cfd analysis of exhaust manifold of multi-cylinder si .... cfd analysis.full.pdf · cfd analysis of...

International Journal of Automobile Engineering

Research and Development (IJAuERD)

ISSN 2277-4785

Vol. 3, Issue 4, Oct 2013, 45-56

© TJPRC Pvt. Ltd.

CFD ANALYSIS OF EXHAUST MANIFOLD OF MULTI-CYLINDER SI ENGINE TO

DETERMINE OPTIMAL GEOMETRY FOR REDUCING EMISSIONS

K. S. UMESH1, V. K. PRAVIN

2 & K. RAJAGOPAL

3

1Department of Mechanical Engineering, Thadomal Shahani Engineering College, Mumbai, Maharashtra, India

2Department of Mechanical Engineering, P. D. A. College of Engineering, Gulbarga, Karnataka, India

3Former Vice Chancellor, JNT University, Hyderabad, Andhra Pradesh, India

ABSTRACT

Exhaust manifold is one of the most critical components of an IC Engine. The designing of exhaust manifold is a

complex procedure and is dependent on many parameters viz. back pressure, exhaust velocity, mechanical efficiency etc.

Preference for any of this parameter varies as per designers needs. Usually fuel economy, emissions and power

requirement are three different streams or thought regarding exhaust manifold design. This work comprehensively analyzes

eight different models of exhaust manifold and concludes the best possible design for least emissions and complete

combustion of fuel to ensure least pollution.

KEYWORDS: Multi-Cylinder SI Engine, Exhaust Manifold, Back Pressure, Exhaust Velocity, LBCE, LBSE, LBSER,

LBCER, SBCE, SBSE, SBCER, SBSER

INTRODUCTION

In an IC Engine at the beginning of suction stroke inlet valve of cylinder opens due to pressure difference. Air fuel

mixture (in case of SI engine) or air (in case of CI Engine) is sucked into the cylinder through this intake valve from inlet

manifold. Inlet manifold contains carburetor for mixing of air and fuel in case of SI Engines. Once air or air fuel mixture is

completely sucked into the cylinder whose piston has reached BDC the inlet valve closes and compression stroke begins.

As piston reaches TDC spark is ignited in the mixture (SI Engines require external sparking arrangement whereas in CI

Engine auto ignition takes place on injection of fuel) this marks the beginning of power stroke. Once again as the piston

reaches BDC exhaust stroke begins. During exhaust stroke exhaust valve is opened and the burnt mixture is rejected to

exhaust manifold. As exhaust stroke is completed suction stroke begins once again and cycle continues. The energy

supplied to engine in form of chemical energy of fuel is converted into thermal energy.

In any multi-cylinder IC engine, an exhaust manifold (also known as a header) collects the exhaust gases from

multiple cylinders into one pipe. This header is connected to these cylinders through bends. It is attached downstream of

the engine and is major part in multi‐ cylinder engines where there are multiple exhaust streams that have to be collected

into a single pipe. Exhaust gases comes out of this Header as a single stream of hot exhaust gases through single outlet.

From emission point of view most important parameters are backpressure and exhaust velocity.

Back Pressure

Engine exhaust backpressure is defined as the exhaust gas pressure that is produced by the engine to overcome the

hydraulic resistance of the exhaust system in order to discharge the gases into the atmosphere. The exhaust backpressure is

the gage pressure in the exhaust system at the outlet of the exhaust turbine in turbocharged engines or the pressure at the

outlet of the exhaust manifold in naturally aspirated engines.

46 K. S. Umesh, V. K. Pravin & K. Rajagopal

The word back may suggest a pressure that is exerted on a fluid against its direction of flow indeed, butthere are

two reasons to object. First, pressure is a scalar quantity, not a vector quantity, and has no direction. Second, the flow of

gas is driven by pressure gradient with the only possible direction of flow being that from a higher to a lower pressure.

Gas cannot flow against increasing pressure .It is the engine that pumps the gas by compressing it to a sufficiently high

pressure to overcome the flow obstructions in the exhaust system.

Effects of Increased Back Pressure

At increased back pressure levels, the engine has to compress the exhaust gases to a higher pressure which

involves additional mechanical work and/or less energy extracted by the exhaust turbine which can affect intake

manifold boost pressure. This can lead to an increase in fuel consumption, PM and CO emissions and exhaust

temperature. The increased exhaust temperature can result in overheating of exhaust valves and the turbine.

