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MODELLING AND DESIGNING OF A TURBOFAN ENGINE WITH MORE

ENHANCED OVERALL ENGINE EFFICIENCY DURING OPERATION

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MODELLING AND DESIGNING OF A TURBOFAN ENGINE WITH MORE

ENHANCED OVERALL ENGINE EFFICIENCY DURING OPERATION

P. B. SOB1 & M PITA2

1Department of Mechanical Engineering, Faculty of Engineering and Technology, Vaal University of Technology,

Vanderbijlpark 1900, Private Bag X021, South Africa

2Department of Mechanical and Industrial Engineering, Faculty of Engineering and Technology,

University of South Africa

ABSTRACT

In the current study, a turbofan engine design was model for optimal overall efficiency during engine operation.

This was achieved by modelling the parameters of the engine thrust and the total system efficiency during varying

heat transfer process, kinematic processes and flow velocities that are used to propel the aircraft. The main

parameter being model was the propulsion efficiency being modelled as a proportion of the system mechanical

energy being used to propel the system. The tool of EngineSim was used to modelled the derived models being

developed for a design of a turbofan engine with more enhanced overall efficiency. The models focused on the

turbofan efficiency and the critical parameter such as propulsion efficiency was model for optimal operation. the

model derived were simulated by EngineSim version and the derived models were tested through the empirical

simulation of the turbofan engine for the purposes of critical system observation and analysing the system

performance during operation. The turbofan engine thrust was being iterated during EngineSim simulation process

changing the values of the different engine parameters. It was shown that, the thrust produced by the simulation

impacted the propulsion efficiency which gave varying system performance and overall efficiency of the designed

system. It was also revealed that, the design turbofan can produce enough kinetic energy to propel the airplane to

move forward.

KEYWORDS: Turbofan engine, EngineSim 1.8a, GasTurb 13, Propulsion efficiency, Thrust, Simulation.

Received: Feb 01, 2021; Accepted: Feb 20, 2021; Published: Mar 17, 2021; Paper Id.: IJMPERDAPR202125

INTRODUCTION

A turbofan is basically a modern gas turbine designed with system of variation [1]. In the design, there is a turbo

section which performed the mechanical energy combustion and there is a fan that uses mechanical energy from

the flow system and forces the turbine to increase air inflow in the system [2]. Therefore, there is a turbojet being

used to operate a ducted fan leading to varying thrust developed by the system during operation. the system

works on the principles of air circulation during operation [3]. During operation, the inflow of air in the system is

captured by the fan at the inlet flow stream of the turbofan [4]. Some ratio of the mass flow of air in the inlet of

the turbofan passes through the fan vanes and moves to the compressor and the system burner where the fuel-air

mixture takes place for proper combustion to occurs [5]. For this to happen, the ratio of air compression must be

optimal for ignition to take place which often leads to exhaust strokes and the exhaust gas flow through the

turbine fan and turbine nozzle and the burn gases leaves the engine for another cycles of operation to take place

[6].

Orig

ina

l Article

International Journal of Mechanical and Production

Engineering Research and Development (IJMPERD)

ISSN (P): 2249–6890; ISSN (E): 2249–8001

Vol. 11, Issue 2, Apr 2021, 333–350

© TJPRC Pvt. Ltd.

334 P. B. Sob & M Pita

Impact Factor (JCC): 9.6246 NAAS Rating: 3.11

During operation, the mass flow of air through the fan can only take place if the fan is having a velocity of flow

which is slightly higher that the free air stream in the system. The turbofan received force/thrust in the system from the

core and from the fan during operation [7]. During flow ratio of mass flow of air that bypasses in the engine during

operation gets into the system through the bypass ration in the system core during operation [8]. The system therefore

generates more thrust force during operation using the fuel air ratio which enters the core of the system and changes the

mass flow of the system during operation. during this process, only small amount of mass flow is added to the system by

the fan and therefore energy is considered as the system is more efficient in fuel consumption [9]. It is important to note

that the large bypass fuel ratio in a turbofans system during operation contributed to fuel optimization and the system is

observed to be more efficient at optimal power during operation [10]. It must be noted that the fan of the system is

enclosed by an inlet pipe and the system composed of several blades that increases fuel efficiency and optimize

performance of the system at optimal speeds than of a simple propeller [11].

