Carbonaceous Deposits in a Fuel-Film Cooled Rocket Combustor: Electron Microscopy

Abstract

The high gas–side heat transfer coefficients expected in high-pressure oxygen-rich staged combustion kerosene–oxygen engines require fuel–film cooling in parallel with regenerative cooling to keep metal wall temperatures at acceptable levels. In such engines, the fuel–film transitions from a liquid to supercritical state, leaving behind dense and soot layers of carbonaceous deposits. We used a 4.8 MPa kerosene– fuel–film cooled combustor with removable chamber liner samples for posttest analysis of carbonaceous deposits. Dense layer deposit depths were measured in cross-sectioned samples with a dual-beam scanning electron microscope. The varying fuel–film flow rate did not affect deposit depths in the near field. However, higher film flow rates resulted in longer regions of carbonaceous deposits in the far field. The dense and soot layers were hypothesized to be formed by heterogeneous condensation of polycyclic aromatic hydrocarbons and thermophoretic diffusion of soot, respectively.