Air-breathing engines as ramjets, scramjets, turbojets, and turbofans have higher specific impulse and energetic performance and, hence, longer range for the same amount of fuel than rockets. Ramjets operate at high Mach numbers, typically within the rocket flight speed range of Mach 2-5, beyond the efficient operating flight speeds of turbojet engines. The ducted rocket (ram-rocket) is one of the types of ramjet engines, which may be considered for different missiles (e.g., long range air to air missiles or supersonic cruise missiles). It consists of two combustion chambers: a gas generator chamber where fuel is burned with a small amount of oxidizer (a fuel-rich propellant combination) to generate fuel-rich gases; and a ram combustor where the gases generated in the first chamber are introduced and burned further with ambient air coming through inlets.
This study presents a ducted rocket (DR) using a hybrid gas generator. Such a novel arrangement may exhibit improved safety (due to the separation of fuel and oxidizer), availability, better performance, controllability, and a possible operation with a lower content of oxidizer in the gas generator. The present study simulates flight at Mach 2.5 at an altitude of 3 km. Over 150 successful static firing tests of a ducted rocket with a hybrid gas generator have been performed. These tests took place in a connected pipe facility, simulating multiple ramjet inlet and gas generator conditions. Characteristic velocity efficiency was between 0.8 and 1. Fuel regression rate at the gas generator is displayed. Based on the test performed, it is demonstrated that thrust and fuel-to-air ratio can be controlled via modulating the cold oxidizer flow rate over a broad range of missions and flight conditions. This cold flow control is one of the major advantages of using a hybrid gas generator for a ducted rocket.
