Reciprocating Engine DetailsPlans of the Olympic Class Ships

[Joe Burgard]

I was able to get some of those great drawings of Britannic's engines and I have been using them to get dimensions of the various parts. It takes a while to do.

I plan on doing a Diagram of Volumes for the engine. In order to do this I need the 4 inputs:
1. Cylinder Dimensions (Sam's article)
2. Positions of Crank (Sam's article)
3. Clearance and Receiver Volumes (trying to find from drawings)
4. Steam Distribution (will have to make an educated guess, like 66% cut off for the HP cylinder)

So far I've found the receiver volumes (roughly). The pipes were easy to dimension, but inside the valve chests and the valves themselves are much less accurate.

HP to IP cylinder R1=1.9*volume of HP cylinder
IP to LP cylinders R2=3.1*volume of IP cylinder

These values roughly correspond to the guidelines set in "Marine Engines and Boilers" on page 27. HP to IP receiver 1.8-3.8*volume of HP cylinder. IP to LP receiver 1.3-2.3*volume of IP cylinder.

Next to roughly figure the clearance volumes...

Joe

 

[Bill West]

Here’s the contents of the data files for reference and some design comments:
Change the EditDimen/SetGraphicZoom to 150.00 if you are entering this. Just type over the stock file data and then save it under a different name.

HP -inside admission -file: BritannicHP1.dsi
......Frame Dimensions..................full size................................................full size
..................................................inches..................................................inches
.1...Driver...................Diameter..122.000....Rocker Upper..........Back Set.....0.000.....5.
......Stroke.....................Length....75.000....Rocker Lower.............Length..180.000.....6.
......Main Rod.................Length...164.000....Rocker Pivot.................Vert..179.950.....7.
......Eccentric Circle..............Dia....16.000.........."......"...................Horz..171.000.....8.
.2...Eccentric Dia..........................50.000....Valve Con Rod..........Length..130.000.....9.
.3...Eccentric Angle......ºForward....52.000....Lifting Link...............Length....81.000......
............"........"...........ºReverse....52.000....Reverse Arm Vert.....Length......1.950....10.
......Eccentric Rod.........Forward...171.000......,....".............".....Back Set....-0.102....10.
............."......."............Reverse...171.000....Lifting Arm..............Length...-40.000...11.
......Link.........................Radius..161.000....Rev/Lift Arm Pivot.......Vert......81.000.......
......Link Center Pivot...Back Set......0.000............"..........".............Horz...201.000.......
......Link-Ecc Rod Pivot........Vert....22.000....Rev Arm to Center......Norm......1.040....12.
..........."........."..........Back Set.......1.600.............".........."............Max......1.300....12.
. 4...Rocker Upper Vert...Length..-180.000...................................................................
-all the main dimensions are from the driver center.
-unworkable numbers lock up the data entry with an floating point error, you have to undo something.
-an "err" light also flashes at the top any time something doesn’t fit.

HP frame data notes:
1 -for looks only, the outside of the crank
2 -for looks only
3 -180º from locomotive position because of direct valve actuation. This is direct, inside admission so it is the "open rods" pattern (the rods are not crossed when the crank is pointing towards the cylinder).
4-made negative to fold this locomotive style rocker into itself. Effectively removes it from the mechanism as this is a direct actuation engine.
5 -leave at zero as part of folding the rocker into itself
6 -set high to make the valve con rod motion virtually horizontal
7 -trimmed to reduce blinking of valve con rod pixels
8 -center the rocker's swinging
9 -equals Cylinder ctr to Driver ctr less Eccentric Rod. This is 2" longer than actual because program can only center the valve on the main piston even though it is more to the left on actual engine. See more below.
10 -33"x1.724" ±36º arm cut short to fit. Rev Arm Cent position tips 3º to right.
11 -negative sets arm to right instead of left
12 - ± range fixed in program, not user adjustable.
200.029/201.069/202.109" is gear Fwd/Cent/Rev and gives 67.4/77.0% =72.2% avg cutoff in Fwd.
200.504" Fwd gives 43.2/56.8% =50.0% avg cutoff.

additional info for note 9:
The angles in the main rod to crank relationship are known to make the crank rotation and piston stroke uneven (sinusoidal). But less well known, the relationships are not symmetrical to each other either, because of the differing angles in the long and short triangles outlined by the 1/4 and 3/4 positions of the main rod stroke. This is called "angularity" and a consequence of it is that the cutoffs at each end of the cylinder are not equal. The Valve Con Rod Length choice has not tried to "re-center" this however because while it can vary the error, it can't eliminate it.

