Heat Transfer Analysis Of Medium Duty DI Diesel Engine Agarwal, Aniket Basu, Dr. M.R. Nandgaonkar:...

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www.ijifr.com Copyright © IJIFR 2015

Research Paper

International Journal of Informative & Futuristic Research ISSN (Online): 2347-1697

Volume 2 Issue 10 June 2015

Abstract

Now-a-days engines having smaller size & higher power ratings are in trend. Due to additional power deliverables required from smaller sizes, heat load on engine components have increased. Under this increased heat load, strength of component materials decreases drastically .When fatigue loadings act on these component with decreased strength, chances of engine failure increase. In order to avoid engine failure this heat load transfer inside engine needs to be understood very well .The major heat transfer that takes place inside engine is through engine cooling jacket. The work presented in this paper is numerically predicting the temperatures of engine components for a Direct Injection Medium Speed Heavy Duty Diesel Engine through CFD and validation of the simulated results with experimental results. The above objective is met by conducting in cylinder combustion simulation and then performing Conjugate Heat Transfer (CHT) analysis using boundary conditions obtained from combustion analysis for engine.

Heat Transfer Analysis Of Medium

Duty DI Diesel Engine Paper ID IJIFR/ V2/ E10/ 041 Page No. 3627-3637 Subject Area

Mechanical

Engineering

Key Words Heat Transfer Analysis, Engine Water Jacket, Combustion Simulation,

Conjugate Heat Transfer

Received On 07-06-2015 Reviewed On 19-06-2015 Published On 20-06-2015

1. Deepali Agarwal Deputy Manager Corporate Research & Engineering Department, Kirloskar Oil Engines Limited, Pune

2. Aniket Basu Deputy Manager Corporate Research & Engineering Department, Kirloskar Oil Engines Limited, Pune

3. Dr. M.R. Nandgaonkar Associate Professor Department of Mechanical Engineering College Of Engineering, Pune

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ISSN (Online): 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)

Volume - 2, Issue - 10, June 2015 22ndEdition, Page No: 3627-3637

Deepali Agarwal, Aniket Basu, Dr. M.R. Nandgaonkar: Heat transfer analysis of medium duty DI Diesel Engine

1. Introduction

During the combustion process in internal combustion engines (ICE), a large amount of heat is

generated. This energy is absorbed by the cylinder walls, pistons, and cylinder head. A cooling

system is necessary in any internal combustion engine to effectively dispose off the heat generated.

Therefore, the function of the engine's cooling system is to remove excess heat from the engine and

to keep the engine up to correct temperature under all operating conditions. Therefore, the

management of heat transfer in an engine is critical to engine performance, efficiency and emission.

In the present study, conjugate heat transfer analysis is simulated for which the boundary conditions

are acquired from an in cylinder simulation. Then entire cooling jacket of a 6- cylinder medium duty

DI diesel engine is simulated for heat transfer through commercial CFD code star CCM+ and results

obtained are validated against experimental results which can further form the basis for cooling

jacket modification.

2. Methodology

The basic methodology adopted for numerically predicting the temperature of engine component for

a Direct Injection Medium Speed Heavy Duty Diesel Engine is in cylinder combustion followed by

Conjugate Heat Transfer Analysis. It can be defined as the ability to compute conduction of heat

through solids, coupled with convective heat transfer in fluid. Heat transfer through Convection can

be obtained as:

Similarly, Heat transfer through conduction

On solving these two simultaneous equations we can get Twall.The same idea is extended to 3-D i.e.

in x , y and z directions in our case.

3. In cylinder Simulation

In cylinder combustion analysis deals with attempting to effectively capture the actual combustion

characteristics via AVL FIRE. This CFD simulation tool, allows setting up, performing and

analyzing the injection and combustion process in diesel engines reliably and accurately with

minimum effort.

Since it is a closed

cycle simulation, the

calculation starts at

inlet valve closure

(IVC) and ends at

exhaust valve open

(EVO). It

automatically creates

topological region

meshes at different

crank angles. Figure 1: 2-D Mesh

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Combustion cavity considered is symmetric and the fuel mass flow is the same for all holes of the

injector, so only a segment of the cavity geometry for one injector hole is used. In 2D meshing basic

element size dependent cell size is considered, i.e. the basic cell size changes with respect to crank

angle. From crank angle to crank angle, also a 3D mesh is created based on the 2D meshing

parameters. 3D meshing parameters are important in injector region.

3.1 Inputs

Species transport, Combustion, Emissions and Spray models were selected. Whole simulation is

crank angle based, with numbers of time steps given based on crank angle. In initial conditions since

the calculation duration is from IVC, the pressures, temperature, turbulent kinetic energy, swirl and

direction of rotation axis at IVC is specified.

