1 Experiment No. - 1 Object: Study and working of four stroke petrol engine. Apparatus Required: S. No. Name of Apparatus Specifications Model of Four stroke petrol engine NA Figure 1: Working of four stroke petrol engine [Type text] Page 0
2 Brief Theory: The Otto cycle is the ideal cycle for spark-ignition reciprocating engines. It is named after Nikolaus A. Otto, who built a successful four-stroke engine in 1876 in Germany using the cycle proposed by Frenchman Beau de Rochas in In most spark-ignition engines, the piston executes four complete strokes (two mechanical cycles) within the cylinder, and the crankshaft completes two revolutions for each thermodynamic cycle. These engines are called four-stroke internal combustion engines. Since ignition in these engines is due to a spark, therefore they are also called spark ignition engines or S. I. Engines. The four stroke petrol engine works on following strokes: Suction Stroke: In this Stroke the inlet valve opens and proportionate fuel-air mixture is sucked in the engine cylinder. Thus the piston moves from top dead centre (T.D.C.) to bottom dead centre (B.D.C.). The exhaust valve remains closed throughout the stroke. 2. Compression Stroke: In this stroke both the inlet and exhaust valves remain closed during the stroke. The piston moves towards (T.D.C.) and compresses the enclosed fuel-air mixture drawn. Just before the end of this stroke the operating plug initiates a spark which ignites the mixture and combustion takes place at constant pressure. 3. Power Stroke or Expansion Stroke: In this stroke both the valves remain closed during the start of this stroke but when the piston just reaches the B.D.C, the exhaust valve opens. When the mixture is ignited by the spark plug the hot gases are produced which drive or throw the piston from T.D.C. to B.D.C. and thus the work is obtained in this stroke. 4. Exhaust Stroke: This is the last stroke of the cycle. Here the gases from which the work has been collected become useless after the completion of the expansion stroke and are made to escape through exhaust valve to the atmosphere. This removal of gas is accomplished during this stroke. The piston moves from B.D.C. to T.D.C. and the exhaust gases are driven out of the engine cylinder; this is also called scavenging.
3 Figure 2: Theoretical P-v diagram of Otto cycle Figure 2 shows the ideal P-V diagram of Otto cycle on which the four stroke S. I. engines generally works. In this cycle heat addition (process 2-3) and heat rejection (process 4-1) is assumed at constant volume and remaining processes of compression (1-2) and expansion (3-4) are assumed as isentropic. Conclusions of the present work (what new you have learnt in today s experiment): 2. 3.
4 Viva-voice Questions: What is an engine? Classify them. 2. What do you mean by I.C. engine? 3. Name the different fuels being used in India for transportation? 4. On which cycle Petrol engines work? 5. What do you mean by TDC & BDC? 6. What do you mean by stroke? 7. Why Petrol engines are also called S. I. engine? 8. What is the function of flywheel? 9. What is the auto-ignition temperature of petro? 10. Explain the working of four stroke petrol engine.
5 Experiment No. - 2 Object: Study and working of two stroke petrol engine. Apparatus Required: S. No. Name of Apparatus Specifications Model of two stroke petrol engine NA Figure 1: Two stroke petrol engine
6 Brief Theory: The working principle of 2-Stroke petrol engine is discussed below:- 1) 1 st Stroke: To start with let us assume the piston to be at its B.D.C. position. The arrangement of the ports is such that the piston performs two jobs simultaneously. As the piston starts rising from its B.D.C. position it closes the transfer port and the exhaust port. The charge (mixture, of the air and petrol) which is already there in the cylinder, as the result of the previous running of the engine is compressed at the same time with the upward movement of the piston vacuum is created in the crank case (which is gas tight). As soon as the inlet port is uncovered; the fresh change in sucked in the crank case. The charging is continued until the crank case and the space in the cylinder beneath the piston is filled with the charge. As the end of third stroke, the piston reached the T.D.C. position. 2) 2 nd Stroke: Slightly before the completion of the compression stroke, the compressed charge is ignited by means of a spark produced at the spark plug. Pressure is exerted on the crank of the piston due to the combustion of the piston is pushed in the downward direction producing some useful power. The downward movement of the will first close the inlet port and then it will compress the charge already sucked in the crank case. Just the end of power stroke, the piston uncovered the exhaust port and the transfer port simultaneously the expanded gases start escaping through the exhaust port and the same time the fresh charge which is already compressed in the crank case, rushed into the cylinder through the transfer port and thus the cycle is repeated again. The fresh charge coming into the cylinder also helps in exhausting the burnt gases out of the cylinder through the exhaust port. This is known as scavenging.
