this project aims for the reduction of backpressure from the muffler and vice versa increasing engine efficiency

1. 1
Evaluation of Back Pressure on a Muffler and its Effects on
Engine Efficiency
A Term Paper Report
Submitted in partial fulfillment of the requirements for
the award of the degree of
Bachelor of Technology
in
DEPARTMENT OF MECHANICAL ENGINEERING
by
J.V.ABHISHEK 14007523
SUKHVINDER SINGH 14007551
T.RAVI TEJA 14007569
SUBHAM KUMAR GUPTA 14007582
under the supervision of
Mr. K. SOMESHWARA RAO
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
K L University, Green Fields,
Vaddeswaram- 522502, Guntur (Dist), Andhra Pradesh, India.
February – 2017

2. 2
CERTIFICATE
This is to certify that Term Paper report entitled “Evaluation of Back pressure
on muffler on its effect on engine efficiency” by J.V Abhishek (14007523),
Sukhvinder Singh (14007551), Ravi Teja (14007569), Subham kumar
Gupta(14007582),is a bonafide work carried out by us in Department of Mechanical
Engineering during academic year (2016-2017).
Project supervisor Head of the department
CERTIFICATE

3. 3
DECLARATION
The Term Paper Report entitled “Evaluation of Back pressure on muffler on its
effect on engine efficiency” by J.V Abhishek (14007523), Sukhvinder Singh
(14007551), Ravi Teja (14007569), Subham kumar Gupta(14007582), submitted in
partial fulfilment for the award of B. Tech in Mechanical Department in K L
University. The results embodied in this report have not been copied from any other
departments/University/Institute.

4. 4
ACKNOWLEDGEMENT
Our sincere thanks to Mr. K. Someshwara Rao sir for guiding us throughout the
paper and his outstanding support throughout the term paper for the successful
completion of the work.
We express our gratitude to Dr. A Srinath, Head of the Department for Mechanical
Engineering for providing us with adequate facilities, ways and means by which we
are able to complete this project based Lab.
We would like to place on record the deep sense of gratitude to the honorable Vice
Chancellor, K L University for providing the necessary facilities to carry the project
based Lab.
Last but not the least, we thank all Teaching and Non-Teaching Staff of our
department and especially my classmates and my friends for their support in the
completion of our project based Lab.

5. 5
Abstract
Evaluation of back pressure of a muffler and its effects on engine efficiency has been
carried out by taking different parameters required to calculate back pressure and
varying different design parameters such as Inner Diameter, Muffler resistance and
length of the pipe. This result is then used to determine the variation in efficiency and
fuel consumption.
Evaluation is done by considering the basic formula to calculate the back pressure for
a muffler of stainless steel material.

6. 6
Introduction
In recent years, internal combustion engines have become the state-of-the-art
technology to realize low particulate emission for light, medium or heavy-duty diesel
vehicles. The engine backpressure resulted from these engines is an important
parameter which directly impacts the fuel economy of the engine and efficiency of the
engines. Back pressure refers to pressure opposed to the desired flow of gases in
confined places such as a pipe. It is often caused by obstructions or tight bends in a
confined space such as an exhaust pipe .Because of air resistance, friction between
molecules, the term back pressure is misleading as the pressure remains and causes
flow in the same direction, but the flow is reduced due to resistance.
Figure 1 Different Parts inside a Muffler

7. 7
Literature review
The objective of this work is to provide an estimate of the potential effect of exhaust
system backpressure on engine performance. Parameters include fuel consumption,
CO2 emissions, and horsepower. Backpressure that is created due the following
reason like number of bends starting from exhaust manifold to end of the silencer,
baffle plates, diameter of the pipe, length of pipe, type of muffler used. Basically the
type of muffler used is responsible for the exhaust backpressure and noise
reduction.There are numerous ways to design a muffler but basically commonly used
are, absorptive and reactive type. Generally automotive mufflers have both reactive
and absorptive properties. Backpressure can be minimized to a certain level by
decreasing the number of bends, increasing length and decreasing diameter of pipe,
choosing an appropriate material because materials resistance directly effects on
backpressure.

