Journal of Mechanical Engineering Research and Developments (JMERD) 42(5) (2019) 211-215

Journal of Mechanical Engineering Research and

Developments (JMERD)
DOI : http://doi.org/10.26480/jmerd.05.2019.211.215
ISSN: 1024-1752
CODEN : JERDFO

RESEARCH ARTICLE
ANALYSIS OF EXHAUST MANIFOLD OF SPARK-IGNITION ENGINE BY USING
COMPUTATIONAL FLUID DYNAMICS (CFD)
Mohammed Kadhim Allawi1, Mahmood Hasan Oudah2 and Mohanad Kadhim Mejbel3*

1,2PowerMechanics Engineering Department, Engineering Technical College – Baghdad, Middle Technical University (MTU), Iraq
3MaterialsTechniques Engineering Department, Engineering Technical College – Baghdad, Middle Technical University (MTU), Iraq
*Corresponding author e-mail: mohanad@toc.edu.iq, muhenad_abo_jaafar@yahoo.com

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.

ARTICLE DETAILS ABSTRACT

Article History: The exhaust manifold is a pivotal part of an internal combustion engine. The work of the exhaust manifold is
complicated and depends on many parameters viz. backpressure, velocity, the temperature of the exhaust, etc. In this
Received 2 August 2019 work, the performance of the exhaust manifold of a four-stroke, four-cylinder, spark-ignition engine was analysed
Accepted 5 September 2019 using three types of fuels (gasoline, methane, and methanol) to estimate flow characteristics and backpressure. The
Available online 11 September 2019 manifold modelling is done in Fluent 18.0, followed by analysis and meshing in ANSYS software. Velocity, pressure and
temperature profiles at 1000 rpm engine speed were made. We found that methanol provided the highest exit
temperature and back pressure, whereas methane provided the lowest exit pressure. Backpressure decreased when
using gasoline fuel. Methane resulted in the best exhaust manifold performance.

KEYWORDS

Exhaust Manifold, Analysis CFD, Gasoline Fuel, Back Pressure, Gasoline Engine.

1. INTRODUCTION

Environmental pollution due to the exponential increase in the use of fossil A researcher studied the experimental realization of the impact of
fuels as power sources has become a serious threat to humanity. The manifold geometry on volumetric space and backpressure for a multi-
exhaust manifold collects exhaust gases formed during combustion and cylinder gasoline engine and determined an optimal shape for the exhaust
releases them to the environment. The exhaust manifold is a critical part manifold for maximum volumetric ability [5]. They also investigated the
of the engine. Its function is very complex, and it is involved with many exhaust manifold rendering for eight variants in terms of exhaust velocity
parameters, including temperature, scavenging, exhaust velocity, back and back pressure, etc. [6]. and carried out investigations for various
pressure, etc. Exhaust gases from multiple engine cylinders are collected shapes of exhaust manifolds using CFD program [7]. A researcher
in the exhaust manifold and delivered into a single cylindrical exhaust pipe predicted with a high degree of accuracy the exhaust manifolds failure and
to the atmosphere. Exhaust manifolds are either made from stainless steel removing structural weaknesses on highly loaded exhaust manifolds by
or cast iron. The exhaust manifold performance is directly related to fuel using optimization of design method [8]. A researcher conducted a
consumption and emission efficiencies. The main restrictions for exhaust numeral one-dimensional research on a gasoline engine to study the
manifolds are the lack of space around the engine, the challenging and influence of different geometry types for the intake manifold [9]. A
substantial necessity of having a well-distributed fluid flow at the catalyst researcher studied the existing designs of the exhaust manifold to
entrance. Many studies are carried out for improving the geometrical establish a better understanding of the importance of the different factors
design of the manifold due to the severe heat cycle conditions that might involved in the design process [10]. A researcher analysed the outcome of
damage the manifold because of cracks and extensive plastic deformations two models for back pressure and velocity. The results of their two models
caused by the flow of hot gases. However, computational fluid dynamics acquired a reduction in back pressure leading to an improvement of the
(CFD) simulations by using finite element methods are applied to predict volumetric capacity of the engine [11]. A researcher in their review study,
the deformations and thermal stresses in the manifold area. A researcher summarised the results and conclusions of many types of research on
developed a method to estimate exhaust performance from their work on exhaust manifold optimization and structural analysis [12]. A researcher
the experimental realization and computational analysis of a one-cylinder, concluded that the increase of exhaust gas flow speed is evidenced in the
compression ignition (CI) engine [1]. manifold because of detraction of the passage space [13].

