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Recent Patents on Mechanical Engineering, 2021, xx, xx-xx
RESEARCH ARTICLE
Computational Approach on Acoustic and Flow Performances of a
Combined Resistive and Reactive Muffler
Farlian Rizky Sinagaa, Ubaidillaha,*, Iwan Yahyab, Seung-Bok Choic,*, Siti Aishah Abdul Azizd
and Nurul Azhani Yunuse
a
Mechanical Engineering Department, Universitas Sebelas Maret, Surakarta 57126, Indonesia; bDepartment of Physics,
Universitas Sebelas Maret, Surakarta 57126, Indonesia; cDepartment of Mechanical Engineering, The State of New York
at Korea (SUNY Korea), Incheon 21985, South Korea; dEngineering Materials and Structures (eMast), Malaysia Japan
Internatinal Institute of Technology, Universiti Teknologi Malaysia, Kuala Lumpur 54100, Malaysia; eUniversiti
Teknologi Petronas, Seri Iskandar 32610, Malaysia.
Engineering
Abstract: The internal combustion engine (ICE) based vehicles must follow strict regulations regarding
noise levels, especially in the racing competition. The noise level is typically gauged as per two different
scenarios: stationary engine revolution and maximum achievable revolution. One cannot reach the
required noise level by deploying just reactive or resistive muffler type, separately. This research
recommends a novel mix of reactive and resistive mufflers in a single package solution. For assessing
the noise level, three different types of mufflers are devised and studied by means of a computational
approach. The new exhaust design in this study becomes a novelty of the proposed article. In analyzing
the acoustic capability of the muffler, up to now it has not been able to dampen in various frequency
ranges. In this paper, the author wants to perform a computational analysis of 3 muffler models that
combine several methods of attenuation that are effective at different specific frequency ranges with
different configurations in order to obtain a good combined attenuation capability in various frequency
ranges. Muffler 1 uses simple reactive and dissipative techniques like standard mufflers, while muffler 2
combines the dissipative technique with a Helmholtz resonator acting as the reactive part. Muffler 3 has
a multi-chamber system which uses a combination of several advanced techniques. The three mufflers
are evaluated on the basis of their capacity to decrease noise level. This noise level is assessed by
considering both transmission and insertion loss through mathematical calculations in the frequency
range of 200 Hz to 6400 Hz with the help of pressure acoustic, frequency domain (ACPR) simulation.
Apart from noise evaluation, this study also examines flow parameters to estimate the pressure drop for
the proposed muffler. Comsol simulation provided both insertion loss (IL) and transmission loss (TL)
with different trends. Mufler 3 had broadband response compared to the counterparts. Verifiying the
finite element simulation results, electroacoustic models of each muffler were simulated using Matlab
Simulink to get frequency response. Both finite element and electroacoustic modeling results have a good
agreement. Pressure distribution of each model were also evaluated in terms of isosurface total pressure.
It is demonstrated that the proposed muffler having a multi-chamber setup provides the best
performances showing both superior and consistent noise reduction throughout the 200-6400 Hz
frequency range and good airflow that does not create backpressure due to noise suppression efforts.
ARTICLE HISTORY
Received: Month xx, 20xx
Revised: Month xx, 20xx
Accepted: Month xx, 20xx
DOI:
-
Keywords: Vehicle muffler, noise reduction, reactive-dissipative, insertion loss, transmission loss, electro-acoustic,
frequency-domain simulation.
Recent Patents on Mechanical
1. INTRODUCTION
Ground vehicles create a noise impact on the environment
due to their combustion process [1,2]. Noise directly impacts
the human body utilizing the auditory system and
physiological routes other than hear. Hence, there has been
renewed interest in material sciences to develop
environmentally friendly materials and approaches [1]. One of
the noisiest combustion engines is that of a race vehicle.
Engines are tuned to provide more performance and power;
however, the noise needs also to be reduced. Therefore, most
of the formula races impose limits on the noise level emitted
by the vehicles [3]. ISO standards also regulate constraints on
noise levels of vehicles to limit environmental pollution [4].
