thermodynmic Cycles

7/25/2019 thermodynmic Cycles

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AIR STANDARD CYCLES

The air standard cycle is a cycle followed by a heat engine which uses air as the working medium

Since the air standard analysis is the simplest and most idealistic, such cycles are also called idea

cyclesand the engine running on such cycles are called ideal engines.

ASSUMPTIONS

1. The working medium is a perfect gas with constant specific heats and molecular weight

corresponding to values at room temperature.

2. No chemical reactions occur during the cycle. The heat addition and heat rejection processes

are merely heat transfer processes.

3. The processes are reversible.

4. Losses by heat transfer from the apparatus to the atmosphere are assumed to be zero in this

analysis.

5. The working medium at the end of the process (cycle) is unchanged and is at the same

condition as at the beginning of the process (cycle).

BASIC CONSIDERATIONS IN THE ANALYSIS OF POWER CYCLES

The cycles encountered in actual devices are difficult to analyze because of the presence of friction,

and the absence of sufficient time for establishment of equilibrium conditions during the cycle.

In order to make an analytical study of a cycle feasible, we have to make some idealizations by

neglecting internal Irreversibility and complexities.

Such cycles resemble the actual cycles closely but are made up of internal reversible processes.

These cycles are called ideal cycles.

AIR STANDARD CYCLES

In gas power cycles, the working fluid will be in gaseous phase throughout the cycle.Petrol engines

(gasoline engines), diesel engines and gas turbines are familiar examples of devices that operate on

gas cycles. All these devices are called Internal combustion engines as the fuel is burnt within the

boundaries of the system. Because of the combustion of the fuel, the composition of the working fluid

changes from a mixture of air and fuel to products of combustion during the course of the cycle.


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CARNOT CYCLE. :an ideal reversible closed thermodynamic cycle in which the working substance

goes through the four successive operations of isothermal expansion to a desired point, adiabatic

expansion to a desired point, isothermal compression, and adiabatic compression back to its initial

state. when acting as a heat engine consists of the following steps

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AN OTTO CYCLEis an idealized thermodynamic cycle that describes the functioning of a typical

spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile

engines. Pressure-Volume diagram. Temperature-Entropy diagram.

Process 01 a mass of air is drawn into piston/cylinder arrangement at constant

pressure.

Process 12 is an adiabatic (isentropic) compression of the air as the piston moves

from bottomdead centre(BDC) to top dead centre (TDC).

Process 23 is a constant-volume heat transfer to the working gas from an external

source while the piston is at top dead centre. This process is intended to represent the

ignition of the fuel-air mixture and the subsequent rapid burning

Process 34 is an adiabatic (isentropic) expansion (power stroke).

Process 41 completes the cycle by a constant-volume process in which heat is

rejected from the air while the piston is at bottom dead centre.

Process 10 the mass of air is released to the atmosphere in a constant pressure

process.
https://en.wikipedia.org/wiki/Dead_centrehttps://en.wikipedia.org/wiki/Dead_centrehttps://en.wikipedia.org/wiki/Dead_centrehttps://en.wikipedia.org/wiki/Dead_centre


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DIESEL CYCLE

The Diesel cycleis a combustion process of a reciprocating internal combustion engine. In it, fuel isignited by heat generated during the compression of air in the combustion chamber, into which fuel isthen injected.

Process 1 to 2 isisentropiccompression of the fluid (blue)

Process 2 to 3 isreversibleconstant pressure heating (red)

Process 3 to 4 is isentropic expansion (yellow)

Process 4 to 1 is reversible constant volume cooling

STIRLING CYCLE

Stirling engine components are less than that of internal combustion engine therefore its simplicity

makes this engine friendly usage and maintenance. The increasing of fossil energy demand impacts

on natural resources and leads us facing fuel price crisis. Therefore, alternative and sustainable

energy which is environmental safe is required.

Stirling Cycle Stirling engine is based on Stirling cycle thermodynamically. The internal circulation of

the working gas under expansion and extraction in hot and cold spaces, respectively, moves two

pistons called displacer and power piston. The schematic diagrams of P-v and T-s diagrams are as

shown.

a. Isothermalexpansion.The expansion space is heated externally, and the gas undergoesnear-isothermal expansion.

b. Constant-volume(known asisovolumetric orisochoric)heat removal. The gas is passed

through theregenerator,thus cooling the gas, and transferring heat to the regenerator for use

in the next cycle.

c. Isothermalcompression.The compression space isintercooled,so the gas undergoes near-

isothermal compression.