An increase in NOx emissions is also possible due to the increase in engine load.

Increased backpressure may affect the performance of the turbocharger, causing changes in the air-to-fuel

ratio-usually enrichment—which may be a source of emissions and engine performance problems. The magnitude

of the effect depends on the type of the charge air systems. Increased exhaust pressure may also prevent some

exhaust gases from leaving the cylinder (especially in naturally aspirated engines), creating an internal exhaust

gas recirculation (EGR) responsible for some NOx reduction. Slight NOx reductions reported with some DPF

system, usually limited to 2-3% percent, are possibly explained by this effect.

Excessive exhaust pressures can increase the likelihood of failure of turbocharger seals, resulting in oil leakage

into the exhaust system. In systems with catalytic DPFs or other catalysts, such oil leak can also result in the

catalyst deactivation by phosphorus and/or other catalyst poisons present in the oil.

All engines have a maximum allowable engine back pressure specified by the engine manufacturer. Operating the

engine at excessive backpressure might invalidate the engine warranty.

It is generally accepted by automotive engineers that for every inch of Hg of backpressure (that's Mercury - inches

of Hg is a unit for measuring pressure) approximately 1-2 HP is lost depending on the displacement and efficiency

of the engine, the combustion chamber design etc.

Table 1: VERT Maximum Recommended Exhaust Back Pressure

Exhaust Velocity

Exhaust system is designed to evacuate gases from the combustion chamber quickly and efficiently. Exhaust

gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4-cylinder motor will have 4 distinct pulses

per complete engine cycle a 6 cylinder has 6 pulses and so on. More the pulses produced, the more continuous the exhaust

flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of

the exhaust stream.

CFD Analysis of Exhaust Manifold of Multi-Cylinder SI Engine to Determine Optimal Geometry for Reducing Emissions 47

It is a general misconception that wider exhaust gives helps in better scavenging. But actually main factor behind

good scavenging is exhaust velocity. The astute exhaust designer knows that flow capacity must be balanced with velocity.

The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap.

The guiding principle of exhaust pulse scavenging is that a fast moving pulse creates a low-pressure area behind it.

This low-pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling

at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles

get sucked into this low pressure area causing it to collect on the back of the vehicle.

Exhaustive work has taken place already in this field. Scheeringa et al studied analysis of Liquid cooled exhaust

manifold using CFD. He to improve the fundamental understandings of manifold operation obtained detailed information

of flow property distributions and heat transfer. He to investigate the parametric effects of operating conditions and

geometry on the performance of manifolds performed a number of computations. Yasar Deger et al. did CFD-FE-Analysis

for the Exhaust Manifold of a Diesel Engine aiming to determine specific temperature and pressure distributions. The fluid

flow and the heat transfer through the exhaust manifold were computed correspondingly by CFD analyses including the

conjugate heat transfer.

Kulal et al.(2013)in his “CFD Analysis and Experimental Verification of Effect of Manifold Geometry on

Volumetric efficiency and Back Pressure for Multi-cylinder SI Engine” investigated optimal geometry for exhaust

manifold for maximum volumetric efficiency. Kulal et al.(2013)in his “Experimental Analysis of Optimal Geometry for

Exhaust Manifold of Multi-cylinder SI Engine for Optimum Performance” investigated the effect of attaching a reducer to

the outlet of exhaust manifold.

This work focuses upon study of pressure distribution and velocity distribution inside an exhaust manifold of

different geometries and to conclude best possible geometry from emissions point of view.

DISCUSSIONS

Model Description

We have considered eight different models for this particular research work. We have flaunted with symmetric

and asymmetric designs and have flocked concepts of having either long or short bends (inlet for exhaust manifold).

Additionally we have tried out idea of attaching a reducer at the outlet of exhaust manifold for each of these designs.

The material used for pipe was SA 106 (grade B). Flange material was IS 2602 (Grade B). Elbow material was SA 234

WPB.

