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Numerical modelling of multiphase diesel fuel properties using the PC-SAFT equation of state and its effect on nozzle flow and cavtation under extreme pressurisation

Roncero, A. V. (2020). Numerical modelling of multiphase diesel fuel properties using the PC-SAFT equation of state and its effect on nozzle flow and cavtation under extreme pressurisation. (Unpublished Doctoral thesis, City, University of London)

Abstract

The present work investigates the influence of properties variation of Diesel fuel in the range of injection pressures from 60MPa to 450MPa on nozzle flow and cavitation. The PC-SAFT equation of state is utilised to derive physical property predictions of a grade no.2 Diesel emissions certification fuel. Four candidate multicomponent Diesel surrogates are modelled. Density, viscosity and volatility predictions are compared to experimental data from several other Diesel fuels and against Peng Robinson. PC-SAFT calculations are performed using different sources for the pure component parameters, namely LC and GC methods. An eight-component surrogate yields the best match for Diesel properties with a combined mean absolute deviation of 7.1% from experimental data found in the literature for conditions up to 373 K and 500 MPa. The vapour-liquid equilibrium of this surrogate is then calculated with a novel algorithm, which uses as independent variables the mixture composition, density and temperature. This algorithm is based on unconstrained minimisation of the Helmholtz Free energy via a combination of the successive substitution iteration and Newton-Raphson minimisation. The reliability of two different methods presented in the existing literature is assessed for 7 different cases. The properties of the eight component surrogate are derived and put onto tables to be used in simulations. These simulations are performed on a tapered heavy-duty Diesel engine injector at a nominal fully open needle valve lift of 350μm. Two approaches have been followed: (i) a barotropic evolution and (ii) the inclusion of wall friction-induced thermal effects. Results indicate a significant increase in the mean vapour pressure of the fuel and an unprecedented decrease of cavitation volume inside the fuel injector with increasing injection pressure. This has been attributed to the shift of the pressure drop from the feed to the back pressure inside the injection hole orifice as fuel discharges. The study links friction-induced thermal effects to the preferential cavitation of the fuel components. Lighter fuel components are found to cavitate to a greater extent than heavier ones, independently of the initial fuel composition. Moreover, the final vapour cloud composition was found to differ with injection pressure, as the components within vaporise at their respective rhythm according to their molecular structure and global pressure/temperature conditions.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments: Doctoral Theses
Doctoral Theses > School of Mathematics, Computer Science and Engineering Doctoral Theses
School of Mathematics, Computer Science & Engineering > Engineering > Mechanical Engineering & Aeronautics
Date Deposited: 17 Dec 2020 12:38
URI: https://openaccess.city.ac.uk/id/eprint/25415
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