Effect of air supplementation on the performance of an onboard catalytic inerting system

Abstract

In this work, a catalytic inerting process with an external air supplement was proposed. Based on the molar flow rate of the pumped air in the fuel tank, the flow relationship of each gas component after flowing through the catalytic reactor was derived. The mathematical model of the gas concentration variation in the gas phase space of the tank was established by considering the mass conservation equation and gas equilibrium dissolution relationship, and the core fuel tank model was verified using existing experimental data. The performances of the inerting system for aviation fuels, such as JP8, RP3 and RP5, with and without an external air supplement were compared and studied, and the influence of the key parameters on the performance of the system was determined. The results indicated that the presence of an air supplement can accelerate the process of inerting; a higher fuel vapor pressure corresponds to the requirement for a larger air supplement ratio, which means that more inert gas flow is generated by the reaction and the O2 concentration of the tank decreases more rapidly. For example, when the inerting system of RP5 has a catalytic efficiency of 0.8, the O2 concentration in the gas phase of the tank decreases to 9%; the time required for this process without and with the air supplement is 7.55 min and 0.77 min, respectively. Under the same conditions, the highest inerting rate is for RP5, followed RP3 and JP8. In addition, with the air supplement, the inerting time of the RP3 and RP5 fuels is reduced with the increase of the catalytic efficiency. A larger fuel loading rate corresponds to a smaller gas phase space volume and less inerting time. The inerting time is inversely proportional to the fan flow rate, that is, when the flow rate of the fan increases by N times, the inerting time decreases to 1/N times the original value. Therefore, when designing an onboard catalytic inerting system, the inerting performance can be improved by providing an external air supply, and the influence of the key parameters, such as the catalytic performance, fuel loading rate and fan flow, on the system performance should be considered.