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ISSN(Online): 2319-8753
ISSN (Print): 2347-6710

International Journal of Innovative Research in Science,

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Vol. 7, Issue 4, April 2018

Design and CFD Analysis of Automobile air

Intake Manifold
Nandimandalam Rohith Varma1, Karpe Sanket2, Nimbalkar Vishal 3, Naik Akshay 4, Ashu Kumar 5
U.G. Student, Dept. of Mechanical Engineering, MGMCET, Kamothe, Navi Mumbai, India1
U.G. Student, Dept. of Mechanical Engineering, MGMCET, Kamothe, Navi Mumbai, India2
U.G. Student, Dept. of Mechanical Engineering, MGMCET, Kamothe, Navi Mumbai, India3
U.G. Student, Dept. of Mechanical Engineering, MGMCET, Kamothe, Navi Mumbai, India4
Asst. Professor, Department of Mechanical Engineering, MGMCET, Kamothe, Navi Mumbai, India5

ABSTRACT:In automotive technology, an intake manifold is the component of an engine that transports the air-fuel
mixture to the engine cylinders. The main purpose of the intake manifold is to evenly distribute the combustion mixture
to each intake port of the engine cylinder. Even distribution is important to optimize the volumetric efficiency and
performance of the engine. The scope of this paper is limited to designing the CAD model of the intake manifold using
solidworks software and analysing the air flow inside it using ANSYS fluent CFD package. To do this, four different
intake manifolds would be designed wherein, the shape of the plenum would be varied keeping the dimensions of the
restrictor and the runners same. Flow would be analysed in each of the different geometries of the intake manifold and
the results of each would be compared. After comparing the results of the analysis, the best geometry of the intake
manifold that produces the most favourable outlet conditions would then be selected. Design parameters of the intake
manifold are to be done by considering formula student (FSAE) rules.

KEYWORDS: Intake manifold, Solidworks, Volumetric efficiency, ANSYS, CFD, Plenum, Restrictor, Runner, FSAE

I. INTRODUCTION

In automotive technology, an intake manifold (in American English) is the component of an engine that transports the
air-fuel mixture to the engine cylinders. The term manifold originated from the traditional English word manigfeald
(from the Anglo-Saxon manig [many] and feald [fold]) and relates to the folding together of multiple inputs and outputs.
The main purpose of the intake manifold is to evenly distribute the combustion mixture to each intake port of the
engine cylinder, and to create the air-fuel mixture, unless the engine has direct injection. Even distribution is important
to optimize the volumetric efficiency and performance of the engine, the two most desirable techniques was found to
increase the volumetric efficiency, and they are intake manifold design and variable valve timing technology for intake
and exhaust valves. The design of the variable valve timing technology is quite complex and expensive to produce, and
it offers quite less scope of research, thus almost every researchers and automotive industry is focused on improvement
of intake manifold.
However, there is always room for enhancement on intake system. The air intake system has seen many reiterations and
improvements and substantially increased during the past years by controlling the dimension and shape, and permitting
the engine to produce increasing amounts of power by improving their volumetric efficiency, best possible fuel
consumption, reduced fuel emissions, and most of the research performed, by automotive researchers and engine
manufacturers (i.e. Mazda, BMW, Audi, Ford, Renault etc.). Porsche in the 1980s developed an intake system to use on
their vehicles that adjusted the length of the intake system by switching amongst the longer and shorter pair of tube
utilizing a butterfly valve, developing some positive pressure, which usually enhances overall performance of the
engine. Audi began to use a similar system in some cars in the 1990s and Ford Motor in 1997.

