1 UNDULATIONS & 3:1 EXPANSION RATIO
FRASCA ROTARY ENGINE DESIGN PROGRAMS. Version 98-2e. Copyr., 1986-2000 by Joseph F. Frasca
THE PROGRAMS WILL NOT FUNCTION OUTSIDE OF THE DIRECTORY (FOLDER) FRASCA.
Heat transfer program sections are not included.
|1FRASCA||This program is used to indicate the engine's basic physical characteristics.|
|2FRASCA||This program is used for partition design
of the cam-partition hydrodynamic interaction data.
This program need not be run for the other programs to function properly; i.e. its data is not needed.
|3FRASCA||This program is used for the engine's
and operating environment data and must be run before programs
Program 8FRASCA can be used immediately after this program for the graph of its data.
|4FRASCA||This program generates the basic
for the engine.
Program 8FRASCA can be used immediately after this program to graph the generated data.
|5FRASCA||This program generates the engine's
Program 8FRASCA can be used immediately after this program to graph the generated data.
|6FRASCA||This program determines the engines axial bearing loads, annular cavity circumferences, and the annular cavity and its sections centroid radii and their location.|
|8FRASCA||This program can be used after the programs 3FRASCA, 4FRASCA, and 5FRASCA to graph the VVC temperature and pressure data generated by the respective program sections.|
|CRFRASCA||This program is used to generate the basic design data for an engine with a circular section annular cavity profile and the engine's VVC volume polynomials.|
3:1 EXPANSION RATIO
( FRE ) Frasca Rotary Engine
|PROGRAM SECTION: 1FRASCA SCROLL RIGHT & SCROLL DOWN FOR DATA|
With the selections on this screen are determined whether the 2 cycle engine is a standard cycle type, selection 1 or a Very Low Pressure engine design, selections 2 through 9.
When the latter is selected, the ratio of variable volume to constant volume fuel injection is set along with the arc size between the intake and combustion region.
Unless fuel flame characteristics demand otherwise, choose one of the shorter intervals. (e.g. 6,7,8,9)
These selections reduce partition acceleration and combustion mass loss under constant volume (no work) conditions.
i1) Select the shortest region. Enter 9
i2) Enter a serial number to help track data.
To this point we've selected a very low pressure engine design with 1 undulation and the shortest
available intake and fuel injection region.
Therefore, most injection occurs during VVV expansions; i.e. while the VVC are performing work.
We next -with reference to the design manual discussions- select the actual design dimensions of the
i1) Enter the engine's major radius. Enter: 7" (Enter numbers without the dimension symbols.)
i2) Enter the partition's minimum radius in the annular cavity. Enter: 2"
i3) Enter the number of VVC (working chambers) in the engine. Enter: 8
i4) Enter the partitions' minimum angular extension into the VVC. Enter: 16°.
i5) Enter the partitions' maximum angular movement in the annular cavity. Enter: 20°.
i6) Enter the face surface angle. Enter: 135°.
Here the rotor has a 45° conic section like shape with the wave surface on its outer conic surface.
i7) Enter the partitions' maximum radius in the annular cavity. Enter: 7"
i8) Enter the partitions minimum thickness (at its very tip). Enter (x 1/31): 1
When the tapered partition design is selected later, this will be the partition thickness at the taper end.
Next displayed is the range of possible VVC volume ratios for the engine.
The value entered here closely determines the engine's expansion ratio.
To high a ratio here, and the engine dump pressure will be lower then atmospheric pressure and the program section 5FRASCA will abort.
To low a ratio, and an inefficient engine results.
Inherent with the low pressure in the VVC at the end of the combustion region (dump pressure) is quite engine operation.
Also displayed immediately below the input line for the VVC volume ratio are the engine SN and the partitions' actual minimum and maximum radii in the engine cavity.
i9) Enter the maximum to minimum volume ratio. Enter: 3
The program next generates and displays basic engine data.
The displayed information is generally self-explanatory.
The VVC volumes A(45) & A(46) are determined with partition thickness set to 0.
The adjusted VVC volumes A(41) & A(42) are determined with partition thickness set at their minimum thickness.
The engine intake per revolution utilizes the latter values.
On this screen the partition material and pivot bearing information are selected.
i1) Partition material selections. Enter for SiC : 10
Silicon Carbide ceramic is the optimum chose here, given the lack of heat transfer programming.
It is very light and strong, and most importantly has excellent heat conductivity.
After a material is selected the screen displays its the physical properties which are used later in the programing to determine the partition's taper.
Although hydraulic bearings designs, with their minimal dimensional requirements, their high effectiveness with oscillating loads (squeeze load response) and their lubricants usability as a cooling medium are preferred,
the pivot bearing design for partition taper determination is comprised of a radial bearing at the partition pivot axis in a mating partition hole and co-axial thrust bearings flanking the partition sides.
i2) Enter a partition's pivot radial bearing outside radius. Enter .25"
i3) Enter a partition's thrust bearing outside radius. Enter 1"
i4) Enter a partition's thrust bearing load radius. Enter .9"
Further self explanatory engine dimension data is also then displayed.
