A Comparison of the Performance of Hydrocarbon Fuels in a Uni-Element Combustor

Abstract : Hydrocarbon fuels are being considered for many boost applications due to their higher energy densities compared with hydrogen. RP-1 has been the standard hydrocarbon fuel for the past several decades. However, there is a wide variety of potential hydrocarbon molecules ranging from the common to the exotic that also could be used as fuels. These compounds have potentially higher energy content compared to RP-1, which could lead to engine performance gains. AFRL/PRS has undertaken the task of examining the potential capabilities of a wide range of these hydrocarbon molecules to determine their overall performance as a rocket fuel. In this paper, the authors discuss the initial stages of combustion performance testing of these potential new fuels. The initial sets of fuels that are being characterized include several common hydrocarbon propellants, such as RP-1, JP-7, JP-8, JP-10, and Butane in a sub-scale, uni-element combustor. To ascertain differences between injectors, several injector styles were tested with these fuels and the results were examined to determine the test conditions necessary for making the most accurate assessment. Initial results indicate that this first set of fuels behave as expected. C* efficiency was relatively high, typically exceeding 95%. The variation between fuels (with the same injector) also was relatively low, indicating that the injector and chamber design used are suitable for performance testing with a wide variety of fuels. The present study has established a consistent baseline and shown that the results from this combustion chamber are highly repeatable. It should be noted that fuel performance is just one area that needs to be studied for these high performing molecules to become useful as rocket fuels. In conjunction with the combustion performance testing, efforts are underway to examine other properties, such as regenerative cooling capability, coking and corrosion behavior, and lubricity. (7 figures, 4 refs.)