Showing papers on "Chamber pressure published in 2010"

Effects of Injector Recess and Chamber Pressure on Combustion Characteristics of Liquid–Liquid Swirl Coaxial Injectors

Abstract: Combustion characteristics such as combustion performance and combustion stability have been studied experimentally using a small liquid rocket thrust chamber with 19 liquid–liquid swirl coaxial injectors. Data were obtained from static pressure, temperature, and dynamic pressure sensors installed in propellant manifolds and the combustion chamber. While changing the recess length of the injector, characteristic velocity and pressure fluctuation data were collected and analyzed. In addition, chamber pressure was varied between 42 and 54 bar, which covers the sub- and supercritical pressures of oxygen. The results show that the longer recess length generally promotes combustion performance and the spray interaction between injectors in the multielement combustor increases the characteristic velocity. When the chamber pressure is above the critical pressure of oxygen, the recess length scarcely affects the pressure fluctuation. However, when the chamber pressure is below the critical pressure, the shift fro...

Numerical Investigation of the Effect of a Diaphragm on the Performance of a Hybrid Rocket Motor

Abstract: This paper describes the use of a CFD code (Ansys CFX 12) for the analysis of a hybrid rocket motor with a diaphragm placed in the combustion chamber in order to enhance rocket performance. This work follows the experimental campaign of Matthias Grosse who tested the motor using nitrous oxide and paraffin wax as propellants. Several of his tests have been used as a reference for the numerical simulations. Several approximations have been made: steady state conditions, eddy dissipation combustion model with one-step reaction, gaseous injection of fuel and oxidizer, no droplets entrainment (typical of a paraffin grain). First of all, a single geometry without diaphragm has been analyzed with different turbulence models (k-ω, k-ω SST, k-e, k-e RNG). It has been shown that the k-ω model predicts a lower flame temperature and chamber pressure than k-e. Five geometries have been studied in order to compare the use of two different types of diaphragm (1 hole and 4 holes) in two positions (24% and 33% of the total length) respect to a configuration without mixer. The effect of the diaphragm is an increase of the mixing of the chemical species participating in the combustion process. The use of the diaphragm showed a performance enhancement, as showed in the experimental campaign. There is a good agreement between CFD results and experimental data: the efficiency is overestimated by less than 5.5%. This work proves the capability of CFD codes to predict global hybrid motor performances and to be a useful tool in the study of mixing devices.

Film Cooling in a High-Pressure Subscale Combustion Chamber

Abstract: By the application of film cooling in addition to regenerative cooling, a considerable reduction in thermal and structural loads of rocket combustion-chamber walls can be reached. This paper discusses important influence parameters on film cooling in terms of efficiency of the injected film and wall temperature reduction. For the experimental investigations a high-pressure subscale combustion chamber operated with the cryogenic propellant combination LOX=GH2 was used. A gaseous film with ambient tempered hydrogen was injected in the axial direction at the face plate. Typical film-cooling parameters such as film blowing rate, velocity ratio between film injection velocity and hot-gas velocity, circumferential slot positioning, and film injection slot height were investigated systematically at the European Research and Technology Test Facility P8.

Methane Diffusion Flame Dynamics at Elevated Pressures

Abstract: The chamber pressure and fuel flow rate effects on the flickering behavior of methane-air diffusion flames was studied over the pressure range of 1 to 10 bar. Photomultipliers and high-speed imaging techniques have been used to study the frequency and magnitude of the flame oscillation and the change in global flame shape. The instability behavior of the flame was observed to be sensitive to both the fuel flow rate and pressure. Particularly, it has been observed that the flame responds to the change of pressure more when the pressure is relatively low. High-speed imaging has shown that the periodical break-up of the methane flame at higher flow rates is almost symmetric. However, the methane flames at lower flow rates oscillate in a more waving manner due to the alternating lateral nature of the outer vortices. The average flame luminosity was observed to increase with pressure up to 6 bar and then starts to decrease with the further increase of pressure. The flame oscillation magnitude (L f ) and oscill...