On this screen the ambient air pressure and temperature are enter.
(where the engine operation is expected to occur.)
The screen then displays the intake temperature and pressure as if the engine had standard 2 cycle operation and gives a warning that purging is extant.
i1) Enter the ambient pressure. Enter (p.s.i.): 14.7
i2) Enter the ambient temperature. Enter (F°): 110
i3) Enter the ambient pressure as the intake pressure. Enter (p.s.i.): 14.7
i4) Enter the ambient temperature as the intake pressure. Enter (F°): 110
With the above information, the program generates & displays the thermodynamic properties of dry air at intake.
The program next generates and displays the thermodynamic properties of the VVC under the constant and variable volume conditions using the Sweigert & Beardsley equations to adjust the Specific heats increment by increment.
This data will next be used with the partition material characteristics acquired earlier in the program to determine the loads on the partitions and their subsequent required thickness and taper, or at the program users discretion the partition's through and through thickness.
This screen displays acquisition of the required partition thickness.
It then requires a response to the query whether the pseudo or actual area data should be used to determine the partition taper.
i1) For taper by Tmax (thickness) [L(12)] rather then L(11) enter 1. Enter 1.
The program then displays the partition stresses and the required partition taper angle in degrees and permits selection of the alternative constant thickness partition.
i2) For a constant thickness partition at approximately 5.4 x 1/32" enter 1. Press Enter.
Find below the data screen, SCREEN 7X, for an engine design without partition taper.
Now using the partitions new volume the program regenerates and displays for the last time the final dimensional properties.
Also displayed are the thermodynamic properties used in the the above determinations along with some non relative HT data.
We now select the flat partition rather then the tapered and generate a data set parallel to the topic VLP FRE for comparison.
Generally the flat partition design data will be on a green background and suffixed with an "X".
In the Very Low Pressure FRE, the flat partition engine design is the most effective design path.
When manufacturing cost and simplicity of construction are considered, the minor detriment to engine performance by using flat partitions is more then justified.
i1) For taper by Tmax (thickness) [L(12)] rather then L(11) enter 1. Enter 1.
i2) For a constant thickness partition at approximately 5.4 x 1/32" enter 1. Enter 1.
Note that in the case of the VLP FRE the displacement difference between the tapered and flat partition designs is minor.
The final engine dimensional data with flat partitions follows as:
Program section 2FRASCA is used to determine the necessary partition guide's hydrodynamic bearing characteristics along with the partition's moment of inertia and other critical design parameters.
Where the partition displacement is effected by co-action between a guide spring and guide rotor cam-bearing interaction, the spring parameters are also determined.
Although a second rotor cam and larger lubricant supply are required, engines with partitions having both a proximal and distal guide each with a hydrodynamic bearing which together co-act to effect pivotal displacement should be much less costly to manufacture and much more durable.
The partition guide orientation is selected on this screen.
i1) Select the proximal guide partition by entering: `A'.
The partition's dimensions critical to its pivoting are entered on this screen.
i1) The partition guide's thickness is entered as: .12".
i2) The partition guide's width is entered as : .5".
i3) The rotor cam minimum radius is entered as: 5.5"
i4) The maximum rotor cam grade angle is entered as: 12 degrees.
i5) The partition guide's CCW angle to the rotor axis is entered as: 20 degrees.
With the above information the program determines the maximum allowed guide length as 8.77 inches.
i6) The actual partition guide length is entered as: 6"
Next the program requires the added bearing length beyond the guide thickness.
i7) Entered the added bearing length as (x/32): 14
The program next test the actual rotor cam grade and indicates the +/- guide bearing arc angle minimum requirement and requires an entry of the actual bearing angle selected.
i8) Enter the +/- bearing arc angle as: 11.6 degrees.
The bearing width is next required by the program.
i9) Enter for the bearing width: .5".
The program next displays information relative the bearing operation and lubrication.
Only classical lubricants are used for emulation of the hydrodynamic bearing operation.
New surface treatments and synthetic lubricants/additives when used should permit a significant increase in the engine's actual maximum operating RPM.
The operating RPM displayed on this screen are very rough approximations, as will be demonstrated later in the program.
Enhanced cooling and lower partition inertia are made possible in the program by removing the center third of a partition's strut in very large engines; i.e. the strut is supplied with a cooling vent.
The program asks if this vent is wanted.
i10) Enter for partition vent: "N"
The program next permits the entry of a unique partition inertial moment.
i11) Skip this inertia entry branch by pressing: ENTER.
The program completes the screen by displaying the partition's moment of inertia along with other relative design constants.
The entries for the flat partition with exception of the bearing length are keep the same as for the tapered partition in the above data.
Anticipating an increased moment of inertia for the flat partition the following values are increased.
i6) The actual partition guide length is entered as: 6.5"
i7) Entered the added bearing length as (x/32): 22
i8) Enter the +/- bearing arc angle as: 12.1 degrees.