.......Cylinder Dimensions..............full size................................................full size
..................................................inches..................................................inches
.1...Cylinder ctr to Driver ctr........301.000....ValveBore ctr to ValvePort........24.000.......
.2...Cylinder CL above Driver...........0.000....ValveBore PortWidth.......Rear....5.000.......
......Cylinder Bore........Diameter....54.000............".........."...............Front....5.000.......
.3...Cylinder Bore...........Length....85.000.....Valve Ctr to Inside Edge...........................
......Cylinder Steam Port...Width......7.500............................of Inside Ring..20.500.......
......Piston ctr to Crosshead ctr....................Valve End Width (Outside..........................
............................(Piston Rod)..137.000............Edges of Rings)........Rear...9.000.......
.4...Piston.......................Width....10.000............"......"....................Front...9.000.......
......Valve CL to Cylinder CL............0.000....Valve ctr to Joint.....................................
......Valve Bore...........Diameter....35.000.............................(Valve Stem)....0.000....5.
.4...Valve Bore..............Length....74.000.................................................................

HP cylinder data notes:
1 -equals Main Rod + Piston Rod
2 -needs to be in line for direct actuation
3 -added piston width, not used in calculations
4 -for looks only
5 -for direct actuation this is all in the Valve Con Rod dimension in the Frame section

LP -outside admission -file: BritannicLP1.dso
......Frame Dimensions..................full size................................................full size
..................................................inches..................................................inches
......Driver...................Diameter..122.000....Rocker Upper Vert....Length..-180.000.......
......Stroke.....................Length....75.000....Rocker Upper..........Back Set.....0.000.......
......Main Rod.................Length...164.000....Rocker Lower............Length..180.000.......
......Eccentric Circle..............Dia....16.000....Rocker Pivot.................Vert..179.950.......
......Eccentric Dia..........................50.000.........."......"...................Horz..171.000.......
.1...Eccentric Angle......ºForward..232.000....Valve Con Rod..........Length..130.000......
............"........"...........ºReverse..232.000....Lifting Link...............Length...81.000.......
......Eccentric Rod.........Forward...171.000....Reverse Arm Vert.....Length......1.950.......
............."......."............Reverse...171.000......,....".............".....Back Set....-0.102......
......Link.........................Radius..161.000....Lifting Arm..............Length...-40.000.......
......Link Center Pivot...Back Set......0.000....Rev/Lift Arm Pivot.......Vert......81.000.......
......Link Center Pivot.........Vert......0.000............"..........".............Horz...201.000.......
......Link-Ecc Rod Pivot........Vert....22.000....Rev Arm to Center......Norm......1.040.......
..........."........."...........Back Set......1.600.............".........."............Max......1.300......

LP frame data notes:
1 -opposite of HP because of outside admission. This is direct, outside admission so it is the "crossed rods" pattern (the rods cross when the crank is pointing towards the cylinder).

.......Cylinder Dimensions..............full size................................................full size
..................................................inches..................................................inches
......Cylinder ctr to Driver ctr........301.000....Steam Port Width..........Rear.....7.000.......
......Cylinder CL above Driver...........0.000....Steam Port Width.........Front.....7.000.......
......Cylinder Bore........Diameter....97.000.....Valve Chamber..........Height...38.000....4.
......Cylinder Bore...........Length....76.500.....Valve Chamber..........Length...38.000....5.
......Cylinder Steam Port...Width......9.000.....Valve Height..........................19.000....6.
......Piston ctr to Crosshead ctr.....................Valve Length.........Rear Half....36.000....7.
............................(Piston Rod)..137.000.....Valve Length........Front Half....36.000......
......Piston.......................Width......1.500....Valve ExhCavity.....Rear Half....25.000......
.1...Valve Surface to Cyl CL...........64.000.....Valve ExhCavity....Front Half....25.000......
......Valve Stem CL to Cyl CL...........0.000....Valve ctr to Joint.....................................
.2...Exhaust Port............ Width......4.000.............................(Valve Stem)....0.000......
.3...Bridge Width..............Rear.....22.000.................................................................
......Bridge Width..............Front....22.000.................................................................

