Thermal Cracking And Coking Of Endothermic Hydrocarbon Fuel In Regenerative Cooling Channels With Different Geometric Structures

The application of Endothermic Hydrocarbon Fuels(EHFs)to active cooling of scramjet engine has drawn much attention along with the advancement of hypersonic propulsion technology.A thorough investigation into characteristics of thermal cracking and coking of EHFs is of importance to the design of channel geometry and evaluations of fuel properties.The circular channel is commonly encountered in research though a quadratic structure is more favored in practice.The difference in geometric structure may cause difference in thermal cracking and coking behavior of EHFs,however,papers are seldom reported.In our work,thermal cracking and coking experiments were conducted on three types of channel geometries combined with CFD simulations to better explain the effects of channel geometric structure on thermal cracking and coking behavior.Thermal cracking experiments were undertaken in rectangular,square,and circular channels and temperature and velocity distributions in the outlet cross section were simulated.It is found that fluid temperature is higher and velocity is slower in the near boundary layer of quadratic channels than that of the circular channel.In result,higher pyrolysis conversion is reached(a gap of 17.2% at 4g/s of inlet flow rate and 700 °C of outlet temperature)and correspondingly difference in selectivities to methane and certain primary products are also found.Coking experiments were also conducted in three channels and mass distributions of products were simulated.It is found that production of coke precursors are more favored in quadratic channels than circular channel.Based on the fluid temperature and velocity distribution conditions,the amount of coke is more in quadratic channels than that in circular channel,especially 67% at the corners of rectangular channel more than that at circular channel.Through carrying out thermal cracking and coking experiments in multi-channel panels with different higher aspect ratio,higher thermal cracking conversion was found in larger aspect ratio panel.Many of the experimental parameters indicate that non-uniformity of fluid distribution may lead to block of some channels,and thermal racking and non-uniformity of fluid distribution promotes each other accelerating the process of coke formation.