Multi-Parametric Evaluation of a Novel Benzoylthiourea Derivative as a Combustion Modifier in Diesel–Ethanol Blends Under EGR Conditions

This study reports the first synthesis and full spectroscopic characterization (FT-IR, 1H NMR, 13C NMR) of a novel benzoylthiourea-based compound 2-chloro-N-((2-hydroxy-4-nitrophenyl)carbamothioyl)benzamide (HNCB) and evaluates its behavior as a combustion-modifying additive in diesel–ethanol blends. Blends containing 50, 100, and 200 ppm HNCB were tested in a single-cylinder direct-injection compression ignition engine at five torque levels (0–24 Nm) and four Exhaust gas recirculation rates (0–30%) to assess combustion, performance, and emissions. Ethanol improved mixture formation and combustion stability, while HNCB, particularly at 100 ppm, provided the most favorable overall balance of combustion phasing, heat-release characteristics, and emission control. At 24 Nm and 0% exhaust gas recirculation, Diesel + Ethanol + HNCB (100 ppm) increased maximum cylinder pressure by 4.1% relative to diesel and reduced cyclic indicated mean effective pressure variability. The 50 ppm blend yielded the lowest specific fuel consumption, with reductions of up to 37% at partial loads and the highest brake thermal efficiency values under several exhaust gas recirculation conditions. Nitrogen oxides emissions decreased by up to 65–75%, whereas the 200 ppm blend increased hydrocarbon and soot at 30% exhaust gas recirculation. Overall, HNCB acted as an effective combustion modifier under the tested conditions.