Shock-dominated hypersonic laminar flows over a double cone are investigated using time accurate direct simulation Monte Carlo combined with the residuals algorithm for unit Reynolds numbers gradually increasing from 9.35×104 to 3.74×105 m−1 at Mach numbers changing from about 12 to 16 for nitrogen and reacting air cases. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region show a time-dependent behavior. It was observed that the effects of Reynolds number on the structure and extent of the separation region are profound. As the Reynolds number is increased for the LENS-I cases, larger pressure values in the under-expanded jet region due to strong shock interactions form more prominent λ-shocklets in the supersonic region between two contact surfaces. The chemical reactions for higher enthalpies reduce the size of the separation region significantly and good agreement was observed between the DSMC predicted surface heating values and pressures and the measurements. The catalytic reactions increase the surface heating. A good agreement was also observed between the recent CFD1 calculations and DSMC.