Solid Propellant Gas Generator Research Articles

Prediction of Burning Characteristics of Dihydroxyglyoxime Composite Propellant

An optimized engine start procedure is critical to the successful operation of a liquid rocket engine in launch vehicles. A solid propellant gas generator is widely adopted for the turbine starter during engine startup, and ammonium nitrate and ammonium perchlorate propellants are conventionally used for this purpose. However, these propellants have shortcomings such as high flame temperature, corrosive combustion residues, and low ignitability. In this study, a dihydroxyglyoxime (DHG)-based propellant was applied to turbine starters. The burning rate, characteristic velocity, and combustion temperature of the DHG propellant were evaluated using motor tests. The DHG-based propellant burned 3–11% slower in motor firing tests than that in strand burner tests, and an inversely proportional relationship was observed between the strand burn rate and the burning rate factor (ratio between motor burning rate measurement and strand burner prediction). The temperature sensitivity of the burning rate factor was found to be 0.23–0.24%/°C, and the pressure sensitivity of the characteristic velocity was 0.48–0.50%/MPa. These burning characteristics of the DHG-based propellant from static evaluations provide the evolution of the chamber pressure and the mass flow rate versus the time of the motor using internal ballistic analysis.

Thermodynamic aspects of solid propellant gas generator for aircraft application

Thermodynamic aspects of solid propellant gas generator for aircraft application

АНАЛИЗ ТРЕБОВАНИЙ К ТВЕРДОТОПЛИВНЫМ ГАЗОГЕНЕРАТОРАМ ДЛЯ СИСТЕМ ПОДАЧИ ПОРОШКООБРАЗНОГО ТОПЛИВА РЕАКТИВНЫХ ДВИГАТЕЛЕЙ

The existing sources of the operating fluid used in aviation and rocket-space technology are analyzed. The disadvantages of inert gas cylinders used as a source of the operating fluid of the component supply system in jet engines are considered. An alternative to the gas pressure system is a low temperature solid propellant gas generator (LTGG) with a coolant. Controllable powdery components supply scheme of an air-breathing engine (ramjet) is proposed. The principle of operation of such a feeding scheme is described. To ensure the stability of the output characteristics of the LTGG, a valve system is used. The requirements for the gas source and combustion products (CP) involved in the operating process have been determined. The analysis of the existing methods of cooling the CP is carried out. It was revealed that the low-temperature solid-propellant gas generator with a powdery capacitance coolant meets the most fully the above requirements, the principle of operation, which is based on the heat transfer wave localization effect. Solid propellant with the following composition: 38 % AP + 38 % Octogen + 24 % SKI-NL is selected. The CP temperature, at a pressure in the combustion chamber of 6 MPa, is 1545 K, and the CP gas constant is 459.4 J / kg·K, the condensed phase is absent, and the water vapor content in the operating fluid does not exceed 1.6 %. The combustion of the proposed propellant produces a significant amount of combustible components – 60 % CO, 4 % H2, > 1 % CH4. The use of valves on cold gas ensures the reliability of the controlled supply system of powder components, and, accordingly, the entire engine. Based on the results of the work, conclusions were made about the correspondence of the obtained parameters of solid propellant and LTGG to all the requirements set.

ИССЛЕДОВАНИЕ ТЕМПЕРАТУРНОГО СОСТОЯНИЯ ГАЗОГЕНЕРАТОРА ТВЕРДОГО ТОПЛИВА ПРИ СТЕНДОВОМ ИСПЫТАНИИ МЕТОДОМ ТЕПЛОВИЗИОННОЙ СЪЕМКИ

In this article, the authors described in detail the methodology for conducting fire bench tests for the reusable experimental design of a solid propellant (SP) gas generator, specially designed to study the complex laws of heat and mass transfer under conditions of unsteady combustion of SP during operation of the installation and in the after-treatment mode. The developed technique allows us to study the nonlinear dynamics of temperature field changes, fuel and generator gas consumption, as well as its composition. The paper presents the chronology of the research, describes the used measuring equipment. Based on the carried out thermodynamic analysis of working processes in the combustion chamber of the gas generator under study, an algorithm for the optimal determination of its operating characteristics is proposed. The methodology of experimental studies of the thermal state of the design of the TT gas generator is universal and can be successfully used in working out other gas generating solid fuels with various energy characteristics during the optimal design of special technical systems such as solid propellant rocket motors (the approbation of the methodology is given on the example of an experimental design with a rotating nozzle), emergency rescue systems and aircraft engines. The results of studies of the thermal state of the elements of the TT gas generator by thermal imaging are well verified with the readings of temperature field sensors.

