Non-intrusive Flame to Fuel Surface Radiative Heat Flux Diagnostic for Hybrid Rockets 2D Slab Burner using Two-color Pyrometry and Flamelets

In this study a previously developed two-color flamelet manifold (TCFM) diagnostic to non-intrusively measure flame to fuel surface radiative heat flux for the upward flame spread setup is extended to hybrid rocket 2D slab burner. The optical thickness for the flame is accounted for through the use of steady-state 1D diffusion flamelets coupled with a phenomenological two-equation acetylene-based soot formation model. A monotonic relationship is established between the ratio of the red to green intensities of the flame images and the strain rate on the diffusion flames. The flame solution is tabulated into a manifold form using the intensity ratio and the level-set distance from the flame to oxidizer and fuel as the independent variables. A level-set technique is further utilized to define the flame stoichiometric surface on a reconstructed 3D flame hull that distinguishes between the fuel side and the oxidizer side of the flame. Local flame temperatures and soot volume fraction are looked-up from this manifold using the intensity ratios of the flame image and corresponding level-set distance. A previously developed 3D ray-tracing algorithm is used to solve the radiative transfer equation (RTE) and compute the flame to fuel incident radiative heat flux (RHF). The RHF values from the new technique are compared to the previously measured values to study the effects of self-absorption. The spatial RHF measurements helps supports the modeling effort and improving the existing theories of fuel regression rates.