The eight models considered for this work are

Short Bend Center Exit (SBCE)

Short Bend Side Exit (SBSE)

Long Bend Center Exit (LBCE)

Long Bend Side Exit (LBSE)

Short Bend Center Exit with Reducer (SBCER)

Short Bend Side Exit with Reducer (SBSER)

Long Bend Center Exit with Reducer (LBCER)


Long Bend Side Exit with Reducer (LBSER)

Figure 1: Short Bend Side Exit

Figure 2: Long Bend Center Exit

Figure 3: Short Bend Center Exit

Figure 4: Long Bend Side Exit


Figure 5: Short Bend Center Exit with Reducer

Figure 6: Long Bend Center Exit with Reducer

Figure 7: Short Bend Side Exit with Reducer

Figure 8: Long Bend Side Exit with Reducer


All models have header length of 335mm. ID and OD of headers is 52.48 mm & 60.3 mm respectively. In Short

Bend models the bend radius is 48 mm and exhaust is on one side. ID and OD of bend were 35.08mm and 42.86mm

respectively.

Long Bend models have bend radius of 100 mm and exhaust is at the centre of header. ID & OD of the bend &

exhaust is 52.48mm and 60.3 mm respectively for both models. Length of the outlet of exhaust manifold was kept at

220mm and flange was attached at the end to connect it to exhaust muffler.

For models with reducer the reducer length was kept 70mm its inlet ID was 52.48mm and outlet ID was 38mm.

the straight length after the reducer was kept 100mm and total length of outlet of exhaust manifold was kept at 220mm and

flange was attached at the end to connect it to exhaust muffler.

Methodology

For all 8 models the mass flow rate of flue gasses was evaluated keeping speed constant at 1500rpm.

These calculations were carried out at different loading condition i.e. 2kg, 4kg, 6kg, 8kg, 10kg and 12 kg. Pressure and

velocity contours were obtained for all eight models at six above mentioned loading conditions. All eight models were

prepared using Solidworks and analysis was carried out using Ansys workbench 12.0.

The results were categorized into groups and comprehensive game matrix was prepared to render a peculiar

performance score to each of these models to finally conclude upon the best possible design.

Material Fluid Properties

Exhaust gas will be considered as an incompressible fluid operating at 230‐280 0C. The material properties under

these conditions are

Table 2: Material Fluid Properties

Material Air + Gasoline

Density (kg/m3) 1.0685

Viscosity (Pa-s) 3.0927 x 10‐5

Specific heat (J/kg-K) 1056.6434

Thermal conductivity (W/m-K) 0.0250

Boundary Conditions

The inlet mass flow rates for different models at six different loading conditions are given below using these mass

flow rates the pressure and velocity contours were obtained.

Table 3: Inlet Mass Flow Rate

Load Inlet 1 Inlet 2 Inlet 3 Inlet 4

2 KG 0.000424 Kg/s 0.000424 Kg/s 0.000424 Kg/s 0.000424 Kg/s

4 KG 0.000848 Kg/s 0.000848 Kg/s 0.000848 Kg/s 0.000848 Kg/s

6 KG 0.001272 Kg/s 0.001272 Kg/s 0.001272 Kg/s 0.001272 Kg/s

8 KG 0.001696 Kg/s 0.001696 Kg/s 0.001696 Kg/s 0.001696 Kg/s

10 KG 0.002120 Kg/s 0.002120 Kg/s 0.002120 Kg/s 0.002120 Kg/s

12 KG 0.002544 Kg/s 0.002544 Kg/s 0.002544 Kg/s 0.002544 Kg/s

The flow was considered to be turbulent. 10% turbulent intensity was taken and K-εmodel was considered with

RNG scheme. The hydraulic mean diameter for all four inlets are given below:


Table 4: Inlet Mean Hydraulic Diameter

Boundary Mean Hydraulic Diameter

INLET 1 0.00877m

INLET 2 0.00877m

INLET 3 0.00877m

INLET 4 0.00877m

Outlet pressure was taken as 0atm (Gauge) for all models. The mean hydraulic diameter for outlets of different

models are shown below:

Table 5: Outlet Mean Hydraulic Diameter

Model Mean Hydraulic Diameter

Short Bend Center Exit (SBCE) 0.01302m

Short Bend Side Exit (SBSE) 0.01302m

Long Bend Center Exit (LBCE) 0.01302m

Long Bend Side Exit (LBSE) 0.01302m

Short Bend Center Exit with Reducer

(SBCER) 0.0095m

Short Bend Side Exit with Reducer

(SBSER) 0.0095m

Long Bend Center Exit with Reducer

(LBCER) 0.0095m

Long Bend Side Exit with Reducer

(LBSER) 0.0095m

Engine Specifications

Following engine parameters were considered for calculation of mass flow rate at different loading conditions.

