CN104481726A - Three-piston type free-piston stirling engine - Google Patents

Abstract

A three-piston free-piston Stirling engine belongs to the field of heat engine utilization. It includes a liquid metal heating cap (12), a gas distribution piston cylinder, a first gas distribution piston (15) and a second gas distribution piston (18), a power piston cylinder (19), a power piston (20), and a generator assembly. The gas distribution piston is divided into two parts, and the leaf spring (17) of the gas distribution piston is suspended between the two parts of the gas distribution piston to provide the restoring force of the gas distribution piston; the heating head outside the cylinder of the gas distribution piston is filled with a The liquid metal heating cap (12) whose phase change temperature is equal to the temperature of the heat source makes the engine run stably without fluctuations in the temperature of the heat source. There is a swirl heater (14) inside the cylinder of the gas distribution piston to strengthen the heating of the gas in the cylinder. The invention divides the gas distribution piston into two parts, which makes the suspension and installation of the leaf spring simple, and at the same time reduces the heat conduction loss of the gas distribution piston. Therefore, the whole engine has the advantages of simple structure, no difficulty in installing the leaf spring, and high thermal efficiency.

Description

Three-piston free-piston Stirling engine

Technical field

The invention relates to a three-piston free-piston Stirling engine, which belongs to the field of heat engine utilization.

Background technique

The Stirling Engine is an externally heated closed-cycle piston engine. In this type of machine, the working medium (generally hydrogen, helium or air) is enclosed in the circulation loop, and the flow direction of the working medium in the closed circulation loop is controlled by the variable ratio of the cylinder volume; at lower temperatures and The working fluid is compressed under pressure and expanded under higher temperature and pressure to obtain positive cycle work. Its thermodynamic process is carried out according to the Stirling cycle.

The free-piston Stirling engine is an important branch of the Stirling engine, and it is a power device that realizes a thermodynamic cycle by the reciprocating motion of the piston. This motion is due to gas forces and the interaction of gas forces and dynamics between components. It works as follows:

A free-piston Stirling engine basically consists of three parts: a heavy power piston, a light distribution piston, and a cylinder sealed at both ends. A common free-piston Stirling engine consists of a valve piston rod passing through a power piston. Since the gas distribution piston and the gas distribution piston rod are hollow, and the lower end of the rod is open, the inside of the gas distribution piston and the cylinder volume below the power piston together form a buffer cavity, which becomes a gas spring to return the gas distribution piston. The head of the gas distribution piston is an expansion chamber, and the space between the gas distribution piston and the power piston is a compression chamber, and the expansion chamber and compression chamber are collectively called the working chamber. The long and narrow gap between the inner cylinder and the outer cylinder of the gas distribution piston cylinder is composed of a heating chamber, a regenerator and a cooler from right to left. The heater and the cooler communicate with the expansion chamber and the compression chamber respectively.

The traditional free-piston Stirling engine uses a gas spring as the restoring force of the piston, which is not only bulky, but also the piston that the gas spring acts on will drift without any mechanical fixation, so that the gas distribution piston and the power piston are close together or separately ends, thus losing power. In order to overcome this problem, the Stirling Company of the Netherlands and others have adopted many complicated control methods. The technology of Infinia's free-piston Stirling engine that uses leaf springs instead of gas springs is relatively mature, and the first prototype was tested in October 2007. Based on the technology of Sunpower's 1kW free-piston Stirling engine with leaf springs, Microgen has developed a miniature home combined heat and power system (MCHP). However, the control and structure of these free-piston Stirling engines with gas springs are complicated at present; the structure in which the gas distribution piston rod passes through the power piston will reduce the sealing performance in the compression chamber and the installation is complicated; the board represented by Infinia Spring free piston Stirling engine leaf spring system is complicated to install, especially for small free piston Stirling engines, the diameter of the gas distribution piston cylinder is very small, the installation of the leaf spring system is difficult, and the diameter of the leaf spring is smaller than the diameter of the gas distribution piston cylinder It should be small, so that the displacement of the leaf spring is small, and the displacement distance of the gas distribution piston is limited.

Since the working fluid of the free-piston Stirling engine generally uses inert gases such as helium, its thermal conductivity is low, and it absorbs and releases heat back and forth in the heating chamber and cooler to generate a temperature difference to perform a thermodynamic cycle to drive the power piston to do work. And the frequency is around 50Hz, so its rapid heat absorption and heat release is very necessary. In order to make the working fluid absorb heat to the maximum in one cycle in the heating chamber, it is necessary to strengthen the heat exchange device. The use of porous media and cyclones in the heating chamber is a very good means of enhancing heat exchange with high efficiency. When the swirler piston moves to the heating chamber, the gas will generate a swirl, so that the working gas can rotate rapidly to generate a vortex, improve the heating capacity and temperature uniformity of the gas, and increase the power density and stability of the engine.

