Seyed Mostafa Robati

In this paper, the effects of coaxial airflow swirl number on blow-out limit, flame characteristics, and emission performance of non-premixed methane/air and n-butane/air flames in a miniature-scale swirl burner are investigated experimentally. Swirl numbers ranging from 0 to 0.72 have been chosen to be examined. It was observed that increasing the vane angle does not increase the blow-out limit monotonically and a swirler with 30 ° vane angle ( 0.50 swirl number) results in the greatest blow-out limit. Besides, it was found out that methane outperforms n-butane in the blow-out limit at the same fuel flow rates. The intermittency distribution approach was used to determine flame properties such as lift-off height, length, and width. It was found that the lift-off variation with coaxial airflow Reynolds number at the specified fuel flow rates yields an inverted V-shape for S _n ≥ 0.50. The tip of these plots indicates the airflow rate at which the swirl shows its influence, and after this point, the lift-off height begins to decrease. It was also observed that the airflow related to this point decreases with an increase in the swirl number at a certain fuel flow rate. Furthermore, the results revealed that at high airflow rates, the flame width rises as the swirl number increases. Also, raising the swirl number and airflow Reynolds number reduced the flame length. It was also observed that n-butane/air flames have longer and wider flames than methane/air flames. Additionally, adding swirl to the airflow rate typically reduces N O x and CO concentrations and n-butane/air flames exhibit lower levels of N O x and higher levels of CO than methane/air flames under the same operating conditions.

Combustion and flame characteristics of laminar methane/air and n‐butane/air flames in a 3D‐printed micro‐slot burner is compared and reported in this study. The stability limit, flame appearance, and emission performance are investigated experimentally. In addition, past research on conventional burners is compared with the results of this study throughout the paper. The construction of this micro‐slot burner was met by selective laser melting (SLM) process. Flame characteristics such as lift‐off height, length, visible area, maximum width, and neck width are obtained using an image processing algorithm and are examined at different fuel and airflow rates. The results show that the blow‐out limits of methane/air and n‐butane/air flames are almost the same when compared at the same volume flow rates, although the methane/air flames are more stable than n‐butane/air flames at the same thermal input powers. A region of interesting rope‐like oscillatory flames (that has never been seen before in conventional burners) is observed in a small portion of a stable region for n‐butane with a period ranging from 75.0 to 210.0 ms. It is also observed that the fuel type and fuel and airflow rates affect the flame shape and appearance and the flames formed by heavier fuel (n‐butane) have longer length, lift‐off height, maximum width, and visible area and lower neck width. Furthermore, methane/air flames exhibit lower values of CO and higher values of NO _x in the flue gas when compared to n‐butane/air flames.