STIRLING ENGINE INTRODUCTION HISTORY WHAT IS STIRLING ENGINE WORKING PRINCIPLE OF STIRLING ENGINE DIFFERENT CONFIGURATION OF STIRLING ENGINE COMPARISON BETWEEN ALPHA,BETA & GAMMA STIRLING ENGINE FIVE MAIN COMPONENT OF STIRLING ENGINE EFFICIENCY APPLICATION OF STIRLING ENGINE ADVANTAGE OF STIRLING ENGINE DISADVANTAGE OF STIRLING ENGINE PROTOTYPES OF STIRLING ENGINE CONCLUSION REFERENCES

INTRODUCTION The purpose of this presentation has been to

develop a Stirling engine capable of operating on variety of heat sources, specifically on solar heat and traditional fuel combustion. Such an engine would have applications generating power in remote locations, using solar heat to offset fuel consumption. This project developed a prototype engine that can be analyzed to develop a model for use in designing a full scale engine.

This project, proposed and funded by student sponsor Jaan Nisar, focuses primarily on the engine itself, rather than the heat sources or the electricity generation system. This was advised by Professor Manoj Naik of the Mechanical Engineering Department with Professor Sunil Kammar of the Mechanical Engineering Department acting as faculty sponsor. Through this senior project, the poly source team has gained experience in designing and manufacturing an engine system that combines thermodynamic and kinetic cycles.

The results of this project are available for future developers of Stirling engines, including any students of SUC Poly who wish to take on a similar project.

HISTORY The Stirling engine (or Stirling's air engine as it was

known at the time) was invented and patented by Robert Stirling in 1816. It followed earlier attempts at making an air engine but was probably the first put to practical use when, in 1818, an engine built by Stirling was employed pumping water in a quarry. The main subject of Stirling's original patent was a heat exchanger, which he called an "economiser" for its enhancement of fuel economy in a variety of applications. The patent also described in detail the employment of one form of the economiser in his unique closed-cycle air engine design in which application it is now generally known as a "regenerator". Subsequent development by Robert Stirling and his brother James, an engineer, resulted in patents for various improved configurations of the original engine including pressurization, which by 1843, had sufficiently increased power output to drive all the machinery at a Dundee iron foundry.

Though it has been disputed, it is widely supposed that as well as saving fuel, the inventors were motivated to create a safer alternative to the steam engines of the time,whose boilers frequently exploded, causing many injuries and fatalities.

The need for Stirling engines to run at very high temperatures to maximize power and efficiency exposed limitations in the materials of the day, and the few engines that were built in those early years suffered unacceptably frequent failures (albeit with far less disastrous consequences than a boiler explosion) — for example, the Dundee foundry engine was replaced by a steam engine after three hot cylinder failures in four years.

WHAT IS STIRLING ENGINE A Stirling engine is a heat engine that

operates by cyclic compression and expansion of air or other gas (the working fluid) at different temperatures, such that there is a net conversion of heat energy to mechanical work. More specifically, a closed-cycle regenerative heat engine with a permanently gaseous working fluid. Closed-cycle, in this context, means a thermodynamic system in which the working fluid is permanently contained within the system, and regenerative describes the use of a specific type of internal heat exchanger and thermal store, known as the regenerator. The inclusion of a regenerator differentiates the Stirling engine from other closed cycle hot air engines.

Originally conceived in 1816 as an industrial prime mover to rival the steam engine, its practical use was largely confined to low-power domestic applications for over a century.

The Stirling engine is noted for high efficiency compared to steam engines, quiet operation, and its ability to use almost any heat source. This compatibility with alternative and renewable energy sources has become increasingly significant as the price of conventional fuels rises, and also in light of concerns such as peak oil and climate change. This engine is currently exciting interest as the core component of micro combined heat and power (CHP) units, in which it is more efficient and safer than a comparable steam engine.

WORKING PRINCIPLE OF STIRLING ENGINE

DIFFERENT CONFIGURATION OF STIRLING ENGINE

ALPHA TYPE

BETA TYPE SWASH PLATE DRIVE

GAMMA TYPE

COMPARISON BETWEEN ALPHA,BETA & GAMMA STIRLING ENGINE

ALPHA STIRLING ENGINE

BETA STIRLING ENGINE

GAMMA STIRLING ENGINE

An alpha Stirling contains two separate power pistons in separate cylinders, one "hot" piston and one "cold" piston.

A beta Stirling has a single power piston arranged within the same cylinder on the same shaft as a displacer piston.

A gamma Stirling is simply a beta Stirling in which the power piston is mounted in a separate cylinder alongside the displacer piston cylinder, but is still connected to the same flywheel.

The hot piston cylinder is situated inside the higher temperature heat exchanger and the cold piston cylinder is situated inside the low temperature heat exchanger. 

The displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas from the hot heat exchanger to the cold heat exchanger. When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston. 

The gas in the two cylinders can flow freely between them and remains a single body.

This type of engine has a very high power-to-volume ratio but has technical problems due to the usually high temperature of the "hot" piston and the durability of its seals.