LP cylinder data notes:
1 -valve is left floating above the cylinder because the ports won’t stretch well enough. This is the actual dimension anyway, just picture it turned into line with the engine.
2 -arbitrary, for looks
3 -deducted 1/2 of exhaust port width
4 -diameter of valve piston
5 -for looks only
6 -shows half of valve piston
7 -to outside of rings

The valve is actually a piston type, the dimensions were adapted to the slide valve in the program as:
ValveBore ctr to Valve Port 24.000 -entered as Bridge Width less 1/2 of Exhaust Port
ValveBore PortWidth Front & Rear 7.000 -entered as Steam Port Width
Valve ctr to Inside Edge of Inside Ring 25.000 -entered as Valve ExhCavity Front & Rear
Valve End Width (Outside Edges of Rings) Front & Rear 11.000 -added to Valve ExhCavity size and entered as Valve Length

Optional drawing of lines for the actual Rev Arm:
ReferPoints needs to be turned on. This is troublesome to get entered, it wants to do it from reference points. So using them place cross1 and 2 anywhere with left and right clicks, then in DrawLinesCircles select a row, press the buttons to put in all but the location and then press Draw Close to connect it to the ReferPoints. Get anything you can in and then revise it to the correct numbers. There are buttons in the ReferPoints windows to remove them when you are done.
Data:
........No..Type..Color..Ref to...Line1Vert..Line1Horz....Line2Vert..Line2Horz
Fwd...1....line...green...0,0.......81.000....201.000.......109.943....185.148
Cent..2....line...green...0,0.......81.000....201.000.......113.955....202.724
Rev...3....line...green...0,0.......81.000....201.000.......107.985....219.996

Bill

 

[Bill West]

Although running the engine dimensions in the valve gear program suggests long cutoffs I note that the program also shows that the valve gear can readily be linked up to say 40-50%. A check of Brown's reversing engine shows that it's hydraulic cylinder will lock it in any position you want, just stop moving the control handle. So why design with 70-80% cutoff if you only need to link up to 40-50%? Well it would leave you room to easily adjust the power (up to the maximum that the boilers will support) should you have troubles in meeting the trials requirements or if future needs change. And at sea, if one engine fails it would allow forcing the other engine while you make port and would keep up the supply of exhaust to the turbine too. So I am satisfied that the long maximum cutoff need not exclude the possibility that design performance was based on a much shorter cutoff.

Having said that I have looked at typical water rates for period engines and think we are headed to 13 pounds/hour per IHP for a recip-turb combo exclusive of separate accessory pumps (Engineering Oct 30, 1914 pgs 538-39). For interest, other machinery types were no better than 15 lbs, except geared turbines but they were just starting to learn how to cut gears that could handle ship power levels. For the Britannic at 50,000hp 13 lbs comes out to 10,833lbs/min (650,000lbs/hr) and is in line with the condenser and other pump capacities given in Engineering. The surface feed heater capacity of 700,00lbs/hr may well just be the 620,000lbs/hr condenser air pump rating with the auxiliaries, generators (50,000lbs) and hotel load (16,080lbs) exhausts added in

My own doodling with ideal engine calculations is presently only at half of 10,333lbs. So when I allow for additional steam to cover the engine inefficiencies I am faced with the problem of getting it into the HP cylinder. Only a cutoff up around 70% would swallow that much steam and get it into circulation. So full stroke on the valve gear might be correct after all.

Bill

 

[Joe Burgard]

Bill,

The drawings of Britannic's engines you speak of I have as well. They're real good and I just printed them out on 8.5"x11", which gave them a rough scale of 1cm (elevation/top) and 2cm(side views) to 1m. I'll eventually get around to blowing them up. I agree, millimeters are much easier to measure drawings and scale from.

I just got in the mail a few days ago via Abebooks an actual copy of "Heat-Power Engineering" by Hirshfeld and Bernard (same edition as is online in pdf), so I'll be following their ways of doing PV diagrams.

In regards to steam consumption, my research as well all says 12.5-13 lbs/ihp-hour (and I'm sure we're looking at some of the same resources). Using that as a benchmark, the cut-off has to be at least 70%. Using 10833 lbs/min yields 36.1 lbs/stroke of HP cylinder. At 230 psia the specific volume is 2.00 ft^3/lb therefore cutoff is 72.7%. As mentioned before, I hope to get a good idea of the cut-offs for the IP and LP cylinders later with more calculations.