7 Figure 2: Working of two stroke Petrol engine Conclusions of the present work (what new you have learnt in today s experiment): 2. 3.
8 Viva-voice Questions: Differentiate between two stroke and four stroke engines? 2. Explain the major differences between two stroke and four stroke engines? 3. On which cycle Petrol engines work? 4. What do you mean by TDC & BDC? 5. What do you mean by stroke? 6. Why Petrol engines are also called SI engine? 7. How combustion starts in a diesel engine? 8. What is the auto-ignition temperature of petrol? 9. Explain the working of four stroke petrol engine. 10. Which engine has better thermal efficiency; two stroke or four stroke engines?
9 Experiment No. - 3 Object: Study and working of four stroke diesel engine. Apparatus Required: S. No. Name of Apparatus Specifications Model of four stroke diesel engine NA Brief Theory: In Diesel engines the combustion is realized due to excessive compression and are so called compression ignition engines. Here air alone is sucked inside the cylinder during suction stoke and compressed. Degree of compression is much more than that of spark ignition (SI) engines. After compression of air the fuel is injected into the high pressure and high temperature compressed air. Due to high temperature of air the combustion of fuel gets set on its own. Selfignition of fuel takes place due to temperature of air-fuel mixture being higher than self-ignition
10 temperature of fuel. Thus in CI engines, larger amount of compression causes high temperature, therefore unassisted combustion. Schematic of 4-stroke CI engine is quite similar to that of 4-stroke SI engine with the only major difference that spark plug is replaced by fuel injector for injecting fuel at high pressure into compressed air. 4-Stroke CI engine works with following four processes getting completed in separate strokes. General arrangement in CI engine is similar to that of SI engine with spark plug replaced by fuel injector. Stroke 1: Piston travels from TDC to BDC and air is sucked. Stroke 2: Piston travels from BDC to TDC, while air is compressed with inlet and exit passages closed. Stroke 3: Piston reaches TDC and air gets compressed. Fuel injector injects fuel into compressed air for certain duration. Ignition of fuel also takes place simultaneously as air temperature is much higher than self-ignition temperature of fuel. Burning of fuel results in release of fuel chemical energy which forces piston to travel from TDC to BDC. Contrary to SI engine where heat addition gets completed near instantaneously, in CI engines fuel injection and thus heat addition is spread in certain stroke travel of piston i.e. heat addition takes place at constant pressure during which piston travels certain stroke length as decided by cut-off ratio. This is expansion process and piston comes down to BDC with both inlet and exit valves closed. Stroke 4: After expansion piston reverses its motion upon reaching BDC and travels up to TDC with exit passage open. During this piston travel burnt gases are expelled out of cylinder i.e. exhaust stroke. Completion of above four strokes requires two revolutions of crankshaft. Conclusions of the present work (what new you have learnt in today s experiment): 2. 3.
11 Viva-voice Questions: Differentiate between two stroke and four stroke engines? 2. Explain the major differences between two stroke and four stroke engines? 3. On which cycle Petrol engines work? 4. What do you mean by TDC & BDC? 5. What do you mean by stroke? 6. Why Petrol engines are also called SI engine? 7. How combustion starts in a diesel engine? 8. What is the auto-ignition temperature of petrol? 9. Explain the working of four stroke petrol engine. 10. Which engine has better thermal efficiency; two stroke or four stroke engines?