Noise measurements taken at the vehicle exhaust provide
information about the noise levels [5]. It is widely known that
the performance of a vehicle is assessed using several methods
[6]. Noise reduction is reduced effectively by controlling its
propagation path and sound barriers [7]. Research is required
to determine the optimal muffler design that balances both
vehicle noise and performance [3,4]. Nevertheless, there is a
trade-off between vehicle performance and noise level, where
prioritizing engine performance leads to a compromise on
engine sound. It is well-known that the critical function is to
eliminate high-pressure exhaust from the engine to the
atmosphere, which is at a lower pressure. The difference of
pressure creates a sound whose intensity needs to be decreased
[8]. The muffler serves the additional purpose of acting as a
damper in a system that outputs the exhaust [9]. Acoustic
analysis may be used to determine the noise level and
subsequently decrease it to get better noise levels [3]. Acoustic
analysis should be done from a design perspective to evaluate
the flow inside the muffler. Acoustic damping typically
creates backpressure, which can be managed using an
improved design [4,10]. Performance assessment for a muffler
is conducted using flow and acoustic analyses [11]. These
analyses are performed by measuring the value of the
transmission loss [9]. Transmission loss is the ratio of the
ability to transmit power as measured by using many
approaches like two loadings [12]), two sources [11], and
breaking waves [13–15]. Measuring using this approach is
considered appropriate to determine acoustic ability [16,17].
Noise reduction devices are classified in two based on the
way noise is reduced. The first uses porous (dissipative)
material to absorb the sound waves, while the other way is to
dampen sound using reactive attenuation [18]. In the case of
dissipative damping, a perforated plate is employed to absorb
sound. This technique reduces the sound using the walls.
Therefore, the diameter, shape, and curvature influence the
airflow since this method affects air pressure and velocity
inside the pipe [19]. Dissipative techniques are effective at
mid to high frequency and can conserve space without
affecting the flow. However, the porosity of the material
significantly influences [2,5]. Vehicle mufflers using reactive
techniques typically employ a network of spaces to break the
sound waves [20]. The muffler may break the sound waves
using two techniques: a division of space and having
components arranged in a breakwater pattern in the muffler
[21]. This technique works well at low frequency; however, it
has the drawback of backpressure [2].
*Address correspondence to this author at the Mechanical Engineering
Department, Universitas Sebelas Maret, Surakarta, Indonesia;
E-mail: ubaidillah_ft@staff.uns.ac.id
1874-477X/21 $65.00+.00
Additionally, this technique needs more space to arrange
components that can split and reflect the waves to have
optimal noise reduction. The present muffler design integrates
two sound damping techniques (hybrid) [22] proposed
building hybrid silencers having micro-perforated panels
(MMPs) set to create partitions that achieve the silencing
effects using reactive and dissipative techniques [22].
Additionally, Yu et al. [23] achieved a ventilation gap through
the use of micro-perforated panels (MMPs) in 2016. The
muffler's noise absorption had a better range due to the
primary dissipative effects and the added absorbance
compensation due to resonance [23]. In 2016, Xiang et al. [23]
developed a multi-chamber muffler to achieve a reactive
effect at lower frequencies (between 1000 Hz and 3000 Hz),
where the damping ability had increased by 136%. Apart from
decreasing the vehicle exhaust, mufflers are required to
regulate high-pressure exhaust systems, as indicated by
Williams et al. [24]. The highest magnitude of pressure
gradient at the exit point varies directly with the number of
steps causing a decrease in pressure. Williams et al. studied a
turbine exhaust and used a hybrid reactive-dissipative
technique and splitter silencers to enhance the damping ability
at low and medium frequencies [24]. In that year, Fulkar and
Neihguk [25] evaluated a hybrid-type tractor muffler with
four chambers, which had reactive and dissipative
mechanisms using the COMSOL software. The first chamber
consisted of the perforated material to enhance low-frequency
effects along with rigid baffles in the first chamber. This
model could be useful at vulnerable frequencies between 400
Hz and 1400 Hz [25]. Referring to the studies, hybrid mufflers
have certain damping characteristics that can improve their
ability. The ability of a product to respond to an external
stimulus is part of the set of characteristics termed as smart,
which are reserved for smart materials to enhance their value
[26]. As of date, not many pieces of research have investigated
thoroughly the integrated effects of dissipative and resistive
methods to enhance the acoustic performance inside a muffler.
