Effect of initial pressure on the critical characteristics and overpressure of hydrogen-air premixed gas combustion and explosion

Abstract

In order to ensure the safe utilization of hydrogen, the flame characteristics and explosion overpressure at lean-burn, stoichiometric and rich-burn conditions are investigated systematically by varying initial pressures. Experiments were conducted in a constant-volume combustion chamber using the Schlieren system to investigate the critical characteristics of hydrogen-air premixed flames at different equivalence ratios (from 0.2 to 6.5) and initial pressures (from 50 kPa to 150 kPa). The cellular instabilities of hydrogen-air premixed flames were interpreted and evaluated from the viewpoint of thermal-diffusive and hydrodynamic instabilities. The influence of initial pressure on the cellular instability and combustion and explosion characteristics were analyzed. The results show that the variation of thermal-diffusive instability dominantly governs the cellular instability at lean-burn conditions (φ = 0.3–1.0). In contrast, the cellular instability at rich-burn conditions (φ > 1.5) is governed by the variation of hydrodynamic instability. The increase of initial pressure promotes the cellular instabilities noticeably caused by the rise of the hydrodynamic instability. With the increase of P0, the Lewis number Le and thermal expansion ratio σ almost remain the same while flame thickness δ noticeably decreases. Increasing initial pressure at lean-burn and stoichiometric conditions (φ < 2.0) facilitates cellular instability, making the explosion more intense and resulting in higher explosion overpressure. In contrast, the variation of initial pressure suppresses the laminar combustion at rich-burn conditions (φ > 3.0).