Vibration analysis of ci engine using fft analyzer

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 05 Issue: 01 | Jan-2016, Available @ http://www.ijret.org 293
VIBRATION ANALYSIS OF CI ENGINE USING FFT ANALYZER
Namdev A. Patil1
, Laukik P. Raut2
1
Student, M. Tech CAD/CAM, G. H. Raisoni College of Engineering, Nagpur, India
namdevpatil007@gmail.com
2
Assistant Professor, G. H. Raisoni College of Engineering, Nagpur, India
rautlaukik@gmail.com
Abstract
In automobile industry, the vibrations generated in the IC engine affects the performance of the vehicle and quality of comfort
while riding the vehicle. The factors which are affected under continuous vibration of IC engine are drivability, stability and
comfort. All these factors are reducing while there is an increase in vibrations produced by the engine. Reciprocating as well as
rotating parts of the engine are producing vibrations continuously in the internal combustion engine. The inertial forces are
produced by these reciprocating and rotating parts. These inertial forces are changing with compression and combustion
characteristics inside the engine. The vibrations produced by the engine can be minimized by reducing those unbalanced forces
generated during its functioning, otherwise anti vibration mounts are placed in between engine and its base. Many researchers
have performed experimentations to see reasons behind the vibration generations also to reduce vibrations at interface between
engine and its base. In this paper a thorough collection of data related to engine vibrations is made to provide a platform for
future work. It encompasses various work carried on engine rigid body modeling. The paper is framed as engine rigid body
modeling, engine vibrations in detail and at last some experimental work performed on a single cylinder diesel engine to measure
vibrations using FFT spectrum analyzer.
Keywords: Internal Combustion Engine, Engine Rigid Body, Vibration , FFT Analyzer.
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INTRODUCTION
The internal combustion engine design, itself is a complex
task as it includes multiple parts of various sizes assembled
together. The internal combustion engine is required to be
designed carefully so that the unbalanced forces generated
by the engine parts are reduced. If the design is not optimum
it will generate more vibrations and are transmitted to
supporting structure. It affects driver stability, drivability
and comfort. Taking into account the consumer aspirations
and surrounding considerations vibration reduction is at
most important phenomenon. Four major causes for overall
vibration behavior of IC engine are variation in gas pressure
in each cycle, impact forces due to reciprocating parts,
unbalanced rotating and reciprocating parts and mount
structural characteristics. During working of engine speed,
load on the engine is varying depending upon need. Due to
which fuel supply and combustion characteristics also
changes. Major components of an IC engine are
continuously having relative motion in between them. The
inertial forces changes with respect to compression and
combustion variation inside the cylinder. It is definite that
inertial forces give rise to unbalanced forces and they are
fluctuating with speed of the engine, fuel supplied and
combustion characteristics of the fuel. Hence for fulfilling
consumer satisfaction and calculate the vibration output and
its minimization, a mathematically accurate design model
along with its simulation is at most required.
IC engine produces mainly two types of vibrations i.e.
longitudinal and torsional vibrations. In which reciprocating
behavior of the engine results some torsional vibration
continuously. In compression stroke when piston moves
towards top dead centre the cylinder pressure increases. As
then ignition and combustion of the fuel occurs pressure
again increases and then pressure reduce with piston
movement towards bottom dead centre. The pressure
generated due to combustion of fuel exerts tangential force
on the piston that does required work and crankshaft speed
increases. So the crankshaft speed is increases in
combustion stroke where as decreases during compression
stroke respectively. This changing speed of the crankshaft
gives rise to torsional vibrations for crankshaft. Thus the
change in combustion pressure during downward motion
and changing inertial motion during upward motion of the
piston gives rise to unbalanced forces on the engine block.
These are considered to be responsible for generating the
longitudinal vibrations and these are measured in three
perpendicular directions. These above discussed main two
types of the vibrations can be minimized by reducing
unbalanced forces also by putting mounts.
Thus to measure and minimize the engine vibrations a
dynamic approach is needed. To discuss various methods
used and the assumptions used a collection is done on
engine as a rigid body, and its vibrations. The discussion
followed by an experimental analysis. The experimentation
is conducted on a single cylinder diesel engine.