Therefore, a turbofans system operates with high speed that transfer power to the propeller even at low speed. The

low bypass ratio in the turbofans facilitate fuel efficiency and increases the system power during operation [12]. In today’s

times, most turbofans system are designed and used for commercial airliners due to the fact that the system is designed

with an exhaust speed that is more compactable to the subsonic flight speed of the system during operation [13]. The speed

of the aircraft at the lower exhaust speed from a turbofan in the designed system gives proper fuel consumption when

compared to the designed exhaust speed in the designed turbojet engine and this is excessively too high leading to waste of

energy in the system during operation [14]. There is an increased mass airflow in the system during operation from the fan

that usually gives a higher thrust at low speeds during operation [15]. At the lower exhaust speed of the designed system

during operation the system also produces much lower jet noise during operation. Most of the modern designed turbofans

are designed with low specific thrust in the system during operation and this low specific net thrust is divided by the

airflow in the system in order to keep jet noise at a minimum level and at the same time the system fuel economy is lower

[16].

The system bypass ratio is relatively a higher ratio which normal ranges from 4:1 up to 8:1[17]. Most often in the

designed system, a single stage fan is required to operate the system due to its low specific thrust at this operating range

and therefore a low fan pressure ratio is being generated by the system during operation [6-8]. For most commercial

airliner company to be a success the aircraft mainly depends on its weight, low noise and the ability to minimize fuel

economy and the designed craft should travel longer distance travel, and in the end it should provide lower operating costs

and which in turn leads to lower passenger fares [1-13]. A contributing factor to achieve this is in principle is the engine

design that provides high efficiency and low costs at the same time [14-16]. A turbofan engine is made up of different

components which full fills the purpose of the engine [1-5]. In this section a fan, compressor, combustor, turbine and

nozzle will be discussed [2-8].

Modelling and Designing of a Turbofan Engine with More Enhanced Overall Engine Efficiency During Operation 335

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Figure 1: Components of a Turbofan Engine (Source: Open PR)

The design fan in the system is responsible for the generation of majority of the thrust generated by a turbofan

engine system and is more visible seen when looking at the frontier section of the engine [9-11]. The fan blades of the

system are mostly made of special material of titanium and it draws in high air quantities into the turbofan engine during

operation [2-6]. Normally as the system operate, the air gets into the turbofan’s engine system and as the air moves through

two major parts of the engine [3-8], some of the air in the system goes through the core of the engine’s to the core of the

compressor and some of the air in the system flows through the exterior designed system of the engine known being known

as the bypass air section of the system [3-10]. The designed fan of the system is directly connected through the low-

pressure compressor (LPC) of the system and the low-pressure turbine (LPT) is linked by a shaft called the low-pressure

shaft [1-9]. The designed compressor in the system is situated after the fan and it is mainly used to compress the air in the

system and prepare the system air for proper combustion process by adding more pressure and heat before power stroke

[12-16]. The air that enters the engine flows parallel the shaft engine hence the compressor in the system is normally called

an axial flow compressor based on the design consideration. The compressor uses a series of blades to compress the air and

speed up the air to create more energy. The Compressor consists of two parts namely the low-pressure compressor and the

high-pressure compressor which run off separate shafts. The pressure ratio of the compressor is proportional to the total

downstream pressure of the compressor being divided by the entry pressure of the compressor.

𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝑟𝑎𝑡𝑖𝑜 =𝑃2

𝑃1 [1]

𝑃 = 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒(𝑃𝑎) [2]

The diffuser is the first part of the combustor and the high-speed air being accelerated in the system by the

compressor normally enters the system diffuser of the engine during operation. The increase in pressure of the system

which increases across the compressor is proportional to the temperature increment and enthalpy of the system given as

(Alonzo and Crocker, 2018). This causes a change in enthalpy of the system and this causes an adiabatic change in the

compressor during operation and this is defined as:

𝛥ℎ = 𝑇𝐶𝑃(𝜋0.286 − 1) [3]

Whereby:

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𝛥ℎ = 𝐸𝑛𝑡ℎ𝑎𝑙𝑝𝑦𝑐ℎ𝑎𝑛𝑔𝑒(𝐽 𝑘𝑔⁄ )

𝑇 = 𝐼𝑛𝑙𝑒𝑡𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒(𝐾)

𝐶𝑝 = 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐ℎ𝑒𝑎𝑡(𝑘𝐽 𝑘𝑔⁄ 𝐾)

The system rise in enthalpy in the system is proportional to the mass flow of input power being generated by the

turbine compressor during operation (Alonzo and Crocker, 2018).