d. Constant-volume heat addition.The compressed air flows back through the regenerator and

picks up heat on the way to the heated expansion space.
https://en.wikipedia.org/wiki/Isentropichttps://en.wikipedia.org/wiki/Isentropichttps://en.wikipedia.org/wiki/Isentropichttps://en.wikipedia.org/wiki/Reversible_process_(thermodynamics)https://en.wikipedia.org/wiki/Reversible_process_(thermodynamics)https://en.wikipedia.org/wiki/Reversible_process_(thermodynamics)https://en.wikipedia.org/wiki/Isothermalhttps://en.wikipedia.org/wiki/Thermal_expansionhttps://en.wikipedia.org/wiki/Isometric_processhttps://en.wikipedia.org/wiki/Isochoric_processhttps://en.wikipedia.org/wiki/Regenerative_heat_exchangerhttps://en.wikipedia.org/wiki/Isothermalhttps://en.wikipedia.org/wiki/Gas_compressionhttps://en.wikipedia.org/wiki/Intercoolerhttps://en.wikipedia.org/wiki/Intercoolerhttps://en.wikipedia.org/wiki/Gas_compressionhttps://en.wikipedia.org/wiki/Isothermalhttps://en.wikipedia.org/wiki/Regenerative_heat_exchangerhttps://en.wikipedia.org/wiki/Isochoric_processhttps://en.wikipedia.org/wiki/Isometric_processhttps://en.wikipedia.org/wiki/Thermal_expansionhttps://en.wikipedia.org/wiki/Isothermalhttps://en.wikipedia.org/wiki/Reversible_process_(thermodynamics)https://en.wikipedia.org/wiki/Isentropic


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DUAL COMBUSTION CYCLE

The dual combustion cycle(also known as the limited pressureor mixed cycle, Trinkler

cycle, Seiliger cycleor Sabathe cycle) is a thermal cycle that is a combination of theOtto cycleand

theDiesel cycle,first introduced by Russian-German engineer Gustav Trinkler. Heat is added partly

at constant volume and partly at constant pressure, the advantage of which is that more time is

available for the fuel to completely combust. Because of lagging characteristics of fuel this cycle is

invariably used for diesel andhot spotignition engines. TheP-V diagramis given below:

The dual cycle consists of following operations:

1. 1-2 Adiabatic compression

2. 2-3 Addition of heat at constant volume.

3. 3-4 Addition of heat at constant pressure.

4. 4-5 Adiabatic expansion.

5. 5-1 Rejection of heat at constant volume.

ERICSSON CYCLE

he Ericsson cycle comprises of two isothermal and two constant pressure (isobaric) processes. The

following is a list of the four processes that occur between the four stages of the ideal Ericsson cycle:

Process 1 -> 2:Isothermalcompression. The compression space is assumed to

beintercooled,so the gas undergoes isothermal compression. The compressed air flows into a

storage tank at constant pressure. In the ideal cycle, there is no heat transfer across the tank

walls.

Process 2 -> 3:Isobaricheat addition. From the tank, the compressed air flows through the

regenerator and picks up heat at a high constant-pressure on the way to the heated power-

cylinder.

Process 3 -> 4:Isothermalexpansion. The power-cylinder expansion-space is heated

externally, and the gas undergoes isothermal expansion.

Process 4 -> 1: Isobaric heat removal. Before the air is released as exhaust, it is passed

back through the regenerator, thus cooling the gas at a low constant pressure, and heating the

regenerator for the next cycle.
https://en.wikipedia.org/wiki/Otto_cyclehttps://en.wikipedia.org/wiki/Otto_cyclehttps://en.wikipedia.org/wiki/Otto_cyclehttps://en.wikipedia.org/wiki/Diesel_cyclehttps://en.wikipedia.org/wiki/Diesel_cyclehttps://en.wikipedia.org/wiki/Diesel_cyclehttps://en.wikipedia.org/wiki/Hot_bulb_enginehttps://en.wikipedia.org/wiki/Hot_bulb_enginehttps://en.wikipedia.org/wiki/Hot_bulb_enginehttps://en.wikipedia.org/wiki/P-V_diagramhttps://en.wikipedia.org/wiki/P-V_diagramhttps://en.wikipedia.org/wiki/P-V_diagramhttps://en.wikipedia.org/wiki/Isothermal_processhttps://en.wikipedia.org/wiki/Isothermal_processhttps://en.wikipedia.org/wiki/Isothermal_processhttps://en.wikipedia.org/wiki/Intercoolerhttps://en.wikipedia.org/wiki/Intercoolerhttps://en.wikipedia.org/wiki/Intercoolerhttps://en.wikipedia.org/wiki/Isobaric_processhttps://en.wikipedia.org/wiki/Isobaric_processhttps://en.wikipedia.org/wiki/Isobaric_processhttps://en.wikipedia.org/wiki/Isothermal_processhttps://en.wikipedia.org/wiki/Isothermal_processhttps://en.wikipedia.org/wiki/Isothermal_processhttps://en.wikipedia.org/wiki/Isothermal_processhttps://en.wikipedia.org/wiki/Isobaric_processhttps://en.wikipedia.org/wiki/Intercoolerhttps://en.wikipedia.org/wiki/Isothermal_processhttps://en.wikipedia.org/wiki/P-V_diagramhttps://en.wikipedia.org/wiki/Hot_bulb_enginehttps://en.wikipedia.org/wiki/Diesel_cyclehttps://en.wikipedia.org/wiki/Otto_cycle

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