Hemp Biodiesel–Fueled Compression Ignition Engine Systems: A Comprehensive Systematic Review

The escalating global energy demand, coupled with rising environmental concerns regardinggreenhouse gas emissions and fossil fuel depletion, has demanded the exploration of alternativerenewable fuels for transport and power generation sectors. Industrial hemp (Cannabis sativa L.), aversatile non-food crop, has emerged as a promising feedstock for biodiesel production due to its highseed oil yield, rapid cultivation cycle and minimal agrochemical requirements. Hemp biodiesel,produced via transesterification of hemp seed oil, can be blended with conventional diesel fuel andused directly in compression ignition (CI) engines without major hardware modifications. Thissystematic review synthesizes contemporary research on hemp biodiesel–fueled CI engine systemsacross four primary dimensions: (i) Thermochemical and fuel properties, (ii) Combustion, emissionand performance characteristics, (iii) Advanced engine and fuel optimization strategies and (iv)Sustainability and life cycle considerations.A structured search protocol following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was employed to identify peer reviewed experimental and simulationstudies. Key findings reveal that hemp biodiesel blends (particularly B20 and B30) achieve brakethermal efficiency comparable to or slightly lower than conventional diesel, with brake specific fuelconsumption increasing modestly due to lower energy density. Notably, CO, HC, and smoke emissionsconsistently decrease across all blend ratios, with reductions ranging from 20–40% depending on blendpercentage and operating load. However, NOx emissions typically increase with hemp biodieselcontent, presenting the classic biodiesel emission trade-off. Advanced strategies including injectiontiming optimization, exhaust gas recirculation, nano-additives, and co-fuel blending with oxygenateslike butanol show promise in mitigating the NOx penalty while maintaining or enhancing efficiency.From a sustainability perspective, life cycle assessments suggest potential for reduced greenhouse gasemissions compared with fossil diesel, though region-specific techno-economic analyses remainlimited. This review identifies critical research gaps, including the need for comprehensive long-termdurability studies, advanced combustion modeling and integrated sustainability assessments andoutlines future research directions to unlock the full potential of hemp biodiesel in CI engineapplications.