Micro-mixing combustion is a kind of potential technology to reduce pollutant emissions

and the microtube structure as a basic unit has significant influence on combustion characteristics. Taking the single microtube model burner as the object

the computational fluid dynamics(CFD) method is employed to analyze methane micro-mixing combustion characteristics with different microtube diameters

rear-section lengths

and chamber-to-tube area ratios

under the air-preheated and pressurized condition and the atmospheric condition. The numerical simulation results show that

the flame length increases obviously under the atmospheric condition

and the increase rate is greatly affected by the microtube diameter and the area ratio. With the increase of microtube diameter

the flow and temperature fields in the flame chamber are similar

and the dimensionless flame length does not change significantly. However

when the microtube diameter is smaller

the change of flame length is smaller between two working conditions

and the flexibility is better. With the increase of microtube rear-section length

the turbulence intensity at the microtube outlet reduces greatly

and the flame length increases obviously

but the change trend of flame length is consistent under two working conditions. With the increase of chamber-to-tube area ratio

the flame length decreases at first and then increases. When the area ratio is 4.0～9.0

the flame length is relatively short

and the combustion performance is relatively good. The results have reference value for the gas turbine combustor

and also have certain reference significance for free jet flame.