16-11-2012, 01:06 PM
Stirling engines
FyP OF STIRLING ENGINE.docx (Size: 6.04 MB / Downloads: 1,456)
INTRODUCTION
Aim of Project
To obtain useful mechanical work output from a given heat input by employing a stirling cycle engine mechanism. One of the purposes of this project was to understand the laws and principles of a Stirling Cycle. The Stirling engine works on the laws of thermodynamics mainly the first and second law. The first law states that energy is neither created nor destroyed but it just changes form. The second law states that heat would flow from hot to cold and can only flow from cold to hot if there is work done upon it.
Scope
Stirling Engines offer better energy efficiency and reliability, lower exhaust missions and noise levels. They also permit a greater flexibility than internal combustion engines in the choice of fossil fuels and alternative renewable energy sources.
Stirling Engine
The Stirling engine is an external combustion, closed, cyclic heat engine which works on the Stirling Cycle. A typical Stirling engine consists of two zones which are maintained at different temperatures and a working fluid is shuttled between these regions to extract work. Unlike the conventional engines and steam engines (an external combustion engine), there are no valves and the working fluid never leaves the engine and is used over and over again. The working fluids commonly used are air, hydrogen or helium
The Stirling engine principle
Stirling engines can be hard to understand. Here are the key points. Every Stirling engine has a sealed cylinder with one part hot and the other cold. The working gas inside the engine (which is often air, helium, or hydrogen) is moved by a mechanism from the hot side to the cold side. When the gas is on the hot side it expands and pushes up on a piston. When it moves back to the cold side it contracts. Properly designed Stirling engines have two power pulses per revolution, which can make them very smooth running. Two of the more common types are two piston Stirling engines and displacer-type Stirling engines.
Heat source
The heat source may be combustion of a fuel and, geothermal energy, solar energy or any other source. Since in sterling engine, external combustion takes place so the products do not mix with the working fluid and hence they don’t come into contact with the internal moving parts of the engine. A Sterling engine can run on many fluids that can damage the working of internal combustion engine.
In our case, we are using heat lamp as the heat source and this is fed to the engine by focusing on the engine. Other suitable heat sources are geothermal energy, nuclear energy, waste heat, or even biological. If the heat source is solar power, regular solar mirrors and solar dishes may be used. Also, Fresnel lenses have been advocated to be used (for example, for planetary surface exploration). Solar powered Sterling engines are becoming increasingly popular, as they are a very environmentally sound option for producing power. Also, some designs are economically attractive in development projects
Regenerator
In a Sterling engine, the regenerator part is an internal heat exchanger and temporary heat storage placed between the hot and cold spaces such that the working fluid passes through it first in one direction then in the other direction. Its function is to retain within the system that heat which would otherwise be passed to the environment at temperatures intermediate to the maximum and minimum cycle temperatures, thus enabling the thermal efficiency of the cycle to approach the limiting Carnot efficiency defined by those maxima and minima
The primary effect of regeneration in a Sterling engine is to increase the thermal efficiency greatly by 'recycling' internal heat which would otherwise pass through the engine irreversibly. As a secondary effect, increased thermal efficiency promises a higher power output from a given set of hot and cold end heat exchangers (since it is these which usually limit the engine's heat throughput), though in practice this additional power may not be fully realized as the additional "dead space" (un swept volume) and pumping loss inherent in practical regenerators reduces the potential regeneration efficiency gains.
Heat Sink
The heat sink is typically the environment at ambient temperature. In the case of medium to high power engines, a radiator is required to transfer the heat from the engine to the ambient air. Marine engines can use the ambient water. In the case of combined heat and power systems, the engine's cooling water is used directly or indirectly for heating purposes.
Alternatively, heat may be supplied at ambient temperature and the heat sink maintained at a lower temperature by such means as cryogenic fluid (Liquid nitrogen) or iced water.
Displacer
The displacer is a special-purpose piston, used in Beta and Gamma type Sterling engines, to move the working gas back and forth between the hot and cold heat exchangers. Depending on the type of engine design, the displacer may or may not be sealed to the cylinder, i.e. it is a loose fit within the cylinder and allows the working gas to pass around it as it moves to occupy the part of the cylinder beyond.
Crank shaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation. The crankshaft transforms the linear motion of the pistons into a rotational motion that is transmitted to the load. Crankshafts are made of forged steel.
Connecting rod
Transfers power from the power piston to the crankshaft. Connecting rods may also convert rotating motion into linear motion. As a connecting rod is rigid, it may transmit either a push or a pull and so the rod may rotate the crank through both halves of a revolution, i.e. piston pushing and piston pulling. Earlier mechanisms, such as chains, could only pul
Stirling Engine - External Combustion Engine
Stirling engine uses an external heat source that could be concentrated solar energy through the use of parabolic troughs, flame, combustion of fuel etc, this heat energy flows in and out through the walls and creates a temperature difference which is the key in the operation of the Stirling engine. Due to the external heat source it is known as external combustion engine in contrast to internal combustion engine where the heat source is the combustion of fuel inside the working fluid. Stirling engine uses a permanently sealed gaseous working fluid (air, helium or hydrogen) much like a refrigerant or air‐conditioner
Basics of Stirling Engine
In a Stirling engine, a fixed amount of a gas is sealed inside the engine. The Stirling cycle involves a series of events that change the pressure of the gas inside the engine, causing it to do work. There are several properties of gases that are critical to the operation of Stirling engines
FyP OF STIRLING ENGINE.docx (Size: 6.04 MB / Downloads: 1,456)
INTRODUCTION
Aim of Project
To obtain useful mechanical work output from a given heat input by employing a stirling cycle engine mechanism. One of the purposes of this project was to understand the laws and principles of a Stirling Cycle. The Stirling engine works on the laws of thermodynamics mainly the first and second law. The first law states that energy is neither created nor destroyed but it just changes form. The second law states that heat would flow from hot to cold and can only flow from cold to hot if there is work done upon it.
