FUTURE FUELS FOR IC ENGINES: A REVIEW OF EMERGING PATHWAYS TOWARD NET-ZERO TRANSPORTATION

Transportation is one of the biggest contributors to global greenhouse gas emissions, and some of its toughest sub-sectors - heavy trucking, maritime shipping, and aviation - depend on energy-dense fuels that batteries cannot replace on their own. This review takes a close look at the next generation of fuels for internal combustion engines (ICEs), covering hydrogen, ammonia, biofuels (ethanol and biodiesel), synthetic e-fuels, and compressed/liquefied natural gas. Building on a large-scale bibliometric study of more than 760 research articles published between 2012 and 2023 and drawing on supplementary workshop materials, the paper explores combustion behavior, emissions profiles, NOx control strategies, and the infrastructure required for each fuel pathway. It also discusses advanced combustion approaches, HCCI, RCCI, and dual-fuel operation, as key enabling technologies. Along the way, the review tackles the major hurdles: hydrogen storage challengesand combustion quirks such as backfire and knock; ammonias stubborn resistance to ignition; the high cost of green hydrogen and synthetic fuels; and concerns about biofuel feedstock sustainability. The central conclusion is that no single fuel will do the job alone. Instead, a portfolio approach that matches multiple fuels with advanced engine technologies and well designed policy frameworks offers the most realistic path toward net-zero transport emissions by mid-century.