Optimizing injector nozzle configuration for high efficiency and low emissions in diesel engines fueled with biodiesel and n-butanol blends

Biodiesel, being a renewable fuel, offers significant ecological advantages with low harmful gas emissions and a reduced carbon footprint. This underscores the importance of optimizing the injector nozzle, which plays a key role in enhancing combustion efficiency. This study enhances the performance, emission, and combustion characteristics of a diesel engine operating in dual-fuel mode with an electronic injection system using 3, 4, and 5-hole nozzles. The tested fuels include conventional diesel, blended chlorella vulgaris oil (Extracted from algae), and waste cooking biodiesel (CWB20), and CWB20 mixed with 30% n-butanol. The biodiesel was synthesised using the transesterification method with a graphene heterogeneous catalyst. The synthesised biodiesel thermophysical properties were identified and compared with ASTM standards. Among the tested configurations, the CWB20 + 30% n-butanol blend paired with a 5-hole nozzle demonstrated the most favourable balance between efficiency and fuel economy, achieving a peak BTE of 33% and the lowest BSFC of 0.215 g/kWh at 5 kW BP, alongside substantial reductions in CO and HC emissions. Although the 5-hole with CWB20 fuel configuration exhibited higher NOx emissions due to enhanced premixing and elevated in-cylinder temperatures (up to 14.35 g/kW hr at high BP), these can be effectively mitigated through after-treatment techniques such as EGR and SCR. At full BP, the ignition delay and combustion duration of the engine fuel with CWB20 + 30% n-butanol were observed to be longer by approximately 1°CA and 2°CA, respectively, compared to diesel. Therefore, the CWB20 + 30% n-butanol 5 H combination represents a technically viable, low-carbon alternative for both large-scale and domestic diesel applications.