Scope
Stirling Engines offer better energy efficiency and reliability, lower exhaust missions and noise levels. They also permit a greater flexibility than internal combustion engines in the choice of fossil fuels and alternative renewable energy sources.
Stirling Engine
The Stirling engine is an external combustion, closed, cyclic heat engine which works on the Stirling Cycle. A typical Stirling engine consists of two zones which are maintained at different temperatures and a working fluid is shuttled between these regions to extract work. Unlike the conventional engines and steam engines (an external combustion engine), there are no valves and the working fluid never leaves the engine and is used over and over again. The working fluids commonly used are air, hydrogen or helium
The Stirling engine principle
Stirling engines can be hard to understand. Here are the key points. Every Stirling engine has a sealed cylinder with one part hot and the other cold. The working gas inside the engine (which is often air, helium, or hydrogen) is moved by a mechanism from the hot side to the cold side. When the gas is on the hot side it expands and pushes up on a piston. When it moves back to the cold side it contracts. Properly designed Stirling engines have two power pulses per revolution, which can make them very smooth running. Two of the more common types are two piston Stirling engines and displacer-type Stirling engines.
Heat source
The heat source may be combustion of a fuel and, geothermal energy, solar energy or any other source. Since in sterling engine, external combustion takes place so the products do not mix with the working fluid and hence they don’t come into contact with the internal moving parts of the engine. A Sterling engine can run on many fluids that can damage the working of internal combustion engine.
In our case, we are using heat lamp as the heat source and this is fed to the engine by focusing on the engine. Other suitable heat sources are geothermal energy, nuclear energy, waste heat, or even biological. If the heat source is solar power, regular solar mirrors and solar dishes may be used. Also, Fresnel lenses have been advocated to be used (for example, for planetary surface exploration). Solar powered Sterling engines are becoming increasingly popular, as they are a very environmentally sound option for producing power. Also, some designs are economically attractive in development projects
Regenerator
In a Sterling engine, the regenerator part is an internal heat exchanger and temporary heat storage placed between the hot and cold spaces such that the working fluid passes through it first in one direction then in the other direction. Its function is to retain within the system that heat which would otherwise be passed to the environment at temperatures intermediate to the maximum and minimum cycle temperatures, thus enabling the thermal efficiency of the cycle to approach the limiting Carnot efficiency defined by those maxima and minima
The primary effect of regeneration in a Sterling engine is to increase the thermal efficiency greatly by 'recycling' internal heat which would otherwise pass through the engine irreversibly. As a secondary effect, increased thermal efficiency promises a higher power output from a given set of hot and cold end heat exchangers (since it is these which usually limit the engine's heat throughput), though in practice this additional power may not be fully realized as the additional "dead space" (un swept volume) and pumping loss inherent in practical regenerators reduces the potential regeneration efficiency gains.
Heat Sink
The heat sink is typically the environment at ambient temperature. In the case of medium to high power engines, a radiator is required to transfer the heat from the engine to the ambient air. Marine engines can use the ambient water. In the case of combined heat and power systems, the engine's cooling water is used directly or indirectly for heating purposes.
Alternatively, heat may be supplied at ambient temperature and the heat sink maintained at a lower temperature by such means as cryogenic fluid (Liquid nitrogen) or iced water.
Displacer
The displacer is a special-purpose piston, used in Beta and Gamma type Sterling engines, to move the working gas back and forth between the hot and cold heat exchangers. Depending on the type of engine design, the displacer may or may not be sealed to the cylinder, i.e. it is a loose fit within the cylinder and allows the working gas to pass around it as it moves to occupy the part of the cylinder beyond.
Crank shaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation. The crankshaft transforms the linear motion of the pistons into a rotational motion that is transmitted to the load. Crankshafts are made of forged steel.
Connecting rod
Transfers power from the power piston to the crankshaft. Connecting rods may also convert rotating motion into linear motion. As a connecting rod is rigid, it may transmit either a push or a pull and so the rod may rotate the crank through both halves of a revolution, i.e. piston pushing and piston pulling. Earlier mechanisms, such as chains, could only pul
Stirling Engine - External Combustion Engine
Stirling engine uses an external heat source that could be concentrated solar energy through the use of parabolic troughs, flame, combustion of fuel etc, this heat energy flows in and out through the walls and creates a temperature difference which is the key in the operation of the Stirling engine. Due to the external heat source it is known as external combustion engine in contrast to internal combustion engine where the heat source is the combustion of fuel inside the working fluid. Stirling engine uses a permanently sealed gaseous working fluid (air, helium or hydrogen) much like a refrigerant or air‐conditioner
Basics of Stirling Engine
In a Stirling engine, a fixed amount of a gas is sealed inside the engine. The Stirling cycle involves a series of events that change the pressure of the gas inside the engine, causing it to do work. There are several properties of gases that are critical to the operation of Stirling engines