Fires in tunnels have attracted special attention in recent years due to catastrophic fires, which cause huge human and economic losses. For accurate fire modelling and ventilation system design, it is critical to understand the correct radiative fraction (X_r) of the flame. Recent study has proved that X_r decreases with the increase of longitudinal air velocity in heptane pool fires. However, the impacts of longitudinal air velocity and fuel flow rate on X_r in propane or liquefied petroleum gas tunnel fires have not been studied. To fill the gap, this paper conducts two sets of fire experiments in a 1/20 reduced-scale wind tunnel using a porous burner. Unique visible flame shapes are observed and described by the ‘back-to-back conical frustum’. The geometric parameters and their variations with the momentum flux ratio are discussed. In comparison with the experimental results, the radiation model using the proposed flame shape shows an 80 % accuracy. The predictive radiative fractions of the two tests are calculated and compared with other tests from literature. The coupling effects of longitudinal air velocity and fuel flow rate on the flame radiative fraction are studied in detail. And their influences on key parameters of smoke extraction system are analyzed.

近年来，由于灾难性火灾，隧道火灾引起了巨大的人员和经济损失，引起了火灾的特别关注。为了进行精确的火灾建模和通风系统设计，至关重要的是要了解火焰的正确辐射分数（X _r）。最近的研究证明，在庚烷池火中，X _r随着纵向空气速度的增加而降低。但是，纵向空气速度和燃料流速对X _r的影响丙烷或液化石油气隧道火灾尚未研究。为了填补这一空白，本文使用多孔燃烧器在1/20缩小规模的风洞中进行了两组火灾实验。观察到的独特可见火焰形状由“背对背锥形截头圆锥体”描述。讨论了几何参数及其随动量通量比的变化。与实验结果相比，使用建议的火焰形状的辐射模型显示出80％的精度。计算两个测试的预测辐射分数，并将其与文献中的其他测试进行比较。详细研究了纵向空气速度和燃料流速对火焰辐射分数的耦合作用。分析了它们对排烟系统关键参数的影响。