Investigation of Rocket Exhaust Diffusers for Altitude Simulation

Abstract: The design and operational parameters of rocket exhaust diffusers equipped to simulate high-altitude rocket performance on the ground were investigated and characterized using a comprehensive approach (theoretical, numerical, and experimental). The physical model of concern includes a rocket motor, a vacuum chamber, and a diffuser, which have axisymmetric configurations. Further, the operational characteristics of a rocket exhaust diffuserwereanalyzed froma flowdevelopmentpointof view.Emphasiswasplacedondetailed flowstructure inthe diffuser, to observe the pressure oscillation in both the vacuum chamber and diffuser, which determines the minimum rocket-motor pressure required to start the diffuser. Numerical simulations were compared with experimental data on startup and in operational conditions to understand the effects of major design parameters, including the area ratio of diffuser to rocket-motor nozzle throat, the rocket-motor pressure, and the vacuumchamber size. Nomenclature Ad = inner cross-sectional area of diffuser Ade = exit cross-sectional area of diffuser Ae = exit cross-sectional area of rocket nozzle At = throat cross-sectional area of rocket nozzle

Cold-gas experiments to study the flow separation characteristics of a dual-bell nozzle during its transition modes

Abstract: An experimental investigation has been carried out to study the effect of test environment on transition characteristics and the flow unsteadiness associated with the transition modes of a dual-bell nozzle. Cold-gas tests using gaseous nitrogen were carried out in (i) a horizontal test-rig with nozzle exhausting into atmospheric conditions and, (ii) a high altitude simulation chamber with nozzle operation under self-evacuation mode. Transient tests indicate that increasing δP0/δt (the rate of stagnation chamber pressure change) reduces the amplitude of pressure fluctuations of the separation shock at the wall inflection point. This is preferable from the viewpoint of lowering the possible risk of any structural failure during the transition mode. Sea-level tests show 15–17% decrease in the transition nozzle pressure ratio (NPR) during subsequent tests in a single run primarily due to frost formation in the nozzle extension up to the wall inflection location. Frost reduces the wall inflection angle and hence, the transition NPR. However, tests inside the altitude chamber show nearly constant NPR value during subsequent runs primarily due to decrease in back temperature with decrease in back pressure that prevents any frost formation.

Performance Evaluation of Second-Throat Diffuser for High-Altitude-Test Facility

Abstract: The performance of a second-throat ejector―diffuser system employed in high-altitude testing of large-area-ratio rocket motors is considered under various steady and transient operating conditions. When the diffuser attains started condition, supersonic flow fills the entire inlet section and a series of oblique shock cells occurring in the diffuser duct seal the vacuum environment of the test chamber against backflow. The most sensitive parameter that influences the stagnation pressure needed for diffuser starting is the second-throat diameter. Between the throat and exit diameters of the nozzle, there exists a second-throat diameter value that corresponds to the lowest stagnation pressure for starting. When large radial/axial gaps exist between the nozzle exit and diffuser duct, significant reverse flow occurs for the unstarted cases, which spoils the vacuum in the test chamber. However, the starting stagnation- pressure value remains unaffected by the axial/radial gap. Numerical simulations establish that it is possible to arrive at an optimum diffuser geometry that facilitates early functioning of the high-altitude-test facility during motor ignition phase. The predicted axial variations of static pressure and temperature along the diffuser for the testing of a cryogenic upper-stage motor agree well with available experimental data.

Structure and optical properties of tungsten oxide nanomaterials prepared by a modified plasma arc gas condensation technique

Abstract: With the use of a modified plasma arc gas condensation technique and control of the processing parameters, namely, plasma current and chamber pressure, we synthesized tungsten oxide nanomaterials with aspect ratios ranging from 1.1 (for equiaxed particles with the length and width of 48 nm and 44 nm, respectively) to 12.7 (for rods with the length and width of 266 nm and 21 nm, respectively). The plasma current and chamber pressure, respectively, ranged from 70 to 90 A and from 200 to 600 Torr. We then characterized the tungsten oxide nanomaterials by means of X-ray diffraction, high-resolution transmission electron microscope, UV–visible spectroscope, and photoluminescence (PL) spectroscope. Experimental results show that equiaxed tungsten oxide nanoparticles were produced at a relatively low plasma current of 70 A, whereas nanorods were produced when plasma currents or chamber pressures were increased. All of the as-prepared tungsten oxide nanomaterials exhibited a WO2.8 phase. Compared to the nanoparticles, the nanorods exhibited unique properties, such as a redshift in the UV–visible spectrum, a blue emission in PL spectrum, and a good performance in field emission. With respect to the field emission, the turn-on voltage for WO2.8 nanorods was found to be as low as 1.7 V/μm.