When it is pushed to the cold end of the cylinder it contracts and the momentum of the machine, usually enhanced by a flywheel, pushes the power piston the other way to compress the gas.

This configuration produces a lower compression ratio but is mechanically simpler and often used in multi-cylinder Stirling engines. 

FIVE MAIN COMPONENTS OF STIRLING ENGINE

Working Gas: The Stirling cycle is a closed cycle and the

various thermodynamic processes are carried out on a working gas that is trapped within the system.

Heat-Exchanger: Two heat exchangers are used to transfer

heat across the system boundary. A heat absorbing heat-exchanger transfers the heat from outside the system into the working gas, and a heat rejecting heat-exchenger transfers heat from the working gas to outside the system.

Displacer Mechanism: This moves(or displaces)the working gas

between the hot and cold ends of the machine (via generator).

Regenerator:This acts both as a thermal barrier between the

hot and cold ends of the machine, and also as a “thermal store”for the cycle. Physically a regenerator usually consists of a mesh materia(Household pot scrubbers have even been used in some engines), and heat is transferred as the working gas is forced through the regenerator mesh. When the working gas is displaced from the hot end of the machine(via regenerator) to the cold end of the machine, heat is “deposited”in the regenerator, and the temperature of the working gas is slowered. When the reverse displacement occurs, heat is “withdrawn”from the regenerator again. And the temperature of the working gas is raised.

Expansion/Compression Meahanism: This expands and/or compresses the working

gas.In an engine this mechanism produces a net work output.

EFFICIENCY

APPLICATION OF STIRLING ENGINE1. STIRLING ENGINES FOR PUMPING WATER USING

SOLAR ENERGY AS A SOURCE OF POWER Limited availability of petroleum product and electricity

in rural areas and high demandable human need for water make demand for searching another alternative for pumping water.

One optional and potential engine solving this problem is the solar stirling engine.

In this system, the solar heat collector provides heat for the solar,stirling engine whic h in turn provide AC power. The electrical power can be transferred toa battery charger, then to DC control unit which can either go into a battery or into an inverter. Efficiencies for this type of small scale system can range from 18% - 23%.

Cost of the equipment is low comparetively. Aviation is last major user of leaded fuel, stirling engine

produce less pollution. Altitude performance is the stronger reason why these

engines are needed. If a plane could hold a constant power, it could cruise twice as fast at 40000ft as it can at sea level.

The main reasons these engines are needed in aviation is because their motor is silent, smooth torque and lack of vibration.

ADVANTAGES OF STIRLING ENGINE Silence of operation : There is no expansion in the atmosphere

like in the case of an internal combustion engine, combustion is continuous outside of the cylinders. In addition, its design is such as the engine is easy to balance and generates few vibrations.

The high efficiency : It is function of the temperatures of the hot and cold sources. As it is possible to make it work in cogeneration (mechanical and caloric powers), the overall efficiency can be very high.

The multitude of possible “hot sources” : Combustion of various gases, wood, sawdust, waste, solar or geothermic energy...

The ecological aptitude to respond to the environmental requirements on air pollution. It is easier to achieve a complete combustion in this type of engine.

Reliability and easy maintenance:  The technological simplicity makes it possible to have engines with a very great reliability and requiring little maintenance.

An important lifetime because of its “rusticity”. The very diverse uses because of its autonomy and adaptability to

the needs and the different kinds of hot sources (from mW to MW).

DISADVANTAGES OF STIRLING ENGINE The price : its cost is probably the most important problem, it is

not yet competitive with other means well established. A generalization of its employment should solve this problem inherent in any novelty. 

The ignorance of this type of engine by the general public. Only a few fans know it exists. It is therefore necessary to promote it. 

The variety of models prevents standardization and, consequently, lower prices.

The problems of sealing are difficult to solve as soon as one wishes to have high pressures of operation. The choice of “ideal” gas would be hydrogen for its lightness and its capacity to absorb the calories, but its ability to diffuse through materials is a great disadvantage.

Heat transfers with a gas are delicate and often require bulky apparatuses.

The lack of flexibility : the fast and effective variations of power are difficult to obtain with a Stirling engine. This one is more qualified to run with a constant nominal output. This point is a great handicap for an utilisation in car industry.

PROTOTYPES OF STIRLING ENGINE

CONCLUSION GENERAL: The stirling engine is noted for its high efficiency compared to

steam engines, quiet operations, and the ease with it can use almost any heat source.

This engine is currently exciting interest as the core component of micro combined heat and power (CHP) units,in which it is more efficient and safer than a comparable steam engine.

Substantial reduction of Co &HC emissions Easy to install Payback within a year or less depends upon driving No maintenance required and life long Can be used on any engines as an auxiliary unit for emission

reduction Not much popular Patented secret construction technology

REFERENCESG. Walker (1980),W.R. Martini (1983),T. Finkelstein; A.J. Organ (2001), Sleeve notes from A.J. Organ (2007),F. Starr (2001),C.M. Hargreaves (1991), Graham Walker (1971).

THANK YOU