𝑃 =�̇�𝛥ℎ

𝜂 [4]

Whereby:

𝛥ℎ = 𝐸𝑛𝑡ℎ𝑎𝑙𝑝𝑦𝑐ℎ𝑎𝑛𝑔𝑒(𝐽 𝑘𝑔⁄ )

�̇� = 𝑀𝑎𝑠𝑠𝑓𝑙𝑜𝑤(𝑘𝑔 𝑠⁄ )

𝑃 = 𝐼𝑛𝑝𝑢𝑡𝑝𝑜𝑤𝑒𝑟(𝑊)

𝜂 = 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦

The igniter that is in the combustor ignites the air/fuel mixture causing the mixture to move to the back of the

combustor (Shaw, 2014). The system combustion chamber is design in an area in the cylinder where the ratio of fuel/air

mix must be ignited for exhaust stroke to take place. When the piston in the combustion chamber compresses the mixture

of fuel-air mix ratio and at the end of compression stroke the ratio of air fuel gets ignited by a spark plug and the mixture is

then combusted and this pushes out of the combustion chamber and energy is being created to power the system. During

operation, there are three main basic processes of combustion chambers and these processes are the annular combustion

chamber process, the combination of the two processes being called the can-annular process and the system variations of

these main basic processes during operation. There are also three main systems of operation in most designed system [4-

12] and most of the combustion section in the designed system contains all the main combustion chambers process such as

the igniter plugs that ignites the air-fuel that is being compressed, and fuel nozzles or vaporizing tubes that injects the fuel

ratio in the combustion chamber during operation. The system is normally designed to burn high fuel-air mixture ratio and

the combustion chamber must discharge the burnt gases to the turbine at a desired temperature which must not exceed the

acceptable or allowable limit or the designed turbine inlet during operation [10-17].

During operation the fuel is being introduced or injected at the front end of the burner in the system by a highly

atomized spray nozzle. The injected fuel in combustion mixes with air flows in the fuel nozzle and it mixes with the

desired fuel ratio to form the right fuel-air ratio. In engineering this is called a primary air mixture and this represents

approximately 25% of system total intake of into the engine during operation. Mixture of fuel-air ratio being burned is a

ratio of 15 parts of air to 1 part of fuel by weight being used by the system during operation. It should be noted that the

remaining 75% of air in the system is being used to form an air blanket in the system specifically around the burning gas

section which lower the system temperature. At this period the temperature in the system may reaches a higher temperature

of approximately 3500° F during operation. During operation, when using a percentage of 75 of the air for the cooling

process, the system operating temperature range is usually brought down to approximately half of it normal temperature in

order for the system not to fail during operation [10-15]. The air being used in burning during operation is called primary

air and the air for the cooling system is the secondary air. During operation, the secondary air in the system is being

Modelling and Designing of a Turbofan Engine with More Enhanced Overall Engine Efficiency During Operation 337

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controlled by holes and by the louvers in the system combustion chamber liner during operation.

The igniter plugs in the system function only during starting period of operation. It is being cut out of the circuit

during operation as soon as a combustion process which is a self-supporting system during operation. During a period of

the engine shutdown or a period of engine failure, the combustion chamber of the system is control by a drain valve,

pressure-actuated valve and an automatic drain any remaining unburned fuel from the combustion chamber in the system

during operation. Most combustion chambers in the turbo fan system contain the same basic elements such as: a casing or

outer shell in the system, a perforated inner liner in the system for effective operation or flame tube, fuel nozzles in the

system, and some means of an initial ignition process being design in the system [12-17]. The system combustion chamber

must be designed to be very light weight and it must be constructed and designed to burn fuel in a high velocity airstream

system during operation. The combustion chamber liner in the system is also an extremely critical engine component due

to the fact that it contains high temperatures the burning fuel air mixture during operation [12-17]. The liner in the system

is usually being constructed of a welded high-nickel steel material for optimal operation. Most severe operating parameters

and periods of operation in combustion chambers cycles are encountered in the engine idling strokes and the maximum

rpm ranges during operation is being sustained during operation under these varying conditions of operation that must be

avoided to prevent any failure during combustion [12-16].

Air which is from the combustor flows through the turbine. The turbine has similar blades as the compressor. The

high speed air due to the combustor process flows over the turbine blades. The turbine blades spin and they turn the engine

shaft. This is important because this shaft is connected to the fan, hence allowing the fan to continue sucking air inside the

engine repeating the process (Cutler, 2020). When designing an exhaust nozzle, producers consider several factors that

determine how well the nozzle creates kinetic gases from probable gases, having a 90% efficient nozzle means that the

kinetic energy lost is kept a minimum due to friction which can be excessive if the nozzle is too long. Mass flow rates

within nozzles remain constant and pressure decreases as a result of an increase of the direction of flow of the velocity.

