Stirling Engine. Prof. S. L. Bapat Mechanical Engineering Department

Transcription

1 Stirling Engine Prof. S. L. Bapat Mechanical Engineering Department Department of Energy Science and Engineering Indian Institute of Technology Bombay, Mumbai April 28,

2 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 2

3 Choice of Capacity for Stirling Engine ~ 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 3

4 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 to supply bio-gas for gas based systems or hybrid systems - Use for small capacity pumps for irrigation application Investment $ Rs. required (in 2003) per village 60,000 24,00,000 for India 1.20 billion 48 billion 4

5 Ideal Stirling cycle (Normally explained by using α type) Assumptions Working Compress the gas, heat the gas, and then expand to get power output Internal heat transfer in regenerator (a) P-V and T-S diagrams (b) Piston arrangements at the terminal points of the cycle (c) Displacement-time diagram 5

6 Basic arrangements of Stirling engine Two piston machine (α) Piston Displacer in same cylinder (β) Piston Displacer in separate cylinder (γ) Different types of Stirling engine - Free piston - Free displacer engine - Disciplined (Kinematic) engine 6

7 Selection of drive mechanism Kinematic mechanisms for reciprocating motion (a) Simple slider Crank b) Cross head Crank c) Rhombic Drive 7

8 Operating conditions Sr. no. Parameter Unit Value 1 Speed rpm Mean Pressure bar 30 3 Temperature hot side (th) K Phase angle (motion) Specific heat ratio Fluid Hydrogen /Helium Minimum gas temperature (tc) K 350 8

9 Engine and receiver arrangement 9

10 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 input requirements - Hybrid System using solar concentrator and gas flame - Arrangement for switching over from solar to gas flame and vice-versa 10

11 Issues Involved 2. Requirement: - Engine of the capacity of 1.5 kwe should satisfy most requirements 3. Materials: - Some special materials to be chosen based on specific requirements (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: 11

12 Issues Involved 5. 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 to higher 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 12

13 Issues Involved 6. 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 13

14 Issues Involved 7. 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 14

15 Issues Involved 8. Testing Procedures: i) Test engine with electrical heating to determine minimum heat input ii) Testing with gas flame to find fuel consumption iii) Design dish and test to provide suitable dish area for a given heat input 15

16 Worldwide Scenario Engines upto 30 kw capacity have been made as a Single Cylinder Engine Some of these have been coupled with dish systems iii) Testing over very large number of hours is done with a very small number of units 16

17 Bio-gas requirement : 1 m 3 / h or so. Calorific Value = 20 MJ/m 3 Net heat input required is 5000 Watt for 1.5 kwe capacity Qgas = 5000 Watt Combustion efficiency = 90 % date: 23/03/07] 17

18 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 energy 4. Bio-gas requirement will be about one cubic meter/ hour 5. Hybrid system will be the ideal option if suitable arrangement is possible 18

19 Thank you! 19