Modelling and large eddy simulations of biodiesel spray combustion by Constantin SULA

For the degree of Doctor of Engineering Sciences and Technology

This thesis consists of a detailed study of spray combustion of diesel and biodiesel fuels. Our study is focused on the complex physical and chemical phenomena that take place in such flows and consists of three parts.

In the first part, we investigate atomization and droplet breakup of a non-reactive fuel spray via Large-Eddy Simulations (LES). To this end, we compare three popular droplet-breakup models, the Taylor Analogy Breakup (TAB), Reitz-Diwakar and Pilch-Erdman models. Further, we propose a modification of the original TAB model and assess its predictive capacity. According to our numerical tests, the proposed modification leads to improved accuracy in the computation of important properties of the spray, such as the liquid- and vapor-penetration distance.

In the second part, we present a numerical study of n-dodecane spray flames via LES. With regard to combustion modelling and turbulence-chemistry interaction, we employ the Flamelet-Generated Manifolds (FGM), which is based on tabulated chemistry. Herein, we propose a novel approach for the coupling of the energy equation with the FGM database that offers considerable computational savings. The efficiency of this approach is assessed via comparisons with experimental data and earlier numerical results for n-dodecane spray flames.

In the last part of the thesis, we present an LES study of spray combustion of Karanja Oil Methyl Ester. For computational efficiency, the chemical kinetics is represented by the combustion mechanism of a surrogate fuel that is a blend of n-dodecane (64.32%) and methyl butanoate (35.68%). First, we examine the influence of the initial oxygen concentration level on the spray ignition and the flame topology. Further, we compare the combustion processes of the biodiesel surrogate with the corresponding diesel surrogate (n-dodecane). Finally, we assess the impact of the thermophysical properties of the biodiesel on the evolution of the spray and the overall combustion process.

Jury members :

• Prof. Miltiadis PAPALEXANDRIS (UCLouvain, Belgium), supervisor
• Dr. Holger GROSSHANS (PTB, Germany), supervisor
• Prof. Eric DELEERSNIJDER (UCLouvain, Belgium), chairperson
• Prof. Francesco Contino (UCLouvain, Belgium)
• Dr. Véronique DIAS (UCLouvain, Belgium)
• Dr. Christos VARSAKELIS (Janssen Pharmaceutical, Belgium)
• Dr. Kai Moshammer (PTB, Germany)

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