(Hwang et al.) analysed two brands of exhaust manifolds using workshop A researcher used three types of fuels – LPG, alcohol, and gasoline to
analyses and volatile computational fluid dynamics (CFD) simulations. estimate the minimum backpressure, thermal and flow characteristics, a
Their study showed that the typical cast type manifold yields higher flow manifold modelling followed by analysis and meshing in ANSYS software
uniformity and lower rear pressure than the bending type [2]. A was carried out. They concluded that LPG fuel provided minimum back
researcher studied the effect of thermal influence on the exhaust manifold. pressure and temperature. The researchers recommended LPG fuel as a
A nonlinear thermal, structural strength analysis of exhaust manifold of 4- good choice instead of gasoline on exhaust manifold function performance
four cylinder, 4-four stroke engine was carried out by using Finite element in terms of lowest back pressure [14]. A researcher investigated two
analysis (FEA) and computational fluid dynamics (CFD). they obtained a different fuel mixtures, pure compressed natural gas (CNG) and 29 vol%
good correlation for the failure and suggested a design modification [3]. A H2 in CNG (named HCNG). he concluded that the engine efficiency using
researcher performed a thermomechanical fatigue investigation of HCNG is greater than CNG [15]. A researcher concluded that the gas
stainless-steel exhaust manifolds and an accurate elastoviscoplastic temperature emerging from the engine decreases when using blended
behavior model was identified [4]. gasoline fuels during the analysis of a single-cylinder four-stroke engine
[16], [17]. (Krishnara et al.) prepared a manifold design using CAD/CAM
software, and analysed the design by using ANSYS. thermal and CFD

Cite The Article: Mohammed Kadhim Allawi, Mahmood Hasan Oudah And Mohanad Kadhim Mejbel (2019) Analysis Of Exhaust Manifold Of Spark-Ignition Engine By Using
Computational Fluid Dynamics (Cfd). Journal Of Mechanical Engineering Research And Developments, 42(5) : 211-215.
 Journal of Mechanical Engineering Research and Developments (JMERD) 42(5) (2019) 211-215

