CFD Analysis of Swirl Enhancementin a Direct Injection Diesel Enginewith Vortex Generator in Inlet Manifold

G. Sivakumar and S. Senthil Kumar

Abstract Swirling enhancement is studied numerically for a direct injectiondiesel engine with vortex generators placed in the inlet manifold using commercialCFD code, ANSYS FluentTM. The three-dimensional geometry and mesh arecreated using preprocessor ANSYS ICEM. Simulations have been carried out toinvestigate the effect of vortex generator in inlet manifold for a single cylinderengine. Transient flow characteristics inside the engine cylinder for the intakestroke with RNG k-e turbulent model are studied and the results are presented interms of swirling velocity component, swirl number, and turbulent kinetic energy.It is observed that the modified inlet manifold creates uniform mixing inside theengine cylinder which is essential for effective combustion for diesel engine.Results show that it could be used as a simple and effective swirl creatingmechanism in the in-flow of engine cylinder.

Keywords Swirling enhancement �Manifold � Diesel engine � Vortex generator �Mixing

1 Introduction

In the recent years, engine development researches are focusing mainly onreducing emission and effective utilization of energy from fuel. It is of greatconcern all over the world due to the pollution control which in turn affects the

G. Sivakumar (&)Department of Mechanical Engineering, Vel Tech Dr. RR and Dr. SR Technical University,Chennai, Indiae-mail: sec2.veltech@gmail.com

S. Senthil KumarDepartment of Aeronautical Engineering, Vel Tech Dr. RR and Dr. SR TechnicalUniversity, Chennai, Indiae-mail: s.senthilms@gmail.com

R. P. Bajpai et al. (eds.), Innovative Design, Analysis and Development Practicesin Aerospace and Automotive Engineering, Lecture Notes in Mechanical Engineering,DOI: 10.1007/978-81-322-1871-5_19, � Springer India 2014

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climate change. It is well known that combustion and emission characteristics arecontrolled by the flow created inside the cylinder during the intake and evolves inthe compression stroke. Flow mixing enhancement inside the diesel engine hasbeen studied both experimentally and numerically over several years. It is moreimportant to create swirling inside the engine cylinder as it directly affects thecombustion performance, output, and emission of the engine.

Swirling creation inside the engine was earlier studied by various researchers[1–3] by changing the parameters like manifold shape, combustion chamberconfigurations, and piston head shape. There are two ways of enhancing thecombustion process thereby increasing the engine thermal efficiency. First one isby increasing the compression ratio as high as possible. But the problem is thathigh compression ratio may create knock, which should be avoided for goodperformance. Second one is by enhancing the turbulence in order to have a bettermixing of fuel and air. However, two much turbulence leads to excessive heattransfer from the gases to cylinder walls [3]. Paul et al. [1] studied the swirlenhancement by using spiral-helical and helical-structured manifolds and pre-sented swirling characteristics in terms of flow patterns, turbulent kinetic energy,and swirling number. They conclude that spiral-helical-shaped manifold createshigher swirl flow inside the cylinder than spiral manifold. Martins et al. [2] per-formed a CFD study with modified helical inlet port under different value liftsusing commercial CFD code Fluent and found that the increase in valve liftdecreases the swirl number. It indicates that the valve position also plays animportant role in the in-cylinder flows.

Other approach was used to increase swirling inside the cylinder by changingthe piston top surface with different bowl shapes and bowl positions by Muraliet al. [4]. They experimentally studied, using particle image velocimentry (PIV),the effect of bowl shape on the top piston surface, and found that bowl shape onflat piston shows a good improvement. Jin et al. [5] carried out an experimentalstudy to enhance swirling by using swirl control valve (SCV) with different SCVangles and presented flow patterns and swirl number for different SCV angles. Itwas that this modification enhances the swirling characteristics inside the cylinder.All the geometry shapes and mechanism tried by various researchers [1–6], havedifficulties in manufacturing point of view and would increase the total vehiclecost. Hence, it is of necessity to have simpler mechanism which would give thesame performance at the lower cost.

