1 (2)
Page 1
Introduction
Title: Cycles Thermodynamics
Authors: Hakeem V. Canonio, RPAE, CEA
Institution: Tarlac Agricultural University
Page 2
Cycles Overview
Coverage of Power Cycles:
1913 Gas Power Cycle
Otto Cycle
Diesel Cycle
Vapor Power Cycle
Rankine Cycle
Refrigeration Cycles
Ideal Vapor-Compression Refrigeration Cycle
Page 3
Cycles Review
A cycle consists of a series of processes that return the working fluid or system to its original state.
Page 4
Applications of Cycles in Power Generation
Mechanical Power Generation includes:
Gas Power Cycle
Otto Cycle
Diesel Cycle
Vapor Power Cycle
Carnot Cycle
Rankine Cycle
Refrigeration and Reversed Carnot Cycle
Ideal Vapor Compression Cycle
Page 5
Categories of Mechanical Power Generation
Based on Fluid Phase:
Gas Power Cycles: Working fluid remains in gaseous form throughout.
Vapor Power Cycle: Working fluid transforms between liquid and vapor phases.
Page 6
Fluid Usage in Mechanical Power Generation
Closed Cycle:
Working fluid returns to the original state for the next cycle.
Open Cycle:
Working fluid is expelled and replaced at each cycle.
Page 7
Mechanical Power Generation Engine
Defined as a set of devices or systems interconnected to produce net mechanical power.
Types Based on Energy Source:
Internal Combustion Engine (ICE): Energy supplied by burning fuel inside the system boundary.
External Combustion Engine (ECE): Energy supplied from outside the system boundary.
Page 8
Types of Internal Combustion Engines (ICEs)
Based on Ignition:
Spark Ignition Engines (SI): Combustion of air-fuel mixture via a spark plug.
Compression Ignition Engines (CI): Air-fuel mixture self-ignites by high compression temperature.
Page 9
Engine Nomenclature
Key Terms:
Bore (d): Diameter of the cylinder.
Stroke (l): Distance piston travels.
Top Dead Center (TDC): Highest point of piston.
Bottom Dead Center (BDC): Lowest point of piston.
Intake/Exhaust Valve: Controls gas flow in/out of the cylinder.
Clearance Volume (Vc): Space remaining when the piston is at TDC.
Displacement Volume (Vd): Volume displaced by the piston during stroke.
Page 10
Engine Parameters
Compression Ratio (r):
Defined as [ r = \frac{V_{max}}{V_{min}} ]
Mean Effective Pressure (MEP): Indicates power output, defined as [ MEP = \frac{W_{net}}{V_{d}} ] where [ W_{net} ] is the net work done by the engine.
Page 11
Simplifications in Thermodynamic Analysis
Assumptions:
No friction or non-conservative forces.
Quasi-equilibrium processes.
Perfectly insulated system boundaries.
Neglect potential (PE) and kinetic energy (KE) of working fluid.
Treat chemical reactions as heat absorbed.
Page 12
Otto Cycle Overview
Ideal SI Engine conceived by Beau de Rochas (1862), applied by Nikolaus August Otto (1867).
Known as a "Constant Volume Cycle" in gas power cycles.
Operates as a four-stroke engine.
Page 13
Otto Cycle Stages
Stages in Cycle:
End of combustion.
Exhaust and intake strokes.
Compression and power strokes.
Key Parameters:
TDC, BDC, pressure-volume relations.
Page 14
Reversible Processes in Otto Cycle
Processes are Idealized:
1-2: Isentropic Compression
2-3: Isochoric Heat Addition
3-4: Isentropic Expansion
4-1: Isochoric Heat Rejection
Assumptions of pure gas states.
Page 15
Otto Cycle Characteristics
Relationships among temperatures and pressures during various processes.
Page 16
Otto Cycle Computations
Key Relationships:
States and transitions between points in the cycle.
Page 17
Further Computations in Otto Cycle
Analyzing changes across cycle states:
Pressure, volume, temperature relationships.
Page 18
Polytropic Analysis in Otto Cycle
Utilize the Polytropic Law for analysis:
Relate temperatures and volumes in respective states.
Page 19
Work and Heat in Otto Cycle
Work (W) calculation:
[ W = Q_{in} - Q_{out} ]
Consideration of heat transfer.
Page 20
Thermal Efficiency in Otto Cycle
Formula for Efficiency (n):
[ n = 1 - \frac{T_{L}}{T_{H}} ]
Page 21
Common Problem Solving in Otto Cycle
Identifying states, computing work and heat, and determining thermal efficiency and design ratio.
Page 22
Sample Worked Example in Otto Cycle
Conduct analysis for real air parameters, finding efficiencies, heat inputs, and output work.
Page 23
Worked Example 1: Comprehensive Analysis
Conditions: Air at 100 kPa and 20°C, compression, heating, expansion, cooling phases.
Variables to find: Efficiency, heat input, work output, maximum pressure.
Page 24
Worked Example Solution Steps
Calculation steps using absolute temperatures and values processed to find efficiencies and work.
Page 25
Additional Examples in Otto Cycle
Investigate an engine's parameters connected to bore, stroke, clearance, and actual thermal efficiency.
Page 26
Diesel Cycle Introduction
Developed by Rudolf Diesel (1886) and Nikolaus Otto, operating as a gas power cycle.
Page 27
Diesel Cycle Process Overview
Involves a series of strokes:
Intake, compression, power, and exhaust with specific volumes depicted.
Page 28
Reversible Processes in Diesel Cycle
Reversible Processes:
1-2: Isentropic Compression
2-3: Isobaric Heat Addition
3-4: Isentropic Expansion
4-1: Isochoric Heat Rejection
Page 29
Diesel Cycle Processes
Visual representation of process stages in the Diesel cycle (P-V diagram).
Page 30
Diesel Cycle Computations
Breakdown of state transitions with pressure, temperature, volume analysis.
Page 31
PVT Analysis in Diesel Cycle
Analyze according to the Polytropic Law similar to Otto cycle while adding a cut-off ratio.
Page 32
Work in Diesel Cycle
Work calculation closely resembling the Otto cycle but accounting for heat differences incorporating heat capacities.
Page 33
Thermal Efficiency in Diesel Cycle
Efficiency defined with respect to heat differences and the introduced cut-off ratio.
Page 34
Problem Solving in Diesel Cycle
Identifying key states and calculating work, heat, and efficiency.
Page 35
Sample Example in Diesel Cycle
Analyze an engine's operating conditions and performance metrics.
Page 36
Worked Example in Diesel Cycle
Calculation for air standard efficiency, maximum temperature, heat input, and net work output for a Diesel cycle.
Page 37
Solutions Process for Diesel Example
Steps taken to arrive at pressure, temperature, efficiency, and work done per kilogram of gas.
Page 38
Example 15.9 in Diesel Cycle
Determine cycle performance metrics from initial conditions and derived points in the cycle.
Page 39
Other Gas Power Cycles
Additional cycles to explore:
Ericsson Cycle
Stirling Cycle
Cayley Cycle
Lenoir Cycle
Reitlinger Cycle
Atkinson Cycle
Crossley Cycle