Converging nozzles are popular amongst aircrafts for a couple of reasons; they are good for aircrafts with supersonic speed

and they show of the feature of speeds that are less than the speed of the sound heard through the nozzle. When the

pressure and ambient pressure are equal at the exit of the convergent nozzles (the throat), the flow through it is subsonic.

The use of a converging nozzle aims at producing noise reduction while also avoiding shockwaves. Converging nozzles

can be identified by the throat that gradually decreases from the entrance to the exit causing velocity to gradually increase

through the throat. Converging-diverging nozzles are most used on military aircrafts to achieve supersonic flows.

Assumptions that aid in the design of a nozzle are (a) friction loss is neglected between the walls and the air, (b) gases are

ideal gases, (c) the process is that of a steady flow and a steady state, (d) the process is isentropic, heat or matter is not

transferred, (e) the nozzle conserves energy and mass. This avoids choke flow at the exit of the nozzle; however, jets with

small engines make use of simplistic converging nozzles that are designed with minimal reduction in the cross-sectional

area across the nozzle. The major problem facing the turbofan design is poor overall efficiency during engine operation. In

this study the overall efficiency was improve by modelling the parameters of the engine thrust and the total system

efficiency during varying heat transfer process, kinematic processes and flow velocities that are used to propel the aircraft.

This was achieved by using the tool of tool of EngineSim in modelling and designing of a turbofan engine with more

enhanced overall efficiency. The derived models focused on turbofan efficiency and the critical parameter such as

propulsion efficiency was model for optimal operation.

338 P. B. Sob & M Pita

Impact Factor (JCC): 9.6246 NAAS Rating: 3.11

METHODOLOGY

Theoretical Consideration for Modelling and Designing of Turbofan Engine for improved engine efficiency

Turbofan compressor are becoming more vital in everyday life and they are vital in energy production and in the

Figure 2: Flow Velocity Diagram in a Compressor Stage

Where, the system absolute flow velocity at the inlet of the rotor’s is given as (c1), relative velocity of flow in the

system at the rotor’s inlet is given as (w1), axial flow velocity of the system at the rotor’s inlet during operation is given as

(cx1), absolute flow tangential velocity in the system at the rotor’s inlet is given as (cϑ1), relative tangential velocity of

flow in the system at the rotor’s inlet is given as (wϑ1), blade speed of the system is given as (U), absolute flow velocity of

the system at the rotor’s outlet during operation is given as (c2), relative velocity of the system during operation at the

field of transportation. The fundamental operating principle in a turbofan were established several years ago in the past

decades. In recent years, most efforts are geared on improving and developing better turbofan with more efficient and

operating efficiency. To achieve this the system operation and flow behaviour must be study and well elaborated on the

mass flow during operation. In modelling and improving the turbofan efficiency, it was important to review a gas turbines

engine, turbojets, as well as gas turbine use for conducting theoretical cycle analysis. This includes a look into components

that make up modern small gas turbine having it turbine blades and varying flow angle of operation. During operation, the

system angle convention is usually required when analysing the field flow and blade geometry of the system during

operation. It should be noted that there is very little angular flow standardization and conventions process current literature

source. Researchers and scientist uses an axis plane as a reference line through the mass flow on the blades and the angular

and circumferential flow direction in the system is being measured during operation. Some authors have different view on

the measurement of the flow angle during operation. In most design system the angle of convention must be consist for

blade and field flow angle. All the angles in the system during operation are measured from the axial flow direction and the

angles are always positive in sense of rotation during operation. The diagram shown in Figure 2 revealed the

angular convention in the system being applied in the relative and absolute flow field angles 𝛼′ and 𝛼 respectively, and the

angle of the blade, 𝛽, for the single axial-flow stage turbine system is given as

Modelling and Designing of a Turbofan Engine with More Enhanced Overall Engine Efficiency During Operation 339

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rotor’s outlet is given as (w2), axial velocity of flow at the rotor’s outlet during operation is given as (cx2), absolute

tangential velocity of flow at the rotor’s outlet in the system is given as (cϑ2), relative tangential velocity of flow at the

rotor’s outlet during operation is given as (wϑ2), absolute velocity of flow at the stator’s outlet during operation is given as

(c3), axial velocity of flow at the rotor’s inlet is given as (cx3). The system velocity diagrams during operation are strictly

connected and related to the choice of parameters such as the system reaction during operation, the flow coefficient of the

system during operation and stage loading condition of the system during operation. The separation of flow in the system

during operation is given as

𝜓 =ℎ03−ℎ01

𝑈2 = 𝜙(tan 𝛼2 − tan 𝛼1) [5]