The flow through exhaust manifold was considered density based.

Table 6: Engine Specification

Engine 4 Stroke 4 Cylinder SI Engine

Make Maruti-Suzuki Wagon-R

Calorific Value of Fuel (Gasoline) 45208 KJ/Kg-K

Specific Gravity of Fuel 0.7 gm/cc

Bore and Stroke 69.05 mm X 73.40 mm

Swept Volume 1100 cc

Compression Ratio 7.2 :1

RESULTS

The results obtained by CFD simulations at 2KG loading are shown below. The pressure and velocity contours

have been shown below. Similarly results were obtained at all six loading conditions.

Figure 9: Short Bend Center Exit (SBCE)


Figure 10: Short Bend Side Exit (SBSE)

Figure 11: Long Bend Center Exit (LBCE)

Figure 12: Long Bend Side Exit (LBSE)

Figure 13: Short Bend Center Exit with Reducer (SBCER)


Figure 14: Short Bend Side Exit with Reducer (SBSER)

Figure 15: Long Bend Center Exit with Reducer (LBCER)

Figure 16: Long Bend Side Exit with Reducer (LBSER)

CONCLUSIONS

The backpressure and exhaust velocity for all the models at all loading conditions are listed below:

Table 7: Backpressure for Different Models in Pascals

2KG 4KG 6KG 8KG 10KG 12KG

SBCE 940 976 1002 1036 1079 1111

SBSE 1020 1071 1098 1113 1132 1172

LBCE 850 863 894 923 984 1012

LBSE 973 1005 1039 1076 1099 1125

SBCER 984 1012 1047 1077 1114 1154

SBSER 1180 1214 1222 1268 1272 1303

LBCER 1037 1080 1112 1154 1187 1201

LBSER 1138 1174 1219 1218 1276 1271


The backpressure performance score was evaluated as follows:

Performance Score = x 100

Table 8: Backpressure for Different Models (Performance Score)

2KG 4KG 6KG 8KG 10KG 12KG Score

SBCE 0.904255

319

0.884221

311

0.892215

569

0.890926

641

0.911955

514

0.910891

089

89.90775

74

SBSE 0.833333

333

0.805788

982

0.814207

65

0.829290

207

0.869257

951

0.863481

229

83.58932

253

LBCE 1 1 1 1 1 1 100

LBSE 0.873586

845

0.858706

468

0.860442

733

0.857806

691

0.895359

418

0.899555

556

87.42429

518

SBCER 0.863821

138

0.852766

798

0.853868

195

0.857010

214

0.883303

411

0.876949

74

86.46199

16

SBSER 0.720338

983

0.710873

147

0.731587

561

0.727917

981

0.773584

906

0.776669

225

74.01619

671

LBCER 0.819672

131

0.799074

074

0.803956

835

0.799826

69

0.828980

623

0.842631

141

81.56902

489

LBSER 0.746924

429

0.735093

697

0.733388

023

0.757799

672

0.771159

875

0.796223

446

75.67648

568

Table 9: Exhaust Velocity for Different Models in Meter per Second (m/s)

2KG 4KG 6KG 8KG 10KG 12KG

SBCE 17.03 18.1 18.7 19.52 21.45 23.01

SBSE 18.1 18.6 19.1 20.2 21.6 23.5

LBCE 20.22 21.33 22.07 23.52 23.98 24.77

LBSE 18.71 18.92 19.23 20.12 22.21 23.65

SBCER 17.7 17.79 18.22 19.86 21.1 23.89

SBSER 16.8 17.12 18.6 19.9 21.76 23.92

LBCER 17.3 18.67 19.54 21.96 23.65 24.71

LBSER 17.9 18.01 19.1 20.65 21.86 23.98

The exhaust velocity performance score was evaluated as follows:

Performance Score = x 100

Table 10: Exhaust Velocity for Different Models (Performance Score)

