Cairo 2nd Petrol Lecture 8
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This document provides a summary of key concepts related to internal combustion engines (ICEs). It discusses the basic components and operating principles of ICEs, including intake and exhaust systems, valves, combustion process, and conversion of reciprocating motion to rotation via a crank mechanism. It also defines and explains important engine performance parameters such as power, thermal efficiency, mean effective pressure, specific fuel consumption, and different types of engine efficiencies. Examples of related calculations are provided.
Cairo 2nd Petrol Lecture 8
- 1. Mechanical Engineering Thermodynamics 2nd year Petrol dept. 2011-2012 Lecture (8) Internal Combustion Engines (ICE) Lecturer : Dr. Esmail Bialy
- 3. Air and Fuel will expand due to combustion, pushing the piston downwards.
- 4. If we connected the piston to a crank mechanism, we can convert the reciprocating motion into rotation.
- 5. Air and fuel need intake system to get into the cylinder.
- 6. Combustion products need exhaust system to be pushed out the cylinder.
- 9. Intake valve is oppened.
- 10. The Intake valve is closed, when the piston reached the BDC ( Bottom dead center).
- 11. Both valves are closed
- 12. Now ignition starts to begin the heat addition process.
- 16. Engine Volume. Vcylinder= ¼π d2l. Where, d: cylinder diameter (bore) L: cylinder length (stroke) Vcylinders= ¼π d2l * z where, z: number of cylinders V˚Stroke = ¼π d2l * z * N/60ζ Where, N: number of crank shaft revolutions per minute (rpm) ζ: =2 for 4-stroke engines = 1 for 2-stroke engines
- 17. Engine Performance Parameters. a- Power: 1- Brake Power: the measured power output of the engine BP= T * ω Where, T: Torque (N.m) ω: radial speed (rad/s) and ω= 2πN/60 2- Indicated Power: is the theoretical power of a reciprocating engine if it is completely frictionless in converting the expanding gas energy (piston pressure × displacement) in the cylinders. IP= BP + FP 3- Friction Power FP: increases proportionally with N2
- 18. Engine Performance Parameters. b- Thermal efficiency: 1- Brake thermal efficiency: ηb= BP/Q˚add Where, Q˚add: rate of heat added to engine per second due to fuel burning 2- Indicated thermal efficiency : ηI= IP/Q˚add Q˚add=m˚f * C.V Where, m˚f : consumed fuel flowrate (kg/s) C.V: fuel heating value: heat released per each kg of completely burned fuel (kJ/kg)
- 19. Engine Performance Parameters. c- mean effective pressure: 1- Brake mean effective pressure: Bmep= BP/ V˚Stroke Where, BP : brake power V˚Stroke :engine cylinders volume 2- Indicated mean effective pressure : Imep= IP/ V˚Stroke Mean effective pressure: a valuable measure of an engine's capacity to do work that is independent of engine displacement.
- 20. Engine Performance Parameters. d- specific fuel consumption: 1- Brake specific fuel consumption: Bsfc= m˚f /BP Where, BP : brake power m˚f : consumed fuel flowrate (kg/s) 2- Indicated specific fuel consumption : Isfc= m˚f /IP
- 21. Engine Performance Parameters. e- Engine efficiencies: 1- Mechanical efficiency : ηm= BP/IP ηm= ηb/ηI 2- Volumetric efficiency : V˚Stroke )actual = ηv ¼π d2l * z * N/60ζ
- 22. Brake power calculation: BP=ηb*Q˚add Q˚add=m˚f * C.V =ηb m˚f C.V F/A = m˚f / m˚a =ηb m˚a F/A C.V m˚a= ρa V˚Stroke =ηb ρa V˚Stroke F/A C.V =ηb ηv ρa F/A C.V ¼π d2l * z * N/60ζ BP=ηb ηv ρa F/A C.V ¼π d2l * z * N/60ζ
- 23. Example (6-3): An eight-cylinder, four stroke diesel engine develops 900 kW of brake power at 600 rpm. The cylinder size is 37 cm bore by 46 cm stroke and the engine uses 4.5 kg of fuel per minute. Upon complete combustion, the fuel releases heat energy of 45 MJ/kg. The indicated mean effective pressure is 660 kPa. Calculate the indicated, brake and mechanical efficiencies.