The need to regulate greenhouse gas emissions has driven the search for clean and efficient energy solutions, requiring the integration of alternative fuels for a sustainable future. Alternative fuels (hydrogen, ammonia, biofuels, Sustainable Aviation Fuels, SAF) present different attributes with respect to traditional hydrocarbon fuels, such as burning rate and pollutant emissions, leading to new challenges. Undertaking these tasks involves the need for numerical combustion modeling and, due to the complexity of such systems, sophisticated strategies for efficient simulations. In this context, soot formation has been considered a major challenge due to its complex nature, and that would still be present in future energy systems (e.g., biofuels or SAF). As a first part of the presentation, I will introduce two different approaches of soot modeling. The first one is the so-called virtual chemistry approach, developed at EM2C. This method involves the creation of a global mechanism comprising virtual species and reactions. Machine learning algorithms optimize the thermodynamic properties and kinetic rate parameters of these virtual components. This methodology primarily focuses on capturing essential sooting flame properties such as temperature, laminar flame speed, radiation, and soot volume fraction. It has been adapted for the simulation of turbulent sooting flames using Large Eddy Simulation (LES), which I will exhibit with further details. The second approach, developed more recently at Princeton, is called Bivariate Multi-Moment Sectional Method (BMMSM). BMMSM is designed for computationally efficient tracking of soot size distribution in turbulent reacting flows. It combines the sectional method with the method of moments to characterize the size distribution. Notably, BMMSM employs fewer soot sections compared to traditional sectional models while considering three volume-surface moments per section to account for soot’s fractal aggregate morphology. Then, I will present LES results of the evolution of the soot size distribution in a turbulent nonpremixed flame. In the second part of this presentation, I will present insights into the emissions from the combustion of other candidate fuels, including recent work on the use of ammonia, determining if they exhibit sufficiently low levels compared to current fuels, while minimizing societal and environmental impacts. Then, I will present simulation results of partially cracked ammonia combustion, which are representative of the design of future gas turbines for power production, to identify the mechanisms behind the production of other carbonless greenhouse gases, such as N2O, and pollutants, such as NOx, and how they might compare with the emission trends associated with traditional hydrocarbon fuels. Finally, a few points highlighting that the needs and challenges in combustion science are evolving will be discussed.