<p>This study investigates the effects of Fe₃O₄ nanoparticles and compression ratio on the performance, combustion, and emission parameters of a diesel engine using a tamarind biodiesel blend (B20). Tamarind biodiesel was produced through transesterification of tamarind seed oil, and Fe₃O₄ nanoparticles were blended into the biodiesel using a probe-type ultrasonicator. Experiments were conducted with B20 blends containing 50 and 100&#xa0;ppm Fe₃O₄ nanoparticles at compression ratios (CRs) of 16, 17.5, and 19. The results show that at compression ratios of 19 and 100&#xa0;ppm Fe₃O₄, the engine performance was significantly improved, achieving a 6.4% increase in brake thermal efficiency and a 6.02% reduction in specific fuel consumption compared to CR 16. Emissions analysis revealed a 53.64% reduction in carbon monoxide emissions and a 10% reduction in hydrocarbon emissions, with NOx emissions showing a slight increase of 39.02%. This combination also achieved the highest cylinder pressure (73.08&#xa0;bar), and heat release rate of 44.72&#xa0;J/°CA. Additionally, an artificial neural network (ANN) model was developed to predict engine performance and emissions, achieving high accuracy with <i>R</i> values between 0.99951 and 0.99998, and a mean absolute percentage error (MAPE) ranging from 0.346 to 3.339%. This study highlights the potential of Fe₃O₄ nanoparticle additives in enhancing VCR diesel engine performance and demonstrates the effectiveness of ANN modeling in optimizing the engine parameters.</p>