Effect of hydrogen‑citronella biofuels on dual‑fuel diesel engine efficiency and emissions: machine learning validation for sustainability

Global reliance on fossil fuels continues to drive greenhouse gas emissions and energy insecurity, highlighting the urgent need for sustainable combustion alternatives. Hydrogen, with its high flame speed and carbon-free nature, offers promise for dual-fuel diesel applications but faces challenges of stability, NOx formation, and integration with existing engines. This study develops and evaluates a novel integration of hydrogen-enriched citronella biofuel stabilized with SiO 2 nanoparticles and neem extract in a modified dual-fuel diesel engine, validated through interpretable machine learning. Six fuels were tested: diesel (SDL), citronella (C100), C100 with 100 ppm SiO 2 (C100N), and three hydrogen-enriched nanofluids (H20, H40, H60). The aim was to analyze the performance of brake thermal efficiency (BTE), brake specific energy consumption (BSEC), Hydrocarbon (HC), and Nitrogen oxides (NOx). In that context, the blend H40 gave the best compromise where the improvement in the BTE was 6–16% as compared to C100 and 1.5% as compared to diesel, while the reduction in the BSEC was 10–60%, reduction in the HC emissions 36–65%, and reduction in NOx emissions 10–20%. The reliability of the results was proven using six regression models where Polynomial Regression gave R 2 values of 0.93–0.99, validated using five-fold cross validation and SHAP analysis. To our knowledge, we present the first-time research that combines hydrogen-citronella nanofuels, nano-SiO 2 and machine learning validation towards cleaner and efficient dual fuel engine combustion system.