Experimental and semi-empirical study on the radiative characteristics of inclined hydrogen-blended natural gas jet flames

Accurate and rapid prediction of the radiative heat flux from hydrogen-blended natural gas (HBNG) jet flames at arbitrary inclination angles is crucial for fire risk assessment in hydrogen-blending projects, particularly due to the significant variations in flame trajectory. Although computational fluid dynamics (CFD) simulations can capture these effects in detail, developing an engineering model is essential for efficient and rapid fire risk evaluation. This study experimentally investigates the radiative heat flux and trajectory of HBNG jet flames under varying leakage orifice diameters (3–5 mm), hydrogen blending ratios (0–30%), jet inclination angles (−30°–30°), and volumetric flow rates (10–40 L/min). A trajectory model applicable to HBNG jet flames was developed to improve the source emitter location in the radiation model. The flame mixing length was determined using a one-step global reaction for methane and hydrogen. The empirical coefficients α1 and α2 in the trajectory model were quantified as functions of jet inclination angle and fuel/air densities and Froude number, respectively. A comprehensive predictive framework was proposed to estimate the radiative heat flux of HBNG jet flames for both high-pressure and low-pressure leakage scenarios within an inclination range of −90° to 90°. ... mehrThis framework integrates a flame trajectory model, a notional nozzle model, and a line-source radiation model. The validity of the framework was confirmed by comparing with experimental data from this study as well as two large-scale HBNG jet fire experiments. The proposed approach enables rapid generation of high-resolution radiative heat flux contours with defined hazard zones, providing an effective tool for fast and accurate assessments of HBNG jet fires in engineering applications.