This study explores the potential of various alternative fuels and oxygenated additives to
enhance performance and reduce emissions in variable compression ratio (VCR) diesel
engines. Fuel blends investigated include Azadirachta indica oil biodiesel, Madhuca indica oil
biodiesel, tire pyrolysis oil, methanol, 1-octanol, and a Jatropha–Spirulina biodiesel blend with
diesel. These were combined with oxygenated additives such as ethanol, methanol, and diethyl
ether to improve combustion characteristics. Engine performance parameters—brake thermal
efficiency, specific fuel consumption, and exhaust gas temperature—were evaluated alongside
emission metrics, including CO, NOx, HC, and particulate matter. The experimental results
indicate that the inclusion of oxygenated additives significantly enhances combustion
efficiency and reduces pollutant emissions across all tested blends. Blends with diethyl ether
demonstrated the highest improvement in thermal efficiency and the greatest reduction in NOx
and particulate emissions. These findings suggest that combining biodiesel and waste-derived
fuels with oxygenated additives offers a viable and environmentally sustainable alternative to
conventional diesel. Further investigation into long-term engine performance and economic
viability is recommended to support real-world application