Contents of the invention

The purpose of the present invention is mainly to propose a two-section piston plate that can overcome the problems of complex control and structure of the gas spring of the traditional free piston Stirling engine, as well as the shortcomings of the plate spring system represented by Infinia Company, such as complicated installation and large useless volume. A new type of free-piston Stirling engine with reed system installation and a heating head with a high-efficiency swirler. The free-piston Stirling engine is not only simple in processing, low in cost, high in efficiency, but also stable in operation and less disturbed by heat sources Etc.

A three-piston free-piston Stirling engine, which successively includes a gas distribution piston cylinder, a gas distribution piston, a power piston cylinder, a power piston and a generator assembly; the gas distribution piston cylinder includes an outer air and an inner cylinder, and the outer cylinder The interlayer between the inner cylinder and the top is composed of a heating chamber, a regenerator, a cooling chamber and a cooling medium passage from the top to the bottom; the top of the inner cylinder is an open structure; the space between the top of the gas distribution piston and the outer cylinder is an expansion chamber; It is characterized in that: the heating head outside the gas distribution piston cylinder has a liquid metal heating cap filled with liquid metal with a phase change temperature equivalent to the temperature of the heat source, and a swirl heater is installed in the gas distribution piston cylinder; the gas distribution piston Sealed and installed in the inner cylinder, it is divided into the first gas distribution piston and the second gas distribution piston; the first gas distribution piston and the second gas distribution piston are separated by the gas distribution piston leaf spring, and pass through the gas distribution piston leaf spring The gas distribution piston is connected to the connecting rod.

The heating head outside the outer cylinder of the gas distribution piston of the present invention is a liquid metal heating cap filled with a phase transition temperature equivalent to the temperature of the heat source, so that the engine can run stably without fluctuations in the temperature of the heat source, and there is swirl heating inside the gas distribution piston cylinder The device strengthens the gas heating in the cylinder and improves the thermal efficiency of the engine. . The gas distribution piston is divided into two sections, and the gas distribution piston plate spring is between the two sections of the gas distribution piston to provide the restoring force of the gas distribution piston. This method overcomes the shortcomings of traditional gas springs such as large volume, easy drift of the gas distribution piston, complicated installation of the gas distribution piston rod through the power piston and leaf spring, and high requirements for machining accuracy.

The length of the first gas distribution piston is 3-4 times that of the second gas distribution piston. .The first distributing piston is longer to reduce air leakage loss and heat loss, and better isolate the high temperature area in the expansion chamber from the low temperature area in the compression chamber; while the second distributing piston is shorter to reduce the overall The weight and length of the gas distribution piston.

The above-mentioned three-piston free-piston Stirling engine is characterized in that: the swirler can be installed on the top of the first distributing piston or the upper part of the cylinder of the distributing piston.

The three-piston free-piston Stirling engine is characterized in that: the generator assembly includes a generator casing, a power piston rod, a linear generator rotor magnet, and a linear generator stator coil winding; wherein the power piston rod passes through The bearing is supported in the casing of the generator, the upper end of the power piston rod is connected with the power piston, and the lower end of the power piston rod is connected with a leaf spring; the linear generator mover magnet is installed on the power piston rod.

Description of drawings

Fig. 1 is the structural diagram of novel three-piston free-piston Stirling engine;

Label names in the figure: 1. Outer cylinder, 2. Expansion chamber, 3. Inner cylinder, 4. Regenerator, 5. Cooling chamber, 6. Cooling medium channel, 7. Cylinder coupling flange, 8. Compression chamber, 9 . Bearing, 10. Stator coil winding of linear generator, 11. Power piston rod, 12. Heating cap, 13. Liquid metal, 14. Swirl heater, 15. First gas distribution piston, 16. Gas distribution piston connecting rod , 17. Gas distribution piston leaf spring, 18. Second gas distribution piston, 19. Power piston cylinder, 20. Power piston, 21. Linear generator mover, 22. Generator components and housing, 23. Power piston leaf spring.

Detailed ways

The structure of the novel three-piston free-piston Stirling engine of the present invention is further described below in conjunction with FIG. 1 . The gas distribution piston system is composed of double-layer cylinders (outer cylinder 1 and inner cylinder 3), and the interlayer is composed of expansion chamber (heating chamber) 2, regenerator 4 and cooling chamber 5 respectively. Inner cylinder 3 is open at the head heating zone on the left side, and the cylindrical shape of opening is also on the right side.

When the gas is heated by the heating cap and the swirl heater 14 in the expansion chamber 2, it expands in the expansion chamber 2 after being heated, and drives the first distributing piston 5 and the second distributing piston 18 to the right to the compression chamber 8 direction movement, compressing the gas working medium between the first gas distribution piston 8 and the power piston 20; when the first gas distribution piston 5 and the first gas distribution piston 8 move to the right, the gas distribution piston leaf spring 17 is The elastic potential energy to the left is generated by right stretching. When the gas distribution piston reaches the bottom of the right side, the elastic potential energy of the gas distribution piston plate spring 17 reaches the maximum, which is greater than the kinetic energy of the gas distribution piston and the expansion potential energy of the gas in the expansion chamber, so that the first The distributing piston 5 and the second distributing piston 18 move leftward toward the expansion chamber 2 until they reach the left end of the outer cylinder 1 . When the first gas distribution piston 5 and the second gas distribution piston 18 move to the left, part of the gas also enters the regenerator 4 and the cold zone device 5 through the passages in the interlayer of the two cylinders, and enters the first distribution valve after being cooled by the cooling medium. The channel between the gas piston 8 and the power piston 20 enters the compression chamber 8 .

