Fuel reactivity controlled self-starting and propulsion performance of a scramjet: A model investigation

Abstract

The performance of a scramjet engine relies heavily on the combustion characteristics of fuel. This work aims to propose a concept of controlling the self-starting characteristics and propulsion performance of a scramjet via fuel reactivity modification. The fuel reactivity was modified by adjusting the activation energy of each elementary reaction. The thermodynamic analysis was then systemically performed to evaluate the effects of fuel reactivity on the lowest flight Mach number required for self-starting and the specific thrust. The results indicate that the lowest flight Mach number for self-starting of a hydrogen-fueled scramjet reduces from 6.2 to 5.1 when the activation energy is decreased by 50%. Under a given flight condition, fuel reactivity has a remarkable influence on the characteristic ignition length, which affects the specific thrust, especially at low flight Mach numbers. It is demonstrated that there exists an optimal reaction rate to achieve the maximum specific thrust, rather than increase the reaction rate infinitely. The optimal reaction rate relates to the supersonic flow condition, the exothermic heat of fuel, and the wall friction. The results obtained in this investigation provide a theoretical basis for the design of high-reactivity supersonic combustion fuel and further research of advanced scramjet engine operation.