Patent Application
20070240419
1. Field of the Invention
The present invention relates to energy conversion devices and, more specifically, to Engines based on the thermodynamic cycle known as the “Stirling cycle”.
2. Description of the Prior Art
Currently, one of the most commonly employed engines is the internal combustion engine. Combustion is the process of burning a fuel gas mixture. In an internal combustion engine combustion takes place within the housing of the engine. This type of engine is widely used, especially within most current cars and trucks. In contrast, combustion in an external combustion engine, such as the steam engine, takes place outside the engine. Internal combustion engines operate on the thermodynamic cycles known as “Otto Cycle” or “diesel cycle”. Internal combustion engines generally use a reciprocating piston configuration to achieve the required thermodynamic processes of the “Otto Cycle”. A piston is displaced within the cylinder achieving intake, compression, combustion and exhaust of the air/fuel mixture. Improvements have been introduced to the internal combustion piston engine based on the “Otto Cycle” by replacing pistons with a rotor that rotates within a housing. This engine is known as the “Wankel engine”.
The rotary engine is made up of a rotor and housing with three distinct compartments formed between the rotor and housing. Each compartment or chamber goes through the four thermodynamic processes of the “Otto Cycle” as the rotor moves through one full revolution. The rotor is triangular in shape and has three corners and three faces. Each compartment is defined by at least one tip of the rotor and the housing. The three compartments each complete the four phases of the combustion cycle during a complete revolution. In one complete revolution of the rotor, there will be three power strokes. The rotor follows a path similar to that created with a Spiro graph when rotating about the housing. This path keeps each of the three peaks of the rotor in contact with the housing, creating a chamber of gas between adjacent peaks and the housing. As the rotor moves around the chamber, each of the three volumes of gas alternately expands and contracts. It is this expansion and contraction that draws air and fuel into the engine, compresses air and fuel and produces power as combustion takes place. Exhaust from the combustion is then expelled. A rotary engine is only similar to a piston engine in that it is an internal combustion engine based on the “Otto cycle”. The air/fuel mixture is drawn into the housing, compressed, expanded by combustion and then expelled to the outside of the engine. However, a rotary engine takes advantage of the efficiency of a rotating motion instead of the reciprocating motion of cylinders to perform the required operation. In a reciprocating motion, a piston moves in one direction, decelerates, and comes to a stop in order to accelerate again in the opposite direction.
The “Stirling engine”, also known as a heat engine, operates on the “Stirling Cycle”. The Stirling cycle is inherently more efficient than the “Otto cycle” but a commercially successful and viable Stirling engine has not yet been introduced as all Stirling engines have been based on a modified piston engine design.
The gas within a Stirling engine goes through the following thermodynamic processes:
1. Constant Volume Heating;
2. Isothermal Heating and Expansion;
3. Constant Volume Cooling; and
4. Isothermal Cooling and Compression.
The Air/Fuel mixture is not introduced within the Stirling engine, as in the combustion engine. Instead heat is generated externally and exchanged with gas within the engine. The gas is therefore sealed within the housing of the engine with no open exchange of air with the area outside the housing. A heat exchange takes place in order to provide heat to the engine in phase 2, “Isothermal Heating and expansion”, of the cycle and another heat exchange takes place to remove heat from the engine in phase 4, “Isothermal Cooling and Compression”. An internal heat transfer process takes place in phase 1, “Constant Volume Heating”, and phase 3, “Constant Volume Cooling”, wherein heat is exchanged between two compartments. The higher temperature gas in within phase 3 of “Constant Volume Cooling” gives off heat which is exchanged with the gas that is going through phase 1 of “Constant Volume Heating”. There is no exchange of gas but only a heat exchange taking place internally within phase 1 and phase 3. Stirling engines are flexible and many heat sources can be incorporated such as combustion of a variety of fossil fuels, solar, geothermal, thermal battery storage, nuclear etc. The “Stirling engines” produce power indiscriminately of the heat source. However, unlike the internal combustion engine, the Stirling engine does not rely on the ability of certain gasses to combust upon ignition to drive the cylinders. Rather, the Stirling engine relies on different processes; mainly the relation of volume and temperature. These properties help in the realization of an engine based on the Stirling cycle.
