Numerical Simulation of Compressible Multi-Phase Flow in High Pressure Fuel Pump

Abstract

Modern injection systems utilize high injection pressures to enhance the break-up of the injected fuel and the mixing of fuel with air. Elevated pressure level targets high performance, high efficiency and low tailpipe emissions. Such conditions lead to high internal loads of fuel injection equipment and aggressive conditions within fuel injectors and pumps. The high pressure pump is the most critical component assuring appropriate elevated pressure level. Under certain conditions cavitation can occur within the system, which will affect the performance of the pump and in long term also its durability. Namely, cavitation repeatedly appearing at the same location can lead to erosion damage, which is clearly not desired. Therefore, numerical analyses by means of Computational Fluid Dynamics (CFD), represent a powerful tool in the early stage of component definition or design of the pump itself. As the pressure appearing in such systems exceeds 300 MPa, the liquid fuel needs to be treated as compressible. Moving parts of the investigated fuel pump are displaced due to pressure forces, which means that pressure variations and pressure waves need to be accurately predicted in order to predict accurate part displacements and correct wetted volume shape. In order to achieve this, the liquid fuel is treated as compressible, otherwise exact inlet- and outlet check-valve displacements are not predictable. In present work the liquid compressible Euler-Eulerian multiphase model of the commercial CFD code AVL FIRE® has been applied. The domain has been geometrically discretized using the preprocessing part of the applied CFD tool, moving parts have been handled by a novel, so-called “mesh deformation by formula” methodology. The advantage of the approach is that it does not require the pre-definition of all moving parts but allows for an arbitrary, user-defined movement of all mesh nodes. The motion of internal floating parts is performed automatically during the calculation according to the local pressure forces. Due to high pressure levels local flow velocities are typically very high causing the fuel to undergo phase change from liquid to vapor called cavitation. To accurately account for the effect of cavitation, the applied CFD code offers advanced cavitation modeling options. The applied capability enables estimation of flow aggressiveness and the probability for the onset of cavitation erosion on the surface of the components with the objective to optimize or entirely eliminate cavitation. In the present study two simulations have been performed; (i) part load and (ii) full load condition.

Prediction of cavitation and induced erosion inside a high-pressure fuel pump

“…Roemer et al 15 performed a dynamic mesh simulation, in order to predict the compressible flow emerging within a chamber connected to high- and low-pressure manifolds, a layout that corresponds to a simplified unit cell of a digital-displacement pump. Husmeier et al 16 used an Eulerian–Eulerian multiphase model along with a moving-mesh technique in order to predict the two-phase field that emerges inside a fuel delivery pump, where the inlet manifold and discharge nozzle are obliquely located on top of a pressurization chamber.…”