Crank Radius
2 --- Connecting Rod (measured between centers)
3 --- Piston Rod
4 --- Bottom Clearance
5 --- Piston Thickness
6 --- Piston Diameter (also called Cylinder Bore)
7 --- Top Clearance

By entering the values for the Crank Radius, Connecting Rod length, Piston Rod length, and Piston Diameter one defines the piston stroke and piston stroke volume. By entering Top Clearance and Bottom Clearance the total working volume is established -- not just that of the piston stroke. With the final addition of Piston Thickness, the true distance between the cylinder heads is calculated.


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10.2 VALVE GEAR

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Main components of valve gear:

1) Ahead eccentric rod length [mm/inch]
2) Reverse eccentric rod length [mm/inch]

3) For. angle of advance + 90° [°]
4) Rev. angle of advance + 90° [°]
3) / 4) Eccentricity [mm/inch]

5) Link travel [mm/inch]
6) Link slot overhang [mm/inch]

7) Reach rod length [mm/inch]
8) Reversing arm length [mm/inch]

Location of reversing lever pivot:

1) Reversing lever pivot - X [mm/inch]

2) Reversing lever pivot - Y [mm/inch]


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10.3 VALVE CHEST

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Valve face data:

1) Top seat [mm/inch]
2) Top port [mm/inch]
3) Top bridge [mm/inch]
4) Central port [mm/inch]
5) Bottom bridge [mm/inch]
6) Bottom port [mm/inch]
7) Bottom seat [mm/inch]

8) Top clearance [mm/inch]
9) Bottom clearance [mm/inch]

Valve chest data:

1) Valve chest height [mm/inch]
2) Valve chest depth [mm/inch]
3) Straight passage [mm/inch]
4) Steam inlet/exhaust outlet [mm/inch]

Location of valve chest:

Distance to lower bottom port edge:
   1) from crankshaft center X [mm/inch]
   2) from crankshaft center Y [mm/inch]


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10.4 VALVE

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Valve dimensions:

1) Overall length[mm/inch]
2) Valve cavity height [mm/inch]
3) Top valve face [mm/inch]
4) Bottom valve face [mm/inch]
5) Valve body thickness [mm/inch]
6) Valve cavity depth [mm/inch]
7) Valve stem length [mm/inch]

Lap:

1) Outside lap -- top [mm/inch]
2) Inside lap --top [mm/inch]

3) Inside lap -- bottom [mm/inch]
4) Outside lap -- bottom [mm/inch]


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Kopieren

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Kopieren

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ENGINE STOP!

Dear Program Operator:

I hope you've had some fun with my steam program and its animated display. Please feel free to comment. You can call or e-mail me (Translator's note: me too!) with suggestions for improvement. I'll also gladly accept compliments.

No individual is as intelligent as the group of all of us.

I would like this program to be widely distributed and used, so simply ask for an update.

Ronald A. Fossum: sl-artemis@worldnet.att.net

Rainer Radow: radow.rainer@berlin.de


Ablauf-Verzögerung
With the Motion delay you determine the time span that the program pauses between the motion increment steps. With a setting of 0 the program will run as fast as the computer performance will permit.


Winkelschritte
Here you select the Motion increment - the number of degrees between each crank angle at which the program performs calculations and draws a picture. If you enter 10°, then 360° / 10° = 36 pictures or program calculation steps in a complete revolution. The larger the degree number, the less the program must set and calculate in a revolution and therefore the faster the engine turns. (Translators note: and the less accurate the overall results.)


Umsteuerung
This valve governor directly moves the reversing gear. The 0° indicates the reversing lever is in a vertical position. Ideally, the engine is designed so that in this 0° position the link block is positioned mid-way in the link slot.  That is not the case here, but will generally give best results if it can be obtained.


Titel
Here you Start and Stop the motion in all opened windows. All closed windows are not animated and so the fewer windows open, the faster your engine will run.

The correct rotation is automatically given by the valve position. If the valve timing is not correct, or if the steam passages do not open for a full crank revolution, then the engine will not run.


Titel
The crank is turned one motion increment further in a counterclockwise direction. The animation is stopped.


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The crank is brought to TDC (top dead center). This corresponds to the 0° measurement position. The animation is stopped.


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The crank is turned one motion increment further in a clockwise direction. The animation is stopped.


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This counter displays the piston position in inches (or  mm). BDC (bottom dead center) = 0 inches (mm) of piston travel.  TDC (top dead center) is the total travel of the piston, or twice the crank radius.


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This counter displays the piston position in %. BDC (bottom dead center) = 0% of piston travel. TDC (top dead center) is written as 100%.


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This counter displays the actual crank position in angle graduations from 0° to 360°. TDC (top dead center) = 0°,  BDC (bottom dead center) = 180°.


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This counter displays the maximum link block slip for the selected geometry and positioning of the valve gear. The motion of the link block relative to the link can be ascertained by the link block slip (Translators note: the smaller the better).


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This counter displays the maximum travel of the valve stem (and therefore the valve) in the selected geometry and positioning of the valve gear.


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This display gives the program run time for a full crank revolution. The counter measures in system units and serves internal test points.


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This line holds the data name of the actual loaded / stored geometric data.


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For all elements in this window there exists a covering text in Help-Info text. "Click" once with the right mouse button on an element and a brief written text is displayed. A "click" with the left mouse button on the text and the Help window is closed.


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This window displays the engine animation of the steam engine.  All settings and geometry are derived from measurements and computations in other windows.


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This display gives the maximum travel of the valve stem (and therefore the valve) for the selected geometry and settings of the valve gear.

The reach rod should be attached to the link at the end where the forward eccentric rod is connected. This arrangement cause the least link block slip in forward gear, normal for marine use.  (Translators note:  Unfortunattely in the American translation, because of the design of the engine used, this is not the case.  I felt it more important to have the rotation viewed from the after end of the engine--as is customary in the USA--turning clockwise, a "right turning" engine.  If the user wants to see the difference, move the Reversing lever to - 42°, the full reverse position.)