Mitigation of Combustion Instability and NOx Emissions by Microjets in Lean Premixed Flames with Different Swirl Numbers

Swirl combustion serves as a helpful flame stabilization method, which also affects the combustion and emission characteristics. This article experimentally investigated the effects of CO2 microjets on combustion instability and NOx emissions in lean premixed flames with different swirl numbers. The microjets’ control feasibility was examined from three variables of CO2 jet flow rate, thermal power, and swirl angles. Results indicate that microjets can mitigate the combustion instability and NOx emissions in lean premixed burners with different swirl numbers and thermal power. Still, the damping effect of microjets in low swirl intensity is better than that in high swirl intensity. The damping ratio of pressure amplitude can reach the maximum of 98%, and NOx emissions can realize the maximum reduction of 10.1×10−6 at the swirl angle of 30°. Besides, the flame macrostructure switches from an inverted cone shape to a petal shape, and the flame length reduction at low swirl intensity is higher than that of high swirl intensity. This research clarified the control differences of mitigation of combustion instability and NOx emissions by microjets in lean premixed flames with different swirl numbers, contributing to the optimization of microjets control and the construction of high-performance burners.