Thanks for the valve program and the other information. I'll have to go over that in detail later. I'm definitely going to use those animations since I'm building an Erector/Meccano Triple expansion engine with the Joy valve linkage, and yes I it will really run on steam (or compressed air).

Joe

 

[Bill West]

Joe,
Regarding having calculated the HP admission volume and cutoff, have you looked at the LP exhaust volume? 36.1 lbs/stroke HP intake is 18.1 lbs/stroke exiting each LP cylinder. At 9 psia that has a volume of 765 ft^3 in a 321ft^3 cylinder. Now it might be 58% wet which would reduce it’s volume enough to fit. But the energy drop for the engine then becomes 120,000 horsepower or the like. The engine is inefficient but not that inefficient. That’s too much energy to lose, something else is going on in our picture. How are we getting exhaust, that has not given up an excessive amount of heat to condensation, out of the LP without getting excessive volume? Perhaps the release pressure in the LP cylinder is around 20 psia and exhausting expands it to 9 psia so that it will be dry for the long exhaust pipes and the turbine?? More figuring....

For more reading, Internet Archive has an 1898/1908 book that seems to have a good discussion on the uncertainties of cylinder wall condensation. “Thermodynamics of the Steam Engine”, C.H. Peabody. Try pages 142, 199 and 202.

If you haven’t already researched it, here are the Olympic, Titanic and Britannic pages in Engineering that I know of:
vol 90 1910
-Jul 1 pg 14-15 Welin Davits
-Oct 21 pg 564-572 Olympic -hull & machinery
-Nov 10 pg 620-621 Olympic -hull & machinery
-Nov 18 pg 693(and facing plates!) -695, 698 Olympic -hull & machinery, boiler/engine/turbine/electric room plans
vol 91 1911
-May 26 pg 678-679 Olympic(despite article title/lead on Titanic) -general arrangement, deck plans
-Jun 2 pg 734 Titanic -launch announcement
-Jun 16 pg 789-792?? Olympic -accommodation
vol 93 1912
-Jun 14 pg 802-806 Titanic Inquiry -deck plans
-Jun 21 pg 847-850 Titanic Inquiry
-Jun 28 pg 884 Titanic Inquiry
vol 94 1912
-Jul 5 pg 3-12 Harland & Wolff -facilities
-Jul 12 pg 38-51 Harland & Wolff -facilities
-Aug 2 pg 154-157, 166 Belfast graving dock
-Aug 16 pg 237 Olympic -rebuttal letter on steering problem
-Aug 16 pg 239-241 Belfast graving dock
-Aug 23 pg 266-268 Safety Appliances at Sea Report -ice route map
vol 97 1914
-Feb 27 1914 pg 273-283 Britannic -hull & machinery, engine/turbine plans, deck plans, launch

Bill

 

[Bill West]

I did some guessing at the heat loss from the engine jackets to see if it was significant in the engine performance, it didn’t turn out to be much. I used CAD to take a rough area for the top of each cylinder/valve chest (and thus the bottom too). The perimeter of the tops times the cylinder height then gave me the jacket wall area. Adding up these figures for the 4 cylinders, along with a simple guess at the diameter/length of the H-I and two I-L receiver pipes gave the total engine “hot” area that is radiating heat into the room.

The Britannic plans show about 3.5 inches space between the cylinder casting and the jacket. This could have been filled with felt or one of the magnesia compositions. I found easy conductivity data for fiberglass, rock wool and dry wood so I just used it. They are all the same at 0.04 W/Mkº. The poor but simple approach is to assume that this value applies over all the hot surfaces, it of course is incorrect because of the many corners and bolt pads on the castings. But I didn’t consider the transfer resistance for black painted sheet metal to slow moving air either. I used the steam temperatures that go with the pressures in Sam’s Prime Mover paper and 90 deg F for the room.

The final answer was 75,000 BTU per engine which is equivalent to 29 horsepower. As this is only 0.2% of the engine power I did not bother trying to make this guess more correct.

Steam jackets for engines were talked about a lot in the past but I think their virtue is not that they reduce radiant losses, they don't. It is that they improve the efficiency inside the cylinder. Even then however, they did not become commonplace because they didn't always make an important difference.

Bill

 

[Bill West]

For our next CAD measurement I looked at the steam passage clearance that goes with the cylinder volume. This is more critical to the engine performance but fortunately could be measured with fair accuracy. Here’s a picture to show what I found. It is of course from the Britannic plans but I’m not finding that the differences from the Olympic/Titanic would be of concern at all.