Note the difference in partition inertial moment. 00041575 slug-ft² to 00078798 slug-ft²
This screen displays the current guide bearing width and requires the entry of the value to be used.
i1) Enter the displayed current value for the desired value of the bearing width: .5"
This screen first displays the acquired spring characteristics.
Although the bearing cam losses are not that significant, this is probably the most important part of the program.
At the highest possible engine RPM the hydrodynamic bearing must function!
When the lubricant lamina thickness (qth) drops below about 1/10000 "- the program locks up and the program section must be repeated for a new bearing design which will meet the demands of the maximum engine RPM. Increasing the bearing width and length is the quickest fix for this problem; however, cam grade, minimum cam radius, and partition guide angle are also among the other determinate characteristics.
This program section takes a bit of time.
i1) Enter the test rpm: 6000
The program next proceeds to assess a partition's hydrodynamic bearing operating characteristics at the 24000 increments in its complete traverse of the annular cavity.
Note that the flat partition bearing minimum fluid lamina is still less the for the taper partition above. Therefore, the values entered in screen BX might want tweaking.
4FRASCA & 5FRASCA
These program sections contain their own annotation. These annotation screens are skipped here.
Keep in mind the Sweigert-Beardsley equations for Cp variation with temperature date back to the 1938.
Newer and more accurate empirical formulae are now available.
Engine performance data are displayed for 1800, 3600 and 5400 RPM.
Its advisable to save the acquired data to this point in a separate folder to avoid data cross talk when changing values of RPM, fuel type, % air, etc. when running the engine power series programs.
E.g. Make a directory (folder) in the FRASCA directory (folder) Data.
SCREEN 1 (1800 RPM)
This program section generates and displays, in addition to the particular data needed by the program, a great deal of additional information about the initial intake air.
The program first asks if a different ambient temperature is desired for the engine performance data generation, then asks for the relative humidity of the intake air.
i1) To enter a different ambient temperature; otherwise press: ENTER
i2) Enter the relative humidity: 68%
With this information the program determines and displays information including the intake air content, its thermodynamic properties, and the intake air mass.
The program next requires the size of the gap at the partition edge at the rotor wave surface.
i3) Gap (x.001") enter: 2
Next the engine operating RPM for the power generation emulation run is entered:
i4) Test RPM: 1800
Next the screen displays the particular number of increment per VVC that are usable in the compression-
combustion emulation for the current engine design. In the current instant the selections are: 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, 144, 156 and 168.
i5) Enter number of tests per chamber: 168
The circumferential bleed-by gaps (pgap) are entered next. Assuming some type of dynamic flow limiting arrangement multiples of 0.0001" are selected.
i6) Enter (x .0001"): 2
As with the circumferential bleed-by gaps the partition framing slot gap (Fgap) is also entered in multiples of 0.0001".
i7) The partition framing bleed-by gap is entered as .0001 x enter: 2
|SCREEN 1 (For
engine with tapered partitions)
1X (For engine with flat partition)
(Tapered partition engine at 1800 rpm)
In program section 4FRASCA, the engine's fuel is selected from a menu of 20 fuels and the air-fuel ratio is entered as a percentage.
ir-fuel ratio example: 120% air is 120% of the air required for the theoretical complete combustion of the selected fuel.
Using this information the VVC thermodynamic characteristics (insulated with no mass loss processes) are assessed increment by increment in their traverse of the combustion region and the program determines the effective energy (Btu) per pound mass air for the fuel in the particular engine design.
Further explanation of this process is within the program itself.
Program section 6Frasca, generates a large quantity of nut and bolts information, including the main bearing loads, annular cavity circumference lengths which are critical for flow limiter designs and annular cavity centroid information which is critical to engine rotor balancing. To determine the main bearing loads with a good safety margin you'll want to generate special engine data using 3FRASCA, 4FRASCA, and 5FRASCA with the gaps, Fgaps and Pgaps zeroed in program 3FRASCA. Save the current engine data in a separate folder for later retrieval, then start 3FRASCA again. Program 6FRASCA data is self explaining.
In single undulation and 4 cycle engines, ganging ( i.e. sharing the same power shaft) two rotors will cancel all bearing loading moments and power shaft directed forces ( Z-axis forces) leaving only a force perpendicular to and rotating with the rotor shaft when:
the rotors' power cycles are in phase,
the rotors' wave surfaces are directed towards the opposite ends of the power shaft,
the X-Z and Y-Z planes of the 2 rotor coordinate systems are coincident,
the positive X axii of the two rotor coordinate systems point in the same direction from the rotor axis, and
the positive Y axii of the two rotor coordinate systems point in the same direction from the rotor axis.
|6FRASCA MAIN MENU|
|6FRASCA ENGINE MAIN BEARING LOADS|
|6FRASCA CIRCUMFERENTIAL LENGTHS|
|6FRASCA ROTOR CENTROID INFORMATION|