Stirling Engine PPT1
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Transcript of Stirling Engine PPT1
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Stirling Engine
Prof. S. L. Bapat
Mechanical Engineering Department
Department of Energy Science and Engineering
Indian Institute of Technology Bombay,
Mumbai – 400 076
April 28, 2008
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Indian Scenario
• Shortage of Electrical Power Thermal power plants
Nuclear power plants
Hydel power plants
• Solar P-V cells
• Solar Thermal Rankine Cycle
Stirling Cycle
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• ~ 43,000 villages to be electrified
• Features of these villages (Sastry, 2003): – Difficult terrain
– 3-30 km away from grid – No. of household 2 to 200
– Average population ~ 500
– Power demand quite low (Supply for 4-6 hrs/day)
– facilities are minimal (TV, Refrigerators etc.)
– Income levels & paying capacity low
Choice of Capacity for Stirling Engine
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448 billion1.20 billionfor India
24,00,00060,000per village
Rs.$Investment
required (in 2003)
Cost of P-V plants ranges from Rs. 3.6 lakh- 4.8 lakh for 1.5 kW
(Sastry, 2003)
Applications:- For a group of 3-4 households having enough cattle tosupply bio-gas for gas based systems or hybrid systems
- Use for small capacity pumps for irrigation application
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Ideal Stirling cycle(Normally explained by using α – type)
(a) P-V and T-S diagrams (b) Piston arrangements at the terminal
points of the cycle (c) Displacement-time diagram
• Assumptions
• Working – Compress the gas, heat the gas, and
then expand to get power output
– Internal heat transfer in regenerator
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Basic arrangements of Stirling engine
Piston – Displacer
in same cylinder
(β)
Piston – Displacer
in separate
cylinder (γ)
Two piston machine(α)
Different types of Stirling engine
- Free piston - Free displacer engine
- Disciplined (Kinematic) engine
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Selection of drive mechanism
Kinematic mechanisms for reciprocating motion
(a) Simple slider Crank b) Cross head Crank c) Rhombic Drive
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78.5°Phase angle (motion)4
1.43--Specific heat ratio5
750K Temperature hot side (th)3
30barMean Pressure2
1440rpmSpeed1
350K Minimum gas temperature (tc)7
----Fluid – Hydrogen /Helium6
ValueUnitParameterSr. no.
Operating conditions
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Engine and receiver arrangement
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Issues Involved
1. Obtaining heat at temperature level of about 750 K or more- Gas Flame (Bio-gas, CNG, LPG)
- Circulation of burnt gases for reuse in preheating
of combustion air - Dish Concentrator
- Size of the dish depends on heat inputrequirements
- Hybrid System using solar concentrator and gas flame- Arrangement for switching over from solar to gas
flame and vice-versa
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Issues Involved2. Requirement:
- Engine of the capacity of 1.5 kWe should
satisfy most requirements
3. Materials:
- Some special materials to be chosen based on specificrequirements (properties) e.g.
O-rings at higher temperature (soft metal- Indium,
Copper)
Sealing rings: – Compression rings
– Oil scrapper rings
– Sealing of displacer
4. Lubrication Problems:
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Issues Involved5. Operating and Resulting Parameters
1. Working spaces and dead volumes in
cooler, regenerator and heater tubes
decide the pressure ratio
2. Large value of pressure ratio leads tohigher value of peak pressure. The
enclosing components such as compression and
expansion cylinders have to be stronger from
mechanical design point of view. So this
parameter needs to be decided
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Issues Involved6. Manufacturing processes:
This will depend on scale of manufacture
- If number crosses 1000, the fabrication processes,
rejection schemes need to be worked out
- Interchangeability is required and hence tolerances
will have to be really fine
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Issues Involved7. Mechanized assembly:
i) Components such as crankcase can be using castings or made out of plates by welding
ii) leak proof ness /porosity has to be checked for enclosing
components
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Issues Involved8. Testing Procedures:
i) Test engine with electrical heating to determineminimum heat input
ii) Testing with gas flame to find fuel consumption
iii) Design dish and test to provide suitable disharea for a given heat input
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Worldwide Scenario
– Engines upto 30 kW capacity have beenmade as a Single Cylinder Engine
– Some of these have been coupled with dishsystems
iii) Testing over very large number of hours is
done with a very small number of units
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Bio-gas requirement : 1 m3 / h or so.Calorific Value = 20 MJ/m3
Net heat input required is 5000 Watt for 1.5 kWecapacity
Qgas = 5000 Watt
Combustion efficiency = 90 %
http://www.mct.gov.jm/energy_7.htm date: 23/03/07]
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Conclusions
1. Stirling engines seems to be viable option
2. Capacity needs to be at least 1.5 kW
3. Major heat input should be through gas flame or
solar energy4. Bio-gas requirement will be about one cubic meter/
hour
5. Hybrid system will be the ideal option if suitablearrangement is possible
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Thank you !