Differential Model and Evaluation of the Formal Kinetic Law in the Analysis of Combustion in a Solid-Propellant Gas Generator

This paper presents an approach to the generalization of the features of solid propellant combustion in gas generators of propulsion systems based on a one-dimensional differential model. The heat release rate function represented by mutually orthogonal Laguerre polynomials in the differential model is identified by solving the inverse problem of combustion theory and using measured gas parameters in the gas generator. This makes it possible to establish the relationship between the solid propellant combustion features and the gas generator operating modes and formulate boundary conditions for numerical investigation of the solid propellant gas generator.

Differential Model and Evaluation of the Formal Kinetic Law in the Analysis of Combustion in a Solid-Propellant Gas Generator

Differential Model and Evaluation of the Formal Kinetic Law in the Analysis of Combustion in a Solid-Propellant Gas Generator

Study of a hybrid gas generator for a ducted rocket

A performance analysis and experimental study of a hybrid gas generator to be used in a ducted rocket are presented. Such a system exhibits potential advantages with regard to safety, performance, costs, availability of the fuel components, storability, and thrust control. A combination of a paraffin wax fuel and oxygen in the gas generator ensures a high regression rate and reveals oxidizer-to-fuel ratios as low as 0.14 in the gas generator (compared to the stoichiometric ratio of 3.4). A fuel regression rate correlation versus the oxidizer mass flux is derived, presenting a major advantage for the fuel flow rate management in comparison to control of the solid propellant gas generator burning rate through the pressure exponent, which requires mechanical interference with the hot nozzle flow to ensure a change in the combustor pressure and a corresponding change in the burning rate. Evaluation of the ducted rocket (with different oxidizers) versus pure ramjet performance shows a higher specific thrust for the former, though the latter exhibits a higher specific impulse.

Improved combustion model of boron particles for ducted rocket combustion chambers

A combustion model of boron particles for detailed Computational Fluid Dynamics (CFD) based simulations of ducted rocket combustion chambers is studied. It is aimed to construct a model for combustion of boron containing gas mixtures ejected from a solid propellant gas generator. This model includes all main physical processes required to define an accurate particle combustion simulation. The reaction rate modeling in similar, previous studies are improved for ramjet combustion chambers and this model provides better predictions for all particle sizes. The reactions in the ignition stage are reformulated as competing reactions for consumption of (BO)n polymers. Large discrepancies between the experimental and calculated ignition times for the 3 μm diameter particles in similar studies are eliminated. The developed model is added to a commercial CFD solver and can be used along with gas phase detailed turbulent combustion simulations of ducted rocket combustion chambers. Our simulation approach has provided us an effective tool, which allows us to forecast the effects of the changes on the performance and efficiency. This detailed combustion model is validated with existing experimental results available in open literature. The model is also compared with the results of similar previous studies.

Experimental check of possibility of research of repeated inclusion of the open gas generator in the water environment

Experimental study of repeated burning interruption with the subsequent ignition in the water environment for bibasic firm fuel as a part of a model open solid propellant gas generator is presented. Video filming of burning zone mobile localizer providing process of repeated inclusion of a gas generator are given. Some parameters of the processes proceeding in these conditions are defined

Hybrid Gas Generator for a Staged Hybrid Rocket Engine

The two-stage combustion hybrid rocket engine with a hybrid gas generator method offers numerous advantages over a solid-propellant gas generator and classical hybrid rocket engines. These advantages include a higher specific impulse in operation, lower lifecycle costs, and lower sensitivity to combustion pressure. This study was mainly designed to discover whether the fuel-rich effluent coming out from the hybrid gas generator was generated to meet the temperature requirement of less than 1300 K. By using parameters such as oxidizer-to-fuel ratios, oxidizer mass flow rates, grain dimensions, and fuel types, experimental tests were attempted the temperature change in the effluent. This study also examined the combustion sensitivity of each parameter to different equivalence ratios and the combustion behavior of each parameter to different temperatures. In the results, a combustion temperature as low as 1290 K was successfully achieved in the fuel-rich combustion of hydroxyl-terminated polybutadiene with a mixture oxidizer containing 28% oxygen. The results also suggested that, when adding ammonium perchlorate to the hybrid gas generator, it helped improve the operational performance by reducing oxidizer-to-fuel variations and provided more uniform radial temperature profiles.

