Numerical Simulation of Diesel Injector Internal Flow Field

AbstractIn Diesel engines, fuel-air mixing process and spray evolution drastically affect combustion efficiency and pollutant formation. Within this context, a detailed study of the effects of injector geometry and internal flow is of great importance to understand the effects of turbulence and cavitation on the liquid jet atomization process. To this end, both numerical and experimental tools are widely employed.Objective of this work is to simulate the complex flow behavior inside the injector nozzle taking the most relevant physical phenomena into account. CFD simulations were carried out using a compressible solver with phase change modeling available in the OpenFOAM framework. In particular, cavitation was modeled by using an homogeneous equilibrium model based on a barotropic equation of state while the RANS k-ω SST model was used for turbulence. Experiments performed at Kobe University (Japan) on simplified nozzle geometries were used to validate the proposed approach in terms of velocity and vapor distributions. A rather good agreement between computed and experimental data was achieved in terms cavitation length, mass flow, momentum flux making possible to apply the proposed methodology also to real injector configurations in the near future

An investigation of the validity of a homogeneous equilibrium model for different diesel injector nozzles and flow conditions

In the present work, a methodology for modeling flow behavior inside the fuel injector holes is applied to a number of cases with different geometries and flow conditions. After assessment of the approach results through various experimental studies looking into the flows behavior inside the diesel nozzles, two series of analyses are defined. In the first study, the effect of inlet pressure is investigated by using a series of different rail pressures in both numerical and experimental tests in a single hole industrial injector. Results show a non-cavitating flow and an approximately linear increase of the velocity, turbulence kinetic energy, and turbulence dissipation energy with the increase of pressure difference and linear increase of the mass flow rate with the square root of the pressure difference in this nozzle. The second study is related to the effect of hole geometry on injector performance. The effects of entrance edge rounding and the tube conicity factor are investigated by changing these parameters in a series of geometries from an industrial diesel nozzle. Results show that cavitation occurs in the geometries with a sharper edge and low conicity. The role of the cavitation in emerging flow properties is emphasized in the values of the injector discharge factor and the turbulence properties. The results of this work can be used in the simulation of the primary breakup of fuel spray, and this approach is useful for design and optimization of the injectors for industrial sectors

Recent Advances in Simulation of Flow in Cryogenic Cooling for Hard-to-Cut Materials

Efficient cooling of the tool and workpiece interface has the key role in the high-performance titanium alloys machining (i.e. Ti6Al4V). Despite the several available conventional methods using for cooling, cryogenic cooling is in the center of the attention for the future machining process. This modern technology requires adequate research and development activities to become a reliable technology for the machining process, specifically because of its severe working conditions and complicated physical phenomena inside cryogenic fluids handling and application. The optimum design, the prediction of operational limits, and the safe control of the cooling process depend upon the availability of realistic and accurate mathematical models. For the analysis of the cooling process, different approaches can be used as experimental studies, numerical simulations, and a combination of both methods. In this research, computational fluid dynamics (CFD) analysis is used to have an estimation of the behavior of the cryogenic fluid inside the milling tool cooling channel and around cutting region. A variety of the simulations have been implemented, regard to the different assumptions about flow condition, introducing to the tool. Results of this study will be used for improving the design of the cryogenic cooling system and defining the proper working conditions and operational limits for a reliable process