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

The operation of a high-pressure, piston-plunger fuel pump, oriented for use in the common rail circuit of modern Diesel engines for providing fuel to the injectors is investigated in the present study from a numerical perspective. Both the suction and pressurization phases of the pump stroke were simulated with the overall flow time be-ing in the order of 12•10-3 s. The topology of the cavitating flow within the pump con-figuration was captured through the use of an Equation of State (EoS) implemented in the framework of a barotropic, homogeneous equilibrium model. Cavitation was found to set in within the pressure chamber as early as 0.2•10-3 s in the operating cycle, while the minimum liquid volume fraction detected was in the order of 60% during the sec-ond period of the valve opening. Increase of the in-cylinder pressure during the final stages of the pumping stroke lead to the collapse of the previously arisen cavitation structures and three layout locations, namely the piston edge, the valve/valve-seat re-gion and the outlet orifice, were identified as vulnerable to cavitation-induced erosion through the use of cavitation-aggressiveness indicators

Solar thermal work generation using the Rankine cycle

209 σ.Παραγωγή μηχανικού έργου και εν συνεχεία ηλεκτρικής ενέργειας με τη χρήση ηλιακών συγκεντρωτικών συλλεκτών. Στο υπολογιστικό κομμάτι της εργασίας γίνεται προσομοίωση του ηλιακού θερμικού σταθμού SEGS VI που λειτουργεί στον κόμβο Cramer της California με χρήση του λογισμικού TRNSYS. Η ονομαστική ισχύς του σταθμού είναι 35 MWe και η λειτουργία του προσομοιώνεται σε καθημερινή βάση χρησιμοποιώντας μετεωρολογικά δεδομένα της περιοχής.Generation of mechanical work and consequently of electric energy using concentrating solar collectors. In the computational part of this thesis takes place a simulation of the solar thermal station SEGS VI which is operating in Cramer junction Ca., using the TRNSYS software. The nominal power of the station is 35 MWe and its operation is simulated in a daily basis using meteorological data of the region.Ιωάννης Κ. Καραθανάση

Numerical Modelling of Cryogenic Flows Under Near-Vacuum Pressure Conditions

A numerical framework for the simulation of two-phase cryogenic flows under a wide range of pressure conditions is presented in this work. Sub-critical injection and near-vacuum ambient pressure conditions were assessed by numerical simulations. Two different computational approaches have been employed, namely a pressure-based solver complemented by a bubble-dynamics model, as well as a density-based solver utilising real-fluid tabulated data to describe the fluid’s thermodynamic properties. The required thermodynamic-data table has been derived using the Helmholtz Equation of State (EoS) and the specific modelling approach can be applied to near-vacuum, sub-critical or even supercritical injection pressure conditions. The geometries of two single-hole injectors have been considered for investigating the flow and spray formation of liquid oxygen (LOx) and liquid Nitrogen (LN2). Both numerical approaches were validated against available experimental data. Overall, the comparison of results to experimentally acquired data demonstrates the suitability of the employed methodologies in describing processes such cryogenic flashing-flow expansion, phase-change and flash-induced spray formation. The density-based tabulated thermodynamics approach in particular, can be considered as a complete numerical framework for treating two-phase cryogenic flows using real-fluid properties, for a wide range of conditions without the need for case-related modifications

Spatio-temporal identification of plume dynamics by 3D computed tomography using Engine Combustion Network Spray G injector and various fuels

Understanding of plume direction and mixture quality in a combustion chamber is crucial to improve engine performance. While a variety of diagnostics using laser and x-ray facilities have been applied to identify plume direction, most applications require sophisticated experimental setup as well as troubleshooting for light attenuation or scattering issues. In this study, we acquire temporally and spatially resolved liquid volume fraction by three-dimensional tomographic reconstruction of ensemble-averaged extinction images to produce unique information on plume movement and growth in the midst of a multi-plume spray. Measurements were carried out in a constant-flow spray vessel coupled with high-speed Mie-scattering, diffused back-illumination extinction, and schlieren imaging. Four different fuels, a single component iso-octane, a multi-component surrogate with di-isobutylene, a multi-component fuel with olefinic molecular structure, and a 70% standardized gasoline 30% ethanol (e30) blend were injected using Engine Combustion Network (ECN) Spray G injector under ECN G2 (50 kPa absolute), G3 (100 kPa absolute), and G3HT (G3 with 393K ambient temperature) conditions. Planar slices, available from the tomographically reconstructed extinction data, confirmed greater plume-to-plume interaction for the flash-boiling G2 iso-octane condition with an approximately 6° smaller plume direction angle relative to the injector axis, compared to the nozzle drill angle. The olefinic and e30 fuels, which have broader distillation curves, exhibited stronger plume growth and eventual complete spray plume collapse and longer time for evaporation. Using the 3D dataset, we show that factors that increase plume growth also create more interaction between plumes to ultimately reduce the plume direction angle