8. 8
Muffler:
If you've ever heard a car engine running without a muffler, you know what a
huge difference a muffler can make to the noise level. Inside a muffler, you'll find
a deceptively simple set of tubes with some holes in them.. They are designed to
reflect the sound waves produced by the engine in such a way that they partially
cancel themselves out.
Figure 2 General Position of Muffler
Types
There are numerous variations of the two main types of muffler designs commonly
used, namely absorptive and reactive. Generally automotive mufflers will have both
reactive and absorptive properties.
 Reactive muffler
Reactive muffler is revered for their ability to silence harsh engine noises. This uses
engineered chambers with plates or perforated tubes, exhaust gets reflected from these
plates and attenuation of sound happens. Reactive muffler works well in lower and
mid-range frequencies but produce higher back pressure.
 Absorptive muffler
It consists of a perforated tube, around which a sound absorbing material, like
fibre glass or steel wool, is placed. This type of muffler attenuates a wide range of
higher frequencies creating less back pressure.
DESIGN PARAMETERS
 Number of chambers
 Number of inlets and outlet pipes
 Diameter of Inlet and outlet pipe
 Holes on the pipe
 Size of muffler

9. 9
GENARAL REQUIREMENTS
 Quiet
 Simple maintenance
 Performance
 Compact design
 Light weight
SPECIFIC REQUIRMENT
 Reduce the sound emissions
 Replaceable
 Doesn’t increase backpressure
 Easy mounting
 Within the budget
 Easy manufacturing
Material properties
Stock exhaust
If you’re still using the stock exhaust system that came on your car, chances are good
that it’s made from 400-series steel (generally 409, but other grades are used as well).
This is a type of carbon steel that offers goodall around performance. It’s relatively
light, relatively durable, and relatively long-lived.
Aftermarket exhaust:
If you’ve had to replace your stock exhaust due to damage or wear, you may have an
aftermarket system in place now. It may use 400-series steel, or it may use something
else depending on the type of system in question.
Aluminized steel: Aluminized steel is an attempt to make the metal more corrosion
resistant. The aluminized coating oxidizes to protect the underlying metal (like
galvanized metal). However, any abrasion that removes this coating compromises the
underlying steel and can allow rust to set in.
Stainless steel: Several grades of stainless steel are used on aftermarket exhaust
systems, particularly the muffler and tips. Stainless steel offers some protection
against weathering and damage, but it will also eventually rust.

10. 10
Cast iron: Cast iron is used mostly in stock exhaust systems, and is used to
manufacture the exhaust manifold that connects the engine to the piping. Cast iron is
very strong, but very heavy. It will also eventually rust and can become brittle over
time.
Other metals: There are many other metals used in automotive exhaust systems, but
they’re generally used as alloy materials with steer or iron in order to promote better
corrosion resistance. These include chromium, nickel, manganese, copper and
titanium.
Backpressure:
Backpressure represents the extra static pressure exerted by the muffler on the engine
through the restriction in flow of exhaust gasses. Generally the better a muffler is at
attenuating sound the more backpressure is generated. In a Reactive muffler where
good attenuation is achieved the exhaust gasses are forced to pass through numerous
geometry changes and a fair amount of backpressure may be generated, which
reduces the power output of the engine. Backpressure should be kept to a minimum to
avoid power losses especially for better performance of vehicle.
Figure 3 Detailed Design of a Muffler
Causes, Effects and Possible Remedies for Backpressure Rise Problem
To minimize the pumping work the backpressure must be as low as possible for
obtaining the optimal output from the engine. The backpressure is directly

