STIRLING ENGINE

Stirling engines are external combustion engines that use air or other gases (such as helium, hydrogen, nitrogen etc.) as working fluid. The stirling engine like all heat engines can burn any solid or liquid fuel as their heat source.

A stirling engine is a closed cycle heat engine that converts thermal energy into work by alternatively heating and cooling a fixed gas (hydrogen, helium, air, nitrogen etc.) or inside a sealed cylinder. It operates on the stirling cycle, which involves four phases. Phase one expansion; the gas heats up and expands pushing the piston. Phase two, displacement; the gas moves to a cooler chamber. Phase there, compression; the gas cools and contracts, pulling the piston back. Phase four, return; the gas returns to the hot chamber to repeat the cycle.

There are several types of stirling engines. The main types are as follows; alpha-type, beta-type, gamma-type and free piston stirling engines.

The alpha-type stirling engine is a type of engine that has two cylinders, one for expansion and one for compression, connected by a regenerator.

The beta-type of stirling engine is a type of engine that has a single cylinder with a displacer and power piston.

The gamma-type stirling engine is a type of engine that has a single cylinder with a displacer and a power piston similar to beta-type but with a separate cylinder for the power piston.

The free piston stirling engine is a type of engine that has a piston that is not connected to a crankshaft allowing for more efficient operation.

The main components of the stirling engine as follows; heater, regenerator, cooler, piston and cylinder, displacer, crank mechanism and working fluid.

The heater is where heat is added to the working fluid (usually a gas such as air or helium) to increase its temperature and pressure.

The regenerator is the critical component that stores heat energy from the working fluid during the cooling process and releases it back to the fluid during the heating process thereby increasing efficiency.

The cooler is where the heat is removed from the working fluid to decrease its temperature and pressure.

The piston and cylinder works together. The piston moves up and down in the cylinder driven by the pressure changes in the working fluid.

The displacer is a component that helps to move the working fluid between the heater and the cooler ensuring efficient heat transfer.

The crank mechanism converts the up and down movement or motion of the piston into rotary motion which can be used to drive a generator or other machinery.

The working fluid is a gas (such as helium, hydrogen, air etc.) that expands and contracts within the engine transferring heat energy into mechanical work.

The advantages of stirling engines are as follows; stirling engines can achieve a high efficiency especially at low temperature differences. Stirling engines are quiet in their operation. Stirling engines can run on a variety of heat sources including solar, biomass and waste heat. Stirling engines produce low emissions, if clean heat source is used making them a cleaner option.

The disadvantages of stirling engines are as follows; stirling engines are complex systems that may require precise engineering and maintenance. Stirling engines are currently more expensive than traditional heat engines. Stirling engines have a limited power output compared to traditional heat engines.

The application of stirling engines find widespread use in industry and they are as follows; stirling engines can be used to generate electricity from solar energy. Stirling engines can be used to generate electricity from biomass. Stirling engines can be used to recover waste heat from industrial processes. Stirling engines can be used in micro-combined heat and power (CHP) systems for residential and commercial buildings.

The future of stirling engines depends on the trends and the development of the following technologies; stirling engines will play a key role in solar power generation especially in concentrated solar power plants (CSP) systems. Stirling engines could be used on a wide scale in the future to recover waste heat from industrial processes reducing energy consumption and emission. Stirling engines could be used in micro-CHP systems for residential and commercial buildings providing both electricity and heat.

 

SOURCES:

• Stirling engines by Graham Walker.
• Stirling engines by A.K de Jong.
• The Phillips stirling engine by Allan J. Organ and C.M.K Hargreaves.
• Stirling engines: inner working and Design by Allan J. Organ.
• Stirling engine design manual by William R. Martini.