Consequently, this study's primary contribution is to
propose a new muffler design that balances the trade-off
between backpressure and acoustic characteristics over a wide
range of muffler operating frequencies. This research uses
COMSOL software to run an ACPR simulation on the basis
of calculating the difference in acoustic pressure to understand
the transmission loss for all muffler models. Three dissipative
and hybrid designs with different configuration with their
insertion loss and transmission loss being measured can help
determine an appropriate muffler design for high-performance
vehicles without compromising performance. This study also
draws a comparison between a muffler having enhanced
damping over a more comprehensive frequency range due to
the use of an integrated set of reactive and dissipative dampers
in a multi-chamber setup, and a muffler technique referenced
in previous studies, but as comprehensively described as the
one in the present study.
© 2021 Bentham Science Publishers
Recent Patents on Mechanical Engineering, 2021, Vol. xx, No. x
a resistor (R) [27]. For a resistor-like device, the formula is
specified in Eq. (5).
2. DESIGN METHODS
2.1. Transmission Loss
𝑍𝑅 = 𝑅
Transmission loss is the difference between the incident
power and the downstream transmission (anechoic
termination). This parameter is used to measure sound waves
penetrating the barriers inside the muffler [11]. Measurement
of transmission loss considers the pressure differential and the
muffler impedance and is achieved using the measurement of
the inlet of the muffler and its outlet [7]. Transmission loss is
described by Eq. (1).
where R denotes device resistance. The electro-acoustic
circuit is considered analogous to an electrical circuit by
assuming pressure incident on an acoustic device (P)
equivalent to the potential difference (V). An acoustic circuit
with a parallel damping design follows the calculations for
parallel circuits for the equivalent electro-acoustic circuit. On
the other hand, a design having series damping uses the
formulae for series circuits.
𝑃
𝑇𝐿 = 20 log10 | 𝑃𝑖+ |
0
(1)
where, Pi denotes the pressure incident on the muffler, while
P0 denotes pressure during anechoic termination.
2.2. Insertion Loss
Insertion loss is stated as the change in acoustic power
with and without using the muffler [11]. This evaluation was
performed by measuring the acoustic characteristics of sound
released directly to the atmosphere and comparing it with the
sound released after its passage through the muffler before
releasing it to the atmosphere [11]. The insertion loss formula
in architectural acoustic is specified in Eq. (2).
𝐼𝐿 = 10 𝑙𝑜𝑔
𝛼
𝜏
(5)
2.4. Muffler Design
Muffler design has been worked on using SolidWorks
2020 SP0 software. Muffler models, one and two, have the
primary pipe diameter of 35 mm, while the third model is
based on a new design having the primary pipe diameter of 45
mm. All models have the exact dimensions apart from the
primary pipe diameter, which is 100 mm outer pipe diameter
and 1 mm plate thickness. Muffler 1 uses a dissipative
damping technique, while muffler 2 uses dissipative and
reactive techniques along with external Helmholtz resonators
to ensure that reactive damping is the primary technique. The
third model, on the other hand, uses both dissipative and
reactive damping through separate chambers. Three mufflers
are shown in Fig. (1).
(2)
where, α denotes the sound absorption coefficient in the
absence of a muffler, while τ denotes the muffler sound
absorption coefficient.
2.3. Electro-acoustic Analogy
Muffler impedance gauged for reactive, dissipative, and
resonance may be used for determining the results. A muffler
using one or more damping techniques can be understood as a
circuit for acoustic damping [27]. Electro-acoustic analogy
uses RLC circuits to represent these acoustic circuits [27]. The
flow through a pipe having no porous media is considered
equivalent to an inductor (L) [30]. Moreover, the impedance
calculated for an inductor is specified by Eq. (3).