When the gas working medium in the compression chamber 8 is compressed, the gas working medium drives the power piston 20 to move to the right; when the power piston 20 moves to the right, the power piston leaf spring 23 generates potential energy to the left, reaching the rightmost end. Maximum, the elasticity of the power piston leaf spring 23 makes it move back to the left toward the direction of the compression chamber 8 . When the power piston 20 moves to the left, part of the gas passes through the cooler 5 and the regenerator 4 in the interlayer of the two cylinders, and returns to the expansion chamber 2 through the heating chamber passage for heating. When the power piston 20 moves to the leftmost end of its stroke, it is affected by the gas in the compression chamber 8 and moves to the right again, and the phase angle difference between it and the movement of the first distributing piston 5 and the second distributing piston 18 is about 70 degrees .

In this way, the first gas distribution piston 5, the second gas distribution piston 18 and the power piston 20 move back and forth in the cylinder, so that the working gas is heated and expanded, cooled and compressed back and forth in the interlayer of the two cylinders, the expansion chamber 2, and the compression chamber 8 . With the reciprocating motion of the power piston 20, the permanent magnet 21 of the generator mover on the power piston rod 11 reciprocates in the stator winding coil 10 to generate electric energy. The power piston rod 11 is supported by bearings 9 . The linear generator assemblies 10 and 21 and the power piston rod 11 are fixed on the generator casing 22 . In order to reduce the flow of gas in the gap between the first gas distribution piston 5 and the inner cylinder 3, it is necessary to carry out precise and gap-free cooperation between the first gas distribution piston 5 and the inner cylinder. Generally, a labyrinth gas sealing device is used to reduce leakage. Reduce air loss and improve engine efficiency.

Since the specific heat capacity of the working fluid of the free piston Stirling engine is very small, it is very sensitive to changes in the temperature of the external heat source, so the operation of the engine is greatly affected by the external heat source. In order to reduce this effect, under the continuous heating of the external heat source, the heating cap 12 transmits heat through the liquid metal 13 to the inside of the gas distribution piston cylinder to heat the gas working medium. Because the specific heat capacity of the liquid metal is very high, when the temperature of the gas heat source changes slightly, it will not affect the large change of the gas temperature in the expansion chamber, so that the engine runs smoothly. In addition, the swirl heater also plays the role of enhanced heating, which improves the thermal efficiency of the engine.

Claims (4)

1. A three-piston type free-piston Stirling engine, it comprises gas distribution piston cylinder, gas distribution piston, power piston cylinder (19), power piston (20) and generator assembly successively; Described gas distribution piston cylinder comprises The outer cylinder (1) and the inner cylinder (3), the interlayer between the outer cylinder (1) and the inner cylinder (3) is sequentially composed of a heating chamber (2), a regenerator (4) and a cooling chamber (5) from top to bottom ) and cooling medium channel (6); the top of the inner cylinder (3) is an open structure; the space between the top of the gas distribution piston and the outer cylinder (1) is the expansion cavity (2); It is characterized by: The heating head outside the gas distribution piston cylinder has a heating cap (12) filled with liquid metal (13) whose phase change temperature is equivalent to the temperature of the heat source, and a swirl heater (14) is also installed in the gas distribution piston cylinder; The gas distribution piston is sealed and installed in the inner cylinder (3), and is divided into a first gas distribution piston (15) and a second gas distribution piston (18); the first gas distribution piston (15) and the second gas distribution piston ( 18) are separated by the valve piston leaf spring (17) and connected by the valve piston connecting rod (16) passing through the valve piston leaf spring (17). 2. The three-piston free-piston Stirling engine according to claim 1, characterized in that: the length of the first distributing piston (15) is 3-4 times that of the second distributing piston (18). 3. The three-piston free-piston Stirling engine according to claim 2, characterized in that: the swirl heater (14) is installed on the top of the first distributing piston (15) or the outer cylinder of the distributing piston ( 1) The upper part of the inside. 4. The three-piston free-piston Stirling engine according to claim 1, characterized in that: the generator assembly includes a generator casing (22), a power piston rod (11), a linear generator mover (21 ), linear generator stator coil windings (10); wherein the power piston rod (11) is supported in the generator casing (22) through bearings (9), and the upper end of the power piston rod (11) is connected with the power piston (20). The lower end of the piston rod (11) is connected with a leaf spring (23); the linear generator mover magnet (21) is installed on the power piston rod (11).