The contents of this page are from "ELEMENTS OF FRASCA ROTARY ENGINE DESIGN"*
*Copyright © 1998 by Joseph F. Frasca


A Frasca Rotary Engine has a casing and a rotor in the casing.

The rotor is journaled to rotate in the casing and has a power output shaft.

A continuous annular cavity about the rotor output shaft axis (i.e. rotor axis) is formed by and between the rotor and casing in the FRE.

The surfaces forming the annular cavity are the wave surface on the rotor and the face surface on the casing.

There is a hollow ring like space formed between the casing and the rotor around the power shaft axis.
The ring's walls are part casing surface and across from the casing surface, part rotor surface.

The casing has a plurality of circumferential spaced slots which extend radial to the rotor axis.

A partition element is mounted in each slot for pivotal extension into the annular cavity.

The partition pivot points are a constant radial distance from the power output shafts axis and a circle about said axis which includes the partition pivot points is referred to as the pivot circumference.

The annular cavity [ i.e. the annular space about the rotor axis formed by and between rotor wave surface and the casing face surface ] may have different orientations about the pivot circumference in different FRE designs.

This annular cavity orientation is indicated by the face surface angle.

The partitions form a plurality of spaced VVC in the annular cavity circumferential the rotor axis.

A Volume Varying Chamber [ i.e. a working chamber] is formed by and between consecutive partitions in the annular cavity and the cavity walls.

The high temperature power generating cycles of the FRE occur in each VVC during its cyclical traverse of the annular cavity with rotor rotation.

The engine rotor has fuel injectors and intake and exhaust channeling.

The casing has intake and exhaust channeling always communicating with their respective rotor counterparts.

The annular cavity has at least one undulation in volume (i.e. a variation in cross section area from one location to another) caused by an undulation [in] the rotor wave surface of the cavity and the annular cavity undulation rotates with the rotor about the rotor axis.

Each partition extends pivotally into the annular cavity through its slot in the casing's annular cavity surface; i.e. the face surface.

The partition pivotal motion is effected by rotor cams or a rotor cam-spring (or other loading means) combination located outside of the annular cavity and the high temperature and pressure extremes therein.

Each partition's edge(s) shape proximal to the rotor wave surface (i.e. the partitions' gap edge) conforms with the wave surface shape and never abuts the wave surface.

There is always a gap between a partition's edge at the wave surface and the wave surface.

With (rotor rotation) annular cavity rotation, the rotor cam surface varies each partition's pivotal extension into the annular cavity so [that each partition ]( it) remains very close to the rotor wave surface in annular cavity compression and combustion regions.

The VVC volumes' vary as the annular cavity undulation traverse their fixed positions.

With the ring's rotation with the rotor, the rotor's cam mechanisms pivot the partition into and out of the ring so that they remain close to and maintain a gap with the rotor's ring surface (the wave surface).

The working chambers (VVC) in the ring therefore vary in volume as the ring moves by their casing locations.

Two cycle engines have at least one undulation, the combustion undulation, which, with rotor rotation, traverses each VVC location causing the VVC's cyclic variation in volume.

The ring's rotor surface (the wave surface) in a two cycle engine has a variation in distance from the ring's casing surface (the face surface) called the combustion undulation.

The combustion undulation, rotating with the rotor, moves by a working chamber's location causing its change in volume.

Fixing our observation point to the annular cavity, the VVC are seen to rotate while the cavity remains fixed.

With said rotation, each VVC during its traverse from the beginning to end of a 2-cycle combustion undulation communicates first with the high pressure air intake port, then a VVC arc distance along (an isolation region) in its traverse, [the VVC] is fuel injected.

On fuel injection, the VVC's fuel-air mixture is ignited by the flow of combustion involved mass  through the gap at the partition separating it from its neighboring VVC preceding it in annular cavity traverse.

The pressure of the combustion involved gases in the VVC, acting on the rotor wave surface, drive the rotor in rotation while the VVC with said rotation increases in volume and continues its traverse of the undulation.

The arc portion of an annular cavity combustion undulation from a VVC's fuel injection to the end of its volume increase is referred to as the cavity's or combustion undulation's "combustion region".

FRE not depending on auto ignition ( i.e. FRE not operating on a diesel [type] cycle) have an ignitor to initiate combustion in the annular cavity; thereafter, each VVC's air-fuel mixture is ignited on fuel injection by the flow of flames from the VVC preceding it in the combustion region through the ever present gap between their common partition and rotor wave surface.

With further traverse of the annular cavity, the VVC decreases in volume and while doing so it expels its products of combustion to outside the engine via the cavity undulation's exhaust port in the rotor wave surface.

From the exhaust port the combustion products are conveyed by the rotor exhaust channeling to casing exhaust channeling to outside the engine.

Continuing its annular cavity traverse (combustion undulation traverse), the VVC arrives at minimum volume in the annular cavity and thereafter traverses the cavity arc necessary to isolate the rotor's exhaust port from the high pressure intake port, usually a VVC arc.

After traverse of this isolation region, the VVC again communicates with the high pressure intake port and begins again the power generating cycle.

The arc portion of an annular cavity combustion undulation in which a traversing VVC decreases in volume is referred to as the cavity's or combustion undulation's "exhaust region".

The 4-cycle version of the FRE has, in addition to a combustion undulation, a compression undulation in its annular cavity.

A VVC entering the compression undulation in its traverse of the annular cavity first increases in volume and while increasing in volume communicates with a fresh air intake port in the rotor supplied by corresponding casing channeling.

Then, on arriving at maximum volume, the VVC's communication with the rotor's fresh air intake port ends and the VVC's volume begins decreasing while the rotor works to compress its fresh air contents.

Arriving at minimum volume in its compression undulation traverse the VVC then enter the engine cavity's isolation-injection-ignition region.

The first part of the IIIR, the isolation region, assures that VVC fuel injection occurs when the VVC is effectively out of the compression undulation.

Beyond this isolation region in its annular cavity traverse, the VVC is in the annular cavity combustion undulation where it functions like a VVC in the 2-cycle engine combustion undulation.

Sealing and wiping abutments between relatively moving surfaces of the FRE's VVC are not extant and are replaced by very small clearances which permit free unobstructed relative motion between said surface.

These clearances eliminate parts wear, inter-part heat transfer and wiping friction power losses.

The engine wear and friction power losses eliminated in Frasca Rotary Engine designs are replaced with a permitted, albeit, smaller power loss resultant the mass flow from the VVC via said clearances.

FRE with two different annular cavity profiles are discussed in this manual.

The engine design most developed has an annular cavity profile based on the partition radius formula: r = a + N, and the second, the CIR engine design, has a circular section for an annular cavity profile.

The CIR engine design relies on a set of twenty-four, forty-one term expansions to accurately determine a VVC's volume at any location in the annular cavity.

Acquisition of the coefficients for these expansions using an 8088 PC without NPU took a full day back when I was doing the basic engineering design work for the engines; therefore, a fuller development of the CIR engine design was ignored.

However, today using a reasonably modern PC, it takes less then a minute to generate those same expansion coefficients.

The CIR engine has the particular attraction of allowing very large engine displacements with very small partition displacements < 5 degrees .

Similar engine displacements in the first engine type would require partition displacements of 20 degrees and greater

Of course in such CIR engines, the partitions' inertial loads to the rotor cam surface will be very large; however, use of partitions with distal guides should significantly reduce this rotor cam load.

The very low pressure FRE, with its large tolerances, lower operating temperatures and low working pressures should prove an excellent engine systems test bed.