Poly(ethylene‐2,6‐naphthalate) nanofiber prepared by carbon dioxide laser supersonic drawing

Abstract: Poly(ethylene-2,6-naphthalate) (PEN) nanofiber was prepared by a carbon dioxide (CO2) laser supersonic drawing. The CO2 laser supersonic drawing was carried out by irradiating the laser to the as-spun PEN fiber in a low-temperature supersonic jet. The supersonic jet was generated by blowing off air into a vacuum chamber from a fiber supplying orifice. The flow velocity from the orifice can be estimated by applying Graham's theorem from the pressure difference between the atmospheric pressure and the pressure of the vacuum chamber. The fastest flow velocity estimated was 396 m s−1 (Mach 1.15) at a chamber pressure of 6 KPa. The nanofiber obtained at Mach 1.15 was the oriented nanofibers with an average diameter of 0.259 μm, and its draw ratio estimated from the diameters before and after the drawing reached 430,822 times. The CO2 laser supersonic drawing is a new method to make nanofiber without using any solvent or removing the second component. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Dynamic force transmitted by hydraulic mount: Estimation in frequency domain using motion and/or pressure measurements and quasi-linear models

Abstract: This article proposes indirect methods to estimate dynamic forces that are transmitted by a fixed or free decoupler type hydraulic engine mount to a rigid base. First, the linear system transfer functions that relate the force transmitted to the top chamber pressure and excitation displacement are derived in the Laplace and frequency domains; these clearly identify the roles of rubber and hydraulic force paths up to 50 Hz. Since hydraulic mounts are inherently nonlinear, a quasi-linear model is developed that incorporates amplitude-sensitive and spectrally-varying parameters such as top chamber compliance and rubber path properties (stiffness and damping). Alternate schemes based on a quasi-linear fluid system formulation work well as dynamic force spectra over a range of harmonic displacement excitations are successfully predicted given motion and/or pressure measurements; these compare well with measured forces over a range of frequencies and excitation amplitudes. In particular, the force to pressure transfer function model is quite promising. Conversely, the analogous mechanical system model fails as it yields highly inaccurate forces. The force time history is also briefly predicted by applying the Fourier expansion with an embedded quasi-linear fluid model with only the fundamental (excitation) frequency.

High Flow Volume Nasal Irrigation Device and Method for Alternating Pulsatile and Continuous Fluid Flow

Abstract: A high flow volume nasal irrigation device for alternating pulsatile and continuous fluid flow includes a segmented dip tube with a free end extending inside a squeeze bottle configured to convey a liquid under an elevated chamber pressure from a reservoir therein to a lower pressure outside the bottle. The device also includes an elastic segment at the free end of the tube configured to oscillate about a bending in the segment in response to a differential pressure between an internal pressure and the chamber pressure, the segment having an elastic restoring force in opposition to the bending. The disclosed device further includes a pulsatile portion of the elastic segment configured to close at the segment bending and to reopen under the elastic restoring force and to thus generate a periodic pulsatile fluid flow through the tube with a period corresponding to the elastic segment oscillation.

Combustion Dynamics and Stability of a Fuel-Rich Gas Generator

Abstract: The dynamic characteristics of fuel-rich combustion have been studied using an experimental combustor simulating a gas generator for a liquid rocket engine. The combustor burns liquid oxygen and fuel (Jet A-1) at a mixture ratio of about 0.32 and a chamber pressure ranging from 4.10 to 7.24 MPa, which covers subcritical to supercritical pressures of oxygen. For the investigation of combustion dynamics, pressure fluctuation measurements using piezoelectric sensors have been a major probe throughout the present study. Two different types of injector heads equipped with biliquid swirl coaxial injectors and either a short nozzle or a turbine manifold nozzle have been used in the study. Fuel-rich combustion of both injector heads with the short nozzle revealed pressure pulsation at frequencies of about 128 Hz, which attenuates along with an increase of a chamber pressure. Combustion tests with the turbine manifold nozzle conducted at chamber pressures lower than the oxygen critical pressure showed combustion instabilities at a frequency of 330 Hz, which has been identified as a longitudinal resonant mode by a linear acoustic analysis. The combustion instabilities seem to be induced by inherent pressure fluctuations from the biliquid swirl coaxial injector when the chamber pressure is below the oxygen critical pressure.

Effects of chamber pressure variation on the grid temperature in an inertial electrostatic confinement device

Abstract: Inertial electrostatic confinement fusion devices are compact sources of neutrons, protons, electrons, and x rays. Such sources have many applications. Improving the efficiency of the device also increases the applications of this device. Hence a thorough understanding of the operation of this device is needed. In this paper, we study the effect of chamber pressure on the temperature of the cathode. Experimentally, the grid temperature decreases as the chamber pressure increases; numerical simulations suggest that this is caused by the reduction of the hot ion current to the cathode as the pressure increases for constant power supply current. Such an understanding further supports the conclusion that the asymmetric heating of the cathode can be decreased by homogenizing the ion flow around the cathode.