The measurements from this tracing tally as follows:

HP cylinder volume = 99.4 ft^3 (54" dia x 75" stroke)
steam passage height = 7.5 inches (Britannic plans)
gives 6000 fpm average steam flow speed through the jog area -70 mph.
passage's plan view area = 24.2 ft^2 (freehand CAD trace)
plus a 1.75' jog with a 4' width adds 7 ft^2 (jog's face area)
So each passage's volume is 19.5 ft^3, equals 19½ % clearance.
A piston end clearance of 1" adds 1.3 ft^3 or 1.3%. (Britannic plans)

IP cylinder volume = 240.5 ft^3 (84" dia x 75" stroke)
steam passage height = 9 inches (proportioned guess, HP’s speed and LP’s height)
gives 6000 fpm average steam flow speed through the jog area.
passage's plan view area = 48.3 ft^2 (freehand CAD trace)
plus a 1.75' jog with a 8' width adds 14 ft^2 (jog's face area)
So each passage's volume is 46.7 ft^3, equals 19½ % clearance.
A piston end clearance of 1" adds 3.2 ft^3 or 1.3%

LP cylinder volume = 320.7 ft^3 (97" dia x 75" stroke)
steam passage height = 9 inches (Britannic plans)
gives 7100 fpm average steam flow speed through the jog area.
passage's plan view area = 56.3 ft^2 (freehand CAD trace)
plus a 1.75' jog with a 9' width adds 15.75 ft^2 (jog's face area)
So each passage's volume is 54 ft^3, equals 17% clearance.
A piston end clearance of 1" adds 4.3 ft^3 or 1.3%. (Britannic plans)

The piston end clearances could be an 1/8” larger or smaller but we can see that it’s not going to matter. Likewise the tracing accuracy is not that critical, one quickly finds that minor freehand mistakes hardly have any effect on the results at all. The fairly large HP & IP clearance figures turn out to not be critical for the performance calculations because the wasted expansion just passes more energy to the next stage. Perhaps that’s why only the LP is held back to a more moderate figure.

In sum we seem to find 21% clearance on the HP & IP and 18½ % on the LP.

Bill

 

[Joe Burgard]

Bill,

Your data for the clearance volume looks good and is in line with the reference material I have. Thanks for doing that. I'm curious as to which plans you have that detail the piston valves and their port sizes? The ones I have for Britannic's engines don't detail that.

There's two things left to figure out to do the Diagram of Volumes: 1) the release points to exhaust steam to the receivers and 2) the compression percentages of the stroke for each of the cylinders. Alot of examples from books I have have a release point at about 92% of the stroke.

For compression the data I have says:
HP cylinder - 4-8% of stroke
IP cylinder - 7-14% of stroke
LP cylinder - 10-20% of stroke

When I get home later, I'll do some calculations regarding these things. My father (also an engineer) gave me an old steam tables book which had a great Mollier diagram that is about 3x4 ft. That Mollier chart should make for better readings.

Joe

 

[Joe Burgard]

Here's some figures I was fooling around with and the results are kind of surprising. When I complete the diagram of volumes, we'll see if they match up at all. I didn't include the clearance volumes since I only was calculating the pressure drops during the expansion phases for each cylinder and I assumed the mass of steam following compression was at about the same as the inlet pressure (it is less in actuality).

The mass flow rate of 36.1 lbs/stroke (based off of 13 lbs/Hp-hr for 50,000 Horsepower) into the HP cylinder at 230 psia. The mass flow into each of the LP cylinders is 36.1/2=18.05 lbs/stroke.


HP Cylinder volume = 99.402 ft^3
Inlet pressure = 230 psia
At 75% Cut off the quality = 0.97
mass of liquid = 1.1 lbs
mass of steam = 35 lbs
Volume at cut off = 74.75 ft
Pressure at cut off = 215 psia

At release of 95% stroke quality = 0.94
mass of liquid = 2.166 lbs
mass of steam = 33.93 lbs
Volume at release = 94.43 ft^3
Pressure at release = 163 psia

IP Cylinder volume = 240.53 ft^3
Inlet pressure = 93 psia
At 70% Cut off the quality = 0.95
mass of liquid = 1.805 lbs
mass of steam = 34.30 lbs
Volume at cut off = 168.4 ft
Pressure at cut off = 90 psia

