Diesel power plant

diesel power plant

1. POWER PLANT ENGINEERING Diesel power plant Suryakanth L G Asst. Prof Mechanical Dept NMREC, Hyderabad

2. Topics include…. Introduction about IC engines Types of IC engines Plant layout of Diesel power plant Fuel supply system Air starting equipment Lubrication system Cooling system Super charging

3. Introduction Diesel power plants produce power in the range of 2 to 50 MW, are used as central stations for supply authorities and work. They are used as standby sets for continuity of supply such as hospitals, telephone exchanges, radio stations, cinema theatres and industries. They are suitable for mobile power generation and widely used in railways and ships. Used as Peak Load Plants, Mobile Plants, Stand By Units, Emergency Plants, Starting Stations, Central Stations, Industries where power requirement is small 500kW.

4. Advantages of Diesel power plant : Design and installation are very simple. It can respond to varying loads without any difficulty. It occupies less space. For the same capacity diesel power plant is compact and smaller than a thermal power plant. Require less quantity of water for cooling purposes. No problem of ash handling system. Dis advantages of Diesel power plant : High operating cost. High maintenance and lubrication cost. The capacity of a diesel plant is limited. They cannot be constructed in large sizes. In a diesel plant noise is a serious problem. Diesel power plants cannot supply over loads continuously where as steam power plants can work under 25% overload continuously.

5. List of Diesel Power Plants in INDIA

6. Heat Engine Any type of engine or device that derives heat energy from combustion of fuel and converts to mechanical energy. In an Internal combustion engine , combustion takes place within working fluid of the engine, thus fluid gets contaminated with combustion products. Petrol engine is an example of internal combustion engine, where the working fluid is a mixture of air and fuel . In an External combustion engine , working fluid gets energy using boilers by burning fossil fuels or any other fuel, thus the working fluid does not come in contact with combustion products. Steam engine is an example of external combustion engine, where the working fluid is steam.

7. Classification of IC Engines 1. According to cycle of operation Two Stroke Engine Four Stroke Engine 2. According to cycle of combustion Otto Cycle Engine(combustion at constant volume) Diesel Cycle Engine(combustion at constant pressure) Dual Combustion or semi – diesel cycle engine. 3. According to arrangement of Cylinder. Horizontal Engine Vertical Engine V-Type Engine Radial Engine 4. According to their Uses Stationary Engine Portable Engine Marine Engine Automobile Engine Aero Engine

8. 5. According to fuel employed and method of fuel supply to engine. Oil Engine Petrol Engine Gas Engine 6. According to method of ignition Spark ignition Compression ignition 7. According to speed of the engine Low speed Medium Speed High Speed 8. According to method of cooling Air Cooled Water Cooled 9. According to number of cylinders Single cylinder Multi Cylinder

9. Air Cooled IC Engine

10. Terms Relating to IC Engine

11. Bore : The inside diameter of the cylinder. Stroke : The linear distance along the cylinder axis between two limiting positions. Top dead centre(TDC) : The top most position of the piston towards cover end side of the cylinder. Bottom dead centre(BDC) : The lowest position of the piston towards the crank end side of the cylinder. Clearance volume( V c ) : The volume contained in the cylinder above the top of the piston, when the piston is at TDC. Swept volume(V s ) : The volume swept through by the piston in moving between TDC and BDC. Total volume = Swept volume + clearance volume Compression ratio (r) : ratio of total cylinder volume to clearance volume. # 5:1 to 9:1 for Petrol engines # 14:1 to 22:1 for Diesel engines

12. Four Stroke Diesel Cycle Engine Intake or Suction Stroke Piston moves from TDC to BDC creating vacuum in the cylinder Intake valve opens allowing only air to enter the cylinder and exhaust valve remains closed.

13. Compression Stroke Both valves stay closed Piston moves from BDC to TDC, compressing air to 22:1 Compressing the air to this extent increases the temperature inside the cylinder to above 600 degree centigrade.

14. Expansion or Power Stroke Both valves stay closed. When the piston is at the end of compression stroke(TDC) the injector sprays a mist of diesel fuel into the cylinder . When hot air mixes with diesel fuel an explosion takes place in the cylinder. Expanding gases push the piston from TDC to BDC.