From the literature review, it is found that understanding the flow character-istics inside the cylinder, which are directly, linked with the engine performanceand emission characteristics. And capturing the flow patterns inside the cylinderusing experimental techniques is expensive and it is difficult to carry out para-metric studies with different combinations of inlet manifolds, piston top surfaces.So the CFD is only effective analysis tool used by many authors [1, 2, 3, and 6] tostudy the flow behavior with various manifolds and piston top bowl shapes. It mustbe emphasized the 3D CFD simulation is necessary to bring more light to theunderstanding of flow dynamics in the cylinder.

146 G. Sivakumar and S. Senthil Kumar

Hence, the objective of this work is to study swirling enhancement by modifyingthe inlet manifold with a simple wedge-shaped vortex generators (VGs) attachedcircumferentially over the inner surface of the manifold at the entry position, asshown in Fig. 1a and compare with the base engine cylinder flow characteristics.The dimensions of the engine are given in Table 1 for a CI diesel engine.

2 Numerical Methodology

Numerical simulations under isothermal conditions have been carried out for asingle cylinder CI engine with modified inlet manifold using vortex generators.Computational domain and mesh structure of the problem are shown in Fig. 1a andb, respectively. For simplicity, simulations are performed with fully opened valvecondition at the inlet port and fully closed valve condition at the exhaust port.Pressure inlet boundary condition is specified for the starting face of the inletmanifold. No-slip boundary conditions are specified at walls of the engine cylinder

Vortex Generator

Inlet Manifold Exhaust Manifold

(a) (b)

Fig. 1 a Geometry of the engine; b Mesh of the computational geometry

Table 1 Dimensions of theengine

Details Value (mm)

Bore 104Stoke 113Inlet valve diameter 35Exhaust valve diameter 45Maximum inlet valve lift 13

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and inlet manifold. Three-dimensional tetrahedral type mesh is created for thegeometry of the problem. Pressure velocity coupling was done using SIMPLECpressure correction method [7]. Unsteady Computations are performed by animplicit time discretization within the domain using incompressible Reynolds—Averaged Navier–Stokes equations with RNG k-e turbulence model with swirlenhancement available with Commercial software ANSYS FLUENTTM. TheDiffusion terms are discretized with second-order central scheme and the con-vective terms are with second-order upwind scheme. For all the computations,residuals of continuity, momentum, and turbulence kinetic energy equations aremonitored, and the convergence criterion value used equal to 10-4.

3 Results and Discussion

Computations are performed for intake stroke with fully opened value conditionfor both the base engine and base engine with VGs attached at the inlet manifold,as shown in Fig. 1a. Flow characteristics in terms of velocity vectors and turbulentkinetic energy (TKE) are presented for a single cylinder engine at different cross-sections along the axis of the cylinder. Figure 2 shows the turbulent intensity(Left) and the velocity vector plots (Right) for a center plane (x = 72 mm, wherex is the distance measured in the perpendicular to the axis of the cylinder)) cutparallel to the cylinder axis for the both cases, namely, inlet manifold with andwithout VGs. It is clearly seen from Fig. 2 (Top-Left), the turbulent intensity is notuniform and having many small vortices (see Fig. 2: Top-Right), which are notgood for better combustion, whereas the inlet manifold with VGs having uniformturbulent intensity and not having many small vortices, which are good for bettercombustion, as observed in Fig. 2 (Bottom) and in Fig. 5.

Having better air-fuel mixture is depending on how big the size of vortex andthat should too cover the whole size of the cylinder. In order to increase com-bustion speed and reduce ignition time, the large vortex inside the cylinder to becreated with higher TKE.

To check the effect of VGs in turbulence enhancement, the variations of TKE atdifferent planes perpendicular to the axis of the cylinder (say, z = 20, 40, 60, and80 mm, where z is the distance along the axis of the cylinder measured from BDC)are shown in Figs. 3 and 4, for with VGs case and without VGs case, respectively.It can be seen from Fig. 3 that VGs create uniform turbulence throughout thecylinder, which are essential for good combustion and emission characteristics.

