The Analysis of the CFD about the Swirl Generation in Four- Stroke Engine

The Analysis of the CFD about the Swirl Generation in Four- Stroke Engine Chang Chun Xu and Haeng Muk Cho a Division of Mechanical and Automotive Engineering, Kongju National University 275, Budae-dong, Cheonan-si, Chungcheongnam-do 331-717, South Korea. a Corresponding author email Abstract In recent years, the car has entered every household, automobile brings convenience at the same time, the environment is also a great harm, so the most important thing now is to solve the automobile exhaust harmful to the environment, to solve the main vehicle exhaust the method is to increase the automobile engine air-fuel swirl. In this paper, we will research the software ANSYS which Computational Fluid Dynamics (CFD) simulation to investigate the influence of the air-fuel swirl with different piston crown shapes inside the combustion chamber of the four-stroke automotive engine. The field flow into the combustion chamber for air-fuel mixing to obtain the air-fuel swirl ratio, combustion rate, and air-fuel combustion efficiency when the air-fuel swirl is appeared in the cylinder. So this analysis is important on this study of the effect with the different piston shapes to the fuel flow and the air into the cylinder, The behaviors of air-fuel swirl occurred inside combustion chamber is represented by two parameters which influences the air streams to the cylinder during intake stroke and improves the swirl of the air-fuel to produce better air-fuel mixing during the compression stroke. To analysis the effect of air-fuel swirl when change the intake valves conditions and the intake ports number and the piston crown shapes. The numerical simulation analysis can be showed the air-fuel mixture swirl ratio when the air-fuel into the combustion chamber that the condition of the intake valves and change the ports number and the shapes of the piston crown in the combustion chamber on the analysis that use the Computational Fluid Dynamics (CFD) mode. Keywords: Computational Fluid Dynamics (CFD), piston crown shape, swirl ratio, fluid flow, air-fuel mixture, intake valve. INTRODUCTION The internal combustion engine (ICE) of the in-cylinder flow, flow through the intake flow structure produced by closely related to the ICE design. The most important factor for stable ignition and flame propagation fast one is to produce high turbulence intensity. In general, these two types of vortex and vortex roll being used to generate and maintain the flow of turbulent flow efficiency. Both types of vortices are the horizontal and vertical planes tissue cylinder of the engine rotation respectively. They improved the engine performance by the mixing of fuel and induced air [1]. It is the development of the internal combustion engine with a high compression ratio to achieve higher turbulence intensity and lean combustion is very important. On the other hand, we can add the shut-off valve to the intake valves or change the ports number to produce airflow swirl before into the chamber. Consider the structure of two intake valves that the first group conventional valve and the second group of valve can be set back shut-off valve that in order to prevent the air-fuel into the combustion chamber at the backside of the intake valve. In this case, we can change the number of ports or use the different ports diameters to analysis the air flow and swirl motion. In addition, how to change the ports number that make one of the ports is blocked to determine the result of the swirl generation as the one intake port. So the results with the single port and a shut-off valve show the higher swirl generation than the multi-ports and no shut-off valve so that improve the efficiency of an engine through increasing the combustion rate of the air-fuel mixture. In the internal combustion engine, two experimental simulations can be achieved to increase the air-fuel mixture: one way is designing the combustion chamber structure for increasing the air-fuel mixture. So the result of another way is like above designing the intake systems by blocking one of the ports or using the shut-off valve to generate a swirling motion into the combustion chamber. The swirl ratio and the fluid motion, which they have important influence on air-fuel mixing, combustion rate, heat transfer and exhaust emissions. CFD MODELING OF ICE PROCESSION In-cylinder flow simulation experiment works have been carried out using a hot wire velocimetry or laser Doppler velocimetry (LDV) to measure the velocity field [1]. This test is a very difficult, because the characteristics measured in the reciprocating engine cylinder flow is highly complex threedimensional turbulence and instability [1]. Therefore, the numerical approach could be changed, use the CFD model to develop for the in-cylinder flow predictions. Computer codes for solving the Navier-Stokes equations, to produce an average velocity and a detailed description of the turbulent velocity field. While the lower shows the ICE case, CFD model should resolve the air - fuel mixture into the combustion chamber of the turbulent flow, high Reynolds number, compressible flow and the air - fuel mixture through the geometric model of specific issues. NAVIER-STOKES EQUATIONS It relates to hydrodynamic motion of the liquid and the gas. Among them, when the macroscopic study, seems to be a continuous structure. All variables are considered to be a continuous function of spatial coordinates and time. Navier- Stokes equations are a set of nonlinear partial differential 8940

