Date: Monday, June 07, 2021, 12:00 PM - 01:00 PM
Engineering applications of unconventional fuels like Heavy Fuel Oils (HFOs) require a detailed understanding of the physics associated with their evaporation. The processing of HFOs involves forming a spray; therefore, studying droplets is of particular interest.
This work tackles two of the most obscure aspects associated with HFOs modelling.
The first aspect is the identification of a valid chemical description of the structure of the fuel. In particular, the focus was on finding a methodology that allows identifying a discrete surrogate to describe the complex pool of molecules of which the fuels are made. Formulating a surrogate allows estimating physical and chemical properties and their dependence on concentration and temperature.
The second part of the work was devoted to understand and model thermally-induced secondary breakup, which is the primary cause of deviation from the "d2" law that multi-component droplet experience.
The generation of a surrogate was successfully achieved by implementing a new algorithm that allows building realistic molecular structures from a set of easily accessible physical and chemical properties. The algorithm was tested on a series of experimental data and ultimately used to formulate the discrete surrogate that served to complete the HFO's physical properties, which were not easily measurable.
Later, the behaviour of HFO droplets exposed at high temperature was studied in a suspended droplet facility. Emulsified and de-asphalted HFOs were also studied in the process to evaluate their potential as optimized fuels. A new methodology for the post-processing of experimental data was formulated. The purpose was to overcome the limitations of a description based on the droplet's normalized squared diameter evolution. The methodology consists of studying the evolution of the normalized distance of the interface from the droplet's centroid instead of its diameter. The new approach allowed the separation between interface deformation and expansion/shrinking. The information was then processed using the dynamic mode decomposition (DMD) to separate the stochastic contribution associated with secondary atomization and the deterministic contribution of vaporization.
Finally, thermally induced secondary atomization was studied using a CFD code appositely developed. The code is based on the geometric VoF method and consists of a compressible, multi-phase, multi-component solver in which phase change is considered.
The novelty in the proposed approach is that the evaporation source term and the surface tension forces are evaluated directly from the geometrically reconstructed interface. The code was validated against the exact solution of analytically solvable problems and experimental data. The solver was then used to study HFO secondary breakup and perform a parametric analysis that helped to understand the problem's physics. A possible application of this framework is the formulation of sub-models to be applied in spray calculations.
Paolo is a Ph.D. candidate in Mechanical Engineering program in PSE, under the supervision of Prof. William Roberts. He obtained his Bachelor's and Master's at Politecnico of Milan in 2015 and 2017, both in chemical engineering. He is currently working on HFO upgrading through ODS and Emulsification. Liquid fuels atomization modelling and AI applied to surrogate formulation.