The rapid H2 release from AlH3 dehydrogenation forming porous layer in AlH3/hydroxyl-terminated polybutadiene (HTPB) fuels during combustion.

• A previously unreported porous layer mechanism of AlH 3 enhancing combustion was proposed. • A 50 μm thick porous layer when combustion was evaluated by SEM, thermo-analysis and a new simplified calculation method. • A new model predicting the overlapping process of AlH 3 dehydrogenation and Al oxidation in air atmosphere was developed. Although the motivation of AlH 3 enhancing combustion were recognized in many research, the promotion mechanism have been rarely explored. Herein, a previously unreported porous layer mechanism when combustion were determined in HTPB/AlH 3 fuels by SEM, thermo-analysis and a new simplified calculation method, owing to rapidly released gas phase H 2 from AlH 3 dehydrogenation exposing in melting layer. 5/10% 40–80 μm and 10% 80–200 μm AlH 3 -HTPB formulas show the regression rate increase by, 25.7%, 29.0% and 43.0% at Gox = 350 kg/m2·s, while by 57.2%, 42.0% and 44.2% enhancement at Gox = 150 kg/m2·s. The low AlH 3 content (≤ 10%) promotes the regression rate obviously, while excess AlH 3 content (≥ 20%) promotes slightly as a result of comprehensive factors combined by energy release, a certain porous layer mechanism, aggregated Al 2 O 3 attached on the burning surface and the blocking effect of the gaseous released H 2. A new model predicting the overlapping process of AlH 3 dehydrogenation and Al oxidation in air atmosphere was developed by superimposing AlH 3 dehydrogenation simulation and corresponding separated Al oxidation simulation. A 1.5th Avrami-Erofeev (A–E) simulation was proposed for Al passivation weight gain between 420 and 520 K with an activation energy of 124.92 kJ/mol and the pre-exponential of 10^12.35. [ABSTRACT FROM AUTHOR]