11. 11
proportional to the pressure drop across the design of complete exhaust system
components. Each alternation in exhaust system causes variations in backpressure on
C.I. engine. There are various factors because of which backpressure rise problem
exists in old as well as new properly designed C.I. engine applications during
complete operating life. Few of them are discussed here - An increased C.I. engine
population has created pressures on controlling engine out emissions. In most of the
C.I. engine applications lack of space availability needs compactness of after
treatment devices, it creates restriction in exhaust flow hence causes backpressure
rise. Diesel after treatment strategies may include muffler, particulate filter or
catalytic converter, thermal reactor, turbocharger, EGR system etc. in the exhaust
system for heat recovery and emission control activities. Particulate filters are
designed to trap particulate matter (PM) to achieve a net decrease in PM emissions.
The device captures ash, but the accumulation of ash in the device is sufficient to
cause a rise in backpressure. In practice, these devices need to be regenerate quickly
and relatively cheaply when they become blocked. The failure of catalyst may be due
to system component meltdown, carbon deposit, catalyst fracture, deactivation of
diesel catalyst etc. After treatment device component failure may cause backpressure
rise, mostly it happens because particulate matter consists of non-combustible
compounds. Poor engine performance may happen as a result of a clogged or choked
after treatment device. The broken pieces can move around and get in position to plug
up the flow of exhaust through the device. They are just melted enough and reduce
surface area. Either way, it doesn’t work much anymore, even though it may look
good on the outside. Engine emissions increase as the engine deteriorates. Normal
engine wear typically causes an increase of particulate matter (PM) emissions and a
decrease of NOx emissions. The major categories of fuel additives include engine
performance, fuel handling, fuel stability, and contaminant control additives. Engine
lubricants are composed of base oil, viscosity modifier and an additive package. One
of the main drivers in the development of oil formulations for engines with exhaust
after treatment is the reduction of sulphated ash, phosphorous and sulphur. Sulphur
increases PM in all classes of engines. Sulphur is also known to interfere with several
engine emission control strategies. Development of alternative fuels once promoted
by the desire to reduce exhaust emissions is now increasingly driven by climate
change issues and energy security. There is a clear correlation between some fuel
properties and regulated emissions. Drawing general conclusions is, however, difficult
due to such factors as Inter corelation of different fuel properties, different engine
technologies, or engine test cycles. Hence a comprehensive and practically feasible
approach is a must to improve the complex system of after treatment. Thus, any
modification in engine system causes rise in backpressure on engine in internal
combustion engines.
Backpressure on engine
Suction pressure remains constant in naturally aspirated engine so it is not considered
as a variable in this investigation. Pressure at exhaust end, which opposes the exhaust
gases flowing outside the engine cylinder, is also called as backpressure on engine.

12. 12
Ideally it should be atmospheric pressure. It is also an independent variable. As per
the complete exhaust system component design and their operating conditions the
value of backpressure varies. Speed and load can be easily controlled also at drivers
or operators will. Future modifications must be done in such a way that each
alternation should not cause backpressure rise. Backpressure on engine is a variable
that can be controlled with proper system design and maintenance practices. So, more
stress is given on the variable backpressure on engine in this work
Table 1: VERT Maximum Recommended Exhaust Back Pressure
Engine Size Back pressure Limit
Less than 50kW 40kPa
50-500kW 20kPa
500kW and Above 10kPa.
Measurement of back pressure:
To find the back pressure in an exhaust system, we have used to methods:
1. Formula Based
2. Measurement Based
 Formula Based:
To find out exhaust engine back pressure we are using the relation:
P=(LxSxQ2
X3.6X106
) + Ps
D5
Where,
P= Back Pressure in Kpa
L= Length of pipe in metres
Q= Exhaust gas flow in Kg/m3
S= Density of gas in Kg/m3
D= Inside Diameter in mm
T= Exhaust Temperature in o
C
Ps= Muffler Resistance in KPa
This equation assumes that the exhaust pipe is horizontal or of short height such that
elevation change between inlet and outlet is not necessary. This is very typical method
to find the backpressure in exhaust systems where gases of low density are used.