1. ENGINE AS A RIGID BODY
In the internal combustion engine there are various parts
such as piston, engine block, connecting rod, engine head,
crankshaft, cam shaft, flywheel, valves, pulleys etc. Among

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all these parts few parts are taken as vibration generating
parts by the research scholars and industry experts. There
are four major components which generate vibrations by
producing unbalanced forces during cycle are piston,
crankshaft, engine block and connecting rod. As these
components are interconnected with each other, produced
unbalancing forces are passed to the engine parts such as
building block of engine and to the contacting structure.
Many researchers developed and studied various
mathematical rigid body models to calculate the unbalanced
forces during engine cycle, by making use of multibody
modeling. Hoffman and Dowling [1] performed thorough
experimentation on the diesel engine with six cylinders to
calculate vibrational force components in three orthogonal
directions at three engine mounts. Hoffman and Dowling [2]
evolved seven DOF model for engine vibrations with low
frequency, which assumes two way coupling. Finally they
have compared results of this with model having one way
coupling assumption. Hoffman and Dowling [3] managed to
get a model with 7 DOF which is conserving energy also it
is giving features of overall IC engine vibration output.
Deana M. Winton and Dowling [4] performed an
experiment with 6 cylinder diesel engine to measure
vibrations of engine building block with its rigid body
analysis. Zeng-Dong Ma and Perkins [5] found the motion
equations used for important parts of the IC engine by using
method of recursive formulation. They prepared computer
program by using C language and FORTRAN sub routines
to derive the equations of motion automatically. Tsuneo T.
and Tetsuya S. [6] gave a vibration reduction method during
idling condition of a heavy duty truck engine. They have
developed FEA model of full engine vibrations. T.
Ramachandran et al. [7] used ant colony optimization
method for the minimization of the internal combustion
engine forces and displacements. They considered a four
cylinder IC engine as a rigid body. Mathematical model is
developed and forces and displacements are minimized by
optimizing the crank angles.
The internal combustion engine looks simple but it is highly
complicated machine containing hundreds of components
which have to perform its functions satisfactorily to produce
required power output. In such a complicated machine while
it is running components have relative motion with respect
to each other producing internal vibrations. The collective
effects of these relative motions are also responsible for
external vibrations of the internal combustion engine as a
whole. Here by using the concept of rigid body modeling the
internal vibrations can be excluded and focus will be on
external vibrations only. The experimentation included in
this paper to obtain vibrations of a single cylinder diesel
engine and its results can be compared with vibrations
obtained by using dynamic analysis of engine as a rigid
body.
2. ENGINE VIBRATION
IC engine composed of various parts produces vibratory
forces which are as a result of the uneven forces as of the
engine components throughout the operation. Engine
produces longitudinal as well as torsional vibrations at the
engine supports. Engine loads and changing combustion
pressures produces torsion vibration at crankshaft of engine.
Longitudinal vibrations at the engine block are produced
with reciprocating as well as rotating sub parts of the engine.
Chung Ha et al. [8] developed a simplified method to get
vibration amplitudes generated by a four cylinder engine
which is supported on a viscoelastic mounts, by modeling
engine components as rigid body connected to rubber
mounts. Snyman et al. [9] provided method of reduction of
engine vibration in a 4 cylinder mounted IC engine. They
developed a mathematical model by taking lead angles and
balancing masses as propose independent variables and the
intended function is vibrating forces transmit to the mounts
at engine base. The method used to lessen the intended
function. Zhang Juhong and Han Jun [10] found change in
engine design for a totally new engine which could lessen
noise with low frequency and the vibration lower than the
presented production also optimizing its noise as well as
vibration characteristics. P. Charles et al [11] studied a fault
detection technique for an internal combustion diesel engine
depending on torsional vibration of crank shaft inside the
engine. In this paper scholars make use of encoder signal to
check speed of a shaft and produced the instantaneous
angular speed (IAS) waveform. They supervised a 16
cylinder diesel engine by using IAS and FFT (Fast Fourier
Transform). They found that FFT improves signal
processing to get the IAS signals. Fredrik Otsman et. al. [12]
have given method of reducing torsional vibration during
running of a common railway diesel engine of reciprocating
type. They found that no uniform torque would be the
reason behind greater than before torsional vibration and
stresses developed inside various parts of the IC engine.
