Blended fuel droplet heating, evaporation and combustion

  • Nawar Al-Esawi

    Student thesis: Doctoral ThesisDoctor of Philosophy


    The previously developed models for fuel droplet heating and evaporation processes, mainly the Discrete Multi Component Model (DMCM), and Multi-Dimensional Quasi-Discrete Model (MDQDM) are studied, improved and generalised for a broad range of bio-fossil fuel blends so that the application areas are broadened with increased accuracy. The main distinctive features of these models are that they consider the impacts of species thermal conductivities and diffusivities within the droplets to account for the temperature gradient, transient diffusion of species and recirculation. The research carried out in this thesis is focused on four key aspects: (1) application of the previously developed models for a broad range of fossil fuels, biofuels and their blends including ethanol/gasoline, biodiesel/diesel, E85-diesel (E85 refers to 85% ethanol and 15% gasoline) and ethanol/biodiesel/diesel fuel blends; (2) formulation of fuel surrogates, using a new model referred to as ‘’Complex Fuel Surrogate Model (CFSM)’’, and analysing their heating, evaporation and combustion characteristics; (3) modelling of fuel droplet heating and evaporation, using a modified version of the MDQDM with a new transient algorithm referred to as ‘‘Transient Multi-Dimensional Quasi-Discrete Model (TMDQDM)’’; and (4) providing a proof of concept with the implementation of the developed model into a commercial CFD code ANSYS-Fluent, for the three-dimensional modelling of complete combustion processes. A case study is made for the CFD modelling of gas-turbine engine using kerosene fuel surrogate. The non-ideal vapour-liquid equilibrium is accounted for, using the Universal Quasi-Chemical Functional–group Activity Coefficient (UNIFAC) model.

    A new approach to the formulation of fuel surrogates in application to gasoline, diesel, and their biofuel blends (including blends of biodiesel/diesel and ethanol/gasoline) is proposed. This new approach, described as a ‘’CFSM’’, is based on a modified version of the MDQDM. The CFSM is aimed to reduce the full composition of fuel to a much smaller number of components based on their mass fractions, and to formulate fuel surrogates. A new algorithm for the auto-selection of Components/Quasi-Components in MDQDM is suggested and applied to the analysis of fuel droplet heating and evaporation. In contrast to the MDQDM, the new model takes into account the transient contributions of all groups of hydrocarbons, aiming for higher accuracy of the selection of quasi-components than that produced using the original MDQDM. Finally, a surrogate for kerosene is proposed using the CFSM. The model is implemented into ANSYS-Fluent via a user-defined function in order to provide the first full simulation of the combustion process. Detailed chemical mechanism is also implemented into ANSYS CHEMKIN for the combustion study.
    Date of AwardMar 2021
    Original languageEnglish
    Awarding Institution
    • Coventry University
    SponsorsCoventry University
    SupervisorMansour Al Qubeissi (Supervisor), Bidur Khanal (Supervisor) & Mike Blundell (Supervisor)

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