In the first phase, gas is heated isothermally, causing the gas to increase in pressure and expand, thus increasing the volume of the gas. In the second phase, the gas is cooled while at a constant volume. This cooling is accomplished internally by exchanging heat with the portion of gas passing through the fourth phase of constant volume heating. In the third phase, the gas is cooled isothermally and compressed, reducing the volume of the gas. The isothermal cooling process requires removal of heat and exchange with environment. In the fourth and final phase, the gas is heated at a constant volume by internally exchanging heat with the portion of gas that is going through the second phase of constant volume cooling, thereby increasing the pressure of the gas.
The method employed by the engine according to invention principles allows reproduction of the Stirling cycle within a rotary motion without the use of reciprocating pistons. In this way more power can be produced within a single revolution than with the piston engine. Additionally, there are other benefits associated with Rotary engines such as fewer moving parts, better heat exchange within the hot side and the cold side and better internal heat exchange between both constant volume processes. Therefore, it would be beneficial to implement the methods of the Stirling cycle, usually implemented in a piston configuration, within the configuration of a rotary engine. Thus, there is a need for an efficient piston-free Stirling cycle engine.
An energy conversion device is provided according to invention principles. The device includes a housing. The housing includes a first section of increasing volume and a second section of decreasing volume. The second section is positioned on a side of the housing opposite the first section. A third section of constant volume is positioned between a first end side of the first section and a first end side of the second section. A fourth section of constant volume is positioned between a second end side of the first section and a second end side of the second section on a side of the housing opposite the third section.
Additionally, a method for converting thermal energy into mechanical energy by rotating a rotor within a housing is provided according to invention principles. The rotor forms a plurality of chambers within the housing. The method includes providing and sealing gas within each of the plurality of chambers. Heat is applied to a first set of chambers positioned within a first section of the housing. The gas within the first set of chambers is then expanded. The rotor is rotated in response to the expansion of the gas within the first set of chambers. The rotation of the rotor causes the first set of chambers to rotate into a second constant volume section of the housing and a second adjacent set of chambers to rotate into the first section where the gas therein is heated. Upon cooling of the gas within the first set of chambers, the first set of chambers are caused to rotate into a third decreasing volume section of the housing, the second set of chambers rotates into the second section and a third set of chambers adjacent the second set of chambers rotates into the first section where the gas therein is heated. Upon isothermal heating of the gas within the third set of chambers, the first set of chambers is caused to move into a fourth constant volume section of the housing, the second set of chambers moves into the third section, the third set of chambers moves into the second section and a fourth set of chambers positioned between the third set of chambers and first set of chambers rotates into the first section where the gas contained therein is heated. Upon constant volume heating of the fourth set of chambers, the first set of chambers is caused to rotate back into the first increasing volume section of the housing, the second set moves into the fourth section, the third set moves into the third section and the fourth set moves into the second section.
