Intake Manifold Design For A Formula Student Vehicle
Intake Manifold Design For A Formula Student Vehicle
Intake Manifold Design For A Formula Student Vehicle
SEM- 4
Force Ikshvaku
NIE, Mysore
aashray.trakroo@gmail.com
parthchelsea15@gmail.com
Abstract- This paper describes the design and analysis procedure (Critical Flow condition), and therein lays the problem.
for the intake manifold for a Formula Student Vehicle. The design Critical Flow exists when the mass flow is the maximum
is influenced by the restrictions provided in the rule book for the possible for the existing upstream conditions, and the
FS event, namely Formula Bharat. The intake thus designed saw
average velocity closely approximates the local sonic
use on the FI04; the fourth FS car from the team.
velocity (speed of sound in air ≈ 330m/s, or Mach 1)
I. INTRODUCTION Since the maximum mass flow rate is now a fixed
parameter because of the restrictor, the aim is to allow
The air intake design for a formula student vehicle is the engine to achieve the maximum mass flow with
primarily focussed on tackling the design constraints as minimal pull from the engine. In short, the pressure
per the event rulebook. The rulebook states that all the difference between atmosphere and the pressure created
air to be fed into the engine should pass through a in the cylinder should be minimal, so that maximum
circular orifice 20mm in diameter called the restrictor. airflow into the engine is ensured at all times.
The presence of the restrictor in the intake manifold if
not managed properly can adversely affect the engine The team currently uses a single cylinder fuel injected
performance with a significant drop in volumetric DOHC KTM Duke 390 engine [2014 series] which
efficiency and the subsequent power output. produces a peak power of 43hp at 9500 rpm and a peak
torque of 28 Nm at 7000 rpm with a cylinder volume of
In a naturally aspirated engine, the engine creates a low 373.2 cc. The stock 6 speed transmission is mated with
pressure during the intake stroke, causing the air from the engine as of now with a primary reduction of 30:80.
the atmosphere to enter the cylinders. The higher the The drive train employs a chain drive with an open
rpm, the greater the pull, and the higher the pressure differential.
created inside the cylinder. According to the
stoichiometric air-fuel ratio, to burn 1 gram of gasoline
14.7 grams of air is required. By reducing the diameter
of the flow path from 46mm to 20mm, the flow cross-
section area gets reduced substantially. At low rpms of
the engine when the engine requires less air, the
reduction in area is compensated by the accelerated flow
of air through the throat (20mm section). But since the
car is designed to run at high rpm’s (6,000rpm to
10,000rpm with the restrictor attached, the flow at the
throat reaches near sonic velocities Fig. 1 Intake Manifold for the FI03
II. DESIGN OBJECTIVES
For naturally aspirated engines, the sequence must be: throttle
The design objectives for the intake manifold design are as body, restrictor, and engine. The maximum restrictor diameters
follows: which must be respected at all times during the competition are:
• Minimize pressure loss, as pressure loss results in a decrease
in output power. (a) Gasoline fuelled vehicles - 20mm
• Maintain equal static pressure distribution in the plenum.
(b) E-85 fuelled vehicles - 19mm
• Minimize the number of bends and sudden changes in
geometry, as these geometric affects can cause pressure loss. IV. DESIGN
• Maximize air velocity and mass flow into the cylinder, as
this provides a better mixture of fuel and air, which results in For the sake of localizing design objectives; the intake manifold
better combustion and performance. is divided into three main components:
• Minimize the mass of the system; a common goal of every
subsystem of the vehicle. The Restrictor
The Plenum
The design of the intake manifold is majorly dependent on the The Runner
target RPM range of the engine. Since the car will mostly be
performing in the RPM range of 6000 to 10,000 rpm at the
event, the intake is designed for an rpm of 7000 rpm. The Each of the aforementioned components of the intake manifold
driving factor behind it is the fact that the KTM engine gives has their performance interdependent on the others.
the maximised torque output at 7000 rpm since we still use the
For obtaining optimum performance from the intake manifold
stock KTM ECU.
as a whole, each of the components is studied individually and
then the overall manifold geometry is analysed.
III. DESIGN CONSTRAINTS
All parts of the engine air and fuel control systems The restrictor by definition is a circular profile of diameter 20
(including the throttle and the complete air intake mm, through which all the airflow to the engine is supposed to
system, including the air filter and any air boxes) must pass.
lie within the surface defined by the top of the roll bar
and the outside edge of the four tires. The restrictor is mostly realised in design in the form of a
Any portion of the air intake system that is less than Orifice or a Venturi.
