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MEng5221 Chapter 1.pptx
- 1. IC Engines andReciprocating Machines(MEng5221) AAiT Chapter one Introduction CHAPTER ONE 1
- 2. Introduction • Heat Engine •Brief Historical Development of IC Engines • Engine Components and Basic Engine Nomenclature, • IC Engine Classification • Four stroke CI engines, Four stroke Cycle SI engines and two stroke Engines CHAPTER ONE 2
- 3. Heat engine Is awork developing machine which is used to convert the chemical energy of a fuel into heat (thermal) energy and then to mechanical energy. A heat engine works on the principles of heat engine cycles CHAPTER ONE 3
- 4. In a heatengine cycle, the following thermodynamic processes repeat over constant intervals of time: 1. A heat "source" generates thermal energy that brings the working substance in the high temperature state. 2. The working substance generates work in the "working body" of the engine while transferring heat to the colder "sink" until it reaches a low temperature state Heat engine cont.… CHAPTER ONE 4
- 5. 3. The workingsubstance is brought back to its initial state by further heat rejection. 4. During this process some of the thermal energy is converted into work by exploiting the properties of the working substance. Heat engine cont.… CHAPTER ONE 5
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- 7. Basically there aretwo types of heat engines external and internal combustion engines A. In an external combustion engines combustion (burning of a fuel) is taking place outside of the engine. Eg. Steam engines B. In an internal combustion (IC) engines combustion is taking place within the engine itself. Eg. Spark Ignition (SI) engines Heat engine cont.… CHAPTER ONE 7
- 8. Brief Historical Developmentof IC Engines • Historical developments of IC engines and Automobiles ( reading assignment) CHAPTER ONE 8
- 9. Engine Components andBasic Engine Nomenclature CHAPTER ONE 9
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- 15. Basic Engine Nomenclature IC Engine Terminologies (Nomenclature) CHAPTER ONE 15
- 16. IC Engine Terminologies(Nomenclature) cont.… CHAPTER ONE 16 • Bore(d) • TDC • BDC • Stroke(s) • Swept volume(vs) • Clearance volume(vc) • Compression ratio(r) • indicated mean effective pressure (imep)
- 17. Areas of applicationsof IC engines IC engines are used: a) To propel a vehicle (automobiles, trucks, locomotives, ships, airplanes, etc.). b) To run stationary engines which are used to drive generators or used for other applications. Classification of Reciprocating IC Engines Reciprocating IC engines can be classified in a number of different ways: 1. Types of Ignition a) Spark Ignition (SI) b) Compression Ignition (CI) 2. Engine stroke a) Four-stroke b) Two-stroke CHAPTER ONE 17
- 18. Engine classification… 3. Valvetrain arrangements a) Over Head Valve (OHV) b) Over Head Camshaft (OHC) c) Double Over Head Cam (DOHC) 4. Number of Cylinders a) Single cylinder b) Multi-cylinder 5. Cylinder arrangements a) In-Line b) V Engine c) Opposed cylinder engine d) Opposed piston engine e) Radial engine 6. Air Intake Process a) Naturally aspirated b) Supercharged 1. Introduction… CHAPTER ONE 18
- 19. Engine classification… 7. Methodof Fuel Input a) Carburetor b) Fuel Injection 8. Fuel used a) Gasoline b) Diesel Oil c) LPG, Natural Gas, Methane d) Alcohol (Ethyl, Methyl) e) Dual(mixed) fuel f) Biodiesel fuel(Vegetable oil) 9. Type of cooling a) Air Cooled b) Liquid Cooled (Water Cooled) 1. Introduction… CHAPTER ONE 19
- 20. TWO STROKE ANDFOUR STROKE CYCLE ENGINE In a two-stroke engine, the working cycle is completed in two strokes of the piston or one revolution of the crankshaft. This is achieved by carrying out the suction and compression processes in one stroke and expansion and exhaust processes in the second stroke (or more precisely in downward stroke). CHAPTER ONE 20
- 21. TWO STROKE ANDFOUR STROKE CYCLE ENGINE In a four-stroke engine, the working cycle is completed in four-strokes of the piston or two- revolutions of the crankshaft. This is achieved by carrying out suction, compression, expansion and exhaust processes in each stroke. CHAPTER ONE 21
- 22. FOUR STROKE CYCLEPETROL ENGINE It is based on Otto cycle. The four strokes of a petrol engine are described below: 1. Suction or charging stroke: In this stroke, the inlet valve opens and charge is sucked into the cylinder as the piston moves downward from top dead centre(T.D.C.). It continues till the piston reaches its bottom dead centre (B.D. C.) as shown in (a). CHAPTER ONE 22
- 23. FOUR STROKE CYCLEPETROL ENGINE 2. Compression stroke: In this stroke, both the inlet and exhaust valves are closed and the charge is compressed as the piston moves upwards from B.D. C. to TD. C. As a result of compression, the pressure and temperature of the charge increases considerably. This completes one revolution of the crank shaft. The compression stroke is shown in (b). CHAPTER ONE 23
