Autoignition Modeling and a Generalized Hot Surface Ignition Criterion

This work investigates the fundamental physics and predictive modeling of thermal ignition in heated volumes and near hot surfaces. Three-dimensional simulations of the ASTM-E659 apparatus revealed how natural convection and fuel stratification influence ignition timing and location, highlighting key limitations in standardized AIT testing. A one-dimensional analog further demonstrated the impact of radial temperature gradients on ignition behavior. To isolate the core mechanisms of thermal runaway, a canonical hot surface ignition problem was analyzed, showing that inclusion of low-temperature chemistry induces two-stage ignition and lowers critical surface temperatures. Building on insights from classical theory, a novel ignition model was developed based on chemical and thermal length scales. The model collapses ignition data across a wide range of configurations and defines a critical Damköhler number. Despite some limitations for NTC fuels and catalytic effects, this unified framework represents a major advance over existing models.