12 Experiment No. - 4 Object: Study and working of two stroke diesel engine. Apparatus Required: S. No. Name of Apparatus Specifications Model of two stroke diesel engine NA Brief Theory: Working of 2-stroke compression ignition engine is shown in figures (a), (b), (c) and (d) explaining the suction, compression, expansion and exhaust processes. During piston travel from BDC to TDC air enters crankcase. When piston reaches TDC and reverses its motion to BDC air in crankcase gets partly compressed and is transferred from crankcase to top of piston through transfer port. Upon reversal of piston motion from BDC to TDC the compression of air occurs by the top side of piston while on the bottom side of piston air again enters into crankcase. Upon piston reaching TDC fuel is injected into compressed air which is at high temperature and pressure. As fuel is injected into compressed air the fuel ignition gets set on its own due to temperature being more than self-ignition temperature of fuel, i.e. compression ignition. Fuel injection is continued for some duration along with its ignition which causes release of excessive fuel energy. This energy release causes piston to go back from TDC to BDC, i.e. the expansion process as shown in (c). As piston reaches BDC it simultaneously forces air in crank case to get transferred to cylinder space and forces burnt gases out of cylinder i.e. exhaust process. Here also cycle gets completed in single revolution of crankshaft i.e. two processes occurring simultaneously in each stroke.
13 Figure: Working of Two stroke Diesel Engine Conclusions of the present work (what new you have learnt in today s experiment): 2. 3.
14 Viva-voice Questions: Differentiate between two stroke and four stroke engines? 2. Explain the major differences between two stroke and four stroke engines? 3. On which cycle diesel engines work? 4. What do you mean by TDC & BDC? 5. What do you mean by stroke? 6. Why diesel engines are also called CI engine? 7. How combustion starts in a diesel engine? 8. What is the auto-ignition temperature of diesel? 9. Explain the working of two stroke diesel engine. 10. Which engine has better thermal efficiency; two stroke or four stroke engines?
15 Object: Study of water tube boiler. Apparatus Required: Experiment No. - 5 S. No. Name of Apparatus Specifications Model of water tube boiler (Babcock & Wilcox boiler) NA Figure: Babcock & Wilcox boiler
16 Brief Theory: Babcock and Wilcox boiler is a water tube boiler. It is a high pressure boiler having inclined tubes. Constructional Details: It consists of a drum connected to a series of front end and rear end header by short riser tubes. To these headers are connected a series of inclined water tubes of solid drawn mild steel. The angle of inclination of the water tubes to the horizontal is about 15 or more. The Babcock and Wilcox Boiler consists of: Steam and water drum (boiler shell) around 9 m length and 2 m diameter 2. Water tubes (Multiple tubes about 10 cm in diameter) 3. Uptake-header and down corner 4. Grate 5. Furnace 6. Baffles 7. Super heater 8. Mud box 9. Inspection door 10. Damper Steam and water drum (boiler shell): One half of the drum which is horizontal is filled up with water and steam remains on the other half. It is about 8 meters in length and 2 meter in diameter. 2. Water tubes: Water tubes are placed between the drum and furnace in an inclined position (at an angle of 10 to 15 degree) to promote water circulation. These tubes are connected to the uptake-header and the down-comer as shown. 3. Uptake-header and down-corner (or downtake-header): The drum is connected at one end to the uptake-header by short tubes and at the other end to the down-corner by long tubes. 4. Grate: Coal is fed to the grate through the fire door. 5. Furnace: Furnace is kept below the uptake-header.
17 6. Baffles: The fire-brick baffles, two in number, are provided to deflect the hot flue gases. 7. Superheater: The boiler is fitted with a superheater tube which is placed just under the drum and above the water tubes 8. Mud box: Mud box is provided at the bottom end of the down comer. The mud or sediments in the water are collected in the mud box and it is blown-off time to time by means of a blow off cock. 9. Inspection doors: Inspection doors are provided for cleaning and inspection of the boiler. Working Of Babcock and Wilcox Boiler: Coal is fed to the grate through the fire door and burnt. Flow of flue gases: The hot flue gases rise upward and pass across the left-side portion of the water tubes. The baffles deflect the flue gases and hence the flue gases travel in the zigzag manner (i.e., the hot gases are deflected by the baffles to move in the upward direction, then downward and again in the upward direction) over the water tubes and along the superheater. The flue gases finally escape to atmosphere through chimney. Water circulation: That portion of water tubes which is just above the furnace is heated comparatively at a higher temperature than the rest of it. Water, its density being decreased, rises into the drum through the uptake-header. Here the steam and water are separated in the drum. Steam being lighter is collected in the upper part of the drum. The water from the drum comes down through the down comer into the water tubes. A continuous circulation of water from the drum to the water tubes and water tubes to the drum is thus maintained. The circulation of water is maintained by convective currents and is known as natural circulation. A damper is fitted as shown to regulate the flue gas outlet and hence the draught. The boiler is fitted with necessary mountings. Pressure gauge and water level indicator are mounted on the boiler at its left end. Steam safety valve and stop valve are mounted on the top of the drum. Blow-off cock is provided for the periodical removed of mud and sediments collected in the mud box.
