2-D analytical study of employment of thermal barrier coatings to evaluate the performance of actively cooled panels for air breathing engines

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Hypersonic vehicles operate at high flight Mach numbers exposing the airframe and engine structures to high heat loads which are quite severe in the combustor part of the high-speed air breathing engine. In order to withstand high heat loads experienced in the combustor region of the engine during hypersonic flight, actively cooled panels are employed. Herein, a fuel before being injected into the combustor serves as a coolant and is made to flow through the combustor heat exchanger panels such that the material and coolant temperatures are maintained below their critical limits. A few of the candidate materials considered for the active panels of the engine are Nb alloy Cb 752, Ni alloy Inconel X-750, and CSiC. To enhance the heat withstanding capacity of these materials, low thermal conductivity thermal barrier coatings (TBC) are employed. Currently Yttria-Stabilized Zirconia (YSZ) material and ceramic materials are being used as popular TBC materials because of their very low thermal conductivity and high phase stability. In this analytical study, thermal properties of air-plasma-sprayed zirconia based lanthanum zirconate (La2Zr2O7) – LZ- coatings were employed in the investigations. Lanthanum-cerium oxide (La2Ce2O7) –LC- is considered as a new candidate material for TBCs because of its low thermal conductivity and high phase stability. With the use of La2Ce2O7 and La2Zr2O7 as TBC materials, the difference in the weight of the active panel material and the heat gained by the fuel are nearly identical as compared to active panel material coated with YSZ TBC. Results showed that the effect of TBC thickness on the weight of the optimised actively cooled panel is negligible, because of very small TBC layer thickness ranging from 0.5 to 3.0 mm and nearly identical thermal properties of the TBC’s. Results showed that Inconel X-750 is capable of sustaining high heat transfer coefficients with fuel/coolant heat gain well below fuel coking temperature with moderate weight to area ratio.