350mm above the ground must be shielded from side
An orifice plate is a thin plate with a hole in the centre. It is
or rear impact collisions.
usually placed in a pipe in which fluid flows. When the fluid
The intake manifold must be securely attached to the
reaches the orifice plate, the fluid is forced to converge to go
engine block or cylinder head with brackets and
through the small hole; the point of maximum convergence
mechanical fasteners. The threaded fasteners used to
actually occurs shortly downstream of the physical orifice, at
secure the intake manifold are considered critical
the so-called vena contracta. As it does so, the velocity and the
fasteners.
pressure change. Beyond the vena contracta, the fluid expands
Intake systems with significant mass or cantilever
and the velocity and pressure change once again. By measuring
from the cylinder head must be supported to prevent
the difference in fluid pressure between the normal pipe section
stress to the intake system. Supports to the engine
and at the vena contracta, the volumetric and mass flow rates
must be rigid. Supports to the frame or chassis must
can be calculated.
incorporate isolation to allow for engine movement
and chassis. The Venturi tube or simply a Venturi is a tubular setup of
In order to limit the power capability from the engine, converging and diverging conical sections. The Venturi effect
a single circular restrictor must be placed in the intake is a jet effect; as with a funnel the velocity of the fluid increases
system and all engine airflow must pass through the as the cross sectional area decreases, with the static pressure
restrictor. The only allowed sequence of components correspondingly decreasing. According to the laws governing
are the following: fluid dynamics, a fluid’s velocity must increase as it passes
through a constriction to satisfy the principle of continuity,
while its pressure must decrease to satisfy the principle of Hence the plenum volume and geometry also plays an
conservation of mechanical energy. Thus a drop in pressure important role in intake manifold design. The plenum design
negates any gain in kinetic energy a fluid may accrue due to its can further be pursued in two ways; one is to design it for rapid
increased velocity through a constriction. filling and discharge such that the plenum volume can be
decreased to some extent. Another is to compromise a bit on the
The team currently makes use of a venturi type restrictor filling time and go for a higher plenum volume [2x to 3x engine
instead of an orifice type because of a much higher discharge volume] so that even a slower fill up is covered up by the excess
coefficient. This also allows for better plenum filling as volume. Design of the second type exhibits a lesser dependence
compared to the orifice type. on the plenum geometry and calls in for a relatively simpler
analysis and is hence preferred by majority of the FS teams
The optimum solution to achieve maximum possible mass flow
including us.
rate of air as quickly as possible is to minimize the pressure loss
through the flow restriction device. The best general design for
this objective is to use the Venturi design. From the data
gathered through the numerous simulations, it can be observed VII. RUNNER
that the values for converging angle and diverging angle of the
Venturi are 18 degrees and 6 degrees respectively. This also The runner is the final part of the intake manifold that feeds
prevents flow separation along the venturi walls. directly to the intake port at the engine. The performance of the
entire intake manifold is largely dependent on the runner
geometry: the runner length and the runner diameter; out of
which the runner length is the more dominant feature.
VIII. PROTOTYPING
Pressure based
Transient
Absolute Velocity Formation
2D
Fig. 8 Intake prototype 3, meshed
Since the boundary condition depicted in fig. 6 is an The pressure- velocity scheme employed was SIMPLEC, with
approximate representation of the actual pressure condition; the default spatial discretization parameters.
whereas the real condition is more smoothened at the cardinal
points. Therefore the Pressure vs. time data was fit to a piece- Transient formulation was kept at first order implicit.
wise function with a second degree polynomial to smoothen the
For complicated flows involving turbulence and/or additional
pressure drop situation.
physical models, SIMPLEC improves convergence only if it is
And also since ANSYS R15 doesn’t support transient boundary being limited by the pressure-velocity coupling.
conditions with inbuilt functions; the above mentioned
B. Post processing
boundary condition was initialized into the solver by writing
the condition as a C-based User Defined Function [UDF]. The The Velocity vector plots for each of the intake iterations at the
UDF was compiled and subsequently interpreted by the solver maximum velocity frame are as shown:
itself. The UDF is mentioned in the appendix.
(c) Meshing
As can be inferred from the figures 8 and 9; the maximum Since the third prototype yielded better results both in
velocity attained by air at the restrictor for prototype 3 is 275.4 simulation and validation phase; it was decided to proceed with
m/s ; whereas the same value in case of the second prototype is the third prototype as the final intake model for the 2018 car ,
230 m/s. Therefore the third prototype has a higher mass flow the FI04.
through the restrictor, since the mass flow at the restrictor is
directly proportional to the maximum velocity attained.
ACKNOWLEDGEMENTS
REFERENCES
Fig. 10 Intake prototype 2, velocity vectors at t= 0.012s [1] Heywood J.B.-Internal Combustion Engines Fundamentals.pdf
[2] Intake Manifold Tech_ Runner Size Calculations - Team Integra Forums -
Team Integra.pdf
[4] Anshul Singhal, Mallika Parveen -Air Flow Optimization via a Venturi Type
Air Restrictor.pdf
APPENDIX
#include "udf.h"
DEFINE_PROFILE(unsteady_pressure, thread,
position)
face_t f;
real t = CURRENT_TIME;
3. Residual Plot for prototype 3 simulation:
begin_f_loop(f, thread)
if(t<0.008)
else
end_f_loop(f, thread)
Prototype 2: