One axial fuel injected vortex-tube combustor with high capacity of combustion stabilization for NO_x reduction

A novel vortex-tube combustor with axial fuel injection for NO_x reduction was proposed to overcome the instability of ultra-lean combustion. The stability limit, flame configuration, NO_x and CO emissions, and flame structure were investigated experimentally under various global equivalence ratios and fuel flow rates. The mechanisms of NO_x emission reduction were analyzed by numerical simulation. Results show that the limit of global equivalence ratio can be as low as 0.01 and the amplitude of pressure fluctuation is always less than 1300 Pa, indicating fairly good performance in combustion stabilization of the combustor. In the operation range, there is a trade-off region with low NO_x and CO simultaneously. The diffusion-like flame structure in this combustor can enhance the local equivalence ratio, whilst the flow field structure can also promote the transport of chemical enthalpy to the flame front, thus facilitating the stabilization. The enhanced stabilization enables the ultra-lean combustion and the ensued small area of the high-temperature zone to conduct, as well as the low NO_x formation through reducing thermal NO. The local fuel-rich region and the flow field structure can promote the NO_x to be reduced further via the Fenimore mechanism.