Скоростная видеосъемка и цифровая обработка изображений выхлопной струи модельного газогенератора на твердом топливе

Скоростная видеосъемка и цифровая обработка изображений выхлопной струи модельного газогенератора на твердом топливе

Modeling of End-Burning Solid Propellant Gas Generator

The Solid Propellant Gas Generator (SPGG) is widely used for special military and space applications, in view of its simplicity, light weight, size and high reliability. A mathematical model that describes the burning characteristics inside the SPGG has been established and validated through the implementation of appropriate software. These two methods enabled to predict the performance and to draw the time variation of chamber pressure. An experimental work is carried out in order to prove the functionality and check the validity of the developed techniques. The comparison between the computational results and the experimental measured parameters showed a deviation error less than 4%. The presented software is considered as a powerful tool for selecting the SPGG design parameters in the stages of preliminary design and for performing further sensitivity analyses.

Experiments on thermal response of low aspect ratio packed beds at high Reynolds numbers with varying inflow temperature

An experimental study for transient temperature response of low aspect ratio packed beds at high Reynolds numbers for a free stream with varying inlet temperature is presented. The packed bed is used as a compact heat exchanger along with a solid propellant gas-generator, to generate room temperature gases for use in applications such as control actuation and air bottle pressurization. Packed beds of lengths ∼200mm and 300mm were characterized for packing diameter based Reynolds numbers, Red ranging from 0.6×104 to 8.5×104. The solid packing used in the bed consisted of Ø9.5mm and Ø5mm steel spheres with suitable arrangements to eliminate flow entrance and exit effects. The ratios of packed bed diameter to packing diameter for 9.5mm and 5mm sphere packing were ∼9.5 and 18 respectively, with the average packed bed porosities around 0.4. Gas temperatures were measured at the entry, exit and at three axial locations along centre-line in the packed beds. The solid packing temperature was measured at three axial locations in the packed bed. An average Nusselt number correlation of the form Nud=3.91Red0.5 for Red range of 104 is proposed. For engineering applications of packed beds such as pebble bed heaters, thermal storage systems, and compact heat exchangers a simple procedure is suggested for calculating unsteady gas temperature at packed bed exit for packing Biot number Bid<0.1.

Production of fire extinguishing mixture by solid propellant propulsion

The behavior of fire suppression by water mist spray has been studied by using the experimental setup which employs the double-based solid propellant gas generator for water mist production. The burning products of solid fuel form a supersonic flow injected through the nozzle into the diffuser chamber having input for the water component ejected from the storage. High values of temperature and pressure at stagnation point impart the substantial kinetic energy to the flow, which provides the atomization of water droplets into mist spray. Since the water evaporation occurs already in the diffuser chamber due to the high temperature of input gas flow, the droplet size is gradually decreases to the lower limit value that could ever exist. The presence of vapor phase enlarges the volume of fire extinguishing jet allowing it to operate as a flooding agent (along with the effect of heat consumption due to water evaporation) at the very beginning of fire suppression process, much before the water droplets evaporation by the flame itself. Proposed technique of the water mist production has showed noticeable fire suppression capability through the series of testing application to the gasoline and wood model fire sources.

Experimental correction of combustion gas properties of AN-based composite solid propellants used for turbo-pump starter

Solid propellant gas generators play a role as a turbo-pump starter in liquid propellant propulsion systems by supplying pressurized gas to power turbines for engine start. Among the required combustion gas properties provided by solid propellant gas generators, the combustion gas temperature should not exceed a certain temperature which may damage the turbine blades. For such purposes, phase stabilized ammonium nitrate (AN)-based propellants have been widely used with a low combustion temperature. However, gas generator propellants with ammonium nitrate have historically exhibited incomplete combustion resulting in increased flame temperatures differing significantly from equilibrium values. In consideration of design requirements, an engineering model of solid propellant gas generator was manufactured using the combustion gas properties calculated by a chemical equilibrium code and then hot-fire tests were performed. Procedures for the correction of T 0 , k and M w of the combustion gas from the experimental results are introduced and the following effects on the design of the solid propellant gas generator are presented. From the experimental correction of the combustion gas properties, it is found that the amount of the propellant could be reduced while providing the same amount of available power to the turbines and consequently, the size of the gas generator could also be decreased.

