The present study investigates the implication of a dual cavity on combustion and mixing characteristics of strut based combustor numerically. A scramjet combustor with and without cavity are considered to evaluate the influence of cavity on combustion characteristics. Moreover, the effect of spacing between the cavities on combustion performance is also discussed. A separate study is carried out to understand the interplay of the Mach number and the spacing between the cavities on combustion characteristics. Our study reveals that the introduction of a dual cavity in scramjet combustor enhances the mixing and improves combustion performance. Further, it is found that the mixing length is lesser and the penetration height is more when a dual cavity is employed in a combustor. It can also be observed that the size of the recirculation region is found to be larger for the combustor with dual cavity among all configurations at the spacing S-2 = 12.7 mm. Further, the combustion efficiency and fuel penetration height are found to be maximum at Mach 2.5 with a spacing S-2 = 12.7 mm. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.