Composition of solid and gaseous primary combustion products of boron-based fuel-rich propellant.

The investigation of the primary combustion products of boron-based fuel-rich propellants is conducive to understanding the mechanism of the two-stage combustion process and provides important information for the prediction and organization of secondary combustion processes. The present investigation methods include numerical simulation and experimental analysis. The former deviates considerably from the actual conditions. The latter is currently a reliable and practical method, although it is difficult to quantify when the components are complex. In this work, SEM, LPSA, XRD, XPS, IC, ICP–MS, AAS, EDS, and chemical analysis methods were employed to qualitatively and quantitatively analyze the 3 solid products (aggregations, condensed-phase products, and flocculent products) at 1, 5, and 10 bar. GC, GC–MS, and IC combined with chemical tests were adopted to investigate the gaseous products (including chlorine-containing gas) for the first time. The solid products primarily included B 2 O 3 , B(HO) 3 , unburned boron, KB 5 O 8 (H 2 O) 4 , KCl, C, NH 4 Cl, NH 4 Mg(H 2 O) 6 Cl 3 , B 13 C 2 , Fe 3 O 4 , Mo, MgO, Mg(OH) 2 , MoO 3 , C 3 N 4 , BN, MgCO 3 (H 2 O) 3 (or MgCO 3), MoO 2 , Fe 4 (Fe(CN) 6) 3 , and FeB (or BFe 4), and the first 7 were dominant. The reaction degree of boron was less than 50 wt% (increasing with increasing pressure), indicating the significance of the secondary combustion process. The reacted boron was likely to react with O and C but not with N. The generated B 2 O 3 vapor easily combined with H 2 O to form B(HO) 3 or reacted with KCl (from the thermal decomposition of KP) and H 2 O to produce KB 5 O 8 (H 2 O) 4 after cooling. There was less B 13 C 2 (its content increased with increasing pressure, resulting in increases in particle size), since it was easily oxidized to generate B 2 O 3. NH 4 Cl was produced by the oxidation-reduction reaction between the NH 3 and HClO 4 released from large-sized AP, and some of it crystallized with MgCl 2 and H 2 O to form NH 4 Mg(H 2 O) 6 Cl 3. The gaseous products primarily included N 2 , H 2 , CO, CH 4 , CO 2 , C 2 H 4 , C 2 H 2 , HCl, C 4 H 6 , C 3 H 6 , Cl 2 , C 6 H 6 , and other hydrocarbons. N 2 and H 2 had the highest content. The N 2 content increased with increasing pressure, while the content of the combustible gases decreased, indicating that high pressure promotes the propellant reaction. The results also show that high pressure was conducive to the low-temperature decomposition of AP (producing more HCl and Cl 2) and the reaction of boron and hydrocarbons (generating more B 13 C 2), while it had an adverse effect on the C reaction (producing less CO x and mostly CO). Nevertheless, the increasing pressure had little effect on the combustion product components but did affect the content within the pressure range. • Solid/gaseous primary combustion products of boron-based propellants were quantified. • Twenty-two solid products and twelve main gases were detected. • Chlorine-containing gaseous products were investigated. • Main products' generating paths were analyzed. • Small pressure changes were observed to affect the content, not the product components. [ABSTRACT FROM AUTHOR]