This dissertation presents the work conducted during the PhD on analyzing the effects of water addition in combustion processes. In the initial phase, the impact of water addition on hydrocarbon combustion, under both premixed and spray flame configurations, is investigated using carrier-phase Direct Numerical Simulations. An Eulerian-Lagrangian hybrid approach with two-way coupling is employed to describe the liquid-gaseous phase interaction. The cooling and dilution effects of liquid water are generally more significant than the chemical effects, leading to the adoption of a simplified chemical model. This approach allows for a thorough analysis of flame propagation characteristics, topology, and structure resulting from water evaporation. Following the study on hydrocarbon combustion, attention shifts to hydrogen/air premixed combustion, notably influenced by preferential diffusion. In this context, the analysis primarily focuses on propagation characteristics and explores whether and how water injection affects the preferential diffusion phenomena. It is observed that water dampens the effects linked to preferential diffusion. Later on, the chemical effects of water are considered and analyzed using a detailed chemical mechanism. Initially, this chemical description is applied to a simple 1D configuration to account for emissions, necessitating an extensive chemical mechanism. It is found that water can decrease emissions even when the adiabatic flame temperature is kept constant. Subsequently, the study delves into multi-dimensional flame structure and characteristics to comprehensively represent the effects on preferential diffusion phenomena and liquid water addition. A detailed chemical description has been considered to analyze a two-dimensional quasi-laminar spherical flame, focusing on flame instability by comparing the effects of different diffusion models, equivalence ratios, and droplet initial diameters. In this context, droplets support the initiation of intrinsic flame instabilities by acting as localized disturbances on the flame surface. Furthermore, the accurate representation of the diffusion process is highlighted as relevant, given the dominant role of mass diffusion. In the final section, an analysis of emissions for this 2D configuration is conducted to examine the influence of flame topology and preferential diffusion on the production of nitrogen monoxide (NO). It is observed that water droplets lead to an increase in NO production at the lowest equivalence ratio considered in this work (𝜑 = 0.5) despite a reduction in temperature. This increase in emissions is attributed to the diminished influence of the thermal NO production pathway compared to others under low equivalence ratio conditions, such as the N2O pathway, which becomes more prominent under lean conditions. At a relatively higher equivalence ratio (𝜑 = 0.8), the thermal pathway becomes more relevant, but droplet evaporation has been found to increase the NO production, always exciting the N2O pathway. However, the increase in nitrogen monoxide with water addition is lowerin 𝜑 = 0.8 cases thanin 𝜑 = 0.5 cases. All the analyses presented in this work show the complexity of the phenomenology involved in the flame-liquid water interaction.This demonstrates the need for deeper understanding for possible practical uses.     «

This dissertation presents the work conducted during the PhD on analyzing the effects of water addition in combustion processes. In the initial phase, the impact of water addition on hydrocarbon combustion, under both premixed and spray flame configurations, is investigated using carrier-phase Direct Numerical Simulations. An Eulerian-Lagrangian hybrid approach with two-way coupling is employed to describe the liquid-gaseous phase interaction. The cooling and dilution effects of liquid water are...     »