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40 OPTIMAL DESIGN OF AUTOMOBILE EXHAUST SYSTEM USING GT- POWER

VIEWS: 42 PAGES: 8

									International Journal of Mechanical and Materials Engineering (IJMME), Vol. 2 (2007), No. 1, 40-47.




                         OPTIMAL DESIGN OF AUTOMOBILE EXHAUST SYSTEM USING
                                             GT- POWER

                                         A.K.M. Mohiuddin, Ataur Rahamn and Mohd. Dzaidin
                                Mechanical Engineering Department, International Islamic University Malaysia,
                                              Jalan Gombak, Kuala Lumpur 53100, Malaysia,
                                                      E-mail: mohiuddin@iiu.edu.my




ABSTRACT                                                                                  The main objective of this paper is to design exhaust
The exhaust system consists of the exhaust manifold, the                             system (particularly the exhaust manifold) using GT-Power
header, the catalytic converter, the muffler, and the tailpipe.                      software and to compare its performance with an existing
Certain flow characteristics must be met for the optimal                             system.
performance of the exhaust system. The main objective of this                        The exhaust manifold, usually constructed of cast iron (due to
paper is to design exhaust system (particularly the exhaust                          cost and manufacturability), is a pipe that conducts the exhaust
manifold) using GT-Power software and to compare its                                 gases from the combustion chambers to the exhaust pipe. It has
performance with an existing system. The newly designed                              smooth curves in it for improving the flow of exhaust gases.
exhaust manifold shows lower back pressure which ultimately                          The exhaust manifold is bolted to the cylinder head. A header is
results better performance of the engine.                                            a different type of manifold; it is made of separate equal-length
                                                                                     tubes. Four tube headers will slightly out perform three tube
Keywords: Exhaust system, GT-Power, Back pressure, Exhaust                           and Ram Air manifolds, and the three tube headers and ram air
manifold, Catalytic converter.                                                       units are a little better than stock manifolds [2].
                                                                                          The exhaust pipe is the bent-up or convoluted pipes that
INTRODUCTION                                                                         connect the entire exhaust system together. Some are shaped to
     A well designed exhaust system is one of the cheapest                           go over the rear axle, allowing the rear axle to move up and
ways of increasing engine efficiency, and therefore increasing                       down without bumping into the exhaust pipe; some are shaped
engine power. In a four stroke cycle engine, only one stroke out                     to bend around under the floor of the car, connecting the
of the four does useful work which is the power stroke. The                          catalytic converter with the muffler. Exhaust pipes are usually
other three strokes which are intake, compression and exhaust                        made of stainless steel, since the high heat conditions involved
will absorb some of the power that was produced during the                           with the muffler system will cause rust. Exhaust pipes are
power stroke. If the amount of power that is lost by these idle                      classified by their diameter, with wider diameters being
strokes can be minimized, more power will be available to                            preferred for increased performance. A 2-1/2" system is
drive the wheels, which is what the engine is supposed to be                         adequate for most street cars, and 3" exhaust pipes might help
doing [1].                                                                           slightly for faster cars. In addition to diameter, the actual design
                                                                                     of the exhaust pipe has a tremendous effect on performance.
     It is clear that there are real gains if the exhaust gasses are                 The more bends, kinks, and rough edges inside the pipe, the
effectively removed from the combustion chamber. The pipe                            greater the internal friction on the exhaust gasses and the less
configurations and/or size will cause back pressure in many                          efficient the exhaust system. Therefore, well performed exhaust
applications. Moreover, smoothly bent pipes, relatively free                         systems usually feature with exhaust pipes that are smoothly
flowing mufflers, headers, and a balance pipe will result in a                       bent, smooth on the inside, and have minimum number of
more efficient exhaust system and thus ensure greater                                bends as possible to reduce the friction inside the pipe. Uniform
performance. A well designed exhaust system can even ‘draw’                          diameter head-pipes of adequate size will improve performance
the gasses out of the chamber, using the momentum of the gas                         over carelessly bent or badly crimped pipes. Mandrel bent pipes
travelling down the pipe to suck the residual gasses out of the                      provide the best available performance.
combustion chamber. The gas travelling down the pipe creates                              To help reduce harmful emissions, modern cars have a
an area of low pressure behind it. This not only purges the                          catalytic converter in the exhaust system. The catalytic
combustion chamber, but also draws more mixture into the                             converter is installed in the exhaust line, between the exhaust
chamber during the valve overlap period. So, instead of having                       manifold and the muffler. Exhaust gases leave the engine under
high pressure exhaust gas popping into the inlet tracts, a partial                   very high pressure. If these gases escaped directly from the
vacuum inside the combustion chamber is available which pulls                        engine the noise would be extremely high. For this reason, the
the fresh charge into the chamber when the intake valve opens.                       exhaust manifold sends the gases to a muffler, which is located
                                                                                     between the catalytic converter and the tail pipe. The muffler