It can also be written like

𝜓 = 𝜙(𝑡𝑎𝑛 𝛽1 − 𝑡𝑎𝑛 𝛽2) = 1 − 𝜙(𝑡𝑎𝑛 𝛼1 + 𝑡𝑎𝑛 𝛽2) [6]

Where (𝑡𝑎𝑛 𝛽1 − 𝑡𝑎𝑛 𝛽2) is the parameters of the rotor turning flow in the system during operation and this gives

the flow coefficient increment, for a stable or fixed stage loading during operation and this uses a required value that is

smaller than the fixed value. As regard the reaction, the connection with the velocity triangles and their respective angles

can be written as,

𝑅 =𝑤1

2−𝑤22

2𝑈(𝐶𝜃2−𝐶𝜃1)=

1

2𝜙(𝑡𝑎𝑛 𝛽1 + 𝑡𝑎𝑛 𝛽2) [7]

Combined equation

𝜓 = 2(1 − 𝑅 − 𝜙 𝑡𝑎𝑛 𝛼1) [8]

Stator:

𝑡𝑎𝑛 𝛼1 =1−𝑅−

𝜓

2

𝜙 [9]

𝑡𝑎𝑛 𝛼2 =1−𝑅+

𝜓

2

𝜙 [10]

Rotor:

𝑡𝑎𝑛 𝛽1 = −𝑅+

𝜓

2

𝜙 [11]

𝑡𝑎𝑛 𝛽2 = −𝑅−

𝜓

2

𝜙 [12]

The flow reaction and angle of flow impacts the volumetric flow rate or mass flow rate through the system as

given as,

𝑑�̇� =𝑑𝑚

𝑑𝑡= 𝜌𝑐𝑑𝐴𝑛 [13]

where d An is being defined as area perpendicular to the direction of flow, c is defined as the stream velocity

density of flow ρ. In the case of one dimensional steady flow system analysis, it is assumed that a steady or constant flow

velocity density is defined for the two consecutive station, 1 and 2, without any control fluid accumulation in the control

volume during operation. That can be derived from the equation of continuity through the system as given as,

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�̇� = 𝜌1𝑐1𝑑1𝐴𝑛1= 𝜌2𝑐2𝑑2𝐴𝑛2

[14]

From the fundament law of turbo machinery, a steady flow energy equation can be modified as fluid flow through

the system and that is given as

�̇� − �̇� = 𝑚[̇ (ℎ2 − ℎ1) +1

2(𝑐2

2 − 𝑐12) + 𝑔(𝑧2 − 𝑧1)] [15]

The flow energy in the system impacts the system efficiency during operation. Most designed turbomachinery

system is operating with an efficiency that are usually expressed in varying approach depending on the performance of the

system such as the isentropic and the polytrophic efficiency. The isentropic efficiency during operation can be related to the

system ideal work per unit mass flow rate and the system polytrophic efficiency during operation can be related to the

actual work per unit mass flow rate per second in the system given as,

𝜂𝑖𝑠𝑒𝑛 =ℎ02𝑠−ℎ01

ℎ02−ℎ01 [16]

The system real work during operation are being represented from the denominator and they are always bigger

than the ideal work in the system which the compressor used during operation and therefore energy is loss during operation

as friction losses takes place during operation. Due to the constant pressure lines in the system during operation on an (h,s),

the diagram normally diverge during operation and at the same time the entropy, the slope of the line which represent high

pressure become higher and the work that is supplied to the series system of isentropic process increases and this can be

compared to the operation of a single stage axial compressor during operation. The designed system is isentropic in process

and is in full compression process. It is therefore possible to have an increase in efficiency of the compression through an

infinite small increment of pressure dp during operation given as,

𝜂𝑝𝑜𝑙𝑦 =𝑑ℎ𝑠

𝑑ℎ [17]

The defined expression given by equation (17) impacts the performance of a gas turbine engine. Any designed gas

turbine system with a continuous internal combustion engine design during operation consist of three major components

and these major components are: compressor, combustor, and turbine. Most basic designed of a turbojet system consists of

a nozzle inlet where a mass flow of air at a free stream velocity is being directed into the system compressor during

operation. The produced high inflow of air in the system is being accelerated and compressed in the system by a

compressor, and then the air flow is being redirected into the system combustion during operation. during this period, fuel

is being injected into the chamber of the system and the chamber is designed with a high-pressure air which can easily

ignited to create combustion during operation. The hot gas in the system expands in the combustion chamber during this

period and it is then forced through the system by the turbine blades which lead to rotation of the shaft which is usually

linked to the turbine of the compressor. During operation, the exhaust gas in the system gets accelerated in the system

through the outlet nozzle during operation. The high flow velocity in the exhaust is operating at a higher speed which is

greater than the free system operating stream velocity for a thrust to be produced during operation. On the basis of the

fundamental Newtonian law of fluid flow in creating thrust in the system during operation, the second law of Newton’s is

applicable and the law states that the force in the system is equivalent to mass multiplied by acceleration of the system

during operation.