Further, a method for providing cooling or heating is provided according to invention principles. This method operates according to the principles of the “reverse Stirling cycle”. The rotor forms a plurality of chambers within the housing. The method comprises providing gas sealed within each of a plurality of chambers. The gas within a first set of chambers positioned within a first section of the housing is expanded. This expansion requires the absorption of heat from outside the housing, thus providing a cooling effect. The rotor is rotated. The rotation of the rotor causes the first set of chambers to rotate into a second constant volume section of the housing and an adjacent set of chambers to rotate into the first section to be expanded. Upon expanding the second set of chambers, the first set of chambers is caused to rotate into a third decreasing volume section of the housing, the second set of chambers rotates into the second section and a third set of chambers adjacent to the second set of chambers rotates into the first section to be expanded. The set of chambers moved into the decreasing volume section are compressed, thus releasing heat to the area outside the housing and providing a heating effect. Upon expanding the gas within the third set of chambers, the first set of chambers is caused to rotate into a fourth constant volume section of the housing, the second set of chambers rotates into the third section, the third set of chambers rotates into the second section and a fourth set of chambers adjacent to the third set of chambers rotates into the first section to be expanded. Upon expanding the fourth set of chambers, the first set of chambers rotates into the first increasing volume section of the housing, the second set of chambers rotates into the fourth section, the third set of chambers rotates into the third section and the fourth set of chambers rotates into the second section.
Even further, a piston-free Stirling cycle engine is provided according to invention principles by incorporating the operation of a Stirling cycle within a rotary engine. The engine includes a rotor located within a housing. The rotor is circular in shape and has chambers or vanes extending into the rotor and positioned around the periphery of the rotor. The rotor is connected to a driver and resides within the housing. A blade at least partially extends from each vane and contacts an inner surface of the housing. Compartments are formed between adjacent extended blades, the housing and rotor. Each compartment contains a gas therein. The housing is of a unique shape consisting of four sections having different arcs or four independent quarter circles. A first quarter section and a second quarter section have distinct radii lengths and a common center. The common center is the point about which the rotor rotates. A third quarter section and a fourth quarter section, positioned between the first and second quarter sections, form opposing sides of the housing and have distinct centers and identical radii lengths. The unique housing configuration provided by these four distinct quarter circles allows for realization of the Stirling cycle as the rotor and thus the compartments rotate. As the Stirling cycle requires the alternating application of high temperatures and low temperatures, a heating element may be placed on a first section of the housing and a cooling element may be placed on the opposing side of the housing.
It is an object according to invention principles to provide a piston-free Stirling cycle engine having a unique shape and allowing the more efficient Stirling cycle to be realized with better thermal and volumetric efficiency.
The foregoing and other objects and advantages will appear from the description to follow. In the description reference is made to the accompanying drawings, which forms a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. In the accompanying drawings, like reference characters designate the same or similar parts throughout the several views.
The following detailed description is, therefore, not to be taken in a limiting sense, and the scope according to invention principles is best defined by the appended claims.
In order that the invention may be more fully understood, it will now be described, by way of example, with reference to the accompanying drawing in which:
a, 1b, 1c are an illustrative view of the housing of the Piston-free Stirling Cycle Engine according to invention principles;
a and 4b are illustrative views of the rotor, housing and blades of the Piston-free Stirling Cycle Engine according to invention principles;
Conventional rotary engines include a housing having an oval shape, more specifically, an epitrochoid shape. This shape is derived so that a triangular shaped rotor will have each of its corners touching a face of the housing at all times. The present system includes a housing having a shape containing four unique quarter circles. The properties associated with the four unique quarter circles are conducive to performing the four thermodynamic processes of the Stirling cycle. A first pair of opposing quarter sections have a common center and distinct radii while a second pair of quarter sections have distinct centers and identical radii. A rotor is positioned within the housing formed by the first and second pair of quarter sections. The rotor includes a plurality of vanes positioned around a periphery thereof. A blade movably is positioned within each vane.
