Stirling Engine PPT1

8/3/2019 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



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]

http://www.mct.gov.jm/energy_7.htm

http://www.mct.gov.jm/energy_7.htm



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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 !

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Stirling Engine PPT1