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ISSN (Print): 2347-6710

International Journal of Innovative Research in Science,

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Vol. 7, Issue 4, April 2018

Nomenclature of Intake
Intake system consists typically of throttle body, restrictor, inlet pipe, plenum, cylinder runner, fuel injectors, air
temperature sensor and manifold pressure sensor. It composed of two main parts, in combination with the throttle body,
which include the plenum and the cylinder runners. Air enters in to plenum through restrictor due to vacuum created by
engine, plenum stores the combustion air as reservoir and then transport the combustion air to engine through the
cylinder runner.
i. Plenum: It is storage device which placed between throttle valve and cylinder runner. The function of the plenum
is to equalize pressure for more even distribution air-fuel mixture in side combustion chamber, because of irregular
supply or demand of the engine cylinder, sometime plenum chamber also work as an acoustic silencer device.
ii. Restrictor (C-D nozzle): Restrictor is part of the intake manifold is similar to what is usually known as a “critical
nozzle”, “critical flow venturi”, or “sonic choke”. Such components are often used in practice of industries as simple
control devices to control the mass flow rate.
iii. Cylinder Runner: The cylinder runners are the parts of the air intake system which delivers air from plenum to the
combustion chamber. In each runner, the principal phenomenon that governs its performance is actually, the effect of
acoustic waves. As the purpose of the cylinder runner is distribution of air, performance to transport the maximum
amount of air, and in the case of the engine, the successive enhancement in volumetric efficiency.

II. RELATED WORK

1. E.R.Burtnett(1927) designed first gaseous-fuel manifold for two stroke cycle internal combustion engines of the
type in which no inlet valves are used to controlling for the entrance of gaseous fuel to the pre-compression chamber.
2. Futakuchi(1984) designed an improved intake manifold, which enhance both charging and volumetric efficiency
of the engine throughout the large range of engine speed and load.
3.Sattler et al. (1999) found that, the previous research broken conventional intake manifold into three separate
parts, plenum, runner cylinder and a supplement portion.
4. Davis et al. (2001) designed multiple stage ram intake manifold for a four-cycle internal combustion engine to
minimize imbalances air/fuel ratio and volumetric efficiency.
5. David Chalet et al. (2011) studied on inlet manifold of internal combustion engine by frequency modelling of the
pressure waves, they perform the simulation of pressure waves on inlet and exhaust manifolds of internal combustion
engine, which remains challenging.

III. METHODOLOGY

First, various restrictor models are designed using solidworks software. In the restrictor models, the inlet and outlet
diameter are kept constant, which will be equal to the engine specifications. The engine considered in this case is the
KTM Duke 390 engine, which is used in two wheelers. The throat diameter of the restrictor is kept at 20mm abiding
by the FSAE rules. The only thing varied in the restrictor models is the convergent and divergent angles. The
convergent angles have values as 12°,14°,16°,18° and 20°, the divergent angles have values as 4°,6°,8°,10° and 12°.
Flow analysis is carried out in these models and the results are compared. After this, the best restrictor model is
selected. Now, various plenum shapes are designed which are cylindrical, elliptical, spherical and square in shape.
The whole intake is then considered for flow analysis. The outlet boundary conditions are obtained by Ricardo
WAVE software. The results of the analysis are compared to then select the best intake geometry giving optimum
results.

Copyright to IJIRSET DOI:10.15680/IJIRSET.2018.0704031 3424

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Vol. 7, Issue 4, April 2018

IV. RESTRICTOR ANALYSIS

The Mass Flow Rate for choking condition(throat) is given by [10],

m  rVA
For an ideal compressible gas,
 1

Apt    1 2  2  1
m  M 1  M 
Tt R  2 
Mass flow rate is maximum when M = 1, which is choked condition.
Therefore, putting M = 1 in above equation,
 1

Apt    1 2  1
m   
Tt R 2 
From above equation, we can calculate mass flow rate by data values given below:
M = 1 (choked flow)
A = 0.001256 m² (20 mm restrictor)
R = 0.286 KJ/Kg-K
γ = 1.4
Pt = 101325 Pa
T = 300 K
Therefore,
Mass Flow Rate, ṁ = 0.0703 kg/s

Inlet Boundary Condition  Ambient Pressure = 101325 Pa

Outlet Boundary Condition  Mass flow rate = 0.0703 kg/s

V. INTAKE MODELS

The next is to select the best plenum geometry. In order to that, four different plenum shapes are modelled, roughly
keeping the volume of the models same. The plenum shapes thus considered were, cylindrical, elliptical, spherical and
square. These were modelled in solidworks software. After modelling fluid flow analysis was done on ANSYS CFX
module.

(a) (b)

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(c) (d)
Fig.1 Various Intake Models: (a) Cylindrical Intake, (b) Elliptical Intake, (c) Spherical Intake, (d) Square Intake

Intake Analysis Procedure:

Transient analysis was done on the whole intake geometry using Ansys CFX CFD package.
The static pressure data at the engine inlet, for one whole engine cycle was found from Ricardo WAVE software.
The outlet pressures have values ranging from 0.7 bar to 1 bar.
The analysis time is found by calculating the time for 1 engine cycle at 8500RPM.
Time for 1 engine cycle = 2*60/8500 = 0.01411764 s
Taking 60 timesteps for more accurate results, time for 1 timestep = 0.0002353 s
Inlet Boundary Condition  Ambient Pressure = 101325 Pa
Outlet Boundary Condition  Function defined by the runner data.

