Ignition Delay in Solid-Fuel Ramjet Combustor

Abstract

The ignition delay requirement and ignition characteristics of a solid fuel in the ramjet combustor were investigated. The shock in a simple diffuser geometry was calculated to obtain the upper limit of ignition delay, and it was determined to be shorter than 1 s. To achieve this short ignition delay, a high-density polyethylene (HDPE) fuel grain coated with an ignition support material and a fuel-rich propellant (FRP) were prepared. The ignition support materials were nitrocellulose with boron potassium nitrate () and an ammonium perchlorate (AP)/hydroxyl-terminated polybutadiene (HTPB)-based composite propellant. For testing purposes, a compact gas generator was built to simulate the conditions in the ramjet combustor. The simulation results revealed that the ignition support material showed the shortest ignition delay of 1.27 s, but the flame in this case was not sufficient to ignite the HDPE. In a demonstration test, an ignition support material composed of and the AP/HTPB-based composite propellant was applied to the FRP fuel grain, in which case a stably sustained flame was obtained. The test results demonstrated that ignition of the FRP and that of the ignition support material occurred simultaneously with an ignition delay of 1.74 s.