Standard WAVE mode for spray with blob injection where initial droplets have the diameter of the

nozzle orifice is used for the simulation, it often happens that there is hardly any fuel vapor close to

the nozzle. Modeling combustion in DI diesel engines requires taking into account the possibility to

burn under different regimes: premixed, non-premixed and partially premixed, due to the

inhomogeneous mixing of the reactants. Hence Extended Cohehrent Flame Model – 3 Zone (ECFM-

3Z) is used as the combustion model. The reaction mechanism to capture NOx formations can be

expressed in terms of the extended Zeldovich mechanism

3.2 Results

Figure 2 shows the comparison between experimental cylinder pressure (P-θ) diagrams with

simulated (P-θ) diagram at full load. This indicates that experimental and simulated result curves

follow similar trend. Computational and experimental results are in excellent agreement throughout

the compression, power and expansion strokes.

Figure 2: Experimental & Simulated Pressure Comparison

Figure 3 shows Heat release rate comparison between experimental and simulated values both

curves follow similar trend.

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Figure 3: Experimental & Simulated Instantaneous Heat Release Rate Comparison

Figure 4 shows curves obtained for heat transfer coefficient for Cylinder Head, Liner &

Piston with respect to crank angle. These values are taken as input for further Conjugate

heat transfer analysis in Star CCM+.

Figure 4: Simulated Heat Transfer Coefficient

Table 1 shows piston top profile as obtained in simulation vs. experimental which shows

that injection location in both simulation and experimental match very closely.

Table 1: Simulation vs. Actual Piston Profile

Simulation Actual

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4. CFD Analysis And Model Setup

In this study, CFD analysis of the existent coolant passage model will be conducted to determine the

critical locations within engine block and head. 3-D CAD (Computer Aided Design) model of the

engine block coolant jacket, the cylinder head coolant jacket, was developed in house. Commercially

available software package Star CCM+ by CD Adapco Group has been utilized for CFD analysis.

Same software was used for cleaning up and meshing purposes and for pre-processing, processing

and post processing steps.

4.1Assumptions for Numerical Simulation

The coolant flow in coolant cavities of a cylinder head was assumed to be 3D steady state,

Incompressible turbulent flow, viscosity in the near wall region was taken into account. Turbulence

model selection made on basis of type of system selected, type of grid used and type of physics

expected in that domain. After referring available help files of STAR-CCM+ and referring to CFD

literature it was decided to choose realizable k-ε model for the present study. There were second

option of SST k-ω mentor model which also stand acceptable for present physics but it strictly

requires very refine mesh around boundaries which will result into y+ within 0 to 1. This was not

possible in present case due to y+ varying all over.

Three dimensional, Steady, Liquid, Segregated flow, Constant density, Turbulent, Reynolds average

Navier-Strokes, K-epsilon turbulence, Realizable K-epsilon two layer, Two layer all y+ wall

treatment, Segregated fluid temperatures and Segregated solid energy solvers are used for fluid

region.

Table 2: 1Assumptions for Numerical Simulation

Solid Boundary Conditions Temperature Heat Transfer Coefficient

Deck Face 1200 625

Exhaust Port 1000 580

Inlet Port 313 100

Exhaust Valve Guide 313 160

Inlet Valve Guide 313 100

Exhaust Valve Seat 1100 600

Inlet Valve Seat 313 600

Solid Head 313 100

Liner Top 650 1360

Liner Middle 540 670

Liner Bottom 460 520

4.2 Simulation Results

The pressure loss as shown in fig 5 between the inlet and outlet is calculated to be as 0.21 bar which

is a good indicator of low resistance in flow and potential. Water pump will have to deliver more

than the pressure loss across the cooling jacket i.e. 0.21 bar in order to force the coolant inside the

circuit and keep it circulating with sufficient velocity.

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Figure 5: Pressure Contour

Figure 6: Fluid Streamlines

In the figure 6, Fluid flow streamlines are shown which show less flow going to cylinders as

a result of which it will suffer high temperature regions.

Figure 7: Cylinder Head Temperature Contour

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Figure 8: Deck Face Temperature

Figure 7 and 8 clearly shows the maximum temperature is found in the region of exhaust port and

the region near the exhaust bridge on the deck face. Thus more attention is given for the pressure and

velocity contours of the cooling jacket as there is the possibility of nucleate boiling of coolant within

this region. Boiling causes a thin film of coolant vapour to form between the fluid flow and the solid,

which acts as an insulator and reduces the heat transfer coefficient.

Figure 9: Velocity Contour in Engine Block

Figure 10: Liner Temperature

Hot Spots

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The analysis of thermal fields of cylinder liner has crucial importance because it provides an insight

into several very important phenomenon’s that are associated with the thermal stresses, strains and

with the heat fluxes exchanged. The dotted circles in Figure 9 show that the flow velocity in this

region is relatively lesser than the other cylinders thereby indicating the possibility of stagnation.

Hence, the heat carried away by the coolant in this region will be reduced. This in turn is a potential

location of hot spot creation visible in Figure 10. It shows how the temperature varies along the

length of the liner. The lower region of liner is only exposed to combustion products for part of cycle

after significant gas expansion has occurred, the temperature decreases significantly.

