Heat Flux Distribution and Predictive Modeling of Wall-Impinging Hydrogen-Enriched Natural Gas Jet Flames

The heat transfer behavior of hydrogen-enriched natural gas (HENG) jet flames impinging on a vertical wall was systematically investigated to clarify the effects of key parameters on wall heat flux distribution. Experiments were performed using nozzle diameters of 3 ~ 5 mm, hydrogen volume fractions of 0–30%, and impingement distances of 10 ~ 50 cm. Spatial distributions of total, convective, and radiative heat fluxes on the wall were measured, and a dimensionless heat flux model was developed based on the Reynolds number and the free flame length. Results indicate that convective heat transfer dominates wall heating, while the radiative contribution remains limited. As the impingement distance increases from 10 cm to approximately 30 cm, enhanced entrainment and recirculation lead to longer residence of high-temperature gases near the wall and a marked increase in total heat flux; beyond 30 cm, the recirculation weakens and the heat flux declines gradually. With increasing hydrogen enrichment, the combustion intensity rises, the wall-attached flame region broadens, and convective heat transfer is strengthened, yielding higher total wall heat flux. Larger nozzle diameters (3 ~ 5 mm) promote stronger entrainment and recirculation, extending the residence time of hot gases and further enhancing convective transfer. The proposed dimensionless model accurately predicts the mean heat flux across different conditions, achieving a correlation coefficient of R2 ≥ 0.91. These findings provide an experimental and theoretical basis for the structural optimization and thermal safety design of hydrogen-enriched natural gas combustion systems.