Pyrolysis and coking of endothermic hydrocarbon fuel in regenerative cooling channel under different pressures

- Pressure effect on pyrolysis and coking of endothermic hydrocarbon fuel is studied.
- Higher pressure promotes pyrolysis by increasing density and bimolecular reaction.
- Reaction pathway under higher pressure approaches towards F-S-S mechanism.
- Higher pressure promotes the formation of amorphous coke.

Endothermic hydrocarbon fuel (EHF) is an ideal on-board coolant for the thermal management of the advanced aircrafts. To get more insights into controllable release of its heat sink in the regenerative cooling channels, the effect of pressure on the pyrolysis and coking of EHF in the temperature range of 500-750 °C was experimentally studied using electrically heated tube reactor under different pressures (0.7-6.0 MPa). At the constant feeding flow rate, the conversion for EHF pyrolysis under 6.0 MPa was 3.3-5.7 times that under 0.7 MPa in the temperature range of 650-720 °C, resulting from longer residence time and enhanced pyrolysis rate by the bimolecular reactions. The selectivity of hydrogen, methane and ethane increased as a function of conversion under elevated pressures, whereas the selectivity of ethylene and propylene decreased. The reaction pathway under elevated pressure approaches towards Fabuss-Smith-Satterfield mechanism where the bimolecular hydrogen abstraction reaction is dominant over the unimolecular β-scission under high substrate concentration. The elevated pressure promoted the coke deposition, mainly in amorphous coke with an increase by 4.4 times from 0.7 to 3.5 MPa due to high concentration of aromatics. The further formation of catalytic filamentous coke was inhibited by increasing amorphous coke indirectly under high pressure. When the pressure elevated to 6.0 MPa the coke rate was too high to complete the 30 min stability test.