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MODELLING AND DESIGNING OF A TURBOFAN ENGINE WITH MORE
ENHANCED OVERALL ENGINE EFFICIENCY DURING OPERATION
Article · March 2021
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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.
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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
Impact Factor (JCC): 9.6246 NAAS Rating: 3.11
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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