To enhance the flame stability of conventional porous burners (CPB)

a porous-free flame burner (PFFB) made of foam nickel metal is designed

and the flame stability limit

flame status

and flame propagation behaviors are experimentally investigated. Additionally

a same size two-dimensional mathematical model is established. The concepts of the fractional hole area

relative height

and specific porosity are introduced. Numerical simulations are conducted to explore the effects of pore parameters on temperature profile

flame status

and flame propagation behaviors. The results show that the fractional hole area and gas velocity are identified as the primary factors affecting the flame front structure. The higher gas velocity at hole area leads to the "hill-like" protrusion of flame front

and the height of this protrusion increases with both gas velocity and fractional hole area. For the PFFB with 4%-hole area

as the specific porosity increases from 15 to 65

the combustion mode turns from the immersed & free flame to the free flame

and the flame height rises from 125 mm to 162 mm. The flame stability is enhanced when the fractional hole area is controlled at 1%

the relative height is between 1/3 and 1/2

and the specific porosity is between 15 and 45. The nickel foam porous medium material with a central hole can achieve stable combustion at a lower equivalence ratio.