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V.Ganesan, Indian Institute of Technology, Chennai The main objective of this work is to study the fluid mechanics aspect of fuel spray in a compression ignition engine and to analyse the fuel injection process taking into account of evaporation and fuel air mixing. This can provide information on precombustion fluid dynamics aspects of sprays. It is rather difficult to conduct experiments to study the injection process alone in an actual engine without combustion. Hence, to study the precombustion fluid dynamics of sprays, a three-dimensional code developed by AMSDEN et al [1] has been adopted. The code solves the three-dimensional, unsteady equations of motion of a chemically reactive mixture of ideal gases. It can also solve the dynamics of liquid fuel spray and coupling between the spray and gas. The original code requires a super computer for the solution. In order to adopt the code to a personal computer major modifications have been done and implemented to work on a stand-alone personal computer. By this a three-dimensional models with all complexities for engine applications can be attempted on a non-CRAY series computers and on computers without transponders to achieve acceptable results. Another important achievement is the development of a post processor for three-dimensional in-cylinder fluid dynamic analysis (specially for spray field analysis). Using the modified code predictions have been made to get the fluid dynamics of the spray for an engine with compression ratio of 16.5 at a speed 1500 RPM. The calculations are started at 90° bTDC with a bowl-in-piston configuration. A computational grid, with 13 cells in radial, 16 cells in circumferential and 19 cells in axial directions have been taken as a test case after grid independence test. Law of the wall and fixed wall temperature are used as velocity and temperature boundary conditions with an initial swirl ratio of 3 (at 90° bTDC). Though it may be argued that the grid size employed is small for engine calculations, this is done only from the point of view of demonstration for flow and spray calculations from 90° bTDC to TDC. The main interest is to analyse the spray calculations upto top dead centre. The spray is assumed to be of hollow cone from a single-hole injector, which is located just below the center of the cylinder head. From the predicted results of compression process, it has been observed that from 27° bTDC swirl and squish velocities increase and squish induced vortices of equal size are formed inside the bowl. Peak turbulence kinetic energy (TKE) is observed at bowl rim showing effect of turbulence shear. Figure 1 shows the velocity vector plot in an axial plane the engine cylinder during compression without injection. Figure 2 shows a similar velocity vector plot at the same piston position with injection. During the process of injection, spray particle distribution (Fig. 3) shows the enlargement and depth of penetration of the fuel spray cone up to 9° bTDC. Air entrainment into the spray cone is also observed along with momentum exchange between spray and surrounding air. Near TDC a bigger vortex, ahead in the direction of spray and smaller vortex behind the spray cone is observed as seen in velocity vector field (Fig. 2). Cool zones and higher TKE levels were also observed in the spray zone. As an effect of change in spray axis inclination from 33.5° to 15° (towards cylinder axis) increased rates of vaporization, more penetration and less spread of spray cloud are observed. Thus, by means of this investigation it is established that the present three-dimensional code can be used on a personal computers to obtain satisfactory results on spray formation, penetration and fuel air interaction, which will be very useful for the engine industry for the first cut design. References 1. KIVA A computer program for two- and three dimensional flows with chemical reactions and fuel sprays; AMSDEN, A.A., Ramshaw, J.D., O.Rourke, P.J.O., Dukiwicz, J.K.; LANL Report No. LA-l0245-MS-, Los Alamos, New Mexico. 1985. Fig.1 Velocity field during compression
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