- 24. FOUR STROKE CYCLEPETROL ENGINE CHAPTER ONE 24
- 25. FOUR STROKE CYCLEPETROL ENGINE 3. Expansion or working stroke: Shortly before the piston reaches T.D.C. (during compression stroke), the charge is ignited with the help of a spark plug. It suddenly increases the pressure and temperature of the products of combustion but the volume, practically, remains constant. Due to the rise in pressure, the piston is pushed down with a great force. The hot burnt gases expand due to high speed of the piston. During this expansion, some of the heat energy produced is transformed into mechanical work. Both the valves are closed and piston moves from T.D.C. to B.D.C CHAPTER ONE 25
- 26. FOUR STROKE CYCLEPETROL ENGINE 4. Exhaust stroke: In this stroke, the exhaust valve is open as piston moves from B.D.C. to T.D.C. This movement of the piston pushes out the products of combustion, from the engine cylinder and is exhausted through the exhaust valve into the atmosphere, as shown in (d). This completes the cycle, and the engine cylinder is ready to suck the charge again. CHAPTER ONE 26
- 27. VALVE TIMING DIAGRAMFOR A FOUR STROKE CYCLE PETROL ENGINE CHAPTER ONE 27
- 28. FOUR-STROKE CYCLE DIESEL ENGINE Thefour strokes of a diesel engine sucking pure air are described below: 1. Suction or charging stroke: In this stroke, the inlet valve opens and pure air is sucked into the cylinder as the piston moves downwards from the top dead centre(TDC). It continues till the piston reaches its bottom dead centre (BDC) as shown (a). CHAPTER ONE 28
- 29. FOUR-STROKE CYCLE DIESEL ENGINE 2.Compression stroke: In this stroke, both the valves are closed and the air is compressed as the piston moves upwards from BDC to TDC. As a result of compression, pressure and temperature of the air increases considerably . This completes one revolution of the crank shaft. The compression stroke is shown in (b). CHAPTER ONE 29
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- 31. FOUR-STROKE CYCLE DIESEL ENGINE 3.Expansion or working stroke: Shortly before the piston reaches the TDC , fuel oil is injected through the fuel injection valve. The compressed air is sufficiently hot to ignite the fuel. It increases the pressure and temperature of the products of combustion. The fuel oil is continuously injected for a fraction of the revolution. Due to increased pressure, the piston is pushed down and some of the heat energy is transformed into mechanical work. During this working stroke, both the valves are closed and the piston moves from TDC to BDC. CHAPTER ONE 31
- 32. FOUR-STROKE CYCLE DIESEL ENGINE 4.Exhaust stroke: In this stroke, the exhaust valve is open as the piston moves from BDC to TDC. This movement of the piston pushes out the products of combustion from the engine cylinder through the exhaust valve into the atmosphere. This completes the cycle and the engine cylinder is ready to suck the fresh air again. CHAPTER ONE 32
- 33. VALVE TIMING DIAGRAMFOR A FOUR-STROKE CYCLE DIESEL ENGINE CHAPTER ONE 33
- 34. TWO-STROKE CYCLE PETROL ENGINE Atwo stroke engine has ports instead of valves. All the four stages of a two stroke petrol engine are described below: 1. Suction stage: The piston, while going down towards BDC, uncovers both the transfer port and the exhaust port The fresh fuel-air mixture flows into the engine cylinder from the crank case, as shown (a). 2. Compression stage: The piston, while moving up, first covers the transfer port and then exhausts port. After that the fuel is compressed as the piston moves upwards as shown (b). In this stage, the inlet port opens and fresh fuel-air mixture enters into the crank case. CHAPTER ONE 34
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- 36. TWO-STROKE CYCLE PETROL ENGINE 3.Expansion stage: Shortly before this piston reaches the TDC (during compression stroke), the charge is ignited with the help of a spark plug. It suddenly increases the pressure and temperature of the products of combustion, but the volume, practically, remains constant. Due to rise in the pressure, the piston is pushed downwards with a great force as shown in (c). During this expansion, some of the heat energy produced is transformed into mechanical work. CHAPTER ONE 36
- 37. TWO-STROKE CYCLE PETROL ENGINE 4.Exhaust stage: In this stage, the exhaust port is opened as the piston moves downwards. The products of combustion, from the engine cylinder are exhausted through the exhaust port into the atmosphere, as shown (d). This completes the cycle and the engine cylinder is ready to suck the charge again. CHAPTER ONE 37
- 38. VALVE TIMING DIAGRAMFOR A TWO-STROKE CYCLE PETROL ENGINE CHAPTER ONE 38