analysis was carried out to measure the performance of the designed Table 1: Engine Specifications
exhaust manifold. The CFD simulations performed to study the volumetric
Engine type 4cyl., 4-stroke
efficiency behavior of the designed manifold. They concluded that
pressure drop occurred leading to an increase in volumetric efficiency Engine model gasoline engine
across the manifold due to inclination angle, on the other hand, the flow Combustion type water-cooled
resistance of the fluid was reduced causing an improvement in engine Swept volume Total 1.99741L
power performance and efficiency [18]. A researcher prepared a Valve per cylinder two
modelling of 2-two exhaust manifolds of the natural frequencies and Bore 87 mm
transient thermal behavior for different manifold materials according to Stroke 84 mm
CFD software. He indicated that 3D modelling was feasible and concluded Compression ratio 11
that manifolds made of stainless steel minimizes heat loss and possess Fuel injection pump Port injection
higher natural frequency compared to cast iron [19]. A researcher adopted Intake valve open (BTDC): 15
an integrated exhaust manifold with an advanced cylinder head in a three- Intake valve close (ATDC): 60
cylinder turbo engine. A series of simulations and experimental test work Exhaust valve open (BTDC): 20
validations were carried out, such as temperature and vibration tests done Exhaust valve close (ATDC): 40
on a rig test. They found that a good correlation between the experimental
tests and simulation results are shown and no cracks or metal damage Table 2: Boundary Conditions of the case understudy
found inside the hot end or cylinder head [20].
From the previous studies that shown many problems raised in the Boundary - INLET
performance of the exhaust manifold caused by adopting different types Type Mass Flow inlet
of fuels. The objectives of this research are the following: Boundary - OUTLET
• to study according to ANSYS analysis the performance of the exhaust
Type Out Flow
manifold by using three types of fuels;
• to predict exit pressure, temperature, back pressure and velocity profiles Boundary – OUTER WALL
of the exhaust manifold with these fuels; and Heat transfer Convection
• to recommend the best fuel type based on manifold highest performance. Mass and momentum No-slip wall
2. METHODS Table 3: Domain physics
Modelling of the geometry was carried out by selecting the actual model of
the four-stroke, four-cylinder gasoline engine (engine specifications are Domain flue gases
listed in Table 1) and using ANSYS design modeler software 18.0 to create Type Fluid
a geometric model of the engine. The engine manifold was generated in Analysis State Steady
three different parts, which were then assembled to give the final sample
Material Flue Gases
of the exhaust manifold (Fig. 1). A meshed model of the assembly of the
exhaust manifold of T-grid scheme type is shown in (Fig. 2). Turbulent model SST
Domain tube
2.1 Boundary Conditions Type Solid
Analysis type Steady-state
The flow domain for this modelling is the exhaust manifold, including
intake and exhaust ports. Tables 2 & 3 describe the boundary conditions Material Steel
and domain physics for each case. Non-slip boundary conditions were Domain motion Stationary
used for the manifold walls (u = v = 0). The generation of tetrahedral mesh
and the statistics elements was 62383. The boundary conditions were Table 4: Illustrates the fuel characteristics
applied to the inlet and outlet exhaust ports for simulation of the exhaust
velocity backpressure. Material Gasoline Methanol Methane
Density (kg/liter) 0.75 0.79 0.0007
2.2 Fuel Properties
Calorific Value (kJ/kg) 43000.0 20000.0 46280
Three types of fuels were conducted in this study to analyse the Molecular Mass
114.230 32.040 17.423
performance of the exhaust manifold. The characteristics of the fuels are (kg/k.mol)
summarized in Table 4.
H/C Ratio Fuel (molar) 1.8000 1.0000 3.87

3. RESULTS AND DISCUSSION

The resulted CFD simulations are reported in the following subsections

3.1 Velocity Profiles (Fig. 3 - 5)

As shown in the velocity figures of the manifold, the velocity of the inlet
using 1000 rpm engine speed is almost the same. Gas velocity decreased
in the front z-direction, where the speed during the entry was 0.6 m/s. The
velocity as per the boundary condition in four inlet sections is 0.6 m/s. It
is noticed in all fuel types that the gas speed continues to increase until the
outlet pressure occurs. Methanol had the widest velocity range (0.56 m/s
to 0.772 m/s at 1000 rpm), Gasoline (0.6 m/s to 0.716 m/s at 1000 rpm)
Figure 1: Solid view of the exhaust manifold
and methane (0.553 m/s to 0.66 m/s at 1000 rpm).

