Zero-Dimensional Ignition Model of Boron Agglomerates

Boron primarily exists in the form of agglomerates inramjet combustionchambers. However, the model used to predict the ignition time ofboron agglomerates is usually based on the single-particle assumption,resulting in inaccurate predictions. This study aims to develop anumerical model that can accurately describe the ignition of boronagglomerates. The model is based on the ignition model of a singleparticle boron proposed by the group of Kuo. Thiele modulus and effectivenessfactor are introduced to represent the diffusion resistance of reactiongases in the pores of boron agglomerates. The model includes the necessaryphysical processes to accurately predict the ignition time. The ratesof evaporation and heterogeneous reactions involved in the oxide layerremoval process are corrected based on the fact that the diffusionrate of (BO)( n ) in the liquid oxide layerequals to its consumption rate at the oxide-air interface. To evaluatethe accuracy of the model, the obtained results for ignition timeare compared with experimental data, showing reasonable consistencybetween them. The model is then applied to investigate the ignitioncharacteristics of boron agglomerates. Parameters, such as initialaverage pore diameter, oxide layer thicknesses, initial particle diameter,O-2 concentration, H2O concentration, and environmentalpressure, are studied for their effects on the ignition time. In summary,the boron ignition model established in this study is a powerful toolto investigate the ignition mechanisms and characteristics of boronagglomerates. It can be further coupled with flow analysis for thedetailed simulation of turbulent combustion in ramjet combustors.

Automated summary

This study aims to develop a numerical model that accurately describes the ignition of boron agglomerates. Based on the single-particle ignition model proposed by the group of Kuo, the model introduces Thiele modulus and effectiveness factor to represent the diffusion resistance of reaction gases in the pores of boron agglomerates. Through comparison with experimental data, the ignition time results of the model show reasonable consistency. The established model can be further used to investigate the ignition mechanisms and characteristics of boron agglomerates.