- 39. TWO-STROKE CYCLE DIESEL ENGINE Allthe four stages of a two stroke cycle diesel engine are described below: 1. Suction stage: In this stage, the piston while going down towards BDC uncovers the transfer port and the exhaust port. The fresh air flows into the engine cylinder from the crank case, as shown in (a). 2. Compression stage: In this stage, the piston while moving up, first covers the transfer port and then exhaust port. After that the air is compressed as the piston moves upwards as shown in (b). In this stage, the inlet port opens and the fresh air enters into the crank case. CHAPTER ONE 39
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- 41. TWO-STROKE CYCLE DIESEL ENGINE 3.Expansion stage: Shortly before the piston reaches the TDC (during compression stroke), the fuel oil is injected in the form of very fine spray by the fuel injection valve, as shown in (c). At this moment, temperature of the compressed air is sufficiently high to ignite the fuel. It increases the pressure and temperature of the products of combustion. The fuel oil is continuously injected for a fraction of the crank revolution. The fuel oil is assumed to be burnt at constant pressure. The piston is pushed with a great force. During the expansion, some of the heat energy produced is transformed into mechanical work. CHAPTER ONE 41
- 42. TWO-STROKE CYCLE DIESEL ENGINE 4.Exhaust stage: In this stage, the exhaust port is opened and the piston moves downwards. The products of combustion from the engine cylinder are exhausted through the exhaust port into the atmosphere as shown in (d). This completes the cycle, and the engine cylinder is ready to suck the air again. CHAPTER ONE 42
- 43. VALVE TIMING DIAGRAMFOR A TWO-STROKE CYCLE DIESEL ENGINE CHAPTER ONE 43
- 44. Comparison of ReciprocatingIC engines Comparison of SI and CI engines 1. Introduction… CHAPTER ONE 44 Parameters SI CI Power and Torque Develops more power but relatively less torque and operates over wide speed range due to shorter stroke. Develops relatively less power but more torque and operates over narrow speed range due to longer stroke (Higher ‘ r ’ ). Thermal Efficiency (b,th) (Fuel Consumption) 20 – 30%, Relatively higher fuel consumption. 30 – 40%, Relatively lower fuel consumption. Emissions Produces HC, CO and NOx. Quieter. Good cold starting. Produces smoke and relatively higher NOx. Noisy and Poor cold staring. Cost Lower initial cost, but more running cost. Higher initial cost, but lower running cost. Reliability Relatively less reliable or durable and needs frequent maintenance. Relatively more reliable or durable, needs less maintenance. Safety Higher fire risk due to ignition system and highly volatile fuel. Lower fire risk due to the absence of ignition system and less volatile fuel.
- 45. 1. Introduction… comparison oftwo-stroke and four – stroke engine CHAPTER ONE 45 Parameters Two-stroke Four-stroke Power and Torque Develops more power ( double) for the same engine capacity. Develops less power ( half) for the same engine capacity. Thermal Efficiency (Fuel Consumption) Lower thermal efficiency due to larger overlapping of the ports for effective scavenging and the scavenging process causes loss of combustible mixture. Hence, lower fuel consumption. Relatively higher thermal efficiency due to shorter overlapping of the valves. Hence, lower fuel consumption. Emissions Produces more pollutants due to the scavenging process. Noisy due to sudden release of burned gases. . Produces relatively less pollutants. Relatively quieter in operation. Cost Lower initial cost and lighter as it uses less component parts of valve gear mechanism. Relatively higher initial cost and heavier as it uses more component parts of valve gear mechanism.
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Editor's Notes
- #21 Differentiates between two and four stroke engines
- #22 Differentiates between two and four stroke engines
- #23 Describes the four stroke petrol engine
- #24 Describes the four stroke petrol engine
- #25 Describes the four stroke petrol engine
- #26 Describes the four stroke petrol engine
- #27 Describes the four stroke petrol engine
- #28 Describes the valve diagram of a four stroke petrol engine
- #29 Describes the four stroke diesel engine cycle
- #30 Describes the four stroke diesel engine cycle
- #31 Describes the four stroke diesel engine cycle
- #32 Describes the four stroke diesel engine cycle
- #33 Describes the four stroke diesel engine cycle
- #34 Describes the valve timing of a four stroke diesel engine
- #35 Describes a two stroke petrol engine
- #36 Describes a two stroke petrol engine
- #37 Describes a two stroke petrol engine
- #38 Describes a two stroke petrol engine
- #39 Describes the valve timing diagram of a two stroke petrol engine
- #40 Describes a two stroke diesel engine
- #41 Describes a two stroke diesel engine
- #42 Describes a two stroke diesel engine
- #43 Describes a two stroke diesel engine
- #44 Describes the valve timing diagram of a two stroke diesel engine