equations of fluid flow. The Navier-equations for irrotational flow are shown below. ρ t u + (ρu) =0 Continuity Equation. (1) t + (u ) u= - 1 ρ p + F+ µ ρ 2 u Equations of Motion (2) ρ ( ε +u ε) (KH T) +p u=0 t Conservation of Energy (3) Where u=velocity vector field, ε= thermodynamic internal energy, p = pressure, T= temperature, ρ= density, μ= viscosity, K H = heat conduction coefficient, F= external force per unit mass. = x i + y j + z k (4) 2 = 2 x 2 + 2 y 2 + 2 z 2 (5) In this study, the CFD code of the capability of moving mesh and boundary algorithms to analysis the result of the fluid flow field with different piston crown shapes and air-fuel movement capability through the shut-off valves. The first to find the better piston crown shape to measure when the same composition of air structure for fuel mixing preparation that occurred inside engine cylinder. Therefore, this study is that the fluid flow with two different combustion chambers influences in air-flow mixing preparation and generation of turbulence for great impact on engine performance. During the air intake and compression strokes, the numerical is performed to obtain the optimum parameters of the engine, in order to achieve rapid combustion chamber shape for the process of better air and fuel mix used to study the fluid flow field impact effectiveness. The numerical computation was used to analysis the intake and compression strokes for the swirl generation of air-fuel mixture into the chamber with two different piston crowns shapes and boundary conditions. Fluid flow characteristics of the two parameters obtained from the simulation will be considered to prepare a mixture of air verify the structure of the same composition, so that, when you can achieve better air-fuel mixture in the compression stroke of the combustion process [1]. In particular, in the experiment process, the different test observed for the two different piston bowl shapes can be drawn-out with the different parameters conformation of fluid flow characteristics during intake and compression strokes [2]. From the simulation experiment, we can observe the piston crown shapes impact the air-fuel swirl combustion processes to improvement of the piston crown shapes for obtaining the higher engine performance and harmless exhaust emissions. The CFD simulations use the moving mesh-boundary algorithm that to use the different meshes and boundary geometries for different crank angles in each step of engine cycle for getting different air-fuel swirl ratios. In order to better implementation process for an internal combustion CFD simulation, analysis and calculations shall be unsteady computing, mobile grid and boundary, high compressible Reynolds, high fluid dynamics, momentum, heat and mass transfer and be through complex geometry of the air-fuel mixture and also depends on the chemical-thermal[1]. In addition, in the calculation of different combustion chamber flow field, measured with a laser Doppler velocimetry (LDV) is compared. The CFD software development collocated grid to simulate a three-dimensional curve domain using the finite volume method. It uses slightly modified vector to introduce the concept of fluid compression standard k-ε turbulence model. It solves the follows transfer equations for describing mass, momentum and energy [3]. (ρφ) t + (ρφu ) = (Γφ (φ)) + Sφ (6) [3] Where, u is the velocity vector with components u, υ and w, ρ the density, φ the generalized transport property and Sφ the source term. In Table 1, all the variables corresponding to the general transport property are shown [3]. Table 1: Variables representing the generalized variable φ in Eq. (6) [3]. Generalized flow Equation Γφ field variable (φ) l Continuity 0 u u-momentum μ eff v v-momentum μ eff w w-momentum μ eff h Enthalpy μ eff/σ h k Turbulent kinetic energy μ eff/σ k ε Turbulent kinetic energy dissipation μ eff/σ ε For the turbulence model, specifically the source terms of the turbulence kinetic energy and its dissipation can be seen in Table 2, where G k is the turbulent kinetic energy production rate [3]. Table 2: Source terms of the turbulence variables [3] Variable Γφ Sφ k μ eff/σ k G K - ρε ε μ eff/σ ε C 1G K ε k C2ρε2 k +C3ρε( u ) The turbulent viscosity is calculated from the following Eq.(7), and the effective viscosity used in the calculations is the sum of the turbulent and laminar viscosity. In addition, all constants used in executing the k-ε turbulence model and enthalpy equations are shown in Table 3 [3]. μ t = ρk2 C μ ε, μ eff =μ 1+μ 2 (7) [3] 8941

