Emission and performance characteristics of biodiesel from Manilkara zapota seed oil with TiO₂ nanoadditive using split injection strategy on CRDI diesel engine

As the world's fossil fuel supplies continue to dwindle, rapid industrialization and growth have resulted in a greater demand for alternative sources of energy. The present study focuses on assessing the thermal performance, combustion, and emission characteristics of a diesel engine running on both Manilkara Zapota biodiesel and a Manilkara Zapota biodiesel blend that has been modified with green-synthesized TiO₂ nanoparticles. By evaluating these parameters, the study aims to determine the viability of using this alternative fuel as a sustainable option. To evaluate the thermal performance, combustion, and emission characteristics of the engine, a split injection strategy was implemented and compared with a single injection technique. The experimental results revealed that the NOx formation, unburnt hydrocarbon (HC), and carbon monoxide (CO) emissions from the engine fueled using the biodiesel blend (S15) with 75 ppm nano additives were reduced, as compared to other concentrations of green synthesized nanoparticles, whereas the CO₂ emissions increased. CO emissions decreased by 7.4%, 14.81%, and 18.51% for S15 biodiesel with 25, 50, and 75 ppm TiO₂ nanoparticles, respectively, compared to S15 without additives. At 75 ppm, CO emissions dropped to 0.22% vol. Using 75 ppm of nanoparticles, HC emissions were reduced by 14.28% and achieved 24 ppm at peak load. The adoption of biodiesel blends resulted in an increase in NOx emissions. However, the emissions were controlled by split injection, where a reduction of 6.66% for diesel and 3.22% for S15 was recorded as opposed to single injection. BTE was maximum at 32.33% with 75 ppm TiO₂, surpassing diesel, which had 30.99% Brake thermal efficiency (BTE) and other lower concentrations of the nanoparticle. However, S15 BTE was somewhat lower than the single injection due to the split injection strategy. Specific fuel consumption (SFC) lowered by 19.23% for S15 with 75 ppm nanoparticles as compared to S100 neat biodiesel. Nevertheless, split injection raised SFC by 11.53% for S15 with 75 ppm compared to S15 with a single injection. Moreover, the use of the split injection strategy resulted in a reduction of NOx, HC, and CO emissions compared to the single injection strategy. However, with split injection, the specific fuel consumption (SFC) increased, and the brake thermal efficiency (BTE) reduced, likely due to the early combustion phase initiated by the pilot injection.