Showing papers on "Ullage published in 2009"

Transient Behavior of H2O2 Thruster: Effect of Injector Type and Ullage Volume

Abstract: ROCKET-GRADE hydrogen peroxide has been used as a monopropellant and a storable oxidizer. However, because of the demand for a higher specific impulse, hydrazine andN2O4 are being used as the monopropellant and storable oxidizer, respectively. Recently, due to concerns regarding propellant toxicity, there has been a renewed interest [1] in the use ofH2O2 in propulsion systems [2–10]. A monopropellant thruster is operated in either the continuous or pulse mode. The thrust force and pressure instability are important issues in the continuous mode. For generating the desired thrust, the catalytic reactor size required for completely decomposing the propellant must be determined [8]. However, in the pulse mode (the main operationmode for attitude control systems), the response characteristics of the thruster are important. The catalyst activity, thruster component design (including the injector design), manifold volume, ullage volume in the reactor, and operating pressure influence the thruster response time. Tian et al. investigated the response time when using a combination of PbO and MnO2 catalysts [11]; they found that Ir=Al2O3 is unsuitable for use as a catalyst in a H2O2 monopropellant thruster [12]. Xu et al. studied the activities of various catalysts during H2O2 decomposition [13]. El-Aiashy et al. reported that the catalyst activity ofMnO2 increased when ZnO was added [14]. Hasan et al. reported that the activity ofMnO2 increased when promoters such as Ni, Cu, Bi, and Ce were added [15]. None of the aforementioned studies have addressed the effect of thruster design parameters on response times, although a few researchers have measured the thruster response time. Optimization of the thruster design (determination of the appropriate injector and ullage volume in the reaction chamber) can also influence the response characteristics. Therefore, we investigate the response characteristics of H2O2 monopropellant thrusters for three different thruster designs andmeasure the response times by varying the injector type, reactor volume, and catalyst grain size. AMnO2=Al2O3 catalyst is used for the decomposition of concentrated H2O2 (90 wt%).

System and method to make a fuel tank inert

Abstract: A fuel tank safety system includes an ullage cooling assembly and a system controller. The ullage cooling assembly includes a compressor configured to extract a quantity of ullage gas from the fuel tank, a heat exchanger coupled in flow communication downstream of the compressor, wherein the heat exchanger is configured to receive the quantity of ullage gas from the compressor and reduce a temperature of the ullage gas. The ullage cooling assembly includes a turbine coupled in flow communication downstream of the heat exchanger, wherein the turbine is configured to further reduce the temperature of the ullage gas and facilitate channeling the ullage gas to the fuel tank. The system controller is operatively coupled to the ullage cooling assembly and is configured to transmit to the ullage cooling assembly one of a start signal to activate the ullage cooling assembly or a stop signal to deactivate the ullage cooling assembly.

Cryogenic Sloshing Tests in a Pressurized Cylindrical Reservoir

Abstract: Coupling between thermodynamic aspects and sloshing propellant is frequently of interest in cryogenic upper stages, especially during the lift-off phase and in missions including multiple restarts. Particularly in the first case, the fluid dynamic condition of the propellant is mainly influenced by various flight maneuvers. In contrast to storable propellant, cryogenic liquid sloshing evokes disturbances of the thermodynamic equilibrium between liquid and vapor. Under some circumstances, this may be critical leading to ullage collapse. The understanding of these phenomena is of major importance concerning the next generation of cryogenic upper stages. In order to investigate the coupled phenomena, benchmark tests are currently being carried out that are focused on sloshing of LN2 in a cylindrical tank. Three different setups are investigated, where the required tank pressure is established by self-pressurization, GN2 pressurization and GHe pressurization.

Systems and methods for making a fuel tank inert

Abstract: A fuel tank safety system includes a heat exchanger in flow communication with a cabin conditioning system, a blower configured to withdraw a quantity of ullage gas from a vehicle fuel tank for routing through the heat exchanger, and conduit interconnecting the fuel tank, the blower, and the heat exchanger. The heat exchanger is configured to reduce a temperature of the ullage gas using cooling providing by the cabin conditioning system and thus reduce the fuel content (or fuel-air ratio) of the ullage below threshold required for combustion.

Measuring Oxygen Concentration in a Fuel Tank Ullage

Abstract: For many years the Federal Aviation Administration (FAA) has been seeking to improve fuel tank safety, particularly center-wing fuel tanks, which were implicated in four fatal explosions over a 10-year period. Fuel tank inerting technologies have been examined by the FAA in depth and evaluated for potential benefit and cost. In support of this, the William J. Hughes Technical Center Fire Safety Branch has examined and evaluated many technologies for measuring oxygen concentration, some of which have been applied for use in a fuel tank ullage. To evaluate existing methods for measuring oxygen concentration in a fuel tank ullage, three different technologies were examined to determine how well they could duplicate calibration gas values, given the method of application, over a range of relevant conditions. Also, each technology/method was installed in a scale fuel tank test article to gauge the ability of the method to accurately determine the oxygen concentration under simulated commercial transport airplane fuel tank ullage conditions. These technologies and methods are 1) a typical lab-based galvanic cell sensor, using a regulated sample train; 2) a light absorption sensor, using an unregulated sample train; 3) an optical fluorescencebased sensor that is used in situ (in place). Preliminary data has illustrated that the light absorption method as well as the optical fluorescence method of sensing can represent calibration gases in a variable environment with some accuracy, but additional work is needed to adequately compare the capability of each method.

