Performance and emission optimization of a CRDI engine in RCCI mode using hydrogen enriched biodiesel through grey relational analysis approach

This study investigates the performance and emission optimization of a Common Rail Direct Injection (CRDI) diesel engine operated in Reactivity Controlled Compression Ignition (RCCI) mode using alternative fuel strategies. Experiments were performed on a single-cylinder, four-stroke, water-cooled CRDI engine operating at a constant speed of 1500 rpm under 25%, 50%, 75%, and 100% load conditions, corresponding to a brake mean effective pressure (BMEP) range of 0.4–1.6 MPa. The test environment was maintained at an ambient temperature of 29 ± 2 °C, relative humidity of 68 ± 5%, and atmospheric pressure of 1.01 bar. The intake manifold pressure was regulated at 1.0 ± 0.02 bar, with coolant and lubricating oil temperatures stabilized at 80 ± 2 °C and 85 ± 3 °C, respectively, to ensure consistent thermal boundary conditions. Four fuel configurations were evaluated: neat diesel (D100), CNG + D100, H₂ + D100, and hydrogen-enriched biodiesel (B20 + H₂). Hydrogen and CNG were inducted through the intake manifold at flow rates of 2, 4, 6, and 8 L/min, while diesel and biodiesel served as pilot fuels injected at a fixed pressure of 500 bar. Engine performance and emission characteristics were analysed in terms of Brake Thermal Efficiency (BTE), Brake Specific Fuel Consumption (BSFC), and exhaust emissions (CO, HC, NO_x, and smoke opacity). Grey Relational Analysis (GRA) was applied for multi-response optimization, identifying B20 + H₂ at 2 L/min as the most favourable condition, offering higher BTE, lower BSFC, and reduced emissions. The study highlights the dual advantage of hydrogen-enriched biodiesel in achieving a cleaner and more efficient RCCI operation. The work aligns with UN SDG-7 and SDG-13 by advancing a cleaner, low-carbon dual-fuel pathway through hydrogen-enriched biodiesel combustion in modern engines.