18 Salient features of Babcock and Wilcox Boiler: Its overall efficiency is higher than a fire tube boiler. 2. The defective tubes can be replaced easily. 3. All the components are accessible for inspection even during the operation. 4. The draught loss is minimum compared with other boiler. 5. Steam generation capacity and operating pressure are high compared with other boilers. 6. The boiler rests over a steel structure independent of brick work so that the boiler may expand or contract freely. 7. The water tubes are kept inclined at an angle of 10 to 15 degree to promote water circulation. Advantages and disadvantages of water tube boilers over fire tube boilers: Advantages of water tube boilers: Steam can be generated at very high pressures (100 bars). Steaming capacity is upto Kg/hr. 2. Heating surface is more in comparison with the space occupied, in the case of water tube boilers. 3. Steam can be raised more quickly than is possible with a fire tube boiler of large water capacity. Hence, it can be more easily used for variation of load. 4. The hot gases flow almost at right angles to the direction of water flow. Hence maximum amount of heat is transferred to water. 5. A good and rapid circulation of water can be made. 6. Bursting of one or two tubes does not affect the boiler very much with regard to its working. Hence water tube boilers are sometimes called as safety boilers. 7. The different parts of a water tube boiler can be separated. Hence it is easier to transport. 8. It is suitable for use in steam power plants (because of the various advantages listed above). Disadvantages of water tube boilers: It is less suitable for impure and sedimentary water, as a small deposit of scale may cause the overheating and bursting of tubes. Hence, water treatment is very essential for water tube boilers. 2. Maintenance cost is high.
19 3. Failure in feed water supply even for a short period is liable to make the boiler overheated. Hence the water level must be watched very carefully during operation of a water tube boiler. Conclusions of the present work (what new you have learnt in today s experiment): Viva-voice Questions: Define boiler. Classify them. 2. Differentiate between Fire tube and Water tube boiler. 3. Which type of boiler has more operating pressure? 4. Describe the various components of a boiler. 5. What do you mean by boiler mountings? 6. What do you mean by boiler accessories? 7. What is the function of superheater? 8. What is the role of baffles? 9. What is use of water level indicator? 10. What is the function of safety valve?
20 Object: - Study of fire tube boiler. Apparatus Required:- Experiment No. - 6 S. No. Name of Apparatus Specifications Model of fire tube boiler (Locomotive boiler) NA Brief Theory: A locomotive boiler is a fire tube, internally fixed, horizontally, multi tubular boiler. These boilers were invented for getting steam to run a steam engine used in locomotives. These are fire tube type of boilers. It has basically three parts i.e. smoke box, shell and fire box. Inside fire box the fuel (coal) is burnt over the grate. For feeding fuel the fire hole is used. Hot gases produced in fire box are diverted by fire brick arch and enter into the fire tubes surrounded with water. Steam produced gets collected in a steam drum fitted on top of the shell. Arrangement for super heating is there in these boilers. The wet steam goes through inlet headers of superheater and after passing through tubes, it returns to the outlet header of superheater and is taken out for steam engine. A very large door is provided at the end of smoke box so as to facilitate cleaning and maintenance of complete boiler. As it is a moving boiler, therefore, its chimney is completely eliminated. For expelling the burnt gases (draught) the exhaust steam coming out from steam engine is being used. Thus it is an artificial draught used in these boilers for expelling burnt gases.
21 Figure 1: Constructional features of Locomotive Boiler Conclusions of the present work (what new you have learnt in today s experiment): Viva-voice Questions: Define boiler. Classify them. 2. Differentiate between Fire tube and Water tube boiler. 3. Which type of boiler has more operating pressure? 4. What are the uses of locomotive boiler? 5. Name the three important parts of locomotive boiler. 6. What is the function of superheater tubes? 7. What is the importance of safety valves? 8. What is the function of damper? 9. What is the function of fire hole? 10. What is the function of grate?
