structural modifications in diesel engine components …€¦ · 4. atv analysis acoustic transfer...

http://www.iaeme.com/IJMET/index.asp 1067 [email protected]

International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 6, June 2018, pp. 1067–1073, Article ID: IJMET_09_06_119

Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=9&IType=6

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

STRUCTURAL MODIFICATIONS IN DIESEL

ENGINE COMPONENTS TO REDUCE NOISE

Vishalkumar K. Dhummansure

Research scholar, Bapuji Institute of Engineering and Technology, Davangere, India

Dr. D. Ramesh Rao

Professor, Mech. Dept. Presidency University, Bengaluru, India

ABSTRACT

Local modifications in structural components have become very important tool to

reduce the noise and vibration related problems. Design improvement in structural

components can be predicted and optimized for Noise Vibration and Harshness (NVH)

issues by using finite element models. This paper presents a methodology to reduce

noise radiated from a four-cylinder diesel engine through modification and

optimization in structural components using finite element method (FEM) and

boundary element method (BEM). The simulation results of radiated noise level from

the engine assembly are used for comparison. Mode shapes corresponding to the

critical noise are considered for the analysis and optimization to reduce the noise. The

procedure focuses on the modification and optimization of the components in local

design to reduce noise level, a considerable reduction in overall radiated noise from

the engine has been observed.

Keyword: NVH, FEM, BEM, ATV, Structural components.

Cite this Article: Vishalkumar, K. Dhummansure and Dr. D. Ramesh Rao, Structural

Modifications in Diesel Engine Components to Reduce Noise, International Journal of

Mechanical Engineering and Technology, 9(6), 2018, pp. 1067–1073

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=6

1. INTRODUCTION

Diesel engines are widely used in automotive sector, where in acoustic emission level is a

prominent criterion for performance assessment. The noise radiated from an engine is

constituted of the aerodynamic and structure borne. Aerodynamic noise can be reduced by

analysis and optimized design of air cleaner and exhaust mufflers [1, 2] and thus, is much

lower than the structural radiated noise. Therefore, it is necessary to study the structural

surface radiated noise, and to reduce the noise radiated.

R. Citarellaa et al. [3] investigated car body by combined FEM-BEM approach to measure

the noise in low frequency range. This approach takes the advantage of modal acoustic

transfer vector algorithm and it is useful when big problems are analyzed. FEM-BEM based

Structural Modifications in Diesel Engine Components to Reduce Noise


on acoustic transfer vector (ATV) / modal acoustic transfer vector (MATV) can be considered

as alternative to FEM-FEM or FEM-BEM. The method adopted was for a low frequency

range whereas; it can be extended for complete speed range of the engine.

The method discussed above can also be used to study the noise contribution of engine

structural assembly, and to find a feasible solution.

Hambric SA [4] used the Approximation techniques for broad-band acoustic radiated

noise design optimization problems and concluded that addition of ribs to cylindrical shell is

one of the critical way to improve the stiffness and its effectiveness on structural radiated

noise. Jie Mao et al. [5] studied the acoustic optimization of the radiated noise and sound

quality numerically and experimentally. The noise from the engine block was predicted by

coupling methodology of finite element analysis and boundary element analysis.

The response of other structural components is not considered in the study discussed

above.

Zhang Junhong et al. [6] suggested the design modifications to the new engine that would

reduce low-frequency-radiated noise and vibration level in the frequency range up to 1 kHz.

The method utilised was based on a combination of finite element analysis (FEA) and multi-

body analysis (MBA). They simulated the vibrational behaviour of the housings, of the crank

train/valve drive and its single components.

However, the analysis can be extended to measure the noise level for the complete speed

range. And also, the analysis time can be reduced based on MATV instead of multibody

analysis.

Yang Pan et al. [7] employed finite element method and Automatically Matched Layer

(AML) technique to acquire the radiated noise from the shell surface of an axial piston pump

in the frequency range of interest, and the noise transmission path was analysed. The main

noise transmission path was optimised, and the piston pump radiated noise is reduced by 1.26

dB (A) of the main noise frequency. Bing Xu et al. [8] conducted a topology optimization of

an axial piston pump for reducing the frequency response function. The vibration and noise

are reduced by using the optimized housing. The analysis was carried out by introducing rigid

body models of moving components (piston, connecting and crank) for excitation of

assembly. However, this method can be simplified by introducing unit force at the loading

point in the assembly (bearing location) for excitation of assembly. This will reduce

computation time by considering, only structural components for analysis. In the present

work, the radiated noise of four-cylinder diesel engine is studied. A coupling method for

radiated noise analysis of engine, namely FEM-BEM based on MATV is proposed.

