The increasing environmental concerns, coupled with the rapid depletion of conventional fossil fuels, havepromptedtheautomotive industry to explore alternative energy sources that can support the continued operation of internal combustion(IC) enginesina more sustainable manner. The need to mitigate greenhouse gas emissions, reduce dependence on finite fossil resources, andmeetstringent environmental regulations has led to extensive research and development efforts in identifying viable alternativefuels. Thesefuels must not only align with the performance requirements of modern IC engines but also minimize their environmental footprint.Thispaper presents a comprehensive comparative analysis of various alternative fuels, including biodiesel, ethanol, hydrogen, natural gas,andsynthetic fuels, each of which offers unique advantages and challenges. The study evaluates these fuels across key parameters, suchasfuel availability, energy content, emissions profile, required engine modifications, and overall sustainability. The analysistakesintoconsideration the economic feasibility and infrastructure requirements for large-scale adoption of each fuel. Further more, thepaperhighlights the technological advancements and modifications necessary to optimize IC engines for these alternative fuels. Thisincludesthe impact of alternative fuels on engine efficiency, power output, fuel economy, and maintenance requirements. Special attentionisgiven to emissions reduction strategies, with a focus on how each fuel contributes to lowering carbon dioxide (CO₂), nitrogenoxides(NOₓ), and particulate matter (PM) emissions. In addition to evaluating the current state of alternative fuels, the paper addressesthechallenges associated with their adoption, including production scalability, distribution infrastructure, and compatibilitywithexistingvehicle technologies. Finally, the future prospects of integrating these fuels into automotive applications are explored, consideringtherapid rise of electric vehicles and other emerging technologies that may further influence the role of IC engines inthetransitiontosustainable transportation. The findings of this study suggest that while no single alternative fuel is likely to fully replaceconventionalgasoline and diesel in the near future, a combination of fuels, along with continued innovation in fuel production, engine technology,andpolicy support, will be necessary to achieve sustainable IC engine operation. The paper concludes by outlining the critical researchareasand policy initiatives needed to promote the wider adoption of alternative fuels in the automotive sector. Keywords: Alternative fuels, bio fuels, diesel engine, eco-fuels