22 Object: Study of steam engine model. Apparatus Required: Experiment No.: 7 S. No. Name of Apparatus Specifications Model of steam engine NA Brief Theory: A steam engine is a heat engine that performs mechanical work using steam as its working fluid. In 1781 James Watt patented a steam engine that produced continuous rotational motion. These 10 h. p. engines enabled a wide range of manufacturing machinery to be powered. The engines could be sited anywhere that water and coal or wood fuel could be obtained. By 1883, engines that could provide 10,000 h. p. had become feasible. Steam engines could also be applied to vehicles such as traction engines and the railway locomotives which are commonly just called steam engines outside America. The stationary steam engine was a key component of the Industrial Revolution, allowing factories to locate where water power was unavailable. Simple steam engine shown in figure is a horizontal double acting steam engine having cylinder fitted with cylinder cover on left side of cylinder. Cylinder cover has stuffing box and gland through which the piston rod reciprocates. One end of piston rod which is inside cylinder has piston attached to it. Piston has piston rings upon it for preventing leakage across the piston. Other end of piston rod which is outside cylinder has cross head attached to it. Cross head slides in guide ways so as to have linear motion in line with engine axis. Cross head is connected to the small end of connecting rod by the gudgeon pin. Big end of connecting rod is mounted over crank pin of the crank. Reciprocating motion of piston rod is transformed into rotary motion of crankshaft by cross head, connecting rod and crank. Cross head transmits the motion of piston rod to connecting rod. Cross head guide ways bear the reaction force.
23 Crank is integral part of crank shaft mounted on bearings. Crankshaft has fly wheel mounted on one end and pulley mounted on other end. Crankshaft also has an eccentric with eccentric rod mounted on it. Eccentric performs function of converting rotary motion of crankshaft into reciprocating motion of valve rod. Other end of eccentric rod transmits motion to valve rod which passes through stuffing box fitted in steam chest. Valve rod controls the movement of D- slide valve inside the seam chest. D-slide valve opens and closes the exhaust and inlet passages from steam-chest to engine cylinder. Steam chest has two openings one for inlet of live steam and other for exit of dead or expanded steam. Live steam refers to the steam having sufficient enthalpy with it for doing work in steam engine. Dead steam refers to the steam having insufficient enthalpy with it and does not have capability to produce work. High pressure and high temperature steam (live steam) enters from main inlet passage into steam chest. D-slide valve occupies such a position that passage (port 1) from the steam chest to engine cylinder gets opened. High pressure steam enters cylinder and forces piston towards other dead centre. Linear motion of piston is transformed into rotation of crankshaft through crosshead, connecting rod, gudgeon pin and crank.
24 When piston reaches other dead centre then the corresponding displacement of valve rod causes shifting of D-slide valve such that other passage (port 2) from steam chest to cylinder gets opened and passage 1 comes in communication with the exhaust passage. Thus the live steam enters from steam chest to cylinder through passage 1 and dead steam leaves from cylinder to exhaust passage through passage 2. Steam forces piston from inner dead centre to outer dead centre and from other side of piston dead steam leaves from exhaust passage simultaneously. Since it is double acting steam engine, both strokes produce shaft work due to steam being injected on both sides of piston alternatively. If it is a single acting steam engine then steam injection takes place on one side of piston only for producing power and return stroke occurs due to inertia of flywheel. Flywheel mounted on crankshaft overcomes the fluctuations in speed, if any due to its high inertia. Pulley mounted on shaft is used for transmitting power. Apart from the components shown in figure the engine has throttle valve, governor mechanism, oil pump, relief valves etc. for its proper functioning. Different major components of steam engine are: Piston and Piston rod 2. Piston rings 3. Connecting rod 4. Crank and Crank shaft 5. Stuffing box 6. Crosshead and guide-ways 7. Eccentric 8. Slide valve Conclusions of the present work (what new you have learnt in today s experiment): 2. 3.
25 Viva-voice Questions: Define engine. 2. Define steam engine. 3. What are the various parts of a steam engine? 4. What is the function of crank? 5. What is the function of piston and piston rod? 6. What is the function of connecting rod? 7. For what purpose stuffing box is used? 8. What do you mean by double acting steam engine? 9. What is the role of cross head in steam engine? 10. What is the role of flywheel in steam engine?
