Synergistic enhancement of combustion efficiency and emission control in a soybean biodiesel engine using carbon nanotubes and aqueous ammonia emulsion

Abstract This study evaluates the combined influence of an aqueous ammonia emulsion (AAE) and carbon nanotubes (CNTs) on the combustion, performance, and emission characteristics of a soybean biodiesel‐fueled diesel engine. A novel ternary fuel comprising soybean biodiesel (SB), AAE, and CNTs was developed to overcome two key limitations of biodiesel, namely elevated nitrogen oxide (NO x ) emissions and moderate thermal efficiency. Soybean biodiesel was produced through transesterification, while the CNTs were characterized using X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) before being incorporated into the SB–AAE blend at concentrations of 50 and 100 ppm. The addition of 10% AAE promoted in‐cylinder hydrogen generation and reduced NO x emissions through charge‐cooling effects associated with its high latent heat of vaporization. However, the SB–AAE blend exhibited higher carbon monoxide (CO), hydrocarbon (HC), and smoke emissions because of the relatively slow decomposition of aqueous ammonia. The incorporation of CNTs enhanced ammonia decomposition, improved fuel atomization, and accelerated oxidation reactions, resulting in more efficient combustion. The CNT‐enriched blends reduced brake‐specific energy consumption by up to 12.8% and substantially lowered CO, HC, and smoke emissions compared with SB–AAE. Although NO x emissions increased slightly relative to SB–AAE, they remained lower than those of neat soybean biodiesel. Overall, the synergistic interaction between AAE and CNTs improved fuel utilization while simultaneously enhancing the emission characteristics of soybean biodiesel, demonstrating the potential of the proposed ternary fuel as a cleaner and more energy‐efficient alternative for diesel engine applications.