𝑍𝐿 = 𝑗𝜔𝐿
(3)
where j denotes the wave phase, ω denotes the angular
velocity (rad / s), while L denotes the inductance of the device
Damping caused by a resonance device may be considered
equivalent to a capacitor (C) [27]. Eq. (4) describes the
impedance for a capacitor-equivalent device.
1
𝑍𝑐 = 𝑗𝜔C
(4)
where, j represents the wave phase, ω denotes the angular
velocity (rad/s), and C is the device capacitance. The damping
caused by a porous material may be considered analogous to
Fig. (1). 3D design of Muffler. (a) Muffler 1, (b) Muffler 2 and (c)
Muffler 3.
3. RESULTS & DISCUSSION
3.1. Muffler Design: Electro-acoustic Analogy
Fig. (2) show a cross-sectional view of the muffler design
as obtained by slicing the three-dimensional model across a
plane. The views present in 2D form the series arrangement of
damping devices used in each muffler.
As shown by the two-dimensional design, the damping
circuit is replaced to obtain an equivalent electro-acoustic
circuit inside the muffler. An alternate view is required to
determine the interaction between devices and to perform
calculations. Fig. (3) depicts the electro-acoustic circuit for
muffler 1.
Fig. (4). Simulink electro-acoustic circuit of Muller 1.
Fig. (2). 2D design of Muffler. (a) Muffler 1, (b) Muffler 2 and (c)
Muffler 3.
Impedance 1 (Zv) denotes the impedance of inductorresistor series and impedance 2 (Zc) denotes capacitor
impedance. The addition of the impedance values provides the
total impedance for muffler 1 Zv and Zc. Fig. (5) depicts the
electro-acoustic circuit for muffler 2.
Fig. (3). Electro-acoustic circuit of Muller 1.
Muffler 1 consists of a silencer that is analogous to an
inductor, capacitor, and resistor. Using the analogy, the circuit
has sufficiently high frequency along with resistive
characteristics. The change in primary pipe diameter, i.e.,
increase or decrease of the diameter, is considered equivalent
to a capacitor; however, the capacitance remains low [27]. Eq.
(6) and (7) describes the electro-acoustic impedance for
Muffler 1.
1
𝑍 = 𝑧𝑅 + 𝑧𝐿 + 𝑧
(6)
𝑍 = 𝑅 + 𝑗𝜔𝐿+ 𝑗𝜔𝐶
(7)
𝐶
where, R represents the combined resistance, j denotes phase,
ω denotes angular velocity, while L represents the inductance
value. As specified in Fig. (3), the circuit design and the
calculations for Eq. (7) can be worked on using Simulink
modeling provided in MATLAB. The electro-acoustic circuit
to determine the impedance for muffler 1 is depicted in Fig.
(4).
Fig. (5). Electro-acoustic circuit of Muffler 2.
For muffler 2, the electro-acoustic circuit comprises two
capacitors (C) connected in parallel with the inductor (L) and
connected in series with the resistor (R). The outset muffler
had the Helmholtz resonator, analogous to capacitors
connected in parallel with the source. Two barrier plates
provide combined inductance. The porous plates have a
combined porosity value equivalent to that of the resistors.
The inclusion of the Helmholtz resonator provides reactive
characteristics to impedance, while the addition of an inductor
and resistor provides resistive characteristics [27]. Eq. (8), (9),
and (10) specifies the electro-acoustic impedance for muffler
2.
𝑍 = 𝑍𝑅 + 𝑍𝐿 +
1
1
𝑧𝐶
𝑍 = 𝑅 + 𝑗𝜔𝐿 + 𝑧𝐶
𝑍 = 𝑅 + 𝑗𝜔𝐿 +
1
𝑗𝜔𝐶
(8)
(9)
(10)
For muffler 2, where a resistor-inductor series is connected
in parallel to the capacitor, the impedance is determined by the
parallel sum. Here, L, C, and R respectively denote
inductance, capacitance, and resistance. The circuit design
depicted in Fig. (5) and the calculation specified in Eq. (10)
may be completed using Simulink in MATLAB. Fig. (6)
depicts the electro-acoustic circuit for determining the
impedance for muffler 2.
