Oxidizer Mass Flow Rate Research Articles

Passive flow control in liquid-propellant rocket engines with cavitating venturi

In a companion liquid rocket engine development project, due to the overall weight constraint of the propulsion system, a cavitating venturi is selected to control the liquid fuel and liquid oxidizer mass flow rates. Two cavitating venturis, one for the fuel and the other for the oxidizer, are designed to deliver the desired mass flow rates for a specified operating inlet pressure, temperature, and inlet cross-sectional area. The converging and diverging angles of the venturis are selected from the literature for minimum pressure losses. An experimental setup is designed to verify that the cavitating venturis can deliver the specified flow rates. Two different techniques are used to pressurize the system: in the first method, pressurized nitrogen gas is used, and in the second method, high pressure combustion gases generated from a solid propellant gas generator are used. Transient mass flow rates could not be measured using standard methods due to the short duration of the water tests; instead, average mass flow rates are calculated. The results verify that the designed cavitating venturis can indeed provide the desired mass flow rates.

Potential Usage of Energetic Nano-sized Powders for Combustion and Rocket Propulsion

ABSTRACTNano-sized energetic metals and boron particles (with dimensions less than 100 nanometers) possess desirable combustion characteristics such as high heats of combustion and fast energy release rates. Because of their capability to enhance performance, various metals have been introduced in solid propellant formulations, gel propellants, and solid fuels. There are many advantages of incorporating nano-sized materials into fuels and propellants, such as: 1) shortened ignition delay; 2) shortened burn times, resulting in more complete combustion in volume-limited propulsion systems; 3) enhanced heat-transfer rates from higher specific surface area; 4) greater flexibility in designing new energetic fuel/propellants with desirable physical properties; 5) nano-particles can act as a gelling agent to replace inert or low-energy gellants; 6) nano-sized particles can also be dispersed into high-temperature zone for direct oxidation reaction and rapid energy release, and 7) enhanced propulsive performance with increased density impulse. In view of these advantages, numerous techniques have been developed for synthesizing nano-particles of different sizes and shapes. To reduce any possible hazards associated with the handling of nano-sized particles as well as unwanted particle oxidation, various passivation procedures have been developed. Some of these coating materials could enhance the ignition and combustion behavior, others could increase the compatibility of the particles with the surrounding material. Many researchers have been actively engaged in the characterization of the ignition and combustion behavior of nano-sized particles as well as the assessment of performance enhancement of propellants and fuels containing energetic nano-particles. For example, solid fuels could contain a significant percentage of nano-sized particles to increase the mass-burning rate in hybrid rocket motors, the regression rate of solid propellants can be increased by several times when nano-sized particles are incorporated into the formulation. Specifically, hybrid motor data showed that the addition of 13% energetic aluminum powders can increase the linear regression rate of solid HTPB-based fuel by 123% in comparison to the non-aluminized HTPB fuel at a moderate gaseous oxidizer mass flow rate. Strand burner studies of two identical solid propellant formulations (one with 18% regular aluminum powder and the other with 9% aluminum replaced by Alex® powder) showed that nano-sized particles can increase the linear burning rate of solid propellants by 100%. In addition to solid fuels and propellants, spray combustion of bipropellants has been conducted using gel propellants impregnated with nano-sized boron particles as the fuel in a rocket engine. High combustion efficiencies were obtained from burning nano-sized boron particles contained in a non-toxic liquid-fuel spray. Materials characterization such as chemical analyses to determine the active aluminum content, density measurements, and imaging using an electron microscope have been performed on both neat nano-sized particles and mixtures containing the energetic materials. In general, using energetic nano-sized particles as a new design parameter, propulsion performance of future propellants and fuels can be greatly enhanced.

Analysis and testing of similarity and scale effects in hybrid rocket motors

In order to derive proper scaling rules in hybrid rocket motors, a theoretical similarity analysis is presented. By taking account of the main phenomena and effects, the similarity analysis defines the following three main conditions for testing a laboratory-scale hybrid rocket motor that can simulate a full-scale motor: (1) geometric similarity, (2) same fuel and oxidizer combination, and (3) scaling mass flow rate of oxidizer in proportion to the motor port diameter. To verify the analysis, tests are conducted on different-size polymethylmethacrylate/gaseous oxygen hybrid rocket motors. These motors are scaled as per the similarity analysis and tested under similarity conditions. A fairly good agreement between the test-results and theoretical prediction verifies the similarity model. This also points out that the main processes and effects associated with hybrid rocket combustion have been considered adequately in the analysis.