لهب الهيدروجين: كيف نقيس قوته الخفية سريع

الملخص الأصلي

كما كتبه المؤلفون، بالإنجليزية arXiv:2603.18852

This study introduces a novel experimental configuration using OH-PLIF imaging to directly determine the stretch factor ($$I_0$$) in laminar premixed hydrogen flames transitioning from a quasi-stable to a thermodiffusively unstable regime. A rod-anchored V-flame is stabilised in a laminar premixed reactant flow. Near the anchoring rod, the mildly strained flame remains quasi-stable, exhibiting a smooth surface and a well-defined inclination angle ($$\theta_{\mathrm{s}}$$) to the main flow. This stable branch is associated with a burning rate $$S_{\mathrm{s}}$$. Farther downstream, the flame abruptly transitions to a regime dominated by thermodiffusive (TD) instabilities, characterised by cellular structures and a wrinkled surface. The distance between this transition and the anchor decreases with increasing equivalence ratio. This TD-unstable branch exhibits a larger mean flame-surface angle ($$\theta_{\mathrm{u}}$$), enabling direct determination of the flame-speed increase, $$S_{\mathrm{u}}/S_{\mathrm{s}}$$. It is assumed that this ratio represents the normalised flame consumption speed, $$S_{\mathrm{c}}/S_{\mathrm{L}}$$. Determination of $$I_0$$ additionally requires the increase in flame-surface area caused by the thermodiffusive instabilities. Three complementary methods are therefore used to evaluate the surface area of the TD-unstable branch ($$A$$) relative to a smooth reference area ($$A_0$$), yielding consistent trends in $$A/A_0$$ over the investigated equivalence-ratio range. The resulting $$I_0$$ values, with the main uncertainty arising from $$A$$, decrease monotonically with increasing equivalence ratio, from about 1.1--1.3 at $$\phi=0.35$$ to 0.8--0.9 at $$\phi=0.40$$, consistent with theoretical predictions. Additional numerical simulations in a reduced two-dimensional representation reproduce the same transition behaviour and yield qualitatively consistent results.