Numerical simulation on thermal decomposition of n-dodecane using CFD with reaction model

A thermal protection makes one of the biggest technical concerns for a reusable hypersonic flight vehicle. A regenerative cooling using fuel should be promising candidate to clear this problem. In general, a liquid hydrocarbon fuel has worse cooling capability than cryogenic fuel like liquid hydrogen. If the thermal decomposition can be utilized, the cooling ability of the liquid hydrocarbon fuel must be improved. To develop the hypersonic flight vehicle with regenerative cooler, the model predicting its endothermic performance is required. The present study tried to simulate the thermal decomposition of the n-dodecane using Computational Fluid Dynamics (CFD) with chemical reaction models. The n-dodecane is the surrogate material of the kerosine- type jet fuel in academical use. First, fuel-heating tests were performed, to collect the reference data of the thermal decomposition characteristics of the n-dodecane sample fluid, for the numerical simulation. New chemical reaction models were developed by modifying and integrating the existing models. Comparing the results between experiment and reaction calculation showed the necessity to consider the spatial distribution of the physical quantities. To do so, the developed reaction models were combined with two-dimensional CFD. The numerical simulation was conducted to reproduce the reference experiments. The developed model accurately predicts the experimental temperature condition and some mole fractions of the n-dodecane thermal decomposition products. The conversion rate and heat absorption quantity given by the thermal decomposition, on the other hand, were underestimated by the simulation. The prediction errors should be coming from the approximation of the physical properties. The n-dodecane and its thermal decomposition products took the supercritical state in the experiment, but their physical quantities were approximated by the ideal gas values in the simulation. Thus, in conclusion, the numerical simulation approximately and/or partially considering supercritical state should be conducted for the future work.