Pyrolytic depositions of hydrocarbon aviation fuels in regenerative cooling channels

• Pyrolytic depositions of hydrocarbon fuel in regenerative cooling channel were studied.
• Pyrolytic deposition is a typical CVD-like process in primary stage.
• The initial coking rate rapidly decreases with extension of time-on-stream.
• A kinetic model of pyrolytic deposition of hydrocarbon fuel was developed.

Coke deposition is one of crucial issues to be carefully taken into considerations in developing regenerative cooling technology for next-generation aircrafts. Pyrolytic depositions experiments of n-decane and Chinese No. 3 jet fuel were experimentally performed using electrically heated tubes (Φ2 × 0.5 mm, Φ3 × 0.5 mm) made of nickel-based alloy at different time-on-stream (TOS = 0–20 min), heat flux density (0.33–0.63 MW/m2), and mass flow rate of hydrocarbon fuel (0.60–1.25 g/s). The local concentrations of coke precursors were also determined by changing the length of electrically heated tubes. The initial coking rates increases with the increasing thermal cracking conversions and wall temperatures, but gradually decreases with extension of TOS. Characterization on reactivities and morphologies of cokes indicates that pyrolytic depositions are produced through surface catalysis and lateral growth mechanisms, and that the decreased coking rate is ascribed to gradual surface coverage with cokes. An empirical coking kinetic model has been developed to calculate the rate of coke formation considering the effect of surface coverage, local precursor concentrations, and wall temperature. The developed kinetic model satisfactorily predicted the pyrolytic depositions with an averaged absolute deviation of 10.5% and a maximal deviation less than 20%.