Download - Ideal Turbojet Parametric Cycle Analysis - Amazon Simple … · 2015-12-18 · Ideal Turbojet –With and Without Afterburning • Performing parametric cycle analysis to an ideal

Ideal Turbojet

Parametric Cycle Analysis

© 2015 SIM University. All rights reserved.

• The steps of parametric cycle analysis to an ideal

turbojet

• The output of parametric cycle analysis of an ideal

turbojet

• The differences in performance between ideal

simple turbojet and one with afterburning


Introduction

• Provides thrust even at V0=0 (vs ramjet)

• Turbine extracts only the power required to drive the compressor

and accessories necessary for continuous operation


Adapted: “Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly

Ideal Turbojet

Figure 4-7 T-s Diagram and H-K Diagram of an Ideal Turbojet

© 2015 SIM University. All rights reserved. Adapted: “Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly

Ideal Turbojet

• Input

• Output

- new term (vs ideal ramjet)


Ideal Turbojet

• Equations


Ideal Turbojet

• Equations


Ideal Turbojet


T0 = 220 K; γ = 1.4; cP=1.004 kJ/(kg K); hPR = 42,800 kJ/kg; Tt4 = 1700K

Variation of Specific Thrust and TSFC against Mach Number

Source: Soon Kim Tat

Turbojet – Mach Number Variation



Variation of Efficiency against Mach Number


Turbojet – Mach Number Variation


T0 = 220 K; γ = 1.4; cP=1.004 kJ/(kg K); hPR = 42,800 kJ/kg; πc = 10

Effect of Turbine Inlet Temperature Variation


Turbojet – Effect of Turbine Inlet Temperature

Variation of Specific Thrust against Compressor Pressure Ratio

Lower

compressor

pressure ratio is

desired at higher

Mach numbers




Turbojet – Compressor Pressure Ratio Variation

Variation of TSFC against Compressor Pressure Ratio




Turbojet – Compressor Pressure Ratio Variation

• Optimum Compressor (for max F/ṁo) Temperature and Pressure Ratio

• Lower compressor pressure ratio is desired for higher Mach number

operation


Optimum Compressor Pressure Ratio

• Thrust of turbojet being increased by afterburner (after the turbine)


Ideal Afterburning Turbojet

Figure 4-10 T-s and H-K Diagram of an Ideal Afterburning Turbojet



• Input

• Outputc

- new term (vs ideal turbojet)



• Equations



• Equations



• Optimum (max F/ṁo) Compressor Temperature Ratio




T0 = 220 K; γ = 1.4; cP=1.004 kJ/(kg K); hPR = 42,800 kJ/kg; Tt4 = 1700K ; Tt4 = 2300K

Variation of Specific Thrust against Compressor Pressure Ratio




T0 = 220 K; γ = 1.4; cP=1.004 kJ/(kg K); hPR = 42,800 kJ/kg; Tt4 = 1700K ; Tt4 = 2300K

Variation of TSFC against Compressor Pressure Ratio



• Afterburning causes increase in:

– Specific thrust F/ṁ0

– Thrust specific fuel consumption S

• Optimum compressor pressure ratio (maximum F/ṁ0 ):

– Reduces as Mach number increases

– For afterburning turbojet is higher than non-afterburning

→Afterburning turbojet with moderate to high πc still offers high F/ṁ0 at

high flight Mach numbers

• Fuel/air ratio

– In main burner (f )is unchanged

– In afterburner (fAB ) increases with M and πc

– Total (ftot ) decreases with M and is not a function of πc

• Thermal, propulsive, and overall efficiencies are reduced by afterburning


Comparison of Afterburning

Engine with =30 operates

optimally at M0=2 with AB, and

near optimum at subsonic speeds

where less thrust is required and

S is lower

Optimum Ideal Turbojet

Compressor Pressure

Ratio

Optimum Ideal Turbojet

Performance


Ideal Turbojet – With and Without Afterburning

• Performing parametric cycle analysis to an ideal

turbojet engines, including with afterburner

• Study of the output of parametric cycle analysis of

an ideal simple turbojet and compare its

performance against one with afterburner.

• Evaluating the optimum compressor pressure

ratio in a turbojet engine.


Summary

• Given an ideal turbojet is operating at the following

conditions:

T0 = 220 K; γ = 1.4; cP=1.004 kJ/(kg K);

hPR = 42,800 kJ/kg; Tt4 = 1700K

• Compute the optimum compressor pressure ratio

when operating at Mach 1.0. You may use the

following expressions

• Determine the maximum specific thrust of this engine

• You may compare the results with the charts given in

this presentation


Reflection Question