Table 3: Constants used in k-ε turbulence model and the enthalpy equation [3]. Constant c1 c2 c3 cμ ch ck cε Value 1.44 1.92-0.373 0.09 1.0 1.0 1.3 GEOMETRIC ANALYSIS ENGINE The Engine model is shown in a typical single-cylinder CNG- DI engine has two intake and exhaust valves in Figure 1 and with two pistons shapes structure shown Fig. 2. From the above mentioned, the two piston crowns are considered investigation vortex behavior and tumbling fluid occurs in the inner cylinder, in order to obtain a better shape for the piston in the engine combustion process. Piston shapes shown in Fig.2, two piston shapes are typical engine geometry model that affect the air-fuel mixture swirl for obtaining the higher swirl ratio as well as the optimum combustion process in the DI engine. Piston A has a bowl in the center of its piston crown,while piston B has the deeper bowl volume than piston A, and piston B bowl is different with piston A that the bowl not in the center of its piston crown[1]. In comparison bowl top surface of the piston, when the airfuel into the combustion chamber to produce a vortex, and depending on the shape of the piston, with formation of an air - fuel swirl in the combustion process of the engine get better piston shape and operating piston boundary conditions of intake and compression process using CFD models analysis. In the course of the compression stroke, the vortex flow generated by the annular jet, the intake stroke during the previous decay quite rapidly and the body seems to be evenly distributed along the engine cylinder. And the air-fuel with quite quickly velocity to make air-fuel mixture full mix whether or not depending on piston crown shape, when the combustion chamber shape of an ICE is affect the velocity field close to the piston top surface during the latter of the compression stroke when the air-fuel injection start and the spark plug ready to burn the air-fuel mixture start end of the compression process. In the compression process, combustion chamber with the different of the piston crown bowl structure that for the purpose of comparing swirl ratio in the combustion chamber. The experiment calculation and analysis obtains variations of swirl ratios for two pistons and display in Fig.3. As can be seen from the figure, the vortex in the cylinder before the start of the intake stroke produced. Because air-fuel before into the cylinder start to become mixture and inside the cylinder due to the piston crown shape air-fuel with quite quickly velocity generate swirl by annular jet to full mix, as shown in Fig.3. The maximum achieved near around 140 after TDC, which piston reaches the maximum speed and the valve opening is in maximum distance. After this, the air - fuel into the cylinder speed is reduced and the eddy current will slowly decline during the intake stroke. In the first part of the compression stroke, swirl velocity due to the trend of the cylinder wall friction continued slow decline. Thus, according to this figure in the development of the vortex flow when approaching TDC, the smaller diameter of the piston bowl to maintain its angular momentum accelerated [3]. During the compression stroke, the vortex is necessary the need to generate a complex flow field of the fuel injection during the enhanced air - purpose fuel mixture. From the analysis, the piston A due to smaller diameter crown shape is able to generate higher swirl ratio than piston B with small range differences during intake and compression strokes. But because of the fraction within the cylinder wall and its intake air flows influence by combustion chamber head shape. Figure 1: Schematic of a typical engine model and piston crown A [1] Figure 3: Calculate the swirl ratio versus crank angle [1] Piston A Piston B Figure 2: Combustion chamber geometry [1] ANALYSIS SWIRL RATIO USE KIVA-3V OF CFD CODES In this case, the investigation on the effect of the swirl ratio intake system design using computer code KIVA-3V in the DI 8942

engine [4]. The KIVA-3V code is used to analyze the application of one or two ports and intake valves position shut-off valve. In this case, the engine is a classic study of two direct intake valve single-cylinder direct injection diesel engine, and its export is tangent to the cylinder wall, as shown in Fig. 4[4]. compression strokes processes, in order to improve the airfuel swirl ratio in the cylinder, a shut-off valve is added to the backside of the intake valve, air flow will only flow in one direction of the intake valve into the cylinder is shown in Fig. 6 [4]. Figure 5: Conventional valve with a shroud (a) Figure 4: Schematic of engine and computational mesh [2] [4] This experiment is to simulate the air flow through the intake stroke and the compression process in the engine. And the mesh about 150,000 cells to analyze the airflow pattern [4]. Pressure inflow boundaries were imposed at the open ends of the intake runners. For this cases, when shut-off valves set up on the backside of the intake valves to prevent the air-fuel into cylinder through backside position of the intake valve is shown Fig.5. Conventional engine, air can flow around all sides with non-shutoff valve through intake port into the cylinder through all directions. During in the intake and (b) Figure 6: Show the flow through (a) shut-off valve, and (b) non-shutoff valve [4] In an automobile running, the engine power provided by the reciprocating motion of the piston, a different crank angle can produce different air-fuel swirl. The values of air-fuel swirl ratio for the different crank angles were calculated and plotted 8943