Figure 3: The speed profile of the exhaust manifold using gasoline at 1000
Figure 2: The meshed sample of the exhaust manifold rpm
Cite The Article: Mohammed Kadhim Allawi, Mahmood Hasan Oudah And Mohanad Kadhim Mejbel (2019) Analysis Of Exhaust Manifold O f Spark-Ignition Engine By Using
Computational Fluid Dynamics (Cfd). Journal Of Mechanical Engineering Research And Developments, 42(5) : 211-215.
 Journal of Mechanical Engineering Research and Developments (JMERD) 42(5) (2019) 211-215

Figure 4: The speed profile of the exhaust manifold with methane at 1000
Figure 7: The pressure profile of the exhaust manifold with methane at
rpm
1000 rpm

Figure 5: The speed profile of the exhaust manifold with methanol at 1000 Figure 8: The pressure profile of the exhaust manifold with methanol at
rpm 1000 rpm

3.2 Pressure Profiles (Fig. 6 - 8)

It is observed that the pressure from the entry branches to exit line
continues to decrease in all fuel types by examining the pressure contour
figures, as it is a necessary condition for the gas flow to pass in the outlet
direction. In the gasoline case, the first two entry pipes have nearly the
same pressure, and the pressure value decreases. Slight back pressure can
be noticed at the linkage of the third inlet pipe. Gasoline provided the
highest exit pressure of about (123.4 kPa at 1000 rpm) at the outlet, while
methane provided a lower pressure of (113.7 kPa at 1000 rpm) and
methanol produced the lowest (113.1 kPa at 1000 rpm).

3.3 Temperature Profiles (Fig. 9 - 11)

By examining the temperature profiles, it is noticed that the temperature

at four entries is almost the same because hot gases emerge from the
engine cylinders at an equal rate and heat capacity, because of the
similarity of all four combustion cylinders conditions. Gasoline fuel
produces the highest exit temperature (868 0C at 1000 rpm), whereas Figure 9: The temperature profile of the exhaust manifold with Gasoline
methanol fuel produced a lower temperature (800 0C at 1000 rpm) and at 1000 rpm
methane produced the lowest (741.7 0C at 1000 rpm).

Figure 6: The pressure profile of the exhaust manifold with gasoline at Figure 10: The temperature profile of the exhaust manifold with methane
1000 rpm at 1000 rpm

Cite The Article: Mohammed Kadhim Allawi, Mahmood Hasan Oudah And Mohanad Kadhim Mejbel (2019) Analysis Of Exhaust Manifold O f Spark-Ignition Engine By Using
Computational Fluid Dynamics (Cfd). Journal Of Mechanical Engineering Research And Developments, 42(5) : 211-215.
 Journal of Mechanical Engineering Research and Developments (JMERD) 42(5) (2019) 211-215

3.6 Engine Speed viz Gas Temperature (Fig. 14)

Fig. 14 shows the relationship between engine speed and the exhaust gas
temperature. The use of gasoline resulted in an exhaust gas temperature
(about 868 to 994 oC) at various engine speeds (1000 to 4000 rpm), and
provided the highest temperature at 1000 rpm, whereas the use of
methanol fuel resulted in the highest temperature at engine speeds (3000
to 4000 rpm). Methane produced the lowest temperature at various
engine speeds (1000 to 4000 rpm). The temperature increased rapidly
with methanol at higher engine speeds and had the widest temperature
range (798 to 1032 oC).

Gasoline Methanol Methane

1050
Figure 11: The temperature profile of the exhaust manifold with methanol
at 1000 rpm 1000
3.4 Engine Speed viz Gas Velocity (Fig. 12)
950

Temperature 0C
Fig. 12 shows the relationship between engine speed and exhaust gas
velocity at the first cylinder. It is observed that using gasoline resulted in 900
the highest exhaust gas velocity (about 0.6 to 0.723 m/s) with various
engine speeds (1000 to 4000 rpm). On the other hand, using methanol 850
resulted in a lower exhaust gas velocity than gasoline and higher exhaust
gas velocity than methane at various engine speeds (1000 to 4000 rpm).
800

