Optimisation of Water, Surfactant and Dual-Biodiesel Concentration for a Least-Phase-Separation Emulsified Neem–Palm Blend in a Diesel Engine: Stability, Performance and Emission Study

Abstract

Fossil-fuel depletion and the harmful exhaust emissions of compression-ignition (CI) engines have intensified the search for cleaner alternative fuels. Emulsification of water into biodiesel–diesel blends is an attractive technique because the micro-explosion of dispersed water droplets improves atomisation and lowers the peak combustion temperature, simultaneously enhancing performance and reducing oxides of nitrogen. This study optimises the water, surfactant and dual-biodiesel content of a least-phase-separation emulsified fuel and evaluates it in a single-cylinder CI engine. A B30 blend of Neem and Palm biodiesel (15% Neem + 15% Palm + 70% diesel, denoted N15P15D70) was selected as the base fuel. Water-in-oil emulsions were prepared with water concentrations of 1–5 v/v %, surfactant (SPAN 80 / TWEEN 80) of 1–2 v/v %, and hydrophile–lipophile balance (HLB) values of 4.3, 5.3 and 6, using a mechanical stirrer. Emulsion stability was assessed from the phase-separation percentage over six hours, and the optimum formulation was tested for engine performance and exhaust emissions against neat diesel. The emulsion with 5% water, 2% surfactant and HLB 6 (W5S2HLB6) gave the best stability, with only 8% separation after six hours. Relative to diesel, this fuel delivered about 14% higher brake thermal efficiency, 42% higher carbon dioxide (indicating more complete combustion), and roughly 60% lower carbon monoxide and 61% lower NOx, although brake specific fuel consumption rose by about 16.7% and smoke increased marginally. The study concludes that an emulsified fuel of 30% dual biodiesel, 2% surfactant, 5% water and HLB 5.3–6 markedly reduces harmful emissions while improving engine performance, and can be used in existing engines with little or no modification.