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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