Large-scale experimental study on jet flame length of hydrogen-blended natural gas and inverse methods for optimizing the weighted multi-point source model

Adding hydrogen into natural gas significantly impacts the flame length and radiation characteristics of a jet fire. A series of large-scale hydrogen-blended natural gas (HBNG) jet fire experiments within a pressure range of 1.6 to 4 MPa and hydrogen contents varying from 0 % to 100 % are conducted in this paper, and the flame length and radiative heat flux are measured. The flame length of HBNG jet fire decreases by 5 % when hydrogen volume fraction increases from 0 % to 20 %, and decreases by 25 % when it increases to 100 %. The higher radiative heat flux region (>4kW/m2) remains essentially invariant when the hydrogen volume fraction is less than 20 %, while decreases significantly when it exceeds 50 %. A model based on initial conditions has been proposed, resulting in a significant 10 % improvement in the accuracy of flame length prediction. An inverse method is employed to determine the distribution of weighting coefficients under various hydrogen contents. As the hydrogen content increases, the enhanced momentum effect leads to a more uniform geometric shape and a more balanced distribution of weighting coefficients. The deviations between the predicted values of the radiation model and the experimental data indicate the accuracy of the radiation model is strongly dependent on the flame length prediction model. By employing the new flame length correlation formula and optimizing weighting coefficients, the accuracy of the weighted multi-point source (WMPS) model is significantly improved.