26 Experiment No. - 8 Object: Study of impulse and reaction turbine. Apparatus Required: S. No. Name of Apparatus Specifications Model of impulse and reaction turbine NA Brief Theory: The steam turbine is a prime mover in which the potential energy of steam is transformed into kinetic energy and latter in its turn is transformed into the mechanical energy of the rotation of the turbine shaft. Classification of steam turbine: With respect to the action of steam, turbines are classified as: Impulse turbine 2. Reaction turbine Impulse turbine: It is a turbine, which runs by the impulse of steam jet. In this turbine, the steam is first made to flow through a nozzle. Then the steam jet impinges on the turbine blades with are curved like bucket and are mounted on the circumference of the wheel. The steam jet after impinges glide over the concave surface of blades and finally leave the turbine. The top portion of Impulse turbine exhibits a longitudinal section through the upper half, the middle portion shows one set of nozzle which is followed by a ring of moving blades, while lower part indicate changes in press and velocity during the flow of steam through the turbine. The principle equation of this turbine is the well-known De level turbine.
27 2. Reaction turbine: - In a Reaction turbine, the steam enters the wheel under pressure and flow over the blades. The steam while gliding proper the blades and then makes them to move. The turbine runner is rotated by the reactive forces of steam jets. In this, there is a gradual pressure drop takes place continuously over the fixed and moving blades. The fuel of fixed blades is that they after allow it expand to a larger velocity as the steam passes over the moving blades. Its K.E. is absorbed by them a three stage Reaction turbine.
28 Compounding: - If the steam is expended from the boiler pressure in one stage the speed of rotor becomes tremendously high which drop up practical complicacies. There are several methods of reducing this speed to lower value; all these methods utilized a multiple system of rotor in series. Keyed on a common shaft and the steam pressure or jet velocity are absorbed in stage as the steam flows over the blades. This is known as compounding. Velocity compounding: Steam is expanded through a stationary nozzle from the boiler or inlet pressure to condenser pressure. So the pressure in the nozzle drops, the K. E. of steam increase due to increase in velocity. A portion of this available energy is absorbed by a row of moving blades. The steam then flow through the second row of the blades which are fixed. They redirect the steam flow without altering its velocity to the following nearest row moving blades. Where again work is done on them and steam with a low velocity from the turbine. 2. Pressure compounding: In this rings of fixed nozzle incorporated between ring of moving blades. The steam of boiler pressure enters the first set of nozzle and expands partially. The K.E. of steam thus obtained in absorbed by the moving blades. The steam then expands partially in the second set of nozzles where its pressure again falls and the
29 velocity increases. The K.E. thus obtained is observed by the second ring of moving blades. This is repeated in stage 3 and steam finally leaves the turbine at low velocity and pressure. 3. Pressure-Velocity compounding: - This method is the combination of velocity and pressure compounding. The total drop in steam pressure is divided into stages and velocity obtained in each stage is also compounded. The ring of nozzle, are fired at beginning of each stage and pressure remains constant during each stage. Conclusions of the present work (what new you have learnt in today s experiment): Viva-voice Questions: Define prime mover? 2. What do you mean by steam turbine? 3. What do you mean by compounding? 4. Differentiate between I. C. engine and steam turbine? 5. What type of steam should be used in steam turbine and why?