                                                                               40
quiets the noise of the exhaust by "muffling" the sound waves
created by the opening and closing of the exhaust valves.                 suppliers. It is also used for ship and power-generation engines,
                                                                          small two and four stroke engines and racing engines (F1,
GT-SUITE                                                                  NASCAR, IRL, etc.). It provides the user with many
                                                                          components to model any advanced concept. Among its
     GT-SUITE is an integrated set of computer-aided                      advantages is its ease of use and its tight integration with the
engineering (CAE) tools developed by Gamma Technologies,                  rest of GT-SUITE, which give GT-Power a "virtual engine"
Inc. for design and analysis of engines, power trains and                 perspective [4]. GT-Power environment is shown in Fig. 1. The
vehicles. These tools are contained in a single executable form           GT-SUITE environment also provides GT-Power with a proven
which is essential to its use in "Integrated Simulations" [3]. GT-        set of high-productivity features for pre- and post-processing,
SUITE comprised of six solvers (GT-Power, GT-Drive, GT-                   optimization, neural networks and control modeling. Its
Vtrain, GT-Cool, GT-Fuel, and GT-Crank), a model-building                 usefulness is further enhanced by integration with STAR-CD,
interface (GT-ISE), a powerful post-processing package (GT-               Fluent, Simulink and MS/EXCEL [4]. GT-Power is specifically
POST), and a collection of supporting tools. GT-ISE provides              designed for both steady state and transient simulations. In
the user with the graphical user interface (GUI) that is used to          addition it can be used for analysis of engine/ power train
build models as well as the means to run all GT-SUITE                     control. GT-Power is available as a standalone tool, or coupled
applications.                                                             with GT-Drive, GT-Fuel and GT-Cool as the GT-SUITE / flow
                                                                          product.
GT-POWER
    GT-Power is the industry-standard engine simulation tool,
used by all leading engine and vehicle manufacturers and their




                                                     Figure 1: GT-Power Environment




                                                                     41
METHODOLOGY AND SIMULATION SETUP                                       exhaust manifold. The newly designed exhaust manifold is
     The methodology used in performing the present work is            designed by reducing the angle of bend pipes throughout the
as follows:                                                            exhaust gases path from the header up until the outlet of the
1. Engine Selection - The specification of the engine is needed        exhaust manifold itself. By reducing the angle of bend pipes,
     as the input parameters.                                          the back pressure will be reduced so that the exhaust gases will
2. Exhaust Manifold Measurement – The dimension of the                 be removed easily from the engine cylinder and thus will give a
     existing exhaust manifold has to be measured; several             better breathing capability to the engine. In addition, the
     dimensions of the newly designed exhaust manifold are             diameter of the exhaust manifold pipes are also been enlarged a
     proposed by creating several geometry of the exhaust              bit to increase the rate of the exhaust gases velocity but must be
     manifold; and the geometry of the newly designed exhaust          kept within an acceptable range to avoid other unwanted factors
     manifold which gives the optimum performance will be              to affect the performance.
     chosen to be fabricated.
3. GT-Power Modeling – The dimensions for both existing and            MODEL SETUP PREPARATION
     newly designed exhaust manifold will be modeled in GT-                The drag and drop method is used to copy all the listed
     Power software for simulation.                                    templates/objects of table - 1 from the example object tree. If
4. GT-Power Simulation – The simulation will be performed              the listed template/object is not inside the example object tree,
     and the result of both existing and newly designed exhaust        it could be copied from template library.
     manifold will be compared.                                             Modeling is started from pipe parts of air induction
     The engine that has been selected is Proton Iswara 1.5L           process. First of all, the pipe from inlet (intake part) to air
gasoline engine [5]. The major area of concern in this work is         cleaner will be modeled. Next, throttle part is modeled. It
to focus on the design of exhaust manifold instead of the whole        covers from air cleaner intake site to throttle, which is located
components of exhaust system. However, in using the GT-                in front of the surge tank. After intake manifold, engine is
Power software, the whole components of exhaust manifold               modeled. The modeling will cover the engine head (intake port,
must be included in the simulation and analysis because the            intake valve, exhaust port and exhaust valve) including the
exhaust manifold by itself cannot perform its function if there        engine cylinder. For the existing exhaust manifold, the pipes
are no combinations of all exhaust components. In this project,        are discretized into eight stages for the exhaust manifold. The
the pipes and flowsplits dimensions i.e. length, bend angle,           makes it easier to measure the angle of bend, radius of bend and
bend radius, of the existing exhaust manifold of Proton Iswara         the length. There are four bend pipes at the first stage, another
are measured and they are being used as input data in the GT-          four bend pipes at the second stage, four pipes at the third
Power software. The other parts such as air cleaner, intake            stage, two flowsplits at the fourth stage, two bend pipes at the
manifold, fuel system, the engine, catalytic converter, muffler        fifth stage, two pipes at the sixth stage, one flowsplit at the
and tailpipe will be kept same to use with the newly designed