Transient Momentum and Enthalpy Transfer in Packed Beds at High Reynolds Numbers

An experimental study for transient temperature response and pressure drop in a randomly packed bed at high Reynolds numbers is presented.The packed bed is used as a compact heat exchanger along with a solid-propellant gas generator, to generate room-temperature gases for use in control actuation, air bottle pressurization, etc. Packed beds of lengths 200 and 300 mm were characterized for packing-sphere-based Reynolds numbers ranging from 0.8 x 10(4) to 8.5 x 10(4).The solid packing used in the bed consisted of phi 9.5 mm steel spheres. The bed-to-particle diameter ratio was with the average packed-bed porosity around 0.43. The inlet flow temperature was unsteady and a mesh of spheres was used at either end to eliminate flow entrance and exit effects. Gas temperature and pressure were measured at the entry, exit,and at three axial locations along centerline in the packed beds. The solid packing temperature was measured at three axial locations in the packed bed. A correlation based on the ratio of pressure drop and inlet-flow momentum (Euler number) exhibited an asymptotically decreasing trend with increasing Reynolds number. Axial conduction across the packed bed was found to he negligible in the investigated Reynolds number range. The enthalpy absorption rate to solid packing from hot gases is plotted as a function of a nondimensional time constant for different Reynolds numbers. A longer packed bed had high enthalpy absorption rate at Reynolds number similar to 10(4), which decreased at Reynolds number similar to 10(5). The enthalpy absorption plots can be used for estimating enthalpy drop across packed bed with different material, but for a geometrically similar packing.

Modeling the process of methane-air plume extinguishing by a solid-propellant pulse aerosol generator

Operation of a pulse aerosol system of fire fighting designed for effective extinguishing of fires in gas wells is modeled by an example of quenching a methane-air subsonic plume escaping from a nozzle. The system consists of two separate parts: a charge of a unitary solid propellant (gas generator) and a container with fine-grain powder of a flame retardant. The combustion of the mixture is described by a one-step global reaction; the effect of the concentration of flame-retardant vapors on the combustion process is taken into account through reduction of the pre-exponent in the Arrhenius law and is described by an empirical dependence. A computational experiment shows that the use of the pulse aerosol system of fire fighting ensures effective transport of fine aerosol particles of the flame retardant and its vapors to the combustion zone in amounts sufficient to suppress the ignition spot.

On the effect of filters for the design of solid propellant gas generators

Solid propellant gas generator (SPGG) plays a role as a turbo pump starter in liquid propellant propulsion systems by supplying pressurized gas to power turbines for engine start. For such a purpose, the propellant should burn with a low flame temperature and the combustion gas should not contain corrosive constituents. Stabilized AN-based propellants have been used as the most appropriate propellant compositions that meet these requirements. However, because of its low burning rate, the burning area of the propellant intends to increase to satisfy the required mass flux and consequently the burning area increment brings on the SPGG size augmentation. A flow restriction such as filters, which are usually employed to filter off impurities in the combustion gas, is applied to decrease the SPGG size by rising up the combustion pressure resulting in increasing the burning rate. Pressure loss coefficient effects on the combustion pressure and on the SPGG/turbines system are investigated with the experimental results. Then the feasibility of the SPGG size reduction by the employment of filters has been studied. The preliminary results of this study show that the considerable reduction of SPGG size would be achievable just by installing a filter with a relatively high pressure loss coefficient.

A Modeling Investigation of Suppressant Distribution from a Prototype Solid-Propellant Gas-Generator Suppression System into a Simulated Aircraft Cargo Bay

One new technology for fire suppressant distribution in total-flooding applications is the solid-propellant gas-generator (SPGG) technology. This article presents experimental and modeling studies of one such prototype system in order to better understand observations in the testing of this system. This particular SPGG system generates fine particles that act to suppress any fire in conjunction with inert gases also generated in the SPGG system. Initial conditions for the simulations are obtained from the available measurements of the prototype system. The modeling provides key information related to the distribution of the particles and their potential effectiveness as a fire suppressant. The primary variable in the SPGG design as identified in the initial measurements, also presented here, was the particle size, with typical particle sizes being measured at 2 and 15 µm. The key modeling result is that there is a tradeoff between the most uniform distribution of particles and the available surface-to-volume ratio for chemical suppression. Information is also provided regarding the thermal dissipation from the SPGG system.

Simulation of the dispersion and ignition of fine-dispersed aluminum particles by a gas generator

Using numerical modelling, we studied the formation and propagation of a cloud of fine-dispersed aluminum particles generated by a special unit under the action of high-temperature combustion products of a solid propellant gas generator, as well as the ignition conditions of these particles. The results of numerical modelling show that the dynamic characteristics of the cloud of particles and their ignition substantially depend on the temperature of gas generator combustion products, particle sizes, and the energy characteristics of the generator itself. The results obtained are in a qualitative agreement with experiments carried out at the Fraunhofer Institute for Chemical Technology (Pfinztal, Germany) [6].