Over the past decades, the aviation sector has experienced significant growth, driven by route expansion and the spread of low-cost carriers. Alongside performance and reliability requirements, the aeronautical community is now facing a challenge concerning the environmental sustainability of the sector. Promoting the sustainable development of aviation without reducing operations requires effective strategies and tools to minimize its environmental impact. In this context, optimizing aircraft propulsion systems at the earliest design stages is a key pathway to meeting national and international green targets. Therefore, early-stage estimation of chemical emissions plays a crucial role in supporting the sector's sustainable transition. This thesis focuses on the development and assessment of modelling strategies for the preliminary estimation of chemical emissions from aircraft propulsion systems operating with both conventional liquid fuels and Sustainable Aviation Fuels (SAFs).