Experimental investigations on a new active swirl based microcombustor for an integrated micro-reformer system

In this paper, a new active swirl based concept has been proposed to enhance the flame stability limits in backward facing step microcombustors with premixed methane–air mixtures. A two step backward facing microcombustor with an inlet diameter of 2 mm along with 4 mm for first step and 6 mm diameter for second step is considered and the performance of various active and passive swirl generation techniques has been investigated and compared. For passive swirl techniques, such as strip and wire swirlers, the upper flame stability limits are enhanced as compared to the no swirl case. However, for active swirl case, when precisely controlled secondary flow is used for swirl generation, both upper and lower flame stability limits are significantly enhanced. For instance, the upper flame stability limits are enhanced by 54% and lower flame stability limits are enhanced by 17% at a mixture equivalence ratio of ϕ = 0.6 with active swirl flow. A stable flame has been observed to exist for a wide range of mixtures with equivalence ratio varying from 0.6 to 1.3 and flow rates varying from 98 to 1270 SCCM (equivalent thermal input 4.58–91.66 W). A minimum thermal input of 4.58 W with a heat release density of about 9.75 MW/m3 was observed in the present experiments.

► An active swirl based technique to enhance flame stability limits in backward facing step microcombustors is presented.
► Upper and lower flame stability limits are significantly enhanced through active control of secondary swirl flow injection.
► The secondary flow affects the flame position in the microcombustor.
► Wall temperature profiles are more uniform than no swirl case.