An Improved Passive Scalar Model for Hazardous H2-Air Ignition Prediction

As hydrogen becomes an increasingly popular alternative fuel for transportation, the need for tools to predict ignition events has grown. Recently, a cost-effective passive scalar formulation has been developed to address this need [1]. This approach employs a self-reacting scalar to model the hydrogenair chain-branched explosion (due to reactions of the type Reactant + Radical → Radical + Radical). The scalar branching rate is derived analytically from the kinetic Jacobian matrix [2]. The method accurately reproduces ignition delays obtained by detailed chemistry for temperatures above crossover, where branching is the dominant process. However, for temperatures below the crossover temperature, where other phenomena like thermal runaway are more significant, the scalar approach fails to predict ignition events correctly. Therefore, modifications to the scalar framework have been made to extend its validity across the entire temperature range. Additionally, a simple technique for approximating the molecular diffusion of the scalar has been developed using the eigenvector of the Jacobian, which accounts for differences in the radical pool’s composition and non-unity Lewis number effects. The complete modified framework is presented, and its capability is evaluated in canonical scenarios and a more challenging double mixing layer.