Fig. (6). Simulink electro-acoustic circuit of Muffler 2.
Impedance 1 (Zc) denotes the impedance equivalent to a
replacement capacitor having the Helmholtz resonator
arranged in parallel, impedance 2 (Zv) denotes the combined
impedance of the resistor and inductor, while impedance 3
(Zc) denotes the capacitor impedance. The total impedance of
the muffler is given as the sum of the abovementioned
impedance values.
Fig. (7). Electro-acoustic circuit of Muffler 3.
Fig. (7) depicts the electro-acoustic circuit for muffler 3.
The following equation specifies the electro-acoustic
impedance for the muffler 3 circuit.
𝑍 = 𝑍𝑅3 + 𝑍𝑅4 + 𝑍𝐿2 + 𝑍𝐿3 + 𝑍𝐿4 +
𝑍 = 𝑅3 + 𝑅4 + 𝑗𝜔(𝐿2 + 𝐿3 + 𝐿4 ) +
1
1
1
+
𝑧𝐶3 𝑧𝐶
3′
1
𝑗𝜔(𝐶3 + 𝐶3′ )
analogous to the total inductance of segment 2 denoted as
impedance 1 (Zv). Segment 3 comprises two Helmholtz
resonators analogous to a parallel capacitor arrangement with
the impedance values represented by impedance 2 (Zc) and
impedance 4 (Zc). Segment 2 also consists of reactive pipes
acting as dampers analogous to the total inductance of the
three segments. At the same time, the set of porous plates is
analogous to three resistors connected in series. The
impedance for the analogous inductive and resistive part of the
circuit is denoted by impedance 3 (Zv). Segment 4 has
inductive and resistive absorption analogous to a resistorinductor combination present in segment 4 whose impedance
is denoted as impedance 5 (Zv). Muffler 3 has dampening
devices present in every segment, and, therefore, it has
complex impedance. R, C, and L denote, respectively, the
values of resistance, capacitance, and inductance.
3.2. Transmission Loss and Insertion Loss
The acoustic pressure frequency domain (ACPR) method
was used to conduct the simulation. The three-dimensional
design of the muffler was fed through the live-link feature of
the COMSOL software. Muffler simulation was conducted to
understand the acoustic performance of the muffler.
Performance measurement was done using transmission loss
(TL) and insertion loss (IL). This calculation determines the
noise at every frequency point between 200 Hz to 6400 Hz.
Muffler 1 employs a common damping technique where a
porous plate is attached to a reactive plate. Fig. (3) depicts the
electro-acoustic circuit; Muffler 1 predominantly uses the
dissipative damping technique. Calculations for muffler 1
indicated a maximum transmission loss of 81,859 dB at 5600
Hz, while the maximum insertion loss is 31,037 dB at 4800
Hz. Fig. (9) depicts the acoustic performance simulation in
COMSOL for muffler 1 using a graph.
(11)
(12)
Muffler 3 consists of dampening devices in the individual
parts, and the muffler impedance determination using the
electro-acoustic analogy is complex. L, C, and R, respectively
denote the inductance, capacitance, and resistance. The circuit
design depicted in Fig. (7) and its calculation specified by Eq.
(11) and (12) may be completed using Simulink in MATLAB.
Fig. (8) depicts the electro-acoustic circuit required to
calculate the impedance for muffler 3.
(a) Muffler 1
Fig. (8). Simulink electro-acoustic circuit of Muffler 3.
Muffler 3 has its electro-acoustic range split into three
parts based on the sections inside the muffler. In the first
segment, no damping device is present, while in the second
segment, a series of branching pipes are present, which is
(b) Muffler 2
(c) Muffler 3
Fig. (9). Transmission loss and insertion loss of (a) Muffler 1, (b) Muffler
2 and (c) Muffler 3.
(a) Muffler 1
(b) Muffler 2
Muffler 2 comprises a porous plate, an integrated reactive
dampening device, and a reactive Helmholtz resonator that
causes the muffler to have a predominantly reactive nature.
