The Ramjet engine is a simple air-breathing device without any moving parts such as compressors or turbines. The basic idea behind ramjet propulsion is aerodynamic compression of air, making it suitable for supersonic flight speed. At Mach numbers of 2-4, the ramjet is highly efficient and has superiority over other types of engines.
The solid fuel ramjet (SFRJ) is the simplest type of a ramjet engine and it is characterized by increased energy density, simplicity, relatively low cost and safety. The solid fuel combustor is made of a hollow cylinder of fuel, where air flows through its port and combustion takes place between the gasifying fuel surface and the bulk airflow. A diffusive flame is established within the boundary layer over the solid fuel surface.
Metal additives to the commonly used hydrocarbon fuels can provide better energetic performance, especially for volume-limited systems. Boron exhibits remarkable theoretical energetic performance (40% more than hydrocarbons) with the highest energy density of all elements, about three times of hydrocarbon fuels. In order to realize these advantages, the boron particles must ignite and combust completely within a limited time residence. However, this is difficult since boron particles are initially coated with an oxide layer, which inhibits combustion.
The present study focuses on modeling the combustion of the hydrocarbon solid fuel with boron particles.
A 2-D axisymmetric model of a ramjet combustor, at Mach 2.5 was solved numerically utilizing the ANSYS FLUENT computational fluid dynamics (CFD) code. A series of simulations were performed for various parameters such as flight altitude, fuel port diameter, bypass ratio, boron content and boron particle diameter. The sensitivity of the SFRJ flowfield and the performance on the various parameters was studied. The results show a strong dependence of the engine performance on particle initial diameter and after-burner length.
