Thermally regulated hydrogen release from ammonia-borane for enhanced diesel engine performance and emission mitigation

The present research examines the potential of ammonia-borane (AB) as a hydrogen-enriched additive to enhance the energy and environmental metrics of diesel fuel (DF) in a single-cylinder diesel engine that is operated under varying brake mean effective pressures (BMEPs). In contrast to previous enrichment methods that necessitate pressurized storage or catalytic reformers, this study evaluates solid AB when used directly at ppm levels as a temperature-activated, in-cylinder hydrogen source under standard engine operation. DF was blended with AB at concentrations of 100 ppm, 200 ppm, and 300 ppm via ultrasonication. Thermogravimetric analysis confirmed AB's controlled, temperature-responsive hydrogen release, facilitating enhanced combustion. Increasing AB concentration shortened ignition delay and extended combustion duration. Peak in-cylinder pressure was reduced by 2.1 %, 5.3 %, and 6.5 % for DF100AB, DF200AB, and DF300AB, respectively. Corresponding peak net heat release rate reductions were 1.7 %, 2.4 %, and 3.6 %, indicating consistent energy delivery via sustained hydrogen decomposition. At peak BMEP, BSFC decreased by 2.6 %, 6.4 %, and 5.3 % for DF100AB, DF200AB, and DF300AB, with BTE improvements of 2.2 %, 5.8 %, and 4.2 %, respectively. Emission analysis showed significant reductions at 4.14 bar BMEP: NOx by 5.3–13.4 %, HC by 4.3–16.8 %, and CO by 6.5–19.3 %. CO 2 emissions increased by 7.7–20.5 %, reflecting more complete combustion. The results confirm that AB provides safe, thermally controlled hydrogen release supporting process safety, with the 200-ppm blend offering optimal improvements in combustion efficiency and emission reduction for cleaner diesel engine operation, whereas 300 ppm showed diminishing returns.