Influence of oblique angle and heating height on flame structure, temperature field and efficiency of an impinging laminar jet flame

An experimental study is performed to determine the combined effects of oblique angle (θ) and heating height (H) on the flame structure, temperature field and thermal efficiency of a laminar premixed methane-air flame impinging on a plane surface. A double-flame burning of a Bunsen flame under a fuel-rich condition is used. It is found that the flame structure, temperature distribution and thermal efficiency depend strongly on the oblique angle and heating height. The influence of the oblique angle on flame structure is stronger for lower heating heights but is relatively weak for higher heating heights. For normal impingement, axisymmetric temperature distributions are found, which is attributed to the axisymmetric flame structure. However, a jet flame impinging at an angle onto the horizontal plate creates an asymmetric flame structure and, thus, results in asymmetric temperature distributions. The results show that as the oblique angle is reduced from 90° to 60°, the high-temperature zone shifts toward the major flow region. An optimum operating condition of the burner, identified by the widest high-temperature zone and the highest thermal efficiency, is achieved under the condition of θ = 60° and H = 12 mm. In general, a decrease of the oblique angle leads to a decrease in thermal efficiency. However, for the cases of lower heating heights (i.e. H ⩽ 12 mm), the trend may be reversed. Furthermore, for a fixed oblique angle, as the heating height is increased, the thermal efficiency first increases to a maximum value and then decreases.