Surface-area engineered nanocomposite for cleaner compression ignition combustion with water–diesel emulsions

This study addresses fuel scarcity and emission control in compression-ignition engines by integrating water–diesel emulsification with a surface-area engineered hybrid nanocomposite. Unlike conventional water–diesel emulsions using single-phase nanoparticles, this approach employs a surface-area-enhanced MWCNT–Al 2 O 3 nanocomposite to improve heat transfer and catalytic oxidation. Nitrogen sorption analysis of the proposed nanocomposite confirmed a type-IV isotherm with H3 hysteresis, a modal pore size of ∼3 nm, a cumulative mesopore volume of 0.12–0.13 cm 3 g -1 , and a BET surface area exceeding 180 m 2 g -1 . These features provide a large density of accessible reactive sites at ultra-low additive loading. Water–diesel emulsions containing 5% (E5W) and 10% (E10W) water were prepared using a non-ionic surfactant, and the nanocomposite was dispersed at 100 ppm into the 10% emulsion (E10W–NC). Engine analysis showed that E5W reduced peak in-cylinder pressure (ICP) and brake thermal efficiency (BTE) by 1.3% and 7.1%, respectively, while E10W caused larger reductions of 2.5% and 11.1%, accompanied by higher fuel consumption. In contrast, E10W–NC recovered combustion intensity and efficiency. Compared with E10W, the E10W–NC fuel increased peak ICP and net heat-release rate by 3% and 13.3%, respectively, while improving BTE by 12.8% and reducing fuel consumption by 11.6%. At the same time, it lowered NO x , hydrocarbon, carbon monoxide, and smoke emissions by 3%, 4.8%, 5.8%, and 5.6%, respectively. Overall, the results demonstrate that surface-area architecture governs the effectiveness of water–diesel emulsions, offering a practical pathway to cleaner and more efficient CI engine operation without hardware modification.