Based on the fundamental principles of conservation of linear momentum of flow, the thrust force produced by a

turbojet must be proportional or equal to the system mass flow rate being generated by the exhaust gas which is normally

Modelling and Designing of a Turbofan Engine with More Enhanced Overall Engine Efficiency During Operation 341

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multiplied by the system velocity which is relative to the system free stream velocity of air that is entering the system

compressor during operation. The greater the consumption of fuel by the engine during operation, is greater the thrust

being created by the system and it is assumed to be a constant efficiency of the system during operation. One of the method

of increasing the thrust in the system during operation is by optimising the combustion process which is also known as

thrust augmentation process. The design system normally consists of a separate burner that improve combustion process.

this led to an increase in thrust which substantially increase fuel consumption in the system during operation. Depending

on the design of the gas turbines, some design does not generate thrust but have better power generation at an optimal

efficiency.

Most turbojet and turbofan engines system generate thrust from the system reaction forces during operation and

create high system velocity of flow in the exhaust gas. A turbofan engine used in an air craft uses a fan which is an

upstream compressor, and the fan is driven by the turbine. During operation, the bypasses air in the compressor re-joins the

air in the flow downstream system of turbine. Such design improves fuel efficiency during operating at cruising speeds

which is similar to civil airline travel. Such turbojet engine, unlike most turbofan engine, does not allow any air to bypass

the compressor during operation. Most turboprop and turbo shaft system uses exhaust gases in the system to drive a turbine

that also drives a propeller shaft in the system during operation. The difference in design consideration between the two

systems is due to the fact that the turbo shaft uses all exhaust gas generated in the system to drive the propeller shaft during

operation, whereas in the turboprop system it uses few of this exhaust gas generated in the system to produce thrust during

operation. Most of the designed turbo shaft engines are mostly used in helicopters system, such as the Sikorsky CH-53G as

shown in Figure 3.

Figure 3: Four Types of Gas Turbine Engines Components

To understand the operating principles of a small turbojet engine, it is vital to understand the functionality of

different components in the system during operation. Therefore, it is vital to understand the different conceptual physical

and thermodynamics processing in the different system. The compressor is basically a engine which creates high pressure

ratio of air to achieve combustion process of the system during operation. There are two main types of compressors which

are commonly in used in turbojet engines and there are the axial and centrifugal compressor. The axial compressor system

usually directs all the air flow stream parallel to the rotational axis of the system during operation whereas the centrifugal

compressor directs the flow radially outward in the perpendicular direction of rotation during operation. Most small gas

turbines system produces a power of less than 5 MW and the system is not bulky but often designed within the centrifugal

compressors. Though the designed system is less efficient than a multi-stage axial compressors system, a centrifugal

compressor is more reliable to produce excess pressure ratios of approximately 8:1 with a single stage during operation.

The system pressure ratio generated is proportional or equal to the total pressure downstream produced by the compressor

which is divided by the pressure at the inlet of the compressor during operation.

342 P. B. Sob & M Pita

Impact Factor (JCC): 9.6246 NAAS Rating: 3.11

𝜂 =𝑃1

𝑃2 [18]

The produced ratio in equation (18) impacts fuel consumption, thrust and engine operating efficiency. Figure 4

revealed a centrifugal compressor used in the system.