They finally concluded that this active cylinder scheme
reduces the torsional vibrations. Rajendran and Narasimhan
[13] have focused on combined torsional as well as
vibrations with no bending mainly in the single cylinder
engine crankshaft. They have developed finite element
models and concluded that the introduction of inertial
coupling affects the free vibrations characteristics. Under
such circumstances they have concluded that in modeling of
crankshaft, the pure torsional system may have considerable
errors. H. Ashrafioun et al. [14] have looked on response in
terms of frequency for a engine of aircraft to measure
exciting forces. The transmitted forces minimization was
critical as far as location, orientation and type of mount is
concerned. They have also considered most of the
applicable Vibration Isolation Systems. Conti and Bretl [15]
have created a totally renovated method for getting the
investigative model of rigid body on its supportive mounts
and a way for data acquisition system. Using external
impact excitation in a vibration analysis test through mounts
they found mass of a engine rigid body yielding properties
and mounts stiffness properties from data extracted during
experimentation. They have evaluated location of centre of
gravity, mass moment, principle axes of inertia as well as
triaxial stiffness for mounts with mass of complete system.
Nader Vahadati and L. Ken Laudrebaugh Saunders [16]
have tested a machine with high frequency performance

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using rubber mounts. They have presented a mathematical
comprehensive model of a test machine having large
frequency. They have compared outputs of both
mathematical model and simulation at the frequency of 5000
Hz. Accordingly they implemented changes in design of
fixtures, mass and mounts as well. They found that the
designed fixture should be of minimum weight.
By looking into the different methods of vibration analysis
of above discussed research scholars, a vigorous and
accurate mathematical model and with simulation is
required to cover gap between vibration modeling and its
isolation from its base. The internal combustion engine itself
is a complicated design containing many components; at
most care is required in developing such multibody
modeling and simulation.
3. EXPERIMENTATION
In the experimentation the longitudinal vibration
acceleration signatures are measured in three orthogonal
directions X, Y and Z directions respectively on a single
cylinder Kirloskar diesel engine by using FFT spectrum
analyzer setup. In the experimentation while taking readings
an acceleration transducer having piezoelectric sensor is
used, this is placed at three different locations to get
signatures in X, Y and Z directions. All vibrations measured
are for 100% diesel fuel that is without blending with any
kind of biodiesel. While taking readings diesel engine is run
idle for 2 minutes without load and then readings are taken.
As the test rig is attached to the engine other observations
are also taken and enlisted in the table.
Parameters focused in the experimentation are as follows:-
 Mainly Rotating and Reciprocating members produces
Unbalanced Inertial Forces, Torsion are responsible for
vibration generation.
 Independent parameters used in the experimentation
are as follows:
• Load on the engine.
 Output parameter measured is Vibration Acceleration
Signatures.
 Also some other measurements on test rig are :-
• Speed of the engine.
• Fuel Rate.
• Air flow rate inside the engine.
• Temperature of Exhaust gas.
The loading on the engine is done by using Eddy current
Dynamometer. The load is increased in the steps zero, five,
ten percent and so on up to thirty percent. Due to engine
operating constraints the load is not increased above thirty
percents.
Figure 1. Schematic Line Diagram of Experimental Setup
Equipments used in the experimentation are enlisted below
:-
1. Single Cylinder Diesel Engine
2. OR3X Analyzer
3. PC with NV Gate Software installation
4. Ethernet link
5. Transducer: Piezoelectric Accelerometer
6. Tachometer
Engine Specifications Details are as follows:-
1. Kirloskar Single Vertical Cylinder Diesel Engine
Power = 18 BHP (7.4 KW)
Loading = Eddy Current Dynamometer.
Maximum Torque = 32 Nm
Stroke = 116 mm
Compression Ratio = 17.5:1
Engine speed rpm = 1500
Bore = 102 mm
Specific Fuel Consumption = 0.251 kg/ Kw-hr.
