Experimental study of Al agglomeration on solid propellant burning surface and condensed combustion products

Aluminum(Al) particles are commonly added to energetic materials including propellants,explosives and pyrotechnics to increase the overall energy density of the composite,but aluminum agglomeration on the combustion surface may lower the combustion efficiency of propellants,resulting in a loss in twophase flow.Therefore,it is necessary to understand the agglomeration mechanism of aluminum particles on the combustion surface.In this paper,a high-pressure sealed combustion chamber is constructed,and high-speed camera is used to capture the whole process of aluminum accumulation,aggregation and agglomeration on the combustion surface,and the secondary agglomeration process near the combustion surface.The microscopic morphology and chemical composition of the condensed combustion products(CCPs) are then studied by using scanning electron microscopy coupled with energy dispersive(SEM-EDS) method.Results show that there are three main types of condensed combustion products:small smoke oxide particles oxidized by aluminum vapor,usually less than 1 μm;typical agglomerates formed by the combustion of aluminum agglomerates;carbonized agglomerates that are widely distributed,usually formed by irregular movements of aluminum agglomerates.The particle size of condensed combustion products is measured by laser particle size meter.As the pressure increases from 0.5 MPa to 1.0 MPa in nitrogen,the mass average particle size of aluminum agglomerates decreases by 49.7%.As the ambient gas is changed from 0.5 MPa nitrogen to 0.5 MPa air,the mass average particle size of aluminum agglomerates decreases by 67.3%.Results show that as the ambient pressure increases,the higher oxygen content can improve combustion efficiency and reduce the average agglomeration size of aluminum particles.

Mutagenicity of Urine From Individuals Exposed to LPG Combustion Products

The mutngenicity of urine from individua1s exposed to the combustion products of liquefied petroleum gas (LPG) was detected with Salmonella typhimurium TA98 and its newly developed derivatives YG1021 (nitroreductase overproducing) and YG1024 (O-acetyltransferase overproducing). The detection showed significantly increased mutagenicity for the two YG strains and increased positive rates for all three stralns in the presence of both rat liver S9 and β-glucuronidase. Further analysis demonstrated that urine samples taken from smoking and non-smoking exposed individuals exhibited significantly higher mutagenic potency (revertants/10 μl urine concentrate) than their corresponding controls. These results indicate that the increased urine mutagenicity is caused by the exposure to LPG combustion products or smoking. The mutagenic potency of urine samples of all exposed individuals tested with YG1024 was found to be about 7 times higher than with TA98. The difference in mutagenic potency was smaller for the sarne samples when comparison was made between YG1021 and TA98. This suggests that the mutagenic compounds present in the urine samples contaln mainly arotnatic compounds as glucuronide conugates. our results demonstrate that YG1024 is more sensitive than TA98 in detecting the mutagenicity of these samples. In addition, no significant difference in the mutagenic poency between the' pure' exposed (non-srnokers') and the ' pure' smokers' (unexpeed) samples was found in all three tester strains. This might mean that the exopure extent Of mutagens/carcinogens in LPG combustion products for exmped individuals roughly corresponds to the smoking level of smokers who smoke 20-40 cigarettes per day. Furthermore, the results also suggest that sguergism might exist in the mutagenic effects of exposure to LPG combustion products and cigarette smoking.

Elaborative collection of condensed combustion products of solid propellants:Towards a real Solid Rocket Motor(SRM)operational environment

A novel constant-pressure and constant-quenching distance Condensed Combustion Products(CCPs)collection system was developed,coupled with a timing control system,to collect the CCPs formed in the course of burning of aluminum-based composite propellants.The effects of adiabatic graphite plating,collection zone,quenching distance,time series of collection,and propellant burning rate on the microscopic morphology,particle size distribution and unburned aluminum content of CCPs were investigated.It was verified that the graphite plating can provide a high-fidelity high-temperature environment for propellant combustion.The combustion efficiency is improved by 2.44% compared to the bare propellant case.The time series of collection has a significant effect on the combustion efficiency of aluminum,and the combustion efficiency of aluminum in the thermal state(1.2-2.4 s)is 2.75% higher than that in the cold state(0-1.2 s).Similarly,the characteristics of the CCPs in different collection zones are different.At the quenching distance of 5 mm,the combustion efficiency of aluminum in the core zone(85.39%)is much lower than that in the outer zone(92.07%),while the particle size of the CCPs in the core zone(172μm)is larger than that in the outer zone(41μm).This indicates that the core zone is more likely to produce large-sized and incompletely burned agglomerates during the propellant combustion process.Different burning rates also lead to a significant difference in particle size distribution and combustion efficiency.High burning rates result in higher combustion efficiency.A detailed sequence of the elaborative collection process of CCPs is proposed,mainly including the setting of ignition delay time,burning rate,working pressure,plating length and time series of collection.The findings of this study are expected to provide a reliable tool for the evaluation of the combustion efficiency of solid propellants.