Effect of area ratio and heat release method on the Ma∞ = 2-6 operation performance of rocket-based combined cycle engine

Abstract

Ballistic trajectories with rapidly changing and variable ambient conditions impose higher requirements on integral multi-component rocket-based combined cycle (RBCC) engines. A central strut-based RBCC engine was numerically simulated by solving Reynolds-averaged Navier-Stokes equations together with a k-ω SST turbulence model under various flight conditions, Ma∞=2 to Ma∞=6, which cover ejector, ramjet and scramjet modes. Ground direct-connect tests were carried out to analyze heat release performance in the combustor and the pressure balance relationship between various components. Results indicate that scramjet combustion should be conducted in the foremost combustor where geometry expansion is slightest. As the oncoming velocity decreases, the combustor expansion ratio should be increased and the location of heat addition moves to downstream larger area region. Distributed fuel injection with 20%∼30% upstream is beneficial for increasing the initial temperature of the mixing gas and thus the combustion efficiency under Ma∞3-6 conditions. At lower flight Mach numbers (Ma∞<3), different dual-ramjet engine, a section with larger area ratio, over 2, should be added behind the ramjet combustor. Since off-design inlet operation causes a decrease on the intake mass flow rate, concentrated heat addition should be adopt to ensure effective thermal choking.