The study includes:

1. To Build a finite element model of structural components (engine block, oil sump

upper, valve cover, cylinder head and oil sump lower) for modal analysis;

2. To calculate modal participation factor to identify dominant frequency;

3. To Measure the radiated sound pressure level (SPL) in existing assembly;

4. To Modify and optimize the components subjected to critical noise;

5. To evaluate the differences of noise between original optimized assembly.

The sequential procedure is illustrated in figure1.

Whereas the specifications of engine under study are given in table1.

Vishalkumar, K. Dhummansure and Dr. D. Ramesh Rao


Table 1 Engine specifications

Fuel Type Diesel

Number of cylinder 4 cylinder inline

Cubic capacity 2000cc

Power 120 bhp

Figure 1 Sequential steps for model generation and radiated sound optimization

2. FINITE ELEMENT MODAL ANALYSIS

The engine block, oil sump, valve cover, cylinder head and oil sump lower are the main parts

affecting the vibration and noise transmission. Their Finite element models are established for

performing finite element modal analysis as shown in figure2. Lubrication interfaces between

components are not included in the model as the results are not good. This is acceptable not

only for reducing computing time, but also in identifying the real effect of components on

vibration and noise of engine. Tetra elements are used to model engine block, oil sump, valve

cover, cylinder head and oil sump lower and there are 413020 (135411 + 31684 + 47231 +

170735 + 27859) elements. The bolts are modelled by 1D beam elements having the same

radius that of actual bolts. The beam elements are connected to surrounding elements by rigid

element (rbe2) with three translational degree of freedom.

The Engine block, cylinder head and oil sump upper are made of grey cast iron HT 230

having density 7280 Kg/m3, elastic modulus 120000 MPa and Poisson’s ratio 0.265. Valve

cover is made of aluminum alloy and recommended properties are density- 3900 Kg/m3,

elastic modulus 340000 MPa and Poisson’s ratio 0.22. Oil sump lower is made of steel having

density 7800 Kg/m3, elastic modulus 200000 MPa and Poisson’s ratio 0.25.

Figure 2 Finite Element model of assembly

A free-free modal analysis of the engine assembly is carried out to find natural

frequencies and associated mode shapes. The authors of this paper focused their work to

identify the design modification in structural components to reduce noise and vibration of the

engine over the frequency range 0-3000 Hz. The structure mode shapes are numerous (about

37 modes in the range of interest) with a larger modal density than the acoustic modal density.

Mode shapes corresponding to critical frequency only are discussed in later section.



3. FORCED RESPONSE ANALYSIS

Modal based force response analysis is carried out to calculate modal participation factor. The

result file (op2) of modal analysis is imported into LMS Virtual lab. 2% of viscous damping

is added to all modes. Frequency dependent unit load is applied at two main bearing nodes in

X, Y and Z direction. The analysis is carried out in the frequency range of 1-3000 Hz with a

step size 10Hz. Critical points based on modal analysis results are selected for output

response. Modal participation factor result shows the dominant frequencies of concerns as

highlighted in figure4. Mode shapes with respect to dominant frequencies are considered for

further study.

Figure 3 Modal participation factor

4. ATV ANALYSIS

Acoustic transfer vector (ATV) analysis is carried out to measure the radiated sound pressure

level in the selected assembly. The acoustic mesh elements size is calculated by equation 1.

Speed of sound in air is 340 m/sec2 and the maximum frequency considered for analysis is

3000 Hz. The wavelength of sound is found to be 113.3mm and element size to capture this

wavelength is equal to 18.8mm for this assembly.

� = �� 1

Where C is Speed of sound in air

f is maximum frequency and

λ is wavelength and calculated value is 113.3mm.

Minimum element size to capture this wavelength is = 113.3/6

Element size = 18.8mm

All the major external cavities are filled to avoid reflection. Acoustic mesh is created with

18.8mm shrink wrap element in HYPERMESH and file is exported in LMS virtual lab format

(.dat/. bdf). LMS virtual lab and set for ATV analysis as shown in figure4. The fluid

properties are: velocity of sound in air as 340E-3mm/sec2

and mass density as 1.225e-3

tons/mm3. A symmetry plane is inserted to represent the ground at a distance of 450mm

below the assembly. ISO power field is created to represent noise measuring locations. ATV

analysis is carried out in the frequency range of 1 -3000 Hz with step size of 10 Hz. The

surface velocity results from forced response analysis are transferred to acoustic mesh for

representing structure as a source and ISO field point as response points. The analysis resulted

in overall sound pressure level (SWL) of 116.44 dB and, critical frequency range is 2400-

2600Hz (highlighted in figure 5). The components corresponding to critical mode shape in the

range are examined for local modifications.



