Evaluation of Thermal Oxidative Stability of Sustainable Aviation Fuels Using a Novel Thermal Stability Measurement Method

Abstract

In aviation industry, fuel is used as both propellant and coolant. Because the fuel is used as coolant, it is exposed to thermally stressed. This thermal stress leads to occur thermal oxidative reactions at some temperature levels (150 – 350°C). However, all fuels have different thermal oxidative stability depends on their fuel physical and chemical properties. Thermal oxidative stability can be basically identified as the resistance of autoxidation of fuel. The aim of this study is to develop a new test method and test range of alternative fuels in it, for generation of knowledge in the area of thermal stability of alternative fuels. In order to measure thermal stability of aviation fuels, a novel thermal stability measurement method has been developed in this study. After considering and setting a novel test rig up, experiments have been conducted for some fuels, such as diesel fuel, two Jet A fuels from different manufacturers, Jet Propellant - 5 (JP-5), Jet Propellant - 8 (JP-8) and some sustainable aviation fuels (SAFs), such as HEFA-SPK (Hydro-processed esters and fatty acids)-(Synthetic paraffinic kerosene), Alcohol-to-Jet (ATJ), Biojet and Gevo jet blend fuels. Diesel fuel has been used in this study mostly to analyze if this new measurement method has been working properly. Jet A fuel is also most common used in commercial aviation industry; so, it is a good reference fuel to compare the results of sustainable fuels with. SAFs have a great deal of potential to be used in aviation industry for the future due to their environmentally friendly properties. Unlike other fuels, JP-5 and JP-8 are mostly employed in military aircrafts. Throughout the experimental period, these fuels have been heated to get exposed to thermally stressed, and dissolved oxygen (DO) sensors have been run to analyze oxygen (O2) content inside of each thermally stressed fuel. By measuring the O2 content inside of fuel, fuel break point has been measured. Fuel break point is determined where the thermal oxidative reactions begin. At the end of this study, all results of fuel break points and O2 consumptions of fuels during the thermal oxidative reactions have been compared, and it has found that HEFA-SPK has higher fuel break point than ones of other fuels, while one of Jet A, JP-8, and F-T/ATJ have the lowest one. This study shows that different fuels have different decomposition rate, and trend of fuel break point and oxygen consumption rate of tested fuels has been provided in this study.