Evaluation and Validation of ELSA Model in Diesel Sprays: 3D Cavitating Nozzles Case

Computational Fluid Dynamic (CFD) techniques have become one of the main tools in the design and development of diesel engines. There exist, however, some drawbacks and problems that must be overcome in the next years. One of the challenges is to predict accurately the couple between the flow inside the nozzle and the spray, including the primary break-up and the secondary atomization. In the last years, several authors have been developed the Eulerian-Lagrangian Spray Atomization (ELSA) model. ELSA model combines an Eulerian and Lagrangian descriptions by coupling these two methods properly. ELSA model also accounts for the modeling of droplets and their formation process, particularly in the dense spray region. The ELSA model for diesel spray modeling has been recently implemented and developed into Star-CD CFD commercial code. Author’s effort was focused on a detailed validation and evaluation of the fuel injection in diesel engines using this last implementation. Spray atomization, spray formation and macroscopic characteristics of diesel spray behavior were investigated. The overall work has been conducted in non-evaporative conditions. As cavitation greatly affects to spray behavior and it is though that cavitating nozzles will be present in most of close future engines, this sort of configuration has been chosen for validation. Velocity profiles at the section area of the nozzle exit obtained from trusted and experimentally validated RANS internal flow simulation were used. Results have been validated again experimental data, mostly coming from CMT-Motores Térmicos institute. It was found that the ELSA model reproduces accurately the experimental results. Introduction The primary break-up and secondary atomization of liquid sprays are up to now not totally understood. In the case of diesel engines, the fuel spray occurs in a small chamber inside the combustion engine. The fuel comes from a tiny nozzle cross section (hundred micrometers) at very high pressure and everything happens at an extremely short time (few milliseconds). Regardless the reactive part of the processes, diesel spray study includes several fundamentals, and not totally resolved topics, as can be the spray structure itself, break-up and atomization processes, or the behavior of two-phase turbulent flows. Probably, one of the main problems is the lack of experimental techniques which can be used in the vicinities of the nozzle. Computational Fluid Dynamic (CFD) techniques have become one of the main tools in the design and development of diesel engines. There exists, however, some drawbacks and problem that must be overcome in the next years. One of the challenges is to predict accurately the couple between the flow inside the nozzle and the spray, including the primary break-up and the secondary atomization. Fuel injection and spray characterization have been investigated thoroughly during the last decades and there exist many techniques to model diesel spray. Each one of these methods has its own advantages and disadvantages, mainly due to the fact that they focus in a particular region of the spray. The traditional Eulerian method performs well in the liquid phase while the Lagrangian drop method describes accurately the dispersed region. Transition between both zones is not particularly well resolved, mainly due to time and computational power restrains. The ELSA model combines Eulerian and Lagrangian descriptions by coupling these two methods properly. It accounts for the modeling of droplets and their formation process, particularly in the dense spray region. In the last years several authors have been developed the ELSA model [1], [2], and [3]. This algorithm has been recently implemented in CD-adapco StarCD CFD code conducted together with Renault SA in the version 4.12 and it has been continuously enhanced since then. 12th ICLASS 2012 Evaluation and Validation of ELSA Model in Diesel Sprays: 3D Cavitated Nozzles Case 2 Spray modeling are commonly applied in ideally non-cavitating condition. The code has been pre-validated previously under non-evaporative and non-cavitating conditions, showing an excellent agreement with experimental data [4], [5], and [6]. However, nowadays nozzles cavitate, and this plays a critical role in real applications, affecting heavily on the spray behavior. In the next section the cavitating nozzles used for this validation are presented, together with the experimental data characteristics. The numerical methods are presented in the following section and after that discussed. Last section is devoted to conclusions. Experimental setup The experimental data used in this project were obtained as part of a broader collaboration between Renault and CMT-Motores Térmicos. The only cavitating diesel injection nozzle characterized in this project was a Bosch injector, reference no., DLLA 145 PV3 192 805. A microscopic characterization of this nozzle is presented at Figure 1.