Decarbonizing diesel-based propulsion systems: alternative fuels and hybridization

Decarbonizing Diesel-based propulsion is urgent, yet the operating requirements of high-utilization transport and aviation leave little room for compromise. Solutions must preserve range and rapid energy replenishment, minimize mass and packaging penalties, and maintain durability and safety over long service lives while meeting stricter climate and air-quality targets. This thesis frames decarbonization as a progressive engineering transition: it shows how Diesel-derived power units can be re-engineered to deliver lower-carbon operation with measurable performance and emissions benefits. Within the title theme “Decarbonizing Diesel-Based Propulsion Systems: Alternative Fuels and Hybridization”, the manuscript addresses three tightly connected questions: which sustainable fuels can be adopted with minimal disruption; how far hydrogen can be exploited within Diesel-derived concepts while respecting mechanical and safety limits; and where hybridization provides measurable benefits. A coherent methodology is used throughout, combining 0D/1D system simulation with 3D-CFD to quantify how design choices influence combustions, overall efficiency, and pollutant formation. The thesis first frames the integration “envelope” for near-term fuel substitution, clarifying the engineering trade-offs between drop-in solutions and deeper redesign. It then develops a CFD-guided approach to diesel–hydrogen dual-fuel combustion, focusing on diesel injection-law design as the key lever to reach high hydrogen utilization while controlling peak pressure and pressure-rise rates and mitigating NOx and CO₂. To extend hydrogen capability toward demanding operating conditions, the thesis develops a full-hydrogen, spark-ignited concept derived from an existing diesel engine, with the scavenging process specifically optimized for hydrogen, two stroke operation. Finally, it evaluates mission-oriented hybridization for ultralight aircraft, showing how carefully sized electrification can complement efficient compression-ignition operation without mass penalties. Overall, the thesis provides a structured set of design principles and simulation-validated pathways that enable credible, scalable decarbonization of Diesel-based propulsion, combining sustainable fuels, advanced combustion strategies and targeted hybridization to improve efficiency, reduce emissions and support technology readiness.