Figure 4: The Designed System Centrifugal Compressor

No matter the system geometry of the centrifugal compressor, the main objective is to redirect the radially air

generated in the system along the axis of rotation during operation. The air flows nature along the system blades geometry

of the compressor is forced through the radial direction of air flow in the compressor by centrifugal propel force. The high-

speed air generated in the system usually accelerates by the compressor during operation and the air enters the diffuser

stage of the system during operation. The system increase in pressure during operation on the compressor is usually

accompanied by an increase in temperature that impacts the system enthalpy. Therefore, the change in enthalpy across the

system during operation is related to an adiabatic process in the compressor given as

𝛥ℎ = 𝑇 × 𝐶𝑝(𝜋0.286 − 1) [19]

The sudden increase or rise in enthalpy being generated by the system is proportional to the input power generated

by the turbine to the compressor and this is given as,

𝑃 = �̇�𝛥ℎ

𝜂 [20]

From empirical data and computer simulation, performance of overall efficiency during operation is given by

EngineSim. The results in Figure 5 (a-c) revealed the varying of design parameters on performance in EngineSim turbofan

simulation. This gave different design performance on the overall efficiency of the design system as shown in

Figure 6 (a-d).

Modelling and Designing of a Turbofan Engine with More Enhanced Overall Engine Efficiency During Operation 343

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(a) (b)

(c)

Figure 5: (a-c) EngineSim Turbofan Simulation

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(a) (b)

(c) (d)

Figure 6: (a-d) EngineSim Turbofan Simulation

The results in Figure 6 (a-d) revealed overall efficiency of the model turbofan engine in the current study. It is

shown from Figure 6 (a-d) that the varying model parameters in this study impacts the performance of the turbofan engine

during operation. Figure 6(a) shows an initial increase in performance of the model turbofan performance during initial

change in pressure. As the pressure increase due to increase in mass flow rate through the fan, the volumetric flow rate and

mass flow rate in the system increases as shown in Figure 6 (b-d). It was further observed as shown in Figure 6 (c-d) that

an increase in volumetric flow rate significantly impacted the pressure and temperature in the system during operation.

This is where optimal overall performance is enhanced without any indication of mechanical failure in the turbofan during

operation. At this optimal performance there are observation in the model parameters of the turbofan. The following

parameters in table 1 were used to obtain results of the turbofan engine.

Modelling and Designing of a Turbofan Engine with More Enhanced Overall Engine Efficiency During Operation 345

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Table 1: Turbofan Parameters

Variables (Parameters) Name of Variable Value Unit

Ambient Conditions

System Total Temperature (T1) 218 K

System Total Pressure (P1) 23.897 kPa

System Ambient Pressure (Pa) 23.897 kPa

Altitude 10668 m

Basic Engine Parameters

Mach 0.8

Bypass ratio 2.76

System Fuel Flow Rate 0.819 Kg/s

System Intake Pressure Ratio 1.99

System Compressor Pressure Ratio 0.995

System Burner Exit Temperature 1765 K

System Fuel Heating Value 43.124 MJ/kg

System Burner Pressure Ratio 0.995

System Turbine Exit Duct Pressure Ratio 0.95

System Turbine Inlet Temperature 1047 K

Engine Efficiency

System Mechanical Efficiency 98 %

System Isentropic Compressor Efficiency 99.45 %

System Isentropic Turbine Efficiency 85 %

System Combustion Efficiency 99.45 %

Table 2: The Station Parameter in the Turbofan during Operation

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Table 3: Simulated And Parameters of Intake, Compressor, Combustion, Turbine and Nozzle at Varying Stations

Intake (stations 1 to 2)

Compressor (stations 2 to 3)

Combustion (stations 3 to 4)

Turbine (stations 4 to 5)

Nozzle (stations 5 to 8)

The results in table 1 to table 3 revealed varying operating parameters and station parameters during operation. It

is shown that, all the system parameters changes during operation to an optimal efficiency. At the optimal efficiency the

fuel consumption was minimal in the design system. The results of the varying parameters and stations during operation

are shown in Figure 7 It is revealed as shown in Figure7 that the total temperature in the system initially started at a

low temperature that was stable before the system experiences a significant increase in temperature at an optimal

temperature of 1750k where the system experienced a slight decreased in temperature at 1600K where the temperature

stays constant during operation. During this period, the mass flow rate in the system experienced a change that is

constant at 12.3 kg/s and the system experienced a steady decrease at a mass flow of 115 kg/s which was accompanied

by a steady increase in mass flow of 12.7 kg and the mass flow was kept constant throughout the operation. It was also

observed that, the total pressure in the system experienced a decreased that is none linear from a pressure of 36.2 kPa to

a pressure of 34.1 kPa. During this period, the static pressure was observed to increased from 30.01 kPa to an optimal

static pressure of 34.8 kPa where the static pressure start dropping at a none linear rate to a static pressure of 22.8 kPa.

These characteristics are due to the varying efficiency in the system that is affected by the system characteristics during

operation.

