Effects of EGR and Fe₃O₄ nanoadditives on performance of a variable compression ratio diesel engine fueled with tamarind biodiesel

The rising demand for energy and the rapid depletion of fossil fuels underscore the need for sustainable alternatives that can ensure efficient engine operation while meeting emission regulations, such as biodiesel. Tamarind seed biodiesel has emerged as a renewable option; however, its tendency to increase nitrogen oxide (NOx) emissions restricts its large-scale application in the automotive industry. This study explored an innovative approach that integrates magnetite (Fe₃O₄) nanoparticle additives with exhaust gas recirculation (EGR) to enhance combustion, performance, and emission characteristics of a variable compression ratio (VCR) diesel engine. Experimental investigations were performed on a single-cylinder engine using TB20 (20% tamarind biodiesel and 80% diesel) and its nano-enhanced blends containing 50 ppm (TB20N50) and 100 ppm (TB20N100) of Fe₃O₄ under loads from 0% to 100% with EGR rates of 0%, 10%, and 20%. The results demonstrated that the addition of Fe₃O₄ nanoparticles enhanced the brake thermal efficiency by 2.61% and reduced the specific fuel consumption by 3.34% for TB20N100 relative to TB20. The combustion characteristics also improved, with the cylinder pressure and heat release rate increasing by 2.5–5% when nanoadditives were used. In terms of emissions, NOx levels were significantly reduced by 25.5–56.3% at higher EGR rates. CO emissions decreased by approximately 18% with nanoparticle addition, although the application of EGR led to a 20–40% increase in CO and HC emissions at high loads. Smoke opacity decreased by nearly 3% for the nanoblends but increased by up to 7% at higher EGR levels. The synergistic use of Fe₃O₄ nanoparticles and controlled EGR provides an effective strategy for optimizing biodiesel-fueled engines. This innovative approach demonstrates the potential of tamarind biodiesel nanoblends to balance efficiency and emissions, offering a sustainable pathway toward cleaner engine technologies.