At release of 95% stroke quality = 0.90
mass of liquid = 3.61 lbs
mass of steam = 32.49 lbs
Volume at release = 228.5 ft^3
Pressure at release = 61 psia

At release of 95% stroke quality = 0.94
mass of liquid = 2.166 lbs
mass of steam = 33.93 lbs
Volume at release = 94.43 ft^3
Pressure at release = 163 psia

LP Cylinder volume = 320.74 ft^3
Inlet pressure = 39 psia
At 64% Cut off the quality = 0.93
mass of liquid = 1.264 lbs
mass of steam = 16.79 lbs
Volume at cut off = 205.3 ft
Pressure at cut off = 34 psia

At release of 95% stroke quality = 0.88
mass of liquid = 2.166 lbs
mass of steam = 15.88 lbs
Volume at release = 304.7 ft^3
Pressure at release = 21 psia


Some thoughts here. The pressure drops at the release point and the inlet pressure seems rather large, especially from the HP to IP cylinders. However, looking at PV diagrams for triple expansion engines, the pressure drop at the "toes" of the diagrams for HP cylinders do drop dramatically.

Bill, I think you are correct with your theory regarding the high exhaust pressure of 21 psia from the LP cylinder to the receiver pipes for the turbine is to ensure dry input steam at 9 psia.

If the turbine produces 18,000 hp, the input of 9 psia dry steam and a mass flow rate of 10833 lbs/min needs an output of 1 psia and its quality is 0.9664, not very wet at all.

Also, the above calculations were done assuming that the mass flow rate is constant. Meaning, I've read that some engines would drain the receivers of any condensate to help keep the steam dry.

Joe

 

[Bill West]

Sorry I missed your post last Monday, Joe!

For the port dimensions let’s start with a co-relation of the figures in the French journal:
From Engineering (London 1866- ) Vol 97 Feb 27 1914, ISSN: 0013-7782, between pgs 278-279
plate 28-
Fig 31 engine side elevation------------------French figure 1
Fig 32 engine top view------------------------French figure 4
Fig 33 engine cross section aft of port HP---French figure 3
---------------and aft of Starboard LP-A-----French figure 2
Plate 29-
Fig 34 HP cylinder side cross section--------French figure 6
Fig 35 LP cylinder side cross section---------not in French journal??
Plate 30-
Fig 36 LP valve end cross section------------French figure 5

Engineering Fig 31 & 33 have more identification of the controls, and which engine they are on than the French journal. And Fig 34 & 36 have a few more dimensions. French figures 1-6 are the ones that were on the HospitalShipBritannic site.

I deduce that you are short the figures from plates 29 & 30. They are where I enlarged the cross sections to a nice scale and found that the port and spool dimensions could be readily measured. When I ran the valve gear program it become clear that any uncertainty about the measurements, that is under ½ inch, is not going to make a big difference in timing. At least not so big that it couldn’t be covered by just linking the engine up a bit.

I’m presently placing a scan of the engine cross section drawing into CAD so I can trace some of the valve gear measurements more closely. This may result in refining the data file I posted 2 weeks ago, but I don’t think it will make a radical change.

For the exhaust valve opening and closing times get the valve gear program running. It calculates and graphs all the valve events and instantly refigures them if you want to try a different cutoff. If you hand step the engine the program precisely displays the valve position for any crank angle. It even draws PV diagrams with both cylinder ends overlaid, running forward and reverse if you want. The only trivial downside was that I could only print them with a time delayed screen capture from a PaintShop program. For the compression interval one of the period texts discusses it’s setting, it seemed to get around to an estimate of the piston momentum that needs to be absorbed to avoid knocking at the end of the stroke.

By the way, nice catch on the big Mollier chart. I got lazy however and got Excel to do my look ups and interpolations in an old set of steam tables that I got from the Internet Archive. I could then write performance calculations and when I try alternate cutoffs and the like, Excel automatically gets the correct properties values for me. I can find the cutoff that gives a particular exhaust condition by some very quick trial and error. I can also keep track of the BTU work and the PV work at the same time so that I end up at feasible exhaust locations on the chart. That seemed to resolve a lot of the condensation/reevaporation issue. I get a big condensation drop and then reevaporation brings the enthalpy back up so that there is just enough net drop to account for the PV work. If you run Excel I could send you a copy of the file.

Bill