The damper circuit has its corresponding electro-acoustic
circuit shown in Fig. (4). The muffler's acoustic simulation
shows a maximum TL of 65.216 dB at 4800 Hz, whereas the
maximum IL is 32.802 dB at 4400 Hz. Fig. (9) depicts the
acoustic performance simulation in COMSOL for muffler 2
using a graph. Muffler 2 has been determined to have
maximum acoustic performance inside the middle-frequency
range; however, the acoustic performance is acceptable at low
frequencies and falls below 10 dB at high frequencies.
Muffler 3 comprises several chambers having four
segments. Fig. (5) depicts the electro-acoustic circuit, where
the second segment of the muffler predominantly uses
reactive damping. In contrast, the third and fourth segments
are based on reactive and dissipative damping techniques and
use a Helmholtz resonator in the third segment, while segment
four comprises porous plates. Simulation results show that
muffler 3 has a maximum TL of 158,202 dB at 200 Hz and a
maximum IL value of 130,749 dB at 200 Hz. Fig. (9) depicts
the acoustic performance simulation in COMSOL of muffler
3 using a graph.
3.3. Transmission loss and Impedance
Measurement of transmission loss provides data which is
used for comparing the impedance characteristics of muffler
1 with the help of the electro-acoustic analogy. Graphs for
impedance and TL provide the data as depicted in Fig. (10).
(c) Muffler 3
Fig. (10). Transmission loss and impedance of (a) Muffler 1, (b) Muffler
2 and (c) Muffler 3.
Using the measurements depicted in Fig. (10), it is inferred
that Muffler 1 has a similar impedance trend towards the TL
value and achieves its maximum value at 5600 Hz. This curve
is compared with an equivalent electro-acoustic circuit having
resistive characteristics of resistors and inductors where the
effective frequencies are in the medium to high-frequency
range. The presence of a capacitor in the circuit due to a
difference in pipe diameters influences these properties,
which do not reach maximum frequency. Fig. (10) depicts a
graph of impedance vs. TL, which is plotted using the results
of having an equivalent electro-acoustic circuit.
Muffler 2 shows a similar tendency considering the
impedance and TL values, while the maximum is achieved at
4400 Hz. This result agrees with the acoustic analogy theory,
which says that the inclusion of a Helmholtz resonator
corresponding to a capacitor into an electro-acoustic setup
provides for reactive characteristics [40]. This inclusion of the
reactive component leads to the muffler having dominant
reactive characteristics, as demonstrated by the electroacoustic analogy results. Fig. (10) depicts a graph that details
the TL and impedance trends obtained from the electroacoustic circuit. The impedance for Muffler 3 follows a
similar trend to the TL measurements, which reach maximum
attenuation at 200 Hz but decreases once frequency increases
over this value. This model can reduce all frequencies because
it uses multiple chambers, with every segment having a
different working frequency.
3.4. Sound Power Level
Sound attenuation in every muffler design may be
evaluated using the changes in sound power level (SWL). Fig.
(11) depicts damping for muffler 1 in 2D by COMSOL.
Referring to Fig. (11), it can be understood that SWL begins
to reduce starting at the inlet (red) and decreases along the way
to the outlet (green). Additionally, the SWL changes near the
porous plate and the barrier plate. Fig. (11) depicts the SWL
transformation for muffler 2 in 2D by COMSOL.
(c) Muffler 3
Fig. (11). Sound pressure level of (a) Muffler 1, (b) Muffler 2 and (c)
Muffler 3.
Fig. (11) depicts the SWL transformation that occurs along
with the primary muffler and Helmholtz resonators. The
Helmholtz resonator section shows the resonance effect, while
the main muffler creates change because of the porous plate
and the barrier plate. Colour changes from the SWL inlet (red)
to the outlet (blue) depict noise reduction. Fig. (11) depicts the
SWL changes for muffler 3 in a 2D view by COMSOL.