Modelling and Designing of a Turbofan Engine with More Enhanced Overall Engine Efficiency During Operation 347

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Figure 7: Station Properties of Turbofan Simulation

The performance of the gas turbine engine is dependent on the mass of air that enters the engine. If the density of

the air decreases, the same volume of air will contain less mass, so less power is produced and vice versa. The mass flow

rate is constant between inlet and compressor at 12.32 kg/s. It decreases during the combustion stage and increases during

turbine stage at a maximum of 12.7 kg/s. From the turbine to the nozzle the mass flow remains constant. Therefore, the

decrease in mass flow rate could be caused by air density that is not constant. The results also show how the flow

temperature varies through a typical turbojet engine. The temperature is color-coded, with blue indicating the lowest

temperature and white the highest temperature. Air is brought into the turbojet through the inlet. The total temperature

increases in the combustion stages of the turbofan engine. The combustion outlet experiences a temperature of 1750K

which is the maximum total temperature in the turbofan. There is a decrease in temperature in the turbine stage. The

turbine outlet experiences a temperature of 1375K and remains constant in the nozzle stage. Therefore, with regards to total

temperature the turbofan engine experiences what temperature is supposed to do. The result also show how the flow

pressure varies through a typical turbojet engine. The pressure is color-coded with blue indicating the lowest pressure and

white the highest pressure. According to simulation results the total pressure decreases throughout the stages of the

turbofan engine. The total pressure is constant during compression stage at 36.2kPa and turbine stage at 36kPa. Due to the

friction losses and low pressure ratios used in this study the total pressure does not increase as it should. Therefore, the

turbofan does not produce enough thrust because pressure is directly proportional to thrust.

The pressure exerted on any part of the airplane depends on how the air is moving around the airplane. Static

pressure is the pressure that would be exerted if the air isn't moving or if the airplane is moving with the exact same speed

348 P. B. Sob & M Pita

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as the air. This means that if the fan in the turbine of a jet engine is speeding up the air, then the static pressure would

decrease. According to simulation results the static pressure changes throughout the cycle. Performance of the jet engine is

not only concerned with the thrust produced, but also with the efficient conversion of the heat energy of the fuel into

kinetic energy. The higher the bypass ratio of a turbofan engine, propulsive efficiency of the engine will increase and the

thrust of the engine will also increase because there is an increase in the amount of air flowing through the engine. Thus,

higher bypass ratio makes the engine more efficient. According to simulation results the propulsion efficiency is 58.69% at

a bypass ratio of 2.97.

Figure 8: State of the Art Turbofan Efficiency Chart (Rolls Royce)

According to John Whurr (2013) the state of the art propulsive efficiency in a turbofan engine is 80%. The

propulsion efficiency of the turbofan engine simulation results is 58.9% at a bypass ratio of 2.76 which is a lower

efficiency compared to what John Whurr provides.

Figure 9: Propulsion Efficiency vs. Airspeed at Increased Bypass Ratio

By increasing the compressor pressure ratio, fan pressure ratio and bypass ratio it is estimated the propulsion

efficiency will be around +70% at air speed of 1000 mph. Therefore, by increasing the bypass ratio the turbo fan simulated

in this study: the thrust of the engine increases due to an increase in the amount of air flowing through the engine, resulting

in increased propulsion efficiency. The design of a turbofan engine must be balanced throughout the engine and system to

Modelling and Designing of a Turbofan Engine with More Enhanced Overall Engine Efficiency During Operation 349

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obtain best overall system performance. Engine cost, maintenance cost, weight, life, reliability, safety and fuel

consumption are some characteristics that will be compromised.

CONCLUSIONS AND RECOMMENDATIONS

The idea behind the project was to demonstrate the basic working principle of a turbofan engine by applying the solid

works skills and modelling of the critical parameters that impacts the design of a turbofan engine for optimal performance.

Based on the provided engine requirements, the thermodynamic cycle has been optimized and basic sizing and

aerodynamic design of the main components have been performed. By applying solid and surface modelling

methodologies, the design and assembly of turbofan engine was completed using EngineSim 1.8a. The model was given

photorealistic render using solid work visualize. The result is a shorter engine of similar diameter with improved efficiency.

The work has provided design details along with some expected performance benefits, and the drawbacks of certain design

choices. Though some engine manufacturers may possess this information, few academic studies providing performance

data for such an application within the public domain have been identified. The design process of a turbofan engine is a

complex process which covers many different disciplines and there is quite often no obvious solution as the improvement

of one parameter often comes at the expense of other. The project can further be improvised by adding other parts such as

the hydraulic, pneumatic and electrical components consisting numerous narrow tubing and wiring.

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