Solid Propellant Gas Generators Research Articles

Solid-propellant gas generators with a gas flow rate stabilization system

Solid-propellant gas generators with a gas flow rate stabilization system

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.

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.

Fire Suppression And Re-ignition Prevention Ina Full-scale Engine Nacelle Simulator

An analysis is presented on the full-scale fire suppression experiments conducted on the F-22 engine nacelle simulator at Wright Patterson Air Force Base. Experiments investigated the relative effectiveness of halogenated agents and solid propellant gas generators (SPGG) in suppressing a series of spray fires with and without a fuel re-ignition source. Several agents were tested including CF3Br (halon 1301), C2HF5 (HFC-125), and two basic types of SPGG, including one that produced inert gases in conjunction with a fine solid particulate composed of K2CO3 and one that produced inert gases only. The measured agent effectiveness was compared to the predicted effectiveness based on results from cup burner suppression experiments. Estimates of the suppression effectiveness of the SPGG were based on the effectiveness of the components of its effluent. The mass fraction of SPGG effluent required to extinguish heptane cup burner flames was estimated as 0.15 and 0.29 as compared to previously measured values of 0.14 and 0.28 for CF3Br and C2HF5, respectively. The predicted suppression requirements (relative to CF3Br) agreed with the full-scale measurements within 35% for the halogenated compounds, whereas the SPGG performed as much as a factor of 3.3 better than predicted. This difference suggests that a large fraction of the SPGG performance may have been related to its fast deployment, which enhances flame straining and thereby reduces agent mass suppression requirements. The SPGG effluent that contained a significant percentage of K2CO3 particulate was particularly effective for re-ignition protection, a scenario that dominates agent mass requirements for the compressed halogenated liquids. In this case, the SPGG required 27 times less mass than CF3Br. INTRODUCTION Halon 1301, or trifluorobromomethane (CF3Br), has been used as a fire extinguishing agent in many applications because of its many positive attributes. Due to its high ozone depletion potential, however, its production has been terminated. In the search for a suitable replacement, novel types of agents are under development. One class of such devices is the solid propellant gas generator (SPGG), a device in which solid-phase combustion yields products which can be used for fire suppression [1]. The key parameters that affect flame stability, control flame extinction and the prevention of re-ignition are agent effectiveness and flow field dynamics. Whereas there is a general understanding of the suppression mechanisms of gaseous agents, little has been published on SPGG effectiveness. Recently, the relative suppression effectiveness of a SPGG has been Copyright © International Association for Fire Safety Science 704 measured in a well-controlled bench-scale experiments [2]. There are many types of SPGG, each with its own composition, packaging geometry, and ignition sequencing. It is expected that gas specie and particulate yields, particulate size distributions, exhaust temperatures, and the rate and duration of effluent generation will vary from one SPGG to another, and each of these parameters may impact SPGG effectiveness. Table 1 shows the species composition of the SPGG effluent for the formulations tested here. For interest, a hypothetical mixture of unfiltered effluent from SPGG 1 is also included. Several SPGG types from Manufacturer 1 were tested and all were assumed to have the same effluent composition [3]. The hot exhaust products were principally gaseous N2, CO2, and H2O vapor and salt particulates. Table 1 shows that there was approximately one-third as much CO2, more than twice as much H2O, and almost two-thirds as much N2 produced in the SPGG 2 effluent than in the filtered SPGG 1 effluent. The SPGG 2 effluent is assumed to be unfiltered, so that it contains K2CO3(s), whereas the filtered SPGG 1 effluent is assumed to contain trace amounts of particulate only. Particle size can influence suppression effectiveness [4]. The majority of the SPGG particulate is very small and it is assumed that the particulate is smaller than the critical diameter [4]. To investigate the suppression effectiveness of SPGG in a simulated F-22 engine nacelle, a series of full-scale fire experiments was undertaken utilizing the Wright Patterson Aircraft Engine Nacelle Test Facility. The experiments described here investigated the relative effectiveness of halogenated agents and SPGG in suppressing spray fires with and without a re-ignition source. Several SPGG types were tested, including one that produced inert gases and a fine solid particulate, and one with the particulate filtered, such that only inert gases were emitted. Table 1 SPGG mole based fractional effluent composition. Species filtered SPGG 1 Unfiltered SPGG 1 SPGG 2 CO2 0.313 0.264 0.0917 H2O 0.219 0.183 0.559 N2 0.468 0.395 0.325 K2CO3 0* 0.158 0.0246 * assumed to be trace amounts only. _______________________________ * Certain commercial materials and equipment are identified in this report in order to specify adequately the procedure. In no case does such identification imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the material or equipment is necessarily the best for the purpose.

