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• 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]

Abstract Hydroxyl-terminated polybutadiene (HTPB) is extensively used in propulsion; however, it's trapped in low regression rate, partly related to poor thermal transfer from combustion. Carbon nanotubes (CNT) act as an energy transfer media, potentially accelerating the heat transfer and combustion performance of HTPB. Herein, multiwall CNT (MWCNT)/HTPB composites were prepared by dispersing MWCNT and surfactant into HTPB and toluene solvent through ball milling. Low MWCNT content (≤1%) promoted combustion, and excess MWCNT (≥2%) depressed, despite MWCNT shifting the HTPB-O 2 reaction to higher temperatures. (0.5%, 1%, 2% and 3%) MWCNT/HTPB composites reinforced the instantaneous regression rate by 11.2%, 31.6%, −21.3%, and −39.7% at Gox = 365 kg/m2·s; by 27.0%, 25.0%, −26.4%, and −36.6% at Gox = 150 kg/m2·s; while strengthened the average regression rate by 0.9%, 8.5%, −17.4%, and −36.7% at Gox = 365 kg/m2·s; and by 5.4%, 8.9%, −8.3%, −22.6% at Gox = 100 kg/m2·s. Specifically, the optimal MWCNT level was 1%, as demonstrated by the optimized reinforced thermal conductivity and slightly reduced energy release, since excessive MWCNT (>2%) hinders combustion through heat dissipation, high viscosity of the melting layer, low energy release and an attached carbon layer on the burning surface blocking the energy transfer. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]