Boron-Spinel Oxide Nanohybrids for Dual-Scale Combustion Enhancement in Energetic Fuels

Abstract

This study presents a dual-scale analysis of boron - spinel oxide nanohybrid additives, demonstrating significant enhancements in thermal behavior and combustion performance at both droplet-scale and engine-scale applications. Droplet-scale combustion events represent the combustion behavior of atomized fuel droplets injected into a cylinder in an engine. The results obtained can help to interpret the changing engine performance characteristics. The effects of boron/spinel oxide nanohybrid particles on liquid hydrocarbon fuel combustion were tested by applying droplet-scale combustion tests of gasoline-based nanofuel droplets with 2.5% and 7.5% particulate loads, and diesel engine tests at 15-60 Nm load (250 ppm particulate load). The hybrid particles were synthesized by combining MgMnO3 (MM) and MgFe2O4 (MF) nanoparticles with ball-milled amorphous boron (AB-BM) via ultrasonication. The MM and MF nanoparticles contained within the boron hybrid structures, with their high oxygen content, helped reduce the soot generated by gasoline combustion while simultaneously acting as an oxygen donor that facilitated the combustion of boron. The presence of 2.5 wt.% AB-MM and AB-MF reduced ignition delay to similar to 0.001428 ms and similar to 0.00357 ms, respectively. AB-MF at 2.5 wt.% increased the gasoline flame temperature by 14.58% compared to pure gasoline, while 7.5 wt.% raised the aggregate temperature by 52.15% compared to AB-BM. Residual aggregates at 7.5 wt.% showed AB-MF as the most effective for boron combustion and soot oxidation. In engine tests, compared to diesel (D100), D100 + 250AB/MF improved heat release rate (HRR) by 11.96%, 6.75%, and 5.42% at torque values 30 Nm, 45 Nm, and 60 Nm, respectively. CO2 emissions increased by up to 7.96%, while HC emissions dropped by 61.11%, 42.85%, and 37.93% at 15 Nm, 30 Nm, and 60 Nm. NOx emissions decreased by up to 9.47%. These findings demonstrate that boron/spinel oxide nanohybrids enhance combustion efficiency and reduce emissions, making them promising additives for cleaner and more efficient fuel applications.