Steam-Assisted Cracking of n-Dodecane in a Packed-Bed Reactor for Hypersonic Thermal Management

Abstract

Heat removal capacity of catalytically cracked supercritical n-dodecane as a jet fuel analogue in a cylindrical packed-bed reactor is examined. Fuel cracking is endothermic, and can be used in designing a potential hypersonic vehicle thermal management system. In this work, n-dodecane endotherm and product distributions were examined using a platinum catalyst on a ceramic support matrix. Although many previous fuel studies have used catalyst coated tubes, this study made use of a solid catalyst structure in a packed bed to distribute the catalyst throughout the fuel flow in order to provide more surface catalyst sites. The packed- bed reactor was treated as an ideal plug flow reactor, which assumes catalytic reactions that are radially uniform across the reactor diameter. Additionally, water was added to study its mitigation effect on coke formation and deposition on the reactor catalyst. Many previous jet fuel studies have either used a catalyst to aid in endothermic thermal management or have focused on water addition to reduce coke formation. This study combines these approaches. A catalyst is used to initiate endothermic reactions at lower temperatures than would ordinarily be achieved by thermal cracking alone, in conjunction with steam addition to mitigate coking. The packed-bed catalyst configuration provides catalytic action even as temperatures increase and thermal cracking becomes dominant, thereby enhancing the chemical heat sink. Water addition also provided coking mitigation, although with an associated decrease in dodecane conversion, and, hence, heat sink capability.