Characterization of Carbon Deposition in Fuel-Film Cooled Rocket Combustors
Abstract
Carbonaceous deposits can reduce heat flux in fuel-film cooled oxygen-rich staged combustion engines, but the deposition process at these conditions is poorly understood. Modeling requires a better understanding of the mechanisms for deposition and the deposits insulating effect on the chamber wall, the latter of which depends on deposit depth and thermophysical properties. A fuel-film cooled combustor, creatively named the Task 1 combustor, was designed and tested to produce carbonaceous deposit samples which were analyzed for deposit depth, physical/chemical characteristics, and thermophysical properties. Additionally, heat flux was measured via an inverse method that took advantage of the heat sink cooled combustor design. An optical profilometer and scanning electron microscope were used to distinguish between two different deposit layers: a smooth, lacquer-like dense layer and a fluffy, soot-like porous layer. Images of the sample indicated that the porous layer is likely formed via thermophoretic diffusion of soot formed in the fuel-rich gaseous boundary layer. Deposit layer depths were measured as a function of axial distance from the fuel-film injector at varying conditions, including fuel-film mass flow rate, bipropellant run time, chamber liner material (thus changing wall temperature), fuel composition, and metal surface roughness. Gas chromatography mass spectrometry, Raman spectroscopy, and x-ray photoelectron spectroscopy were used to characterize the chemical structure of the two deposit layers. All three analysis methods revealed evidence that the dense layer is likely formed by heterogeneous condensation of heavy polycyclic aromatic hydrocarbons (PAHs) on the cool chamber wall.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 2020
- Accession Number
- AD1192443
Entities
People
- Philip Piper
Organizations
- Air Force Research Laboratory