2KG 4KG 6KG 8KG 10KG 12KG Score

SBCE 0.842235

41

0.848570

089

0.847304

033

0.829931

973

0.894495

413

0.928946

306

86.52472

04

SBSE 0.895153

314

0.872011

252

0.865428

183

0.858843

537

0.900750

626

0.948728

3

89.01525

353

LBCE 1 1 1 1 1 1 100

LBSE 0.925321

464

0.887013

596

0.871318

532

0.855442

177

0.926188

49

0.954784

013

90.33447

12

SBCER 0.875370

92

0.834036

568

0.825555

052

0.844387

755

0.879899

917

0.964473

153

87.06205

608

SBSER 0.830860

534

0.802625

41

0.842772

995

0.846088

435

0.907422

852

0.965684

296

86.59090

871

LBCER 0.855588

526

0.875293

015

0.885364

749

0.933673

469

0.986238

532

0.997577

715

92.22893

343

LBSER 0.885262

117

0.844350

68

0.865428

183

0.877976

19

0.911592

994

0.968106

581

89.21194

575


Table 11: Over all Performance Score

Model

Pressure

Performance

Score

Velocity

Performance

Score

Average

Performance

Score

SBCE 89.9077574 86.5247204 88.2162389

SBSE 83.58932253 89.01525353 86.30228803

LBCE 100 100 100

LBSE 87.42429518 90.3344712 88.87938319

SBCER 86.4619916 87.06205608 86.76202384

SBSER 74.01619671 86.59090871 80.30355271

LBCER 81.56902489 92.22893343 86.89897916

LBSER 75.67648568 89.21194575 82.44421571

Figure 17: Backpressure for Various Models at Various Loads

Figure 18: Velocity for Various Models at Various Loads

Thus we conclude that LBCE model is the best possible designs for exhaust manifold from emission point of

view.

REFERENCES

1. PL. S. Muthaiah, Dr. M. Senthil Kumar, Dr. S. Sendilvelan “CFD Analysis of catalytic converter to reduce

particulate matter and achieve limited back pressure in diesel engine”, Global journal of researches in engineering

A: Classification (FOR) 091304,091399, Vol.10 Issue 5 (Ver1.0) October 2010.

2. P. R. Kamble and S.S. Ingle “Copper Plate Catalytic Converter: An Emission Control Technique”, SAE Number

2008-28-0104.

3. Eberhard Jacob, Rheinhard Lammermann, Andreas Pappenherimer, and Diether Rothe Exhaust Gas After

treatment System for Euro 4: Heavy Duty Engines – MTZ 6/2005.

4. Jacobs, T., Chatterjee, S., Conway, R., Walker, A., Kramer, J. and K. Mueller-Haas, Development of a Partial

Filter Technology for Hdd Retrofit, Sae Technical Paper 2006-01-0213.


5. C. Lahousse, B. Kern, H. Hadrane and L. Faillon, “Backpressure Characteristics of Modern Three-way Catalysts”,

Benefit on Engine Performance, SAE Paper No. 2006011062,2006 SAE World Congress, Detroit, Michigan ,

April 36, 2006 [1] M.B. Beardsley et al.,Thermal Barrier Coatings for Low Emission, High Efficiency Diesel

Engine Applications” SAE Technical Paper 1999-01-2255.

6. Rajesh Biniwale , N.K. Labhsetwar, R. Kumar and M. Z. Hasan, “A non-noble metal based catalytic converter for

two strokes, two-wheeler applications”, SAE Paper No. 2001011303, 2001.

7. G. Muramatsu, A. Abe, M. Furuyama, “Catalytic Reduction of Nox in Diesel Exhaust”, SAE 930135, 1993.

8. John B. Heywood, Internal Combustion Engine Fundamentals (Tata McGrah Hill).

9. Nitin K. Labhsetwar, A. Watanabe and T. Mitsuhashi, “Possibilities of the application of catalyst technologies for

the control of particulate emission for diesel vehicles”, SAE Transaction 2001, paper no. 2001280044.

10. K.S. Umesh, V.K. Pravin and K. Rajagopal “CFD Analysis and Experimental Verification of Effect of Manifold

Geometry on Volumetric efficiency and Back Pressure for Multi-cylinder SI Engine” International Journal of

Engineering & Science Research IJESR/July 2013/ Vol-3/Issue-7/342-353

cfd analysis of exhaust manifold of multi-cylinder si .... cfd analysis.full.pdf · cfd analysis of...

Documents