5. Experimental Validation

By focusing on literature survey and CFD analysis done on the engine we finalize the maximum

temperature location in the cylinder head. Along with the bottom of cylinder head the exhaust port is

also exposed to elevated temperatures thus to predict the surface temperature in the exhaust port it is

necessary to install the templug at the exhaust port.

Table 3: Simulation Results

Location Experimental Simulation Error %

1 263 deg C 282 deg C 7.2

2 340 deg C 316 deg C 7.0

3 252 deg C 238 deg C 5.5

4 195 deg C 219 deg C 12.3

5 178 deg C 195 deg C 9.5

4 5

Figure 11: Experimental templug location

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6. Design Improvement

We have witnessed in the simulation results that the temperature of the solids rise at stagnation areas

because of ineffective cooling. Following are the modifications which have been incorporated for

minimizing stagnation region with least pressure drop:

a) Increase in coolant flow rate

b) Varying the diameter of transfer holes

c) New water jacket design

6.1 Increased Coolant Flow Rate

With increased flow rate of the pump, the pressure drop across the circuit is 0.69 bar as against 0.22

with lower flow rate, thus increasing pressure drop by 32 % which is not acceptable.

6.2Varying Diameter of Transfer Holes

On reviewing mass flow distributions for original and modified holes unequal distribution in

cylinders still exists. Therefore, this modification will also not improve stagnation areas.

6.3 New Water Jacket Design

The highlighting features of the new jacket design are the rails through which the coolant passes into

the crankcase jacket. The rails implemented have wavy pattern and constantly decreasing cross

section. The wavy pattern and constantly decreasing cross section area ensures that the flow velocity

does not decrease thereby reducing stagnation.

Due to this modification in rails, the old oil cooler shape was not able to fit in this improved model.

We could see it fouling with the core and hence the alternative approach was too introduced.

Therefore an orifice that would give the same pressure drop as the oil cooler has been given.

Figure 12 shows velocity contours for modified design. Stagnation regions are not present in

modified jacket as evident from this figure. Equal distribution of flow can be seen.

Figure 12: Velocity Contour

Streamlines shows good velocity in all cylinders. Since the stagnation observed is less, the chances

of hotspots are also relatively less. Hence this design gives improvement in terms of pressure drop

and temperature hotspots.

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7. Conclusion

In cylinder simulation results follow similar trend as that of experimental results and all

results match with experimental within 6-10%.This validates our boundary conditions used

for conjugate heat transfer analysis.

The locations at which fuel is injected on piston match exactly with actual locations as

shown by results.

The models for conjugate heat transfer analysis is also validated against experimental results

within 10% error which validates process used for Conjugate Heat transfer. Thus current

procedure can also be used for conjugate heat transfer analysis for any modification done on

water jacket.

Modification 1 shows that by increasing pump flow rate pressure drop across water jacket

increases by 32% which is not acceptable.

Modification 2 shows that flow rate through transfer holes increases in same amount as size

of holes is increased.

Modification-3 shows 16% less pressure drop across jacket as compared to actual model

.Also stagnation regions are removed . Therefore it is recommended.

Boundary conditions obtained from both conjugate heat transfer analysis and in cylinder

simulation can be mapped to engine cylinder assembly as part of coupled approach with

Computational Fluid Dynamics and Finite Element modelling .This approach introduces

many advanced features.

8. Abbreviations and Acronyms

FE Finite Element

CFD Computational Fluid Dynamics

CHT Conjugate Heat Transfer

CAE Computer Aided Engineering

Ts Surface Temperature

Twall Wall Temperature

H Heat Transfer Coefficient

Tfluid Fluid Temperature

qwall Wall heat transfer

L Length

K Thermal Conductivity

Nu Nusselt Number

Re Reynolds Number

B Cylinder Bore

W Local Average Gas Velocity

Sp Mean Piston Velocity

Pr Refernce Pressure

Tr Reference Temperature

Pm Motored Pressure

Vd Displacement Volume

TDC Top Dead Center

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Biographies

1st Deepali Agarwal , working as Deputy Manager CRE in Kirloskar Oil Engines Ltd, Pune .She is also

pursuing M.Tech Thermal Engineering From College of Engineering ,Pune.

2nd Aniket Basu ,working as Deputy Manager CRE in Kirloskar Oil Engines Ltd, Pune .His working areas

and interests include Computational Fluid Dynamics Simulation, Combustion Hardware Optimization

& Common Rail Calibration .

3rd Dr. M.R. Nandgaonkar, working as Associate Professor, in Mechanical Engineering Dept. of College

of Engineering, Pune. He completed his PhD. (IC Engines) from Amravati University in 2002. His

Area of interest includes I C Engine, Alternative Fuels & CFD. He has 21 years of Teaching

Experience along with 10 years Research experience. He has 50 publications in National &

International Journals & conferences.

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