Suppression of a non-premixed flame behind a step

suppression effectiveness under conditions that relate to field applications. In this study, a laboratory-scale facility has been developed to screen the suppression effectiveness of agents that are delivered in a transient fashion, such as solid propellant gas generators. The facility features a pool fire stabilized behind an obstruction, which is known to be a highly challenging suppression configuration. The character of the flame and the impact of the air flow, propane flow, obstruction geometry, and rate of agent addition on the amount of material needed for suppression are examined for N2 and CF3Br. The impact of the injection process on the flowfield and the transport of the agent downstream are examined. A simple mixing model is useful to explain the observed trend of decreasing suppressant mass fraction with increasing injection duration, even for agents as different as CF3Br and N2. Direct numerical simulation of the suppression event is shown to successfully predict the quantity and rate of N2 required to extinguish the flame based upon a published global reaction rate for premixed propane/air flame propagation.

Analysis of a Hybrid Dual-Combustion-Chamber Solid-Propellant Gas Generator

Solid-propellantgas generators (SPGGs) have a number of aerospace applications, includingmunitionsdispersion, pilot emergency escape systems, submarinemissile launching,powering actuators and valves, and short-term power supply. Recently, the increased demand for so-called smart automotive airbags has increased the need for SPGG designs capable of real-time, tailorable output. Dual-combustion-chamber gas generators provide several distinct advantagesover single-combustor units in systems where optimumperformance is needed at several operating conditions. The objective of this work is to evaluate the attainable performance characteristics of a proposed dual-combustion-chambergas generator. The work includes a simulation of the transient, thermochemical events associated with the Ž ring of an SPGG. The simulations also include the dynamics of coupled events such as ignition, heterogeneous combustion, and mass discharge. The baseline gas generator being simulated in this work is a hybrid SPGG in ator with two combustion chambers. Studies are made of the distribution of propellant between combustion chambers and the times at which the propellant within each combustion chamber is Ž red.

Combustion characteristics of low flame temperature, chlorine-free composite solid propellants

Presently, there is an increased interest in composite solid propellants that burn with low flame temperatures and do not contain chlorine or chlorine compounds. Applications for such propellants may be found in solid propellant gas generators and turbine pump starters. Phase-stabilized ammonium nitrate (ANS)-based propellants meet these requirements, but other composite propellant formulations are also feasible, such as propellants based on a rubber binder and nitroglycerin (NG) or trimethylol-ethane-trinitrate (TMETN). In order to compare the combustion characteristics of these propellants, three different families have been developed and tested: 1) Hydroxy-terminated polybutadiene (HTPB) binder with ANS and various catalysts; 2) Polyester-urethane (PU) binder with NG and nitroguanidine (NQ) or guanidine nitrate (GuNi); and 3) PU binder with TMETN and NQ or GuNi. With some exceptions, all propellant formulations have calculated flame temperatures between 1200 and 1400 K. In a special burner, the combustion characteristics of these propellants have been investigated in the pressure region between 1 and 10 MPa. The results of this study show that burning rates up to 7 mm/s at 10 MPa may be obtained, while the burning rate exponent may vary between 0.3 and 0.7. In addition, the importance of catalysts to improve the ignitability of (ANS)-based propellants is confirmed.