in Fig.7[4]. It shows that in this case with a port and a shut-off valve to get maximum air - fuel swirl ratio. The case with one port intake the air-fuel into the cylinder is stronger than two or more ports intake through the pipe. Similarly the shut-off valve in the backside of the valve prevents the air-fuel flow through the backside of the intake valve into cylinder, and makes the air-fuel fluid flow through the front side into cylinder strongly for enhancing the swirling motion. So the experiment simulation results shown this case use one port or a shut-off valve can generate higher air-fuel swirl ratio than two or more ports or non-shutoff valve. Therefore, with intake and compression strokes, the shut-off valve can improve and enhance the swirl ratio when the air-fuel through the valve into the cylinder chamber in the CNG-DI engine [4]. CONCLUSIONS To study the influence of fluid flow in the combustion chamber of the piston crown structure by computational fluid dynamics, and the investigation by the CFD code in the intake system and compression strokes, changing the shape of the intake port and the intake port number to increase vortex ratio. 1) This paper for two different shapes of the piston were analyzed to assess the air-fuel mixture to produce the swirl ratio in the combustion chamber of a different shape, find the shape of the piston for generating best a swirl ratio. 2) For the intake system design can be considered in this case, and investigated through the CFD code of KIVA-3V model. In order to improve the efficiency of the engine by changing the number of ports and add the cut-off valve to consider increasing the airfuel mixture swirl ratio. Results can be obtained using the shut-off valve in the cylinder can get higher swirl ratio is greater than having a non-shutoff valve. ACKNOWLEDGMENT This research was supported by The Leading Human Resource Training Program of Regional Neo industry through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT and future Planning (grant number)(nrf-2016h1d5a1909917) REFERENCES Figure 7: Swirl ratio versus crank angle [4] For this case, the effect of one or two ports to produce swirl ratio can be considered. This method is similar to the shut-off valve and install the intake valve position is to close an air intake port, determine individual intake port than the two air intake ports can produce high swirl ratio. Then similarly this air-fuel swirl ratio can be shown in Fig.7 [4]. OTHER METHODS FOR ENHANCING SWIRL RATIO From above methods, other methods can also enhance swirl ratio during in the intake and compression strokes in the engine. From above mentioned, we can also change port number to enhance the swirl ratio. The effect of port diameter on swirl ratio can be considered [4], reduce the port diameter for enhancing the flow velocity and air-fuel mixture into the combustion chamber. The narrow port obtains the better swirl ratio than width port, because as the port is narrow, the flow pressure is smaller than combustion chamber, so air-fuel is inhaled rapidly due to the pressure difference. Other methods involve change the injection timing [5] [8] and variable valve timing and dual-fuel inside the cylinder [7] and late second injection variations [9] can affect the air-fuel mixture. [1] Wedy Hardyono Kurniawan, Shahrir Abdullah and Azhari Shamsudeen. A Computational Fluid Dynamics Study of Cold flow Analysis for Mixture Preparation In a Motored Four-stroke Direct Injection Engine. Journal of Applied Sciences 7 (19): 2710-2724, 2007. ISSN 1812-5654. [2] F. Payri *, J. Benajes, X. Margot *, A. Gil. CFD modeling of the in-cylinder flow in direct-injection Diesel engines. Computers & Fluids 33 (2004) 995-1021. [3] C.D. Rakopoulos *, G.M. Kosmadakis, E.G. Pariotis. Investigation of piston bowl geometry and speed effects in a motored HSDI diesel engine using a CFD against a quasi-dimensional model. Energy Conversion and Management 51 (2010) 470 484. [4] Ramadan B. A Study of Swirl Generation in DI Engines Using KIVA-3V[J]. Kettering University, 2003. [5] B. Jayadhankara, V. Ganesan *. Effect of fuel injection timing and intake pressure on the performance of a DI diesel engine A parametric study using CFD. Energy Conversion and Management 51 (2010) 1835-1848. [6] Patil Pradip kailas 1, Wagh Hemant K 2, Patil Vijayenra Maharu 3, Kumbhar Anil H 4. Study of Combustion in DI Diesel Engine for Different Compression Ratios Using Experimental and CFD Approach. International Journal of Research in Engineering and Technology(IJRET). Volume :03 Special Issue: 08. 8944

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