Carbonaceous Deposits in a Fuel-Film-Cooled Rocket Combustor: Optical Profilometry

Abstract

Fuel-film cooling is necessary to mitigate heat transfer in high-pressure oxygen-rich staged combustion engines. A 4.8 MPa (700 psia) axisymmetric kerosene–${\mathrm{H}}_2{\mathrm{O}}_2$ combustor used fuel-film cooling to deposit carbonaceous material on removable metal samples. Posttest inspection of the samples revealed a two-layer structure, with a tenacious dense lower layer and a soot-like upper layer. Total deposit depth was measured using an optical profilometer and was repeatable between tests at the same conditions. Combustor conditions of fuel-film flow rate, bipropellant run time, fuel composition, chamber liner material, and chamber liner surface roughness were varied to determine their effects on total carbonaceous deposit depth as a function of position and time. Increasing the fuel-film flow rate by 40% resulted in similar deposit depths to lower fuel-film flow rates, but for longer axial lengths. Longer run times resulted in thicker deposits. The use of lower thermal conductivity chamber liners resulted in three to four times more deposits.