2. FFT Analyzer Specifications:
OR3X Analyzer
OROS 3 Series / NV Gate software
3. Accelerometer with Piezoelectric Sensor
4. Digital Tachometer
RMS Acceleration = Square root (summation of square of
amplitudes divided by no. of observations).
Table 1. Observation Table
Measurement
No.
Load%.
TorqueN-m.
SpeedRPM.
FuelRate
Kg/Hr.
AirRate
m^3/Hr.
Exhaust
Temp.In0
C.
1 0 0 1550 0.78 46 256
2 5 1.6 1541 0.78 37 286
3 10 3.2 1535 0.84 66 307
4 15 4.8 1530 0.96 122 338
5 20 6.4 1523 1.14 130 365
6 25 8.0 1515 1.38 137 410
7 30 9.6 1490 1.50 150 489

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Vibration acceleration signatures are obtained and root mean
square acceleration values are measured.
Longitudinal Vibrations in Y Direction:
Figure 2. Time vs Acceleration measurement 1 in Y
direction
Figure 3. Frequency vs Acceleration Measurement 1 in Y
direction
Figure 4. Time vs Acceleration Measurement 2 in Y
direction
Figure 5. Frequency vs Acceleration Measurement 2 in Y
direction
By taking the signatures of acceleration, vibration behavior
in Y direction is observed. Observations for vibrations in Y
direction are:
• The vibrations amplitude ranging from 50- 130 m/s2
.
• Peak value of acceleration = 130m/s2
.
• RMS Acceleration amplitudes are 61.5, 48.8, 46, 44.5,
42.4, 42m/s2
.
• Highest acceleration amplitudes are at 1500 Hz, 2700Hz,
3300Hz, 3200 Hz, 2600 Hz, 15 Hz, and 700 Hz with
increasing loads.
• Amplitude of vibration are directly varying with respect
to load.
• As the speed of engine decreases, amplitude of vibration
decreases.
• As Fuel rate increases there is decrease in vibration
amplitudes.
Longitudinal vibrations in X direction:
Figure 6. Time vs Acceleration Measurement 1 In X
direction
Figure 7. Frequency vs Acceleration Measurement 1 in X
direction
Figure 8. Time vs Acceleration Measurement 2 in X
direction
Figure 9. Frequency vs Acceleration Measurement 2 in X
direction

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in X direction is observed. Observations for vibrations in X
direction are:
• The vibrations amplitude ranging from 30 - 110 m/s2
.
• Peak value of acceleration = 110m/s2
.
• RMS Accelerations are 69.3, 74.9, 78.4, 82.73, 83,
83.43, 83.43m/s2
.
3300Hz, 4900 Hz, 200 Hz, 2100 Hz, and 700 Hz with
increasing loads.
• Here also increasing load gives increase in vibration
amplitudes.
• In this case engine speed decreases then amplitude of
vibration increases.
• Vibrations of the engine increases in Z direction as the
Fuel Rate is increasing.
Longitudinal vibrations in Z direction:
Figure 10. Time vs Acceleration Measurement 1 In Z
direction
Figure 11. Frequency vs Acceleration Measurement 1 in Z
direction
Figure 12. Time vs Acceleration Measurement 2 In Z
direction
Figure 13. Frequency vs Acceleration Measurement 2 in Z
direction
in Z direction is observed. Observations for vibrations in Z
direction are:
• The vibrations amplitude ranging from 30- 105 m/s2.
• Peak value of acceleration = 105m/s2.
• RMS Accelerations are 67.17, 74.95, 75.66, 76.36,
77.78, 77.8, 78 m/s2.
3700Hz, 2600 Hz, 5000 Hz, 2100 Hz, 3500 Hz
frequencies with increasing loads from 0 to 30 percents.
• Load on engine increased then amplitude of vibration
also increased.
• Speed of engine and amplitude of vibration are changing
with indirect proportionality.
• As Fuel rate and the amplitude of vibration again
directly proportional to each other.
CONCLUSION
In the vibration analysis of internal combustion (IC) engine
the non detrimental technique like FFT spectrum analysis
method is very fruitful. By making use of engine multibody
rigid modeling a mathematical model generation becomes
achievable as well as simplified. There may be number of
such models can be developed by making use of different
initial conditions while considering engine as a rigid body.