According to invention principles the rotor rotates about the common center of the first pair of opposing quarter sections. As the quarter sections have different radii, the blades extend from and retract into the slots of the rotor so that the ends of two diametrically opposed blades have a fixed and constant dimension throughout the full rotation and thus the ends of two diametrically opposed blades are constantly in contact with the inner surface of the housing throughout the full rotation. Gas is provided within the area between blades, housing and rotor and the sealed gas rotates with the rotor and blades. Each quarter of the housing has a different volume. Therefore, as the areas of gas rotate within the housing, the volume of each area in which the gas is contained changes based upon the quarter of the housing in which the gas is positioned. This variation in volume contributes to the four stages of the Stirling cycle. The first stage of the Stirling cycle, isothermal heating and expansion, is accomplished when an area of gas is rotated through a first quarter section having a heating element mounted thereto and where the area in which the gas is contained increases. The second stage of the Stirling cycle, constant volume cooling, is accomplished when the area of gas remains constant as it is rotated through a second quarter section adjacent to the first quarter section. The second quarter section has a larger radius and therefore a larger area than the first quarter section. The third stage of the Stirling cycle, isothermal cooling and compression, is accomplished when the area of gas is rotated into a third quarter section having a cooling element mounted thereto and the area in which the gas is contained diminishes. The fourth stage of the Stirling cycle, constant volume heating, is accomplished when the area of gas is rotated into a fourth quarter section having a smaller radius and smaller area than the third quarter section and the area remains constant.
Thus, the induced temperature difference is converted from thermal energy into mechanical energy. This rotational energy may be utilized by connecting equipment to the center of the rotor. Alternatively, the heating and cooling elements may be removed and a driver may be connected to the rotor for rotating the rotor. Thus, a rotational motion is introduced by the driver which is converted into thermal energy. The thermal energy is released and realized at the first and third quarter sections. This thermal energy may be utilized by systems requiring above or below normal temperatures.
Turning now to the drawings, in which similar reference characters denote similar elements throughout the several views,
The geometry of the enclosed housing is defined by quarter circles. We shall then define the quarter circles using two distinct methods. First method, the most commonly known is to define a circle by distinctly defining a center and a radius. Therefore any given circle can be defined by its radius and its center point and the quarter circle being defined as one quarter of the periphery of that circle. Second method used is by defining three non-linear distinct points. Any given distinct circle can be defined as an arc going through three non-linear distinct points.
a, 1b, 1c are illustrative views of how the inner housing of the Piston-free Stirling cycle is composed according to invention principles. The Housing is formed from four unique quarter circles called QC1, QC2, QC3, QC4. The quarter circles are defined in relation to a horizontal axis X′X, a vertical axis Y′Y and intersection or origin O as indicated in
Circle C1 is shown in
Circle C3 is shown in
Point E is located on the axis X′X at a mid point or mid distance between points B′ and C′. Point F is located on the axis X′X at a mid point or mid distance between points A′ and D′. (See
QC2 and QC4 are shown in
Any line going through the center O and intersecting the housing at two opposed points will have a constant distance between these two opposing points.
A blade 16 is slideably positioned within each vane 14, as illustrated in
b is an illustrative view of the rotor 12 and housing 10 of the Piston-free Stirling Cycle Engine according to invention principles wherein the vanes 18 extend through a diameter of the rotor 12. As previously discussed in
When the temperature of the gas in the first region 22 is increased by external heating element 30, causing the rotor 12 to rotate, the compartments 38 of gas within the first region 22 expand into a second region of larger but constant volume 24. Simultaneously, the pre-expanded compartments 38 of gas which were previously in the second region 24 are rotated into a third region 26. The third region 26 is of an asymmetrical and decreasing shape. The volume of a compartment 38 in the third region 26 decreases as the rotor 12 is rotated in a counter clockwise direction. Thus, as the compartments 38 of gas in the second region 24 are rotated into the third region 26 they are compressed. This compression causes the temperature of the gas to increase. This increase in temperature is balanced by cooling element 32. Cooling element 32 decreases the temperature of the gas in the compartments 38 as they pass through the third region 26. Simultaneously, the compressed gas in the compartments previously in the third region 26 is rotated into a fourth region of smaller but constant volume 28. The compressed gas in the compartments previously in the fourth region 28 is simultaneously rotated into the first region 22 where its temperature is increased due to the heating element 30 and the Stirling cycle begins anew for the compartments rotated into the first region. Therefore, each region (22, 24, 26 and 28) of the housing 10 is responsible for a respective phase of the Stirling cycle.
