Recent climate changes, driven by greenhouse gas emissions, along with global
regulations aimed at mitigating these effects, have intensified research on
carbon-free fuels. Among these, hydrogen stands out as one of the most promising
options. In this study, use is made of a recent 1D kernel expansion model
developed by the authors, which is based on the conservation equations of mass,
energy and deficient reactant. The theory of transient thermo-diffusion is also
adopted to estimate the reactant and temperature gradients at the outer flame
surface. The kernel expansion model accounts for the variability of
thermodynamic properties both inside and outside the flame volume, including
high-temperature ionization and dissociation effects. The kernel expansion model
is used until the non-linear stretch effects are sufficiently relaxed.
Subsequently, the propagation of the premixed flame is described by means of a
two-zone combustion model. During both phases, the effects of hydrodynamic and
thermo-diffusive instabilities are accounted for. The former are modeled
considering the flame wrinkling produced by the density discontinuity across the
flame, evolving towards a self-similar fractal-like behavior. The latter,
induced by a less-than-unity Lewis number, are modeled introducing an equivalent
flame consumption speed to quantify the increase in flame expansion velocity.
The model is validated against experimental data from literature obtained for
premixed hydrogen-air flames propagating in an optically accessible spherical
bomb. The data used for model validation refer to quiescent conditions at
multiple lean equivalence ratios (from 0.45 to 0.97). The capabilities of the
present model are assessed with reference to the measured time histories of
chamber pressure, flame radius and expansion speed. A good agreement is achieved
across all the test cases considered, confirming the consistency of the
integrated ignition-combustion model proposed in this work.