Distributed measurement of isobaric specific heat capacities for endothermic hydrocarbon fuels

Active cooling with endothermic hydrocarbon fuels (EHFs) represents an effective solution to the thermal management problem of a hypersonic aircraft. The isobaric specific heat capacity for EHFs is one of important parameters for designing advanced thermal management systems. Nevertheless, the accurate measurement of the isobaric specific heat capacity presents significant challenges, due to the lack of measurement resolution, the change of fuel compositions resulting from thermochemical reactions and the discrepancy of the energy conservation calculations. To address the aforementioned challenges, this work develops a new distributed flow calorimeter, where the calorimetric microchannel (Φ3.0 × 0.5, 1000.0 mm) is divided into 2200 microelements by infrared thermography with a resolution of 0.45 mm. The mapping relationship of position-temperature-composition for EHFs can then be determined along the microchannel on the basis of the axial difference approach. The credibility analysis on measurements of isobaric specific heat capacity data is carried out by using water, p-xylene as the standard materials with the average absolute deviations of 0.65 % and 1.28 %, and the maximum absolute deviations of 1.32 % and 2.44 %, respectively. The distributed flow calorimeter can be employed for the measurements of the isobaric specific heat capacity and its axial distribution along the calorimetric microchannel in real time at temperatures from 298.0 to 1173.0 K and at pressures from 0.1 to 6.0 MPa. The isobaric specific heat capacities for toluene, decalin and JP-10, a typical high-density hydrocarbon fuel, have been systematically measured with the expanded uncertainty of 2.85 %. It is fully substantiated that the distributed flow calorimetric method can successfully extend the thermodynamic measurements from equilibrium state to steady state with significant temperature gradient.