To better understand Moderate or intense low-oxygen dilution (MILD) combustion, numerical simulations of pulverized coal MILD combustion with different inlet velocities and oxygen concentrations are presented in this work. The flow and chemical reaction characteristics are analyzed and the MILD performance is determined by the Damköhler number, Da, and the circulation coefficient, $K_{\mathrm{\upsilon }}$, with different oxygen concentrations and inlet velocities. Results show that the oxygen concentration has a more pronounced impact on the chemical reaction, and the inlet velocity has a more pronounced impact on the flow time scale. The $K_{\mathrm{\upsilon }}$ values are found increasing with the oxygen concentrations, which is caused by the decreased total amount of flue gas. Modified schematic diagram of combustion regimes is presented based on the analysis. The Da number increases with the increase of oxygen concentration. This is because, on the one hand, the increase in oxygen concentration leads to the decrease in the inlet velocity. On the other hand, the oxygen concentration intensifies the chemical reaction. This indicates that, with the increasing oxygen concentration, the larger $K_{\mathrm{\upsilon }}$ or the smaller Da is required to establish the MILD combustion. If the burner structure is not changed, increasing the oxygen concentration will reduce flue gas entrainment and aggravate chemical reactions, which is not conducive to the MILD coal combustion.

为了更好地理解中度或强烈的低氧稀释（MILD）燃烧，在这项工作中提出了粉煤MILD燃烧在不同入口速度和氧气浓度下的数值模拟。分析了流动和化学反应特性，并通过Damköhler数Da和循环系数确定了MILD性能。${ķ}_{\mathrm{\upsilon }}$，具有不同的氧气浓度和入口速度。结果表明，氧气浓度对化学反应的影响更大，而入口速度对流动时间的影响更大。的${ķ}_{\mathrm{\upsilon }}$发现该值随氧气浓度的增加而增加，这是由于烟道气总量减少所致。在分析的基础上，提出了改进的燃烧方案示意图。该沓数与氧浓度的增加而增加。这是因为，一方面，氧浓度的增加导致入口速度的降低。另一方面，氧浓度加剧了化学反应。这表明随着氧气浓度的增加，${ķ}_{\mathrm{\upsilon }}$或需要较小的Da来建立MILD燃烧。如果不改变燃烧器的结构，增加氧气浓度将减少烟气的夹带并加剧化学反应，这不利于MILD煤的燃烧。