                                         Table 1: Template/ Object from Template Library
                                                   COMPONENT                   COMPOUND                   CONNECTION
       REFERENCE OBJECT
                                                     OBJECT                     OBJECT                      OBJECT

 ● FPropMixtureComb - Air                      - Pipe                         ●   Engine              ●    Orifice Conn
 ● FStateInit - Init                           - FsplitTRight                     CrankTrain               - bellmouth
 ● HeatCComp - ExhManifold                     - FsplitSphere                                         ●    InjAF-Ratio Conn
 ● RLTDependence - FARatio                     - FsplitGeneral                                        ●    ThrottleConn
                                                                                                           - throttle
 ● FPropLiqInComp - Indolene-                  - PipeRoundBend
   combust                                     - ValveCamPR
 ● XYTable                                       Conn - Inval
   - FARvsRPM                                  - ValveCamConn
   - THB50vsRPM                                  - Exval
   - BDURvsRPM                                 - EngCylinder
 ● XYZTable - INTPr                            - EndEnvironment
 ● FPropGas - Indolene-vap.




                                                                  42
seventh stage and one pipe at the final stage. The attribute          meant for Muffler design. Firstly, the muffler would be drawn
folder below (Fig. 2) and connections (Fig. 3 and 4) show the         using the available tools inside the software. Then, it will be
path of exhaust manifold path 1 until it enters the catalytic         converted into parts which is executable by the GT Power.
converter. There is a special application in GT Power which is




                                              Figure 2: Catalytic Converter Attribute




                                                  Figure 3: Catalytic Connections




                                                                 43
                                         Figure 4: Catalytic Converter Connections


RESULTS AND ANALYSIS
  The existing and the newly designed exhaust manifold           geometry is shown in Fig. 5 and 6 respectively.

          Path 1                          Path 2                                                             Path 4
                                                                            Path 3




                                       Figure 5: Existing Exhaust Manifold Geometry



                                                            44
                                       Path 2
      Path 1                                                                 Path 3                             Path 4




                                     Figure 6: Newly Designed Exhaust Manifold Geometry

    Figure 7 shows that the back pressure for the existing          result of the discretized pipe instead of the overall pipe length
exhaust manifold is higher than the back pressure for the           but it is sufficient and clearly shown that reducing the angle of
newly designed exhaust manifold for all values of engine            bend pipes will reduce the back pressure which will give a
speeds. This indicates that the designed exhaust manifold is        better breathing capability to the engine. Fig. 8 shows the
more efficient in terms of reducing the back pressure in the        fabricated exhaust manifold according to design.
exhaust manifold pipe. However, the graph only shows the




                                                               45
          Figure 7: Variation of Back Pressure with Engine Speed




Figure 8: Different Views of Designed and Fabricated Exhaust Manifold




                                   46
                                                                  REFERENCES
CONCLUSION
                                                                  [1] Ganesan, V., 2004, “Internal Combustion Engines,”
  The GT-Power is a very sophisticated simulation software
                                                                  Second Edition, McGraw Hill.
  to be used in designing the automobile exhaust system.
                                                                  [2] Hillier, V.A.W. and Coombes, P., Hiller’s Fundamentals of
  Apart from that, it can also be used to design any other
                                                                  Motor Vehicle Technology, Nelson Thornes Ltd., United
  parts in automobile applications. The newly designed
                                                                  Kingdom, 2004.
  exhaust manifold shows lower back pressure which
                                                                  [3] Gamma Technologies, GT-Suite, www.gtisoft.com, 2004.
  ultimately result better performance of the engine.
                                                                  [4] Gamma Technologies, GT-Power User’s Manual, GT-
                                                                  Suite Version 6.1, 2004.
                                                                  [5] Proton Iswara Features & Specifications, www.eon.com,
                                                                  2005.




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