13. 13
Measurement Based:
In the automotive industry, we usually measure and not calculate the Pressure at the
Outlet of turbine of a turbocharger (that is just before the start of muffler or Exhaust
After-Treatment device), and this is the value of back pressure. This value is
measured at all operational rpm’s of a given Engine.
In this scenario, the measurement and calculation of back pressure are divided in two
parts:
Part I - Exhaust after Treatment Device:
This is usually a Catalytic converter or Diesel Oxidation Catalyst (DOC) or Diesel
Particulate Filter (DPF). Usually the Pressure Drop across these devices is specified
by the Supplier (Vendor) in the Specifications chart or In the Drawing of the Part.
Part II: Exhaust Pipe (Tail pipe): The Pressure drop across a pipe can be easily
calculated based on the Pipe length, Shape, Material and Roughness of Pipe Insides.
Mass flow rate of Exhaust gases = (mass flow rate of air) +(mass flow rate of fuel)
From that Calculate, Volume Flow rate of Exhaust gases (Q)
Then formulate,
Velocity = Q / Area of Pipe Cross section.
Result:
Finally add the Pressure Drops of Part I and Part II.
Back Pressure = Atmospheric Pressure + Pressure Drop.
This is usually done at Maximum power rpm and Maximum Torque rpm.

14. 14
Measurement of back pressure:
For the calculation of back pressure, we are considering two conditions:
1. When length of muffler is constant and the diameter is varied.
2. When diameter of muffler is constant and the length is varied.
Boundary Conditions required:
Table.2 Exhaust Gas Properties
S.No Properties of Exhaust Gas Values
1. Temperature (K) 623
2. Density(Kg/m3
) 0.525
3. Specific Heat(Cp) (KJ/Kg-K) 1.151
4. Viscosity 2.8331x10-5
5. Thermal Conductivity(K) (W/m-K) 0.466
6. Outlet Velocity (m/s) 13.5
Material Chosen:
We have chosen the material properties of Stainless Steel. It is been chosen as it is
one the most common materials used in mufflers because of its properties.
Calculation:
P=(LxSxQ2
X3.6X106
) + Ps
D5
Where,
P= Back Pressure in Kpa
L= Length of pipe in metres
Q= Exhaust gas flow in Kg/m3
S= Density of gas in Kg/m3
D= Inside Diameter in mm
T= Exhaust Temperature in o
C
Ps= Muffler Resistance in KPa

15. 15
Case 1: When Length of muffler is constant and the diameter is varied
Length = 0.3 m
Velocity = 13.5 m/s
Table.3 Different values of diameters and Exhaust Gas Flow
S.No Diameter (m) Exhaust Gas Flow (kg/m3
)
1. 0.020 0.005960
2. 0.022 0.006104
3. 0.024 0.007160
4. 0.026 0.008300
5. 0.030 0.009530
Case 2: When Diameter of muffler is constant and the Length is varied
Diameter = 0.03 m
Exhaust Gas Flow= 0.009530 kg/ m3
Table.4 Various Lengths
S.No Length (m)
1. 0.30
2. 0.32
3. 0.35
4. 0.40
5. 0.50
According to the different cases i.e. when length is constant and diameter is changed.
Due to this exhaust gas flow also changes. All the data is recorded in Table.3 .
Similarly, when diameter is constant and length of the muffler is changed. In this
case, exhaust gas remains constant. All Data is recorded in Table.4.