The SWL changes happening along Muffler 3 are depicted
in Fig. (11). The inlet area around the main pipe portion has a
high SWL (indicated in red). The blue area represents the
main and outer pipes where there is no passage of sound
waves. SWL decrease can be observed in both branches of
segment 2. Subsequently, the SWL decreased continuously
from segment 3 until it reaches the outlet (green).
3.5. Flow Analysis
(a) Muffler 1
While noise reduction is the key consideration, while
working on the acoustic ability, due attention must be given to
ensure that the muffler maintains adequate airflow so that the
high pressure at the engine can be reduced when the exhaust
is vented off. Flow analysis can be performed on the muffler,
where the flow distribution is indicated by pressure using a
colored isosurface. Fig. (12) depicts the acoustic pressure
distribution in COMSOL for muffler 1.
(b) Muffler 2
(a) Muffler 1
(b) Muffler 2
(c) Muffler 3
Fig. (12). Isosurface total pressure of (a) Muffler 1, (b) Muffler 2 and (c)
Muffler 3.
If we observe Fig. (12), the pressure inside the muffler
decreases from the inlet towards the center (red-blue
discoloration); however, it again increases from the center to
the outlet (blue-red discoloration), but it has a lower pressure
compared to the inlet. Inference about Muffler 1 can be drawn
from the results, indicating a reduction in air pressure
compared to the incoming air. However, the maximum
decrease happens at the center of the muffler. So, the muffler
tip creates a back pressure that causes improper airflow inside
the muffler. The acoustic pressure in Muffler 2 is depicted
using a colored isosurface in COMSOL in Fig. (12).
TL and IL measurements for muffler 1 indicate sufficiency
in the medium to high-frequency range. The results establish
that muffler 1 is predominantly dissipative. This result is in
line with the equivalent electro-acoustic circuit having
resistors and inductors' resistive characteristics, providing
effectiveness in the medium to high-frequency range. Both TL
and IL measurements for Mufflers 2 are in line with the theory
of acoustic analogy, where the addition of a Helmholtz
resonator provides reactive properties, which is equivalent to
adding a capacitor in an electro-acoustic circuit. The
simulation results agree with the electro-acoustic analogy,
where the addition of a reactive device modifies Muffler 2 to
be predominantly reactive. In the case of muffler 3, the
acoustic trends indicate damping happening majorly through
the reactive technique, in addition to reduced damping at high
frequencies, thereby enhancing damping through dissipation.
Because of several chambers with every segment having a
distinct and sufficient working frequency, the damping ability
is enhanced for all frequencies. Mufflers 1 and 2 cannot
sufficiently reduce the pressure of the air from the engine due
to backpressure generation inside these mufflers. Insufficient
airflow inside the muffler impacts pressure reduction.
Besides, muffler 3 reduces pressure without backpressure.
Therefore, it is the best among the three mufflers model
concerning the maintenance of airflow. The noise reduction
response for muffler 3 can be improved for high frequency by
having an additional dissipative material. This condition
provides opportunities to develop through further research a
multi-chamber muffler with enhanced acoustic performance.
FUNDING
The authors thank to Universitas Sebelas Maret for the
research funding namely Hibah Pengabdian Masyarakat Grup
Riset 2021.
ACKNOWLEDGEMENTS
The authors thank to Universiti Teknologi Malaysia for
the MATLAB software and Universiti Teknologi Petronas
for using COMSOL Multiphysics.
REFERENCES
[1]
Muffler 2 is observed to have a repeated increase and
decrease of air pressure, while resonance effects are
observed at the Helmholtz resonator. For both mufflers,
the outlet pressure is less than the inlet pressure. Muffler
2 is observed to have air pressure fluctuations that
indicate a back pressure build-up in some muffler parts.
The result is inadequate airflow. Fig. (12) depicts the
acoustic pressure in muffler 3 using an isosurface view
in COMSOL. The figure depicts the characteristics for
muffler 3, where high pressure (red) is observed at the
inlet, which falls as the gas travels through the muffler
(grey) to the outlet without any pressure increase. This
phenomenon indicates good airflow in Muffler 3 due to
the lack of backpressure.
CONCLUSION
[2]
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