Now the observations of conducted experimentation are:-
• Magnitude of Vibration depends upon selection of axis
of engine for acquisition of signatures. In above the
vibrations are greater in Y direction as compared with X
and Z direction.
• Magnitude of vibration depends upon engine speed. As
the speed of engine decreases the vibration acceleration
amplitude also decreases in Y direction but increases in
X and Z direction.
• Vibration Amplitudes also depends upon load on engine.
As load on engine increases vibration acceleration
amplitude also decreases in Y direction but increases in
X and Z direction.
• With increase in load on engine the fuel rate increases,
vibrations in Y direction decreases but increases in X
and Z direction.
In future time, a robust and accurate mathematical model
with its prior simulation is required further more to bridge
the gaps in vibration analysis of such a complicated power
unit like the internal combustion engine.

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REFERENCES
[1] D. M. W. Hoffman, D. R. Dowling, ‘Limitations of rigid
body descriptions for heavy-duty diesel engine vibration’,
ASME Journal of Engineering for Gas Turbine and power
121: 197-204, 1999.
[2] D. M. W. Hoffman, D. R. Dowling,’ Fully coupled
internal combustion engine dynamics and vibration– part II:
Model-Experiment comparison’, ASME Journal of
Engineering for Gas Turbine and power 123: 685-692, 2001.
[3] D. M. W. Hoffman, D. R. Dowling, ‘fully coupled
internal combustion engine dynamics and vibration– part I:
Model development’, ASME Journal of Engineering for Gas
Turbine and power 123: 677-684, 2001.
[4] Deana M. Winton, David R. Dowling, ‘Modal content of
Heavy-duty diesel engine block vibration’ SAE
Paper#971948,1997.
[5] Zheng-Dong Ma, Noel C. Perkins, ‘An efficient
multibody dynamics model for internal combustion engine
systems’, Multibody System Dynamics 10: 363-391,2003.
[6] Tsuneo Tanaka, Mitsuo Iwahara, Tetsuya Sakai, ‘The
optimization of engine vibration reduction by simulation
analysis.’ SAE#962203, 1996.
[7] T. Ramachandran, K. P. Padmanaban and J.
Vinayagamoorthy, ‘Ant Colony Optimization for the
Minimization of Internal Combustion Engine Forces and
Displacements’, Emerging Trends in Science/10.1007/978-
81-322-1007-8_2, Springer India 2012.
[8] Chung-Ha Suh, Clifford G. Smith, ‘Dynamic simulation
of engine mount system’ ‘SAE Paper#971940.
[9] J. A. Snyman, P. S. Heyns, P. J. Vermeulen, ‘Vibration
isolation of a mounted engine through optimization.’ Mech.
Mach. Theory 30 (1): 109-118.
[10] Zhang Juhong, Han Jun, ‘CAE process to simulate and
optimize engine noise and vibration’ Mechanical Systems
and signal processing 20: 1400-1409, 2006.
[11] P. Charles, Jyothi Sinha, F. Gu, L. Lidstone, A. D. Ball,
‘Detecting the crank shaft torsional vibration of diesel
engines for combustion related diagnosis’ J. of sound and
vibration 321: 1171-1185, 2009.
[12] Fredrik Ostman, Hanna T. Toivonen, ‘Active vibration
control of reciprocating engines’ Control Engineering
Practice16:78-88, 2008.
[13] S. Rajendran, M. V. Narasimhan, ‘ Effect of inertia
variation due to reciprocating parts and connecting rod on
coupled free vibration of crank shaft’ ASME Journal of
Engineering for Gas Turbine and power 119 : 257-263.
[14] Ashrafiuon, H., and Natraj, C, ‘Dynamic Analysis of
Engine-Mount Systems’, ASME J. Vibr. Acoust, 114: 79–
83.
[15] P. Conti, J. Bretl, ‘Mount stiffness and inertia
properties from modal test data’, ASME Journal of
Vibrations and Acoustics, Stress and Reliability in Design
111: 134-141.
[16] Nader Vahdati, L. Ken Lauderbaugh Saunders, High
frequency testing of rubber mounts, ISA Transactions 41:
145–154, 2002.

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