Feasibility of Scavenging Propellants from Lander Descent Stage to Supply Fuel Cells and Life Support

Abstract: A feasibility study consisting of both analytical and experimental work was performed to determine if the lunar lander vehicle can use residual propellants remaining in the descent stage tanks after landing to provide reactants to the fuel cell power system and oxygen to life support for a 7-day sortie mission. Initial results indicate that the residual hydrogen will last approximately 19 days at the poles and 15 days at the equator. The residual oxygen will last 21 days at the poles and more than 16.5 days at the equator. Excess hydrogen will need to be vented during the mission to prevent tank over-pressurization, while heat must be added to the oxygen tank at the poles. Tests performed on a liquid oxygen tank pressurized with helium demonstrate that the helium concentrations in the ullage gas can be reduced significantly with venting. Tests on a flow-through fuel cell stack indicate that they can tolerate significant amounts of helium contamination in the reactants without permanent

Fuel system ullage float assembly

Abstract: A fuel system ullage float valve assembly is provided for fuel tank and fuel fill line. This assembly is located near the intersection of the fuel fill line entering the uppermost top section of a fuel tank. A ullage float valve assembly includes a cage enclosure having an upper collar, a plurality of leg members and a base, essentially forming a frame-like structure. The upper collar is partially inserted into, and nest within, the fuel fill line as it enters the tank. The leg members extend downwardly into the tank in a generally vertical position. The assembly also includes a buoyant float chamber, having a generally cylindrical base and a generally converging, conical upper section. The float chamber is buoyant and it housed within the cage enclosure, and is slididly movable within the enclosure. During the fueling process as fuel fills the tank the ullage float assembly rises within the cage enclosure and to reach a sealing engagement with the upper collar of the assembly causing termination of the fueling process. The float assembly also includes a fuel bypass port.

Pulse response times of hydrogen peroxide monopropellant thrusters

Abstract: The transient behavior of a monopropellant thruster was investigated. Throughout the study, MnO2/Al2O3 was used as the catalyst bed in order to eliminate the influence of the catalyst bed on the transient behavior. Three 50 Newton level test thrusters with different injectors, ullage volumes, and bed sizes were built. H2O2 (90 wt%) was used as the monopropellant in the thrusters and experiments were carried out using these thrusters. The transient characteristics of the thrusters—the ignition delay and the time taken for pressure rise and pressure decay—were determined. Among the injectors considered, the transient characteristics of the shower-head injector are better than those of the spray injector The shower-head injector showed the best performance when a catalyst bed with a small volume was used: the ignition delay was 14 ms; the pressure rise, 108 ms, and the pressure decay, 94 ms.

Improvements relating to fabric conditioning compositions

Abstract: A packaged fabric conditioning product comprising a flowable fabric conditioning composition comprising 05-40% by weight of at least one unsaturated quaternary ammonium compound, said composition contained in bottom-dispensing packaging which comprises (i) a deformable container in which the fabric conditioning composition is stored with ullage; and (ii) a dispensing device which is located at the base of the container such that in the inverted position the flowable fabric conditioning composition is positioned beneath the ullage and above the dispensing device

Simulation and optimization of stored gas pressurizing system for liquid propellant tanks in a launch vehicle

Abstract: The primary purpose of this paper is to simulate the “stored gas type pressurizing system” for propellant tanks in a launch vehicle. Preventing the cavitation occurrence in propellant pumps (as the propulsion requirement) and providing required level of pressure in propellant vessels to prevent them from buckling against external aerodynamic forces (as the structural requirement) are the two most important goals of this system. In this paper primarily the basic equations have been derived. A quasi-steady iterative process has been selected to march in time domain. The simulation has been done with time marching steps to take into account the prediction of pressure change in propellant vessels' ullage and propellant pumps' inlet flow during the working time. An optimization has been done to obtain the best system properties such as cutting time and the minimum number of supplier capsules which should be carried by the launch vehicle.

A tank having an air pressure discharge system with feedback to optimise discharge

Abstract: A regulated pneumatic pressure discharge system for the discharge of bulk liquid from a tank / tanker at a predetermined operating discharge pressure comprises a variable speed compressor having an input 26, 28 for adjusting the compressor speed and an air output connected to a tank, a pressure sensor 22 for measuring an operating discharge pressure, and a feedback management system for monitoring the measured operating discharge pressure from the pressure sensor and adjusting the speed of the compressor by said input so that the operating discharge pressure approaches the target operating discharge pressure. A screw compressor is ideally utilised. The feedback system is ideally linked to an engine management system (e.g. of a vehicle, tanker) to adjust the speed of the compressor. The pressure sensor may be located at the air output. In this way the pressure of the air pumped into the ullage space of a container will be optimal for pneumatic unloading / discharge of the product.