It indicates the importance of modification of the inlet manifold with VGs. TKEis not propagating uniformly through the cylinder without VGs case (base engine),as shown in Fig. 4. It may not be good for having better combustion process andmore emission products may come out of the engine at the end of the combustionprocess. It should be mentioned that with VGs case, swirling vortices created in the

148 G. Sivakumar and S. Senthil Kumar

perpendicular and parallel planes, with respect to the cylinder axis, cover thewhole space in that particular plane, which would make better air-fuel mixing so asto have good combustion efficiency and less emission outcomes, as observed inFig. 3. This trend can also be noticed clearly in Fig. 5 with the path lines inside thecylinder for both the cases; with and without VGs.

In order to quantify the effect of turbulent creation inside the cylinder, it isnecessary to calculate the swirl number. The swirl number is the ratio of theangular momentum to the axial momentum. Figure 6 shows the variation of swirlnumber along the stroke length for two inlet manifold configurations, with andwithout vortex generators. It is seen that the swirl number for with VGs is higherthan that for without VGs, which shows the impact of VGs on swirlingenhancement at all the positions along the stroke length. When the distance alongthe stroke length equals to 40 mm, the swirl number value reaches to 16, whichshows the swirling enhancement by the VGs placed at the inlet manifold.

Fig. 2 Contours of turbulent intensity values at center plane axis (x = 72 mm) cut parallel to thecylinder for the inlet manifolds with and without VGs (Top without VGs and Bottom with VGs)

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4 Conclusions

Three-dimensional numerical simulation of flow inside the engine cylinder withand without VGs at inlet manifold has been performed. It is found that the modelpredicts swirling very well which gives confident that swirling inside the cylindercould be enhanced using different manifold configurations. The flow patterns, TKEand swirl number show that VGs placed at inlet manifold could create goodswirling characteristics for better combustion and emission characteristics. Hence,it is very essential to perform combustion and emission characteristics with thepresent VG configurations and it has to be quantified with experimental tech-niques. It would be the next stage of this project. Further study will be carried outfor various manifolds at different locations along the inlet manifold and finally themanifold shape will be optimized for better mixing.

z = 20 mm z = 40 mm z = 60 mm

z = 80 mm

x = 72 mm

Fig. 3 Contours of turbulent kinetic energy at different planes in the cylinder, when the inletmanifold is modified with VGs

150 G. Sivakumar and S. Senthil Kumar

z = 20 mm z = 40 mm z = 60 mm

z =80 mm x= 72 mm

Fig. 4 Contours of turbulent kinetic energy at different planes in the cylinder for the inletmanifold without VGs

Fig. 5 Pathlines based on velocity magnitude; Left with VGs and Right without VGs

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Acknowledgements This research project was carried out in the Vel Tech-Dassault SystemsCentre for Design, Engineering and Manufacturing located at the Research Park, Vel TechTechnical University, Chennai. Support for using the computing facility is acknowledged.

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3. Martins J, Teixeira S, Coene S (2009) Design of an inlet track of a small IC Engine for swirlenhancement, In: Proceedings of the 20th international congress of mechanical engineering,Gramado, 15–20 Nov 2009

4. Murali Krishna B, Mallikarjuna JM (2009) Tumble flow analysis in an unfired engine usingparticle image velocimetry, In: Proceedings of world academy of science, engineering andtechnology, vol 30

5. Lee J-W, Kang K-Y, Choi S-H, Jeon C-H, Chang Y-J (2000) Flow characteristics andinfluence of swirl flow interactions on spray for direct injection diesel engine, In: Seoul 2000FISITA world automotive congress, Seoul, 12–15 June 2000

6. Prasad BVVSU, Sharma CS, Anand TNC, Ravikrishna RV (2011) High swirl-inducing pistonbowls in small diesel engines for emission reduction, Appl Energy 88:2355–2367

7. Versteeg HK, Malalasekhara W (1995) An introduction to computational fluid dynamics: thefinite methods. Longman Group Ltd, London

Fig. 6 Variations of theswirl number along the strokelength for two inlet manifoldconfigurations; with andwithout vortex generators

152 G. Sivakumar and S. Senthil Kumar