טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKomornik Sardas Daniel
SubjectStudy of a Ducted Rocket with a Hybrid Gas Generator
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Alon Gany


Abstract


Supersonic propulsion systems can be divided into rockets and ramjets (air-breathing engines). Ramjets have higher specific impulse and energetic performance. The ducted rocket, also known as ram-rocket, is a type of a ramjet engine, carrying a small amount of oxidizer. It consists of two combustion chambers: a gas generator, where fuel is burned with a small amount of oxidizer to generate fuel-rich combustion gases; and a ram combustor where the hot gases from the gas generator are introduced and burned further with ambient air coming through inlets. Conventional ducted rocket uses a fuel-rich solid propellant as the gas generator.


Our innovative idea introduces a hybrid combustor as the gas generator. This novel arrangement enables an easier way to control fuel supply rate from the gas generator to the ram combustor. Experiments were conducted with a gas generator employing paraffin wax as the fuel, because of its high regression rate, and gaseous oxygen as the oxidizer due to its good performance and ease of operation at laboratory conditions. An analysis of storable oxidizers (e.g., nitrous oxide or hydrogen peroxide) is included as well. Tests revealed gas generator operation at oxidizer/fuel (O/F) ratios as low as 0.10 (vs. stoichiometric ratio of 3.4). Solid propellant-based gas generators operate at significantly higher O/F ratios.


Internal ballistics and thermochemical models were developed on Matlab using CEA thermochemical software. These models enabled prediction of the fuel flow rate over time and its control capability, the amount of available fuel for ram-combustion, and the performance of the ducted rocket.


Over 150 successful static firing tests have been performed using a connected pipe facility supplying vitiated air to the ram combustor at stagnation temperature and pressure encountered in actual flights. Empirical correlation of the fuel regression rate versus oxidizer mass flux in the gas generator has been displayed, and good overall combustion efficiency has been revealed. Thrust and fuel/air ratio control via the cold oxidizer flow rate into the gas generator is a major advantage of the hybrid gas generator. It enables control over broad ranges of flight altitude, Mach number, and thrust, while maintaining the ram pressure throughout the engine. This is in contrast to the thrust control of a ducted rocket employing a fuel-rich solid propellant. The latter involves variation of the gas generator nozzle throat area by a mechanical device within the hot flow, implying a large increase of pressure in the gas generator combustor. Different scenarios of engine control and thrust modulation for variable flight conditions and requirements have been demonstrated.


Computational fluid dynamics (CFD) simulations were performed for some of the conducted experiments to display the distribution of the flow properties within the ram combustor.


The current work has been the first experimental research on a ducted rocket at the Technion. Furthermore, no other experimental and parametric investigation on a ducted rocket employing a hybrid gas generator has been reported in the world professional literature, emphasizing the novelty and original data brought up by this research.