15. Exhaust Stroke Piston moves from BDC to TDC Exhaust valve opens and the exhaust gases escape Intake valve remains closed

16. 17 2-stroke Diesel Engine

17. Layout of a Diesel power plant

18. Essential elements of Diesel Power Plant Engine System Starting System Lubrication System Fuel System Air filter and Supercharge Cooling System Exhaust System Governing System

19. 1. Diesel engine : Diesel engine is a compression ignition(CI) engine. The two –stroke cycle engine is more favored for diesel power plants. The air required for the diesel engine is drawn through the air filter from the atmosphere and compressed inside the cylinder. The fuel(diesel) from the diesel engine is drawn through a filter from the all day tank and injected into the cylinder through fuel injectors. Because of the high temperature and pressure of the compressed air, the fuel ignites. The fuel burns and the burnt gases expand to do work on the moving part inside the cylinder called piston. This movement of the piston rotates a flywheel and the engine is directly coupled to electric generator. The gases after expansion inside the cylinder is exhausted into the atmosphere and passes through a silencer in order to reduce the noise.

20. 2. Starting system Diesel engine used in diesel power plants is not self starting. The engine is started from cold condition with the help of an air compressor. 3. Fuel supply system Fuel from the storage tank is pumped through a filter into a smaller tank called all day tank. This tank supplies the daily requirements of the diesel engine. The all day tank is placed high so that the fuel flows to the engine under gravity with sufficient pressure . 4. Air intake system The air required for the combustion of fuel inside the diesel engine cylinder is drawn through the air filter. The purpose of the filter is to remove dust from the incoming air. The dry filter may be made of felt, wood or cloth. In wet filter, oil bath is used. In this the air passes over a bath of oil where the dust particles get coated on the oil.

21. 5. Exhaust system: The exhaust gases coming out of the engine is very noisy. In order to reduce the noise a silencer(muffler) is used. 6. Lubricating System: This circuit includes lubricating oil tank, oil pump and oil cooler. The purpose of the lubrication system is to reduce the wear of the engine moving parts. Part of the cylinder such as piston, shafts, valves must be lubricated. Lubrication also helps to cool the engine. In the lubrication system the oil is pumped from the lubricating oil tank through the oil cooler where the oil is cooled by the cold water entering the engine. The hot oil after cooling the moving parts return to the lubricating oil tank

22. 7. Cooling system The temperature of the burning fuel inside the engine cylinder is in the order of 1500 to 2000 degree Centigrade. In order to lower this temperature water is circulated around the engine. The water envelopes(water jacket) the engine. The heat from the cylinder, piston, combustion chamber etc., is carried by the circulating water. The hot water leaving the jacket is passed through the heat exchanger. The heat from the heat exchanger is carried away by the raw water circulated through the heat exchanger and is cooled in the cooling tower.

23. for good performance of diesel power plant Necessary to maintain the cooling temp within prescribed limits. Lubricating system should work effectively and required temp and pressure should be maintained. The engine should be periodically run even when not required, should not stand idle for more than 7 days. Air filters, oil filters and fuel filters should be periodically serviced. Periodic checking of engine compression and firing pressure and exhaust temp.

24. Air intake system The air intake system conveys fresh air through pipes or ducts to the 4-stroke engine, scavenging pump & to the supercharger. A large diesel engine requires 0.076 to 0.114 m3 of air /min/KW of power developed. Air is first drawn through a filter to catch dirt or particles that may cause excessive wear in cylinders. Filters may be of following types: Dry type (paper, cloth, felt, glass wool etc) Wet type (oil impingement type, oil bath type where oil helps to catch particles) Air intake system

25. Following precautions should be taken while designing air intake systems Air intake should be located outside the engine room. Air intake should not be located in confined places to avoid undesirable acoustic vibrations. Pressure drop in the air intake line should be minimum to avoid engine starvation Air filters should be accessible for periodic cleaning. In some cases a muffler may be introduced to prevent engine noise from reaching outside air.

26. Lubrication system It includes the oil pumps, oil tanks, filters, coolers and connecting pipes. The purpose of the lubrication system is to reduce the wear of the engine moving parts Part of the cylinder such as piston , shafts , valves must be lubricated. The lubricant is cooled before recirculation. Lubrication also helps to cool the engine.

