A Fluid Model for Simulation of Diesel Injection Systems in Cavitating and Non-Cavitating Conditions

This paper presents a new fluid mathematical model for the numerical simulation of a hydraulic system that can work in cavitation. The fluid model proposed allows to obtain physical properties, such as density, bulk modulus, void fraction and sound speed, of a liquid-vapor-gas mixture so that the mixture itself can be treated as a homogeneous fluid. Thanks to the relationships proposed by the authors, it is possible to study a fluid system while in any operating condition (i.e. in cavitating or in non-cavitating conditions) using the same fluid-model and a unique set of equations. The model takes into consideration the evolution of the vapor and gas bubbles as a consequence of pressure and temperature variations, and its parameters are the physical properties of the mixture components, i.e. liquid, vapor and dissolved gas. The model was applied in the numerical analysis of diesel injection systems. The conservation laws that describe the fluid flow along the pipes were discretized by means of a semi-discrete finite volume method of second-order accuracy both in space and time. The algebraic system obtained was finally solved by means of a predictor-corrector fully implicit iterative method. The algorithm described was tested for several injection-system operative conditions. Such conditions involve high pressure as well as cavitation phenomena.