The second 24 and the fourth 28 regions require a direct or indirect internal heat exchange. In existing Stirling engines, heat exchange is performed by a regenerator (not shown). Alternatively, the heat exchange may be performed by a pipe connected and filled with. In
A driver 34 is connected to the center of rotor 12, located at center point 0 (as illustrated in
Compartments of warm compressed gas are rotated into a first section of increasing volume as described in step S 120. As the rotor rotates, thus moving compartments of gas from the fourth section into the first section, a heat source increases the temperature of the compartments of gas. This rise in temperature causes the gas to expand. The expansion of the gas causes the rotor and thus the compartments of gas in the first section to rotate into a second larger section of constant volume as stated in step S130. The heated expanded compartments of gas in the second section undergo an internal heat exchange with cooled compressed compartments of gas in a fourth section. Thus, the heated expanded compartments of gas are cooled at a constant volume in the second section. The cooled expanded compartments of gas are then rotated into a third section of decreasing volume as discussed in step S140. As the cooled expanded compartments of gas are rotated into an area of decreased volume, the compartments of gas are compressed. This compression of gas causes the compartments of gas to give off heat as they enter the third section. To offset this increase in temperature, a cooling source is operable to decrease the temperature of the compartments of gas in the third section. The cooled compressed compartments of gas are then rotated from the third section into a fourth smaller section of constant volume in step S150. The cooled compressed compartments of gas in the fourth section undergo an internal heat exchange with the heated expanded compartments of gas in the second section. Thus, the cooled compressed compartments of gas are heated at a constant volume in the fourth section. The heated compressed compartments of gas are then rotated into the first section of increasing volume as stated in step S120 and the Stirling cycle begins anew. This process repeats until heat ceases to be applied in step S100. each set of compartments passes through a respective cycle of the Stirling cycle offset by one cycle from the immediately adjacent sets of compartments and offset by two cycles from the opposing set of compartments.
Gas is rotated into a first section of increasing volume as stated in step S210. This is an isothermal expansion. Heat is absorbed during isothermal expansion of the gas. This absorption of heat causes a cooling effect by the first section. The heated expanded compartments of gas are rotated into a second larger section of constant volume as discussed in step S220. The heated expanded compartments of gas of the second section undergo an internal heat exchange with cooled compressed compartments of gas in a fourth section. Thus, the heated expanded compartments of gas are cooled at a constant volume in the second section. The cooled expanded compartments of gas are then rotated into a third section of decreasing volume as described in step S230. As compartments of gas enter the third section of decreasing volume, the gas is compressed. The compression of gas increases its temperature. Thus, the compartments of gas release heat as they are compressed in the third section. In that section heat must be removed from the engine by means of a heat exchanger or radiator. The compressed gas compartments are rotated into a fourth smaller section of constant volume as stated in step S240. The compressed compartments of gas of the fourth section undergo an internal heat exchange with the heated expanded compartments of gas in the second section. Thus, the cooled compressed compartments of gas are heated at a constant volume in the fourth section. The heated compressed compartments of gas are then rotated back into the first section of increasing volume as described in step S210 and the Reverse Stirling cycle begins anew until the rotor ceases to be rotated in step S200. The usual thermodynamic convention is followed in which heat is removed from the environment exposed to portion of engine of increasing gas volume S210 and heat is expelled into the environment exposed to portion of the engine of decreasing gas volume as shown in step S230. Internal heat exchanges are crucial for proper function of the refrigeration cycle. This is accomplished by exchanging heat, thereby removing heat from the constant Volume Cooling section S220 and exchanging it with the constant volume heating section S240.
While certain novel features of this invention have been shown and described and are pointed out in the annexed claims, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit according to invention principles.
Without further analysis, the foregoing will so fully reveal the gist according to invention principles that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.