Figure 4 Acoustic mesh for ATV analysis Figure 5 Sound pressure level of assembly model

The critical mode shapes in the frequency range of 2400-2600 Hz, are observed in oil

sump and valve cover as shown in figure 6 and figure 7. The maximum displacement values

are observed in oil sump at a frequency 2611 Hz and valve cover at a frequency 2473 Hz. Oil

sump and valve cover are considered for modification at these mode shapes.

Figure 6 Oil sump mode shape at 2611 Hz Figure 7 Valve cover mode shape 2473 Hz

4.1. Modification1. Thickness addition to oil sump and valve cover

The oil sump lower and valve cover are modified by increasing overall thickness of 2mm as

shown in figure 8 and figure 9.

Figure 8 Revised valve cover Figure 9 Revised oil sump lower

4.2. Modification2. Addition of rib to oil sump

Two ribs are added to oil sump on lower side externally to add stiffness as shown in figure 10.

Further the thickness of rib is varied from 2mm to 12mm for optimizing the radiated noise.

Figure 10 Modified Oil sump



Sound pressure level of modified engine is simulated. A reduction of 23.75 dB(A) is

observed in overall SWL with 5mm rib and, 23 dB(A) with 12mm rib in modified engine as

shown in figure 11. As the thickness is further increased, the overall sound pressure level also

started increasing as shown in figure 12.

Figure 11 SWL for 5mm rib thickness Figure 12 SWL for 12mm rib thickness

A comparison is made with different thickness in oil rib and optimized results are

observed at 5mm thickness. The results of analysis are compared in the figure 13. Optimized

noise of 92 dB(A) is observed in case of 5mm thick rib in oil sump lower and, 2mm uniform

thickness in both oil sump lower and valve cover. A reduction of 7.45mm displacement is

observed in oil sump lower whereas it is 6.92mm in valve cover as shown in figure 14 and

figure 15.

Figure 13 SWL comparison for base and different thickness of rib.

Figure 14 Oil sump mode shape at 2622 Hz Figure 15 Valve cover mode shape at 2347 Hz

5. CONCLUSIONS

Significant level of reduction in noise and critical vibrations can be attained by FEM-BEM

based on MATV simulation technique. The investigation methodology can be implemented at

engine development phase and also, to investigate existing engine and machine assembly.

From the acoustic analysis of the engine assembly following conclusions is obtained.

1. FEM-BEM methodology can be used for radiated noise measurement; results

obtained can be the basis for further noise reduction by structural optimization.

2. The SPL (sound pressure level) analysis results show that, the most critical

frequencies are 2473Hz and 2611Hz and total SPL is 116.4dB. The main noise

source of engine are, valve cover and oil sump lower by optimizing these

components noise reduction to a considerable level is observed.



REFERENCES

[1] Liu C, Hao ZY, Chen XR. Optimal design of acoustic performance for automotive air-

cleaner. Applied Acoustics 2010; 71:431–8.

[2] R. Citarella and M. Landi. Acoustic Analysis of an Exhaust MANIFOLD by INDIRECT

Boundary Element Method. The Open Mechanical Engineering Journal, 2011, 5, 138-151

[3] R. Citarellaa, L. Federicoa, and A. Cicatiellob. Modal acoustic transfer vector approach in

a FEM–BEM vibro-acoustic analysis. Engineering Analysis with Boundary Elements 31

(2007) 248–258

[4] Hambric SA. Approximation techniques for broad-band acoustic radiated noise design

optimization problems. J Vibrat Acoust Trans ASME 1995; 117:136–44.

[5] Jie Mao, Zhi-yong Hao, Guo-xi Jing, Xu Zheng, Chi Liu. Sound quality improvement for

a four-cylinder diesel engine by the block structure optimization. Applied Acoustics 74

(2013) 150–159

[6] Zhang Junhong_, Han Jun, CAE process to simulate and optimise engine noise and

vibration, Elsevier, Mechanical Systems and Signal Processing 20 (2006) 1400–1409

[7] Yang Pan, Yibo Lia, Minghui Huang, Yashi Liao, Dedong Liang. Noise source

identification and transmission path optimisation for noise reduction of an axial piston

pump. Applied Acoustics 130 (2018) 283–292

[8] Bing Xu, Shaogan Ye, Junhui Zhang. Numerical and experimental studies on housing

optimization for noise reduction of an axial piston pump. Applied Acoustics 110 (2016)

43–52

[9] Shailaja M, V.Vijaya Kumar, Chandragiri Radha Charan, Dr.A V Sitarama Raju,

Development Of Back Propagation Neural Network Model To Predict Performance And

Emission Parameters Of A Diesel Engine, International Journal of Advanced Research in

Engineering and Technology (IJARET), Volume 4, Issue 3, April 2013, pp. 85-92.

structural modifications in diesel engine components …€¦ · 4. atv analysis acoustic transfer...

Documents