27. The following are the important functions of a lubrication system LUBRICATION: To keep parts sliding freely past each other, reducing friction and wear. COOLING: To keep surfaces cool by taking away part of the heat caused by friction. CLEANING: To keep the bearings and piston rings clean. SEALING: To form a good seal B/W the piston rings and cylinder walls. REDUCING NOISE: to reduce the noise of the engine by absorbing vibration.

28. oil tank

29. Exhaust system The purpose of the exhaust system is to discharge the engine exhaust to the atm. outside the building. This includes the silencers and connecting ducts. The exhaust gases coming out of the engine is very noisy. silencer (muffler) is provide to reduce the noise.

30. Exhaust pipe leading out of the building should be short in length with minimum number of bends to provide as low a pressure loss as possible. Flexible tubing may be added in exhaust pipe to take care of misalignments and expansion/contraction and also to isolate the system from engine vibrations. Each engine should have its independent exhaust system. Where possible, exhaust heat recovery should be made to improve plant thermal efficiency. E.g., air heating, low pressure steam generation in diesel-steam power plant etc

31. Fuel system It includes the storage tank, fuel pump, fuel transfer pump, strainers and heater. Pump draws diesel from storage tank to day tank through the filter The day tank is usually placed high so that diesel flows to engine under gravity. Diesel is filtered before being injected into the engine by the fuel injection pump . strainers

32. The fuel injection system performs the following functions Filter the fuel Meter the correct quantity of the fuel to be injected Time the injection process Regulate the fuel supply Secure fine atomization of fuel oil Distribute the atomized fuel properly in the combustion chamber Oil is atomized either by blast or pressure je t. In pressure jet atomization oil is forced to flow through spray nozzles at pressure above 100 bar . It is known as solid injection

33. Classification of solid injection systems Common rail injection system: The system is named after the shared high-pressure (100 to 200 bars)reservoir (common rail) that supplies all the cylinders with fuel. With conventional diesel injection systems, the fuel pressure has to be generated individually for each injection. With the common rail system, however, pressure generation and injection are separate, meaning that the fuel is constantly available at the required pressure for injection. Individual pump injection system Distributor system

34. Common rail injection system The system is named after the shared high-pressure (100 to 200 bars)reservoir (common rail) that supplies all the cylinders with fuel. With conventional diesel injection systems, the fuel pressure has to be generated individually for each injection. With the common rail system, however, pressure generation and injection are separate, meaning that the fuel is constantly available at the required pressure for injection.

35. Individual pump Injection System The schematic is shown in fig. An individual pump or pump cylinder connects directly to each fuel nozzle. Metering and injection timing controlled by individual pumps. Nozzle contains a delivery valve actuated by the fuel pressure.

36. Distributor System The schematic is shown here. The fuel is metered at a central point. A pump meters, pressurizes and times the fuel injection. Fuel is distributed to cylinders in correct firing order by cam operated poppet valves which admit fuel to nozzles.

37. Cooling system The cooling system consists of a water source, pump and cooling towers. The pump circulates water through cylinder and head jacket. The water takes away heat form the engine and it becomes hot. The hot water is cooled by cooling towers and re circulated for cooling. There are two systems to circulate the water through the jacket, @Gravity system @Forced circulation system

38. Cooling system The temperature of the hot gases inside the cylinder may be as high as 2750 c . If there is no external cooling, the cylinder walls and piston will tend to assume the average temp. of the gases. Cooling is necessary because: To avoid deterioration or burning of lubricating oil. The strength of the materials used for various engine parts decreases with increase in temperature. Local thermal stress can develop due to uneven expansion of various parts. Increase in pre-ignition and knocking Due to high cylinder head temp. the volumetric efficiency and hence power output of the engine are reduced.

39. cooling system

40. Elements of cooling system

41. There are two methods of cooling I.C. engines Air cooling: Heat is carried away by the air flowing over and around the engine cylinder. It is used in scooters , motorcycles etc. Liquid cooling: the cylinder walls and heads are provided with jackets through which the cooling liquid can circulate.

42. Air cooling : In this method, heat is carried away by the air flowing over and around the engine cylinder. Fins are added on the cylinder which provide additional mass of material for conduction as well as additional area for convection and radiating modes of heat transfer.

