Experimental and theoretical study on the burning and pulsation behaviors of hydrogen-containing and hydrocarbon jet flames

Hydrogen-containing and hydrocarbon fuels have been widely used in industrial production. Jet fires involving these fuels emerge frequently after leakage or explosion accidents for gas pipelines and processing equipments. To reveal the influencing mechanisms of inclination angle on the pulsation behaviors of jet fires, the burning experiments of hydrogen, syngas, methane and propane jet fires with a nozzle diameter ($D$) of 15 mm, inclination angles (${\theta }_0)$ of 0°∼90°, fuel flow rates ($Q_f)$of 2.5–40 L/min were conducted. The variations of the global and spatial pulsation frequencies with inclination angle and fuel flow rate are sensitive to the fuel types. Subharmonic pulsation was found at large fuel flow rates ($Q_f>Q_{\mathrm{cri}}$). For hydrogen-containing jet flame, a transition from natural pulsation to subharmonic pulsation occurs at a critical inclination angle (${\theta }_{\mathrm{cri}}$). In this case, the transition height where the local pulsation frequency begins to be dominated by subharmonic pulsation, increases with the inclination angle. The local Richardson number ($R{i}_y$) at the transition height is close to 1. The interaction between the inner and outer vortices increases with the decrease of inclination angle, resulting in decreased natural frequency at the nozzle exit. With the theoretical velocity and flame width at y/D = 2, a unified dimensionless model of natural pulsation frequency was developed, $S{t}_y=0.41{\left(1/F{r}_y\right)}^{0.5}$, reasonably predicting the natural pulsation frequency of jet flames under different conditions.