Heat Flux and Pressure Profiles in an Oxygen/Hydrogen Multielement Rocket Combustor

Abstract: Proof of the predictive accuracy of models used in simulation of the high-pressure, high-heat flux environments inside operating rocket combustion chambers is limited by several factors including multiple phases, unsteadiness, high energy release, turbulence, and complex flow geometry. The severe environment also complicates the measurement of temperature, pressure, and chemical composition within the combustor. This paper describes an experiment to collect and analyze benchmark-quality validation data for a multi-element rocket combustor using liquid oxygen and gaseous hydrogen operating at chamber pressures from 300 to 1000 psia at mixture ratios from three to six. For these propellants, the stoichiometric mixture ratio is eight. The combustor was instrumented with 44 coaxial thermocouple pairs to measure axial and circumferential temperature fields and 8 pressure transducers to measure axial pressure profiles. The local heat flux at the inner wall of the combustion chamber computed at each temperature measurement location was found to vary between 4 and 20 Btu/in. 2 /s. The circumferential variation of heat flux seems to indicate mixing and radial outflow of combustion gases between injector elements, a phenomenon that is not observed in injector configurations with tighter spacing. Further, the axial pressure profiles and head-end temperature measurements suggest the presence of recirculation zones near the injector face.

Table-top flash X-ray diagnostics of dodecane sprays

Abstract: Time resolved radiography of pure dodecane and cerium doped dodecane sprays expanding through micrometric nozzles in a high pressure injection chamber inflated up to 30 bar have been performed for the first time using a table top flash X-ray source. The radiograph analysis indicates that strong mixing between liquid and ambient gas occurs in the very near nozzle region. The spray is described as two different density components having different penetration velocities which amplitudes also depend on the chamber pressure.

Large area spray cooling by inclined nozzles for electronic board

Abstract: To cool a 1 kW 6U electronic card, an innovative inclined spray chamber with multiple nozzles has been developed and investigated with a closed-loop refrigeration system. A large heated surface (12.3 × 15.5 cm2) was sprayed by four gas-assisted nozzles with an inclined angle of 39° relative to the normal direction. A reasonable spray coverage area can be obtained by the inclined spray chamber while enabling a relatively lower spray chamber height than that required by a normal spray chamber. R134a was implemented as the working fluid in this study. The mass flow rate, pressure drop across the nozzles, and the spray chamber pressure were varied experimentally, and the results suggest that the increases of the mass flow rate, the pressure drop across the nozzles, and the spray chamber pressure can improve the thermal performance of the inclined spray. The average heated surface temperature can be maintained within 20.0°C, and the maximum heat transfer coefficient of 4742.2 W/m2·K can be achieved at a suitable working condition.

Exhaust Gas Analysis of a Vortex Oxidizer Injection Hybrid Rocket Motor

Abstract: Previously a vortex oxidizer injection hybrid rocket motor was developed at the U.S. Naval Academy to investigate possible enhancements to fuel regression rate due to injection method. The motor was developed to operate with a conventional axial injector and a novel vortex injector design using high density polyethylene for fuel and a gaseous oxygen oxidizer. The motor was instrumented with pressure transducers and high-speed gas analyzers to measure exhaust gas carbon dioxide, carbon monoxide, oxygen and unburned hydrocarbons. After multiple tests of both injector configurations measurements for the vortex case indicated fuel regression was more evenly distributed across the fuel grain except at the head end, the average regression rate and chamber pressure were higher and exhaust gas analysis indicated a lower oxidizer-fuel ratio. In order to characterize the rocket chamber and compare with the gas measurements, a rocket chamber simulation was developed. The simulation is a one dimensional Lagrangian combustion analysis developed using Matlab and flame mechanisms available in Cantera, an open source gas/chemical analysis package which included an applicable combustion mechanism for ethylene. The model solves a series coupled ordinary differential equations, which include species balance, energy conservation and conservation of mass. The outputs include species mass fraction, temperature, velocity, density and specific gas constant. The system of equations solved quickly and provided realistic results. Because of low velocities in the chamber, the full kinetics model and equilibrium model differed only slightly. Also comparison with measured carbon dioxide was not consistent with the experimentally determined oxidizer-fuel ratios and requires further study. In this iteration of the model heat transfer were neglected.

Effects of Variable Chamber Pressure on Swirl Coaxial Injection: A Cold Flow Study

Abstract: A geometrically full-scale swirl injector element was subjected to cold flow testing to explore the influence of steady chamber pressure on spray characteristics and selfatomization at conditions that reflect real liquid rocket combustor conditions. Propellant simulant flow rate was held constant at 0.82 kg/s over a chamber pressure range of 0.95 MPa to 3.45 MPa. Imaging studies observed free cone spray angle to deviate from the theoretical value when conditioned with positive variation in chamber pressure. Additionally, sheet penetration length decreased as a function of chamber pressure conditions. Phase Doppler Particle Analyzer measurements resolved droplet velocity and diameter profiles through the spray envelope. Analysis showed mean velocities and diameters in the primary atomization region to behave inversely to chamber pressure.