43. Liquid cooling In this method, the cylinder walls and head are provided with jackets through which the cooling liquid can circulate. The heat is transferred from the cylinder walls to the liquid by convection and conduction. The liquid gets heated during its passage through the cooling jackets and is itself cooled by means of an air cooled radiator system.

44. Types of Water Cooling System Thermo Siphon S/m In this system the circulation of water is due to difference in temperature (i.e. difference in densities) of water. So in this system pump is not required but water is circulated because of density difference only.

45. Phases in CI engine combustion In the C.I. engine, combustion may be considered in four distinct stages, Ignition delay period Period of rapid or uncontrolled combustion Period of controlled combustion After burning

46. Combustion phenomenon in CI engine

47. Ignition Delay The ignition delay in a diesel engine is defined as the time interval between the start of injection and the start of combustion. This delay period consists of (a) physical delay, wherein atomization, vaporization and mixing of air fuel occur and (b) of chemical delay attributed to pre-combustion reactions. Physical and chemical delays occur simultaneously.

48. Due to the delay period the pressure reached during second stage will depend up on the duration of delay period. The longer delay will cause rough running and may cause diesel knock . Delay period should be as short as possible both for the sake of smooth running and in order to maintain control over the pressure changes. But , some delay period should be necessary other wise the droplets would not disappear in the air for complete combustion.

49. It is the second stage of combustion in C.I engine. This period is counted from end of the delay period to the point of maximum pressure on the indicator diagram. The rise of pressure is rapid because during the delay period the droplets of fuel have had time to spread themselves over a wide area and they have fresh air all around them. About 1/3 of heat is evolved during this period Period Of Rapid Or Uncontrolled Combustion

50. At the end of the second stage of combustion , the temperature and pressure are so high that the fuel droplets injected in third stage burn almost as they enter and any further pressure rise can be controlled by injection rate . The heat evolved at the end of the compression is about 70 to 80 percent. PERIOD OF CONTROLLED COMBUSTION

51. After burning The combustion continues even after the fuel injection is over , because of poor distribution of particles This burning may be continue in the expansion stroke up to 70 to 80( deg ) of crank revolution from TDC. The total heat evolved by the entire combustion process is 95 to 97%; 3 to 5% of heat goes as un burnt fuel in exhaust.

52. Delay Period in CI engines It is the time immediately following injection of the fuel during which the ignition process is being initiated and pressure does not rise beyond the value it would have due o the compression of the air. The delay period extend for about 13deg C, movement of the crank. Delay period depends upon following: Temperature and pressure in the cylinder at time of injection. Nature of the fuel mixture strength. Presence of residual gases. Rate of fuel injection. It should be as short as possible

53. Diesel Knock If the delay period of C.I. engine is long a large amount of fuel will be injected and accumulated in he chamber. The auto ignition of this large amount of fuel may cause high rate of pressure rise and high maximum pressure which may cause knocking in the diesel engine.

54. Cetane number Cetane rating of a diesel fuel is the measure of its ability to auto ignite quickly when it is injected into the compressed and heated air in he engine. Reference mixture of cetane (C 16 H 34 )(high ignitability) and alpha methyl napthalene (C 11 H 10 )(low ignitability) are used, The mixture is made by volume and ignitability of the test fuel is quoted as the percentage of cetane in the reference mixture which has same ignitability. For higher speed engines: cetane number is 50 For medium speed engines: cetane number is 40 For slow speed engines: cetane number is 30 Cetane number effect the following : Exhaust emissions: more if C.N is less Noise: More if C.N is less Start ability of diesel engine: lessens if C.N. is less

55. Supercharging The purpose of supercharging is to raise the volumetric efficiency above that value which can be obtained by normal aspiration. The engine is an air pump, increasing the air consumption permits greater quantity of fuel to be added, and results in greater potential output. The power output is almost directly prop. To the air consumption. 3 methods to increase the air consumption of an engine are: 1. Increasing the piston displacement: leads to more size and weight, cooling problems 2. Running the engine at higher speeds leads to mechanical wear and tear. 3. Increasing the density of the charge, so that greater mass of charge is introduced in same volume. {Widely Used}

56. Effects of Supercharging The Power output of a supercharged engine is higher than its naturally aspirated counterpart. The mechanical efficiencies are better than naturally aspirated engines. It has higher specific fuel consumption that naturally aspirated engines.