Gas Generator-Fed Ramjets Gaining Traction
Innovations in gas generator-fed ramjets are enabling more flexible thrust modulation for variable-mission missiles. The "unchoked gas generator" approach allows for practical throttling, addressing a classic ramjet limitation. Defense primes are increasingly interested in solid-fuel and variable-geometry ramjets for air-to-air and surface-to-air missile systems.
Gas generator-fed ramjets date back to Albert Fonó's 1915 design for increasing artillery range. His concept involved a gun-launched projectile with a ramjet propulsion unit, allowing for long range even with relatively low muzzle velocities. The "unchoked gas generator" allows practical throttling, a significant advantage. Traditional ramjets struggle with thrust modulation, limiting their mission flexibility. This innovation improves fuel-air mixing and overall pressure recovery. Solid-fuel ramjets (SFRJ) offer high energy density and mechanical simplicity, bypassing complex turbomachinery. Unlike liquid systems, SFRJs don't allow direct control over mass flow rate, as heat from combustion drives fuel gasification. NRL is actively working on understanding the combustion dynamics within SFRJs. Variable geometry inlets are being explored to regulate air ingestion and thrust in SFRJs. These inlets minimize actuator hardware and provide a novel control mechanism. Precise control remains a challenge due to complex combustion dynamics and sensitivity to geometric variations. Ramjets operate most efficiently at supersonic speeds, around Mach 3 to Mach 6. They are particularly suited for high-speed applications like missiles, where a compact mechanism is crucial. Weapons designers are exploring ramjet technology to extend the range of artillery shells, with a 120 mm ramjet-assisted mortar shell potentially reaching 35 km. L3Harris is leveraging its solid rocket motor expertise to build advanced ramjets, utilizing 3D printing for rapid and affordable production. They've increased internal investments in ramjet technology by 170% over the past three years.