VI. RESULTS & DISCUSSION

The static pressures at the throat section and the outlet for the various restrictor models are summarized in the
following table. All values are in Pascals.

DIVERGING
C Angles 4° 6° 8° 10° 12°
O
12° 75310 75370 74850 74250 73680
N
V 14° 74570 74420 73680 73060 72370
E
R 16° 73800 73280 72480 71730 71270
G
I 18° 72980 72280 71490 70580 69810
N
20° 72170 71260 70110 69430 68640
G
Table1. Static pressure values at throat section

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DIVERGING
C Angles 4° 6° 8° 10° 12°
O
N 12° 98340 98370 98340 95620 95510
V
14° 98310 98330 98270 95430 95290
E
R 16° 98280 98260 98200 95200 95120
G
I 18° 98230 98200 98140 95010 94860
N
G 20° 98190 98130 98040 94810 94660

Table2. Static pressure values at outlet

(a) (b)
Fig.2 Fluid flow analysis of restrictor with 12° converging and 6° diverging angles (a) Velocity streamline, (b) Pressure Contour

The results of the transient fluid flow analysis on the intake geometries are as follows:

(a) (b)

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(c) (d)

(d)
Fig.3 Velocity streamlines of different intake geometries (a) Cylindrical Plenum, (b) Elliptical Plenum, (c) Spherical Plenum, (d) Square
Plenum

From the figures 2 and 3, we can make conclusions about the fluid flow in the restrictor model and the intake models
respectively. In the figure 2, we can see that the restrictor model with 12° and 6° convergent and divergent angles
respectively has the lowest pressure drop and fits our objective perfectly. Also this model is easy to manufacture. From
the figure 3, the velocity streamline of the fluid, which is air in our case, can be seen. In order to select the best intake
model, we want the vortices created in the plenum to be minimum and the velocity of central flow to be maximum.
Also, the pressure drop in the intake should be less.

Fig.4Comparative graph depicting the central flow velocities of different intakes

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Fig.5Comparative graph depicting the pressure drop along the length of different intakes

Optimum runner length calculation:

The formula for optimum intake runner length (L) according to induction wave theory is:
L = (EVCD*0.25*V*2/RPM*RV) – (0.5*runner diameter)
Where,
L = Runner Length
EVCD = Effective Valve Closed Duration
V = Pressure Wave Speed
RV = Reflective Value = 4
EVCD = (726° – 226° + 20°) = 514° {20° is added to get effective valve open duration}
V = 1152 ft/s
RPM = 8500
Runner Diameter = 1.81102 inch {Diameter of throttle body on engine}
Therefore,
Optimum intake runner length (L) = 352.806 mm

VII. CONCLUSIONS

From the results obtained from the restrictor analysis, it can be inferred that the restrictor model in which the pressure
loss observed is minimum, is the best restrictor model. In this case the restrictor with converging and diverging angles
as 12° and 6° respectively has the minimum pressure loss, so we considered it to be the ideal restrictor model.
After transient analysis, velocity vectors in different plenum shapes are compared. In square plenum, central high
velocity flow has wider flow area, as fewer vortexes are created. Also, velocity values are higher for this central flow in
square plenum when compared with other shapes. Therefore, this geometry of the intake is considered to be best model.
It is observed that engine performance at higher speeds improves with increase in plenum volume (torque peak shifts
towards higher engine speeds). However, as design is primarily targeted at lower speed range of 4000 to 6000rpm,
volume twice the engine displacement is best solution. The optimum runner length has been obtained by the
calculations shown before and its value is L = 352.806 mm.The runner diameter has been taken as 46mm since it is the
diameter of the throttle body and it accounts in ease of manufacturability of the model.

Copyright to IJIRSET DOI:10.15680/IJIRSET.2018.0704031 3429

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ISSN(Online): 2319-8753
ISSN (Print): 2347-6710

International Journal of Innovative Research in Science,

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Vol. 7, Issue 4, April 2018

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