Energy loss in combustion processes in industries is of great importance, and most of the loss occurs in the combustion chamber. The performance of a non-premix burner operating on natural gas is experimentally examined. However, in most of the burner designs, the focus has been on changing the inlet air flow regime in the fuel and air mixture in the combustion chamber. But the aim of this study is to employ second law of thermodynamic (calculating irreversibility) to improve the flame structure and flame temperature profile with focus on changing the fuel flow regime in combustion chambers, and the non-premix combustion in multi-branch burners is studied experimentally. In this regard, the effect of geometrical parameters such as nozzle diameter, number of branches and fuel injection angle on total irreversibility is investigated in burner with non-premixed flame. In addition, the Taguchi analysis is used to find the optimum number of tests and an orthogonal array L9 [33] is utilized to minimize the irreversibility rate, which reduces the number of experiments from 27 to 9 tests. The results show that the number of fuel injection branches in combustion chamber has the greatest impact on irreversibility. Increasing the number of branches with a fuel injection angle of 45° leads to better air/fuel mixing, more uniform distribution of flame radial temperature in combustion chamber and reduces the total irreversibility and a fuel injection angle of more than 45° leading to flow divergence and as a result, increasing the retention time of combustion products, followed by increasing the NOx concentration. It is concluded that compared to the original burner structure, a burner head with 8 branches, nozzle diameter of 3.5 mm and fuel injection angle of 45° decreases the total irreversibility and concentration of NOx in combustion products by about 52% and 26 ppm, respectively

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