16. 16
Graphs and Results:
Here the Graphs show how the back pressure varies with length , diameter and
exhaust gas flow.
Case 1: When Length of muffler is constant and the diameter is varied
Figure 4 Diameter Vs Back Pressure
Fig.3 show Graph between diameter and backpressure. We can clearly observe that
with the increase in diameter, backpressure decreases.
This shows that diameter is inversely proportional to the back pressure.
Results from graph:
S.No Diameter (m) Backpressure (Kpa)
1. 0.020 8.6000
2. 0.022 6.2906
3. 0.024 6.0400
4. 0.026 5.6900
5. 0.030 4.5600s
Optimum Value:
S.No Diameter (m) Bckpressure (Kpa)
1. 0.030 4.5600s
0
1
2
3
4
5
6
7
8
9
10
0.02 0.022 0.024 0.026 0.03
Back Pressure

17. 17
Case 2: When Diameter of muffler is constant and the Length is varied
Figure 5 Length Vs Back Pressure
Fig.4 show Graph between length and backpressure. We can clearly observe that with
the increase in length , backpressure increases.
This shows that length is directly proportional to the back pressure.
Results from graph:
Optimum Value:
S.No Length (m) Backpressure (KPa)
6. 0.30 4.56
0
1
2
3
4
5
6
7
0.3 0.32 0.35 0.4 0.5
Back Pressure
S.No Length (m) Backpressure (KPa)
1. 0.30 4.56
2. 0.32 4.70
3. 0.35 4.90
4. 0.40 5.25
5. 0.50 5.939

18. 18
Conclusion:
As we can see that the optimum dimensions for the muffler are :
Length = 0.30 m
Diameter = 0.030
For these dimensions, back pressure calculated :
Back pressure = 4.56 KPa.
Taking any length or any large diameter would be impractical as these
values are considered after considering the space present in the exhaust
systems.
Effect of back pressure on engine efficiency:
Fuel Consumption:
Reduction in back pressure allows engine to use less fuel for the same
power. As world is facing a hike in oil pricing and fast extinction of oil,
our work will surely help in contributing some aid to this situation.
This will also improve efficiency of the engine as less fuel comsumption
means more power output and hence more efficiency.
Power Saving:
With reduction in back pressure , the engine power which goes waste in
doing extra work to eliminate the exhaust is now saved and the engine
will be able to deliver more power to automobiles.
Further study can be done to reduce the sound level much below than
standard value, with the backpressure remain untouched or be reduced.

19. 19
References:
1. Mikulic, I., Zhan, R., and Eakle, S., "Dependence of Fuel Consumption on
Engine Backpressure Generated by a DPF," SAE Technical Paper 2010-01-
0535, 2010, doi:10.4271/2010-01-0535.
2. http://www.eng-tips.com/viewthread.cfm?qid=331618
3. https://www.dieselnet.com/tech/diesel_exh_pres.php
4. Sudarshan Dilip Pangavhane , Amol Bhimrao Ubale , Vikram A Tandon , Dilip R
Pangavhane, “Experimental and CFD Analysis of a Perforated Inner Pipe Muffler for the
Prediction of Backpressure “.International Journal of Engineering and Technology
(IJET)13-05-05-163.
5. Peter Hield” The Effect of Back Pressure on the Operation of a Diesel
Engine” Maritime Platform Division DSTO-TR-2531
6. Niraj B. Dole #1, Jayant H. Bhangale *2” A review on effect of backpressure
on exhaust system” IORD Journal of Science & Technology
E-ISSN: 2348-0831 Volume 3, Issue 1 (Mar–April 2016) PP 163-168 IMPACT
FACTOR 1.719
7. Puneetha C G, Manjunath H, Shashidhar M.R” Backpressure Study in Exhaust
Muffler of Single Cylinder Diesel Engine using CFD Analysis”.
8. Mohd Umair,Abdul Basit, Arun Prabhakar,Anshul Gautam Modification in
Muffler Design to Reduce the Backpressure.
9. Ch.Indira Priyadarsini, Madhav Modali, Sangepu Vamshi Krishna, N Dinesh
Reddy“DESIGN AND ANALYSIS OF MUFFLER TO REDUCE THE
BACK PRESSURE”.