2016/09/08 by Nick Sirmas, Sirmas, Nick, Matei I. Radulescu +1
Engineering · Mathematics · #Chemical Physics (physics.chem-ph) #Combustion and Detonation Processes #Combustion and flame dynamics #Computational Physics (physics.comp-ph) #FOS: Physical sciences #Gas Dynamics and Kinetic Theory
paper · pdf · doi:10.48550/arxiv.1609.02458
openalex publication_date 2016/09/08 · openalex created_date 2022/10/04 · openalex updated_date 2026/07/28
The problem of thermal ignition in a homogeneous gas is revisited from a\nmolecular dynamics perspective. A two-dimensional model is adopted, which\nassumes reactive disks of type A and B in a fixed area that react to form type\nC products if an activation threshold for impact is surpassed. Such a reaction\nliberates kinetic energy to the product particles, representative of the heat\nrelease. The results for the ignition delay are compared with those obtained\nfrom the continuum description assuming local thermodynamic equilibrium, in\norder to assess the role played by molecular fluctuations. Results show two\nregimes of non-equilibrium ignition whereby ignition occurs at different times\nas compared to that from the continuum description. The first regime is at low\nactivation energies, where the ignition time is found to be higher than that\nexpected from theory for all values of heat release, in agreement with\npredictions from Prigogine and Xhrouet who attribute this departure to\nnon-equilibrium effects. Results suggest the ignition is spatially homogeneous\nin this regime. The second regime occurs at high activation energies and\nsufficiently large heat release values. In this regime, ignition times are\nfound to be dependent on domain size, with larger domains yielding shorter\nignition delays than expected. Results for larger systems agree with the\nexpectations by Prigogine and Mahieu, who predict a non-equilibrium reaction\nrate larger than expected for a homogeneous system in equilibrium. Results\nyield a large variance for ignition times under these conditions, suggesting a\ndeparture from homogeneous combustion. The results obtained are in qualitative\nagreement with experimental observations of auto-ignition at relatively low\ntemperatures, where hot-spot ignition and associated ignition delays lower than\npredicted are generally observed.\n