Gasoline Methanol Methane 750

0.75
700
0.7 1000 2000 3000 4000
Engine Speed RPM
0.65
Velocity m/s

0.6 Figure 14. The relation between gas temperature and engine speeds of
different fuels at the first cylinder
0.55
3.7 Back Pressure of Fuels (Fig. 15)
0.5
Fig. 15. Shows the variation of backpressure of different fuels at the first
0.45 cylinder. When using gasoline, the backpressure was decreased compared
to methanol that provided the highest backpressure, which reduces the
0.4 engine efficiency considerably.
1000 2000 3000 4000
1000
Engine Speed RPM
900
Figure 12: The relation between exhaust gas velocities and engine speeds 800
of different fuels at the first cylinder
Back Pressure (Pa)

700
3.5 Engine Speed viz Gas Pressure (Fig. 13) 600

Fig. 13 shows the relationship between engine speed and the exhaust gas 500
pressure in the entrance of the first cylinder manifold. It is observed that
400
the use of gasoline resulted in the highest exhaust gas pressure (about 146
kPa) at engine speed (4000 rpm), whereas using methanol fuel resulted in 300
lower exhaust gas pressure than gasoline and higher exhaust gas pressure
than methane at the various engine speeds (1000 to 4000 rpm). Methanol 200
had the widest pressure range. 100
0
Gasoline Methane Methanol

Figure 15: The backpressure of different fuels at the first cylinder

4. CONCLUSIONS

The flue gas characteristics generated within the spark ignition engine
were investigated using CFD. Findings of this work are summarized below:
• Fuels have significant effects on manifold performance.
• Methanol provided the highest range of exhaust gas speed, and its
magnitude lies closer to gasoline than to methane.
• Gasoline provided the highest exit pressure at the outlet, whereas
methanol provided a lower pressure than gasoline but higher than
methane.
• The exit temperature is highest with gasoline and lowest with methane
at 1000 rpm.
Figure 13: The relation between inlet pressure and engine speeds of • The highest exhaust gas temperature occurred when using methanol at
different fuels at the first cylinder engine speeds of 3000 to 4000 rpm.

Cite The Article: Mohammed Kadhim Allawi, Mahmood Hasan Oudah And Mohanad Kadhim Mejbel (2019) Analysis Of Exhaust Manifold O f Spark-Ignition Engine By Using
Computational Fluid Dynamics (Cfd). Journal Of Mechanical Engineering Research And Developments, 42(5) : 211-215.
 Journal of Mechanical Engineering Research and Developments (JMERD) 42(5) (2019) 211-215

• The exhaust gas velocity at engine speeds from 1000 to 4000 rpm is [9] de Souza, G.R., Pellegrini, C., Ferreira, S.L., Soto Pau, F., Armas, O. 2019.
highest with gasoline and lowest with methane. Study of intake manifolds of an internal combustion engine: A new
• The backpressure was lowest with gasoline and highest with methanol. geometry based on experimental results and numerical simulations,
Therm. Sci. Eng. Prog., 9, 248–258.
From the above conclusions, we recommend the use of methane as an
alternative fuel in SI engines because its performance is closer to gasoline [10] Raghuwanshi, G., Kakirde, A., Sharma, S. 2018. Design and Analysis of
than methanol, on the other hand, the exhaust manifold operating life will Exhaust Manifold Comparing Different Specifications, Int. J. Eng. Trends
be longer because of the lower temperature generated from fuel Technol., 62(1), 42–45.
combustion.
[11] Manikandan, P., Samuel, A. CFD Analysis of Exhaust Manifold, 257–
ACKNOWLEDGEMENTS 261.

The authors would like to thank Power Mechanics Engineering [12] Srivastava, A. 2017. A Literature Review on Exhaust Manifold
Department and their staff for their kind support. Optimisation and Structural Analysis through F.E.A Approach, 3, 727–729.

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Cite The Article: Mohammed Kadhim Allawi, Mahmood Hasan Oudah And Mohanad Kadhim Mejbel (2019) Analysis Of Exhaust Manifold O f Spark-Ignition Engine By Using
Computational Fluid Dynamics (Cfd). Journal Of Mechanical Engineering Research And Developments, 42(5) : 211-215.