30 Object: Study of gas turbine model Apparatus Required: Experiment No. - 9 S. No. Name of Apparatus Specifications Model of gas turbine model NA Brief Theory: The Brayton cycle was first proposed by George Brayton for use in the reciprocating oil-burning engine that he developed around Today, it is used for gas turbines only where both the compression and expansion processes take place in rotating machinery. Gas turbines usually operate on an open cycle, as shown in Figure Fresh air at ambient conditions is drawn into the compressor, where its temperature and pressure are raised. The high-pressure air proceeds into the combustion chamber, where the fuel is burned at constant pressure. The resulting hightemperature gases then enter the turbine, where they expand to the atmospheric pressure while producing power. The exhaust gases leaving the turbine are thrown out (not recirculated), causing the cycle to be classified as an open cycle. Figure 1: An open-cycle gas turbine
31 The open gas-turbine cycle described above can be modeled as a closed cycle, as shown in Figure 2, by utilizing the air-standard assumptions. Here the compression and expansion processes remain the same, but the combustion process is replaced by a constant-pressure heataddition process from an external source, and the exhaust process is replaced by a constant pressure heat-rejection process to the ambient air. The ideal cycle that the working fluid undergoes in this closed loop is the Brayton cycle, which is made up of four internally reversible processes: 1-2 Isentropic compression (in a compressor) Constant-pressure heat addition Isentropic expansion (in a turbine) Constant-pressure heat rejection Figure 2: A closed cycle gas turbine
32 A simple gas turbine is comprised of three main sections a compressor, a combustor, and a power turbine. The gas-turbine operates on the principle of the Brayton cycle, where compressed air is mixed with fuel, and burned under constant pressure conditions. The resulting hot gas is allowed to expand through a turbine to perform work. In a 33% efficient gas-turbine approximately two-third of this work is spent compressing the air, the rest about one third is available for other work (mechanical drive, electrical generation etc.) Figure 3: Construction of Gas turbine The P-v and T-s diagrams of an ideal Brayton cycle are shown in Figure 3 and 4 respectively. Applications of Gas Turbines: These days gas turbines are widely used in industrial, automotive, aircraft, free piston engines and combined gas steam cycles. Advantages of gas turbines over Internal Combustion engines: As compared to I. C. Engines Gas turbines are simple in construction, compact, light in weight, less maintenance and installation cost associated, variety of fuels can be used and are able to be operated at high altitudes.
33 Figure 3: P-v diagram of an ideal Brayton cycle Figure 3: T-s diagram of an ideal Brayton cycle
34 Conclusions of the present work (what new you have learnt in today s experiment): Viva-voice Questions: Define gas turbine. 2. What do you mean by prime mover? 3. On which cycle gas turbine work? 4. Differentiate between gas turbine and steam turbine. 5. In which areas gas turbines are used? 6. Compare gas turbines with I. C. engines. 7. Differentiate between open-cycle gas turbine and closed-cycle gas turbine.
35 Object: Study of fire tube boiler. Apparatus Required: Experiment No S. No. Name of Apparatus Specifications Model of fire tube boiler (Lancashire boiler) NA Brief Theory: It is a horizontal fire tube boiler. General arrangement in the boiler is shown in Figure Boiler is mounted on a brick work setting with front end of shell sloping about 1:250 for emptying the shell. It has a circular shell connected to end plates supported by gusset plates. Two fire tubes run throughout the length of the boiler. Fire tubes are of diameter less than half the diameter of shell and diameter of fire tubes is reduced as shown to have access to lower side of boiler. Fire bridge is provided to prevent fuel from falling over the end of furnace. Fire bridge also helps in producing a better mixture of air and gases for perfect combustion by partly enveloping the combustion space. Hot gases start from grate area, enter into fire tubes and come out at back of boiler from where these gases flow towards the front of boiler through bottom flue. Upon reaching the front these hot gases flow through the side flues and enter the main outlet. Outlet passage may also be used commonly by more than one boiler. About 85% of actual heat transferred is transferred through surface of fire tubes while 15% is transferred through bottom and side flues. Plan, elevation and side views of Lancashire boiler shown in figure explain the furnace, different fire tubes, bottom flues, side flues etc. Dampers are provided at the end of side flues for regulating the pressure difference (draught) for exit of burnt gases. Other mountings and accessories are shown in the elevation of Lancashire boiler. Working pressure in these boilers are in the range of 0.7 MPa to 2 MPa and efficiency of the boiler is about 65% 70%. Size of these boiler depends upon size of shell which may be 2 m to 3 m in diameter and 6 m to 10 m in length.
36 Figure 1: Lancashire boiler
37 Conclusions of the present work (what new you have learnt in today s experiment): Viva-voice Questions: Define boiler. Classify them. 2. Differentiate between Fire tube and Water tube boiler. 3. Which type of boiler has more operating pressure? 4. What is the importance of safety valves? 5. What is the function of damper? 6. What is the function of fire hole? 7. What is the function of grate? 8. Differentiate between mountings and accessories. 9. Explain the function of feed check valve. 10. What is the role of water level indicator?
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