Showing papers on "Chamber pressure published in 2014"

Ignition Characteristics of Diesel Fuel in a Constant Volume Bomb under Diesel-Like Conditions. Effect of the Operation Parameters

Abstract: A constant volume chamber system was used to characterize the ignition and combustion of a diesel fuel. Fuel is injected in the chamber through a standard diesel common rail injection system. Injection parameters and initial chamber conditions were varied: fuel injection pressure (600 to 1000 bar), injection duration (500 to 3000 μs), initial temperature (808 to 923 K), initial pressures (6 to 21 bar), and oxygen mole fractions (15 to 30% diluted in nitrogen). Multiple measurements confirmed the repeatability of the measurements. Most of the experiments showed a two-stage combustion process, especially at low chamber pressure and highly premixed conditions. This is characteristic of large paraffinic hydrocarbons such as those composing around two-thirds of commercial diesel fuels. Combustion pressure data from diesel fuel have shown a moderate effect of injection pressure and injection duration on the ignition delays, especially when compared to the effect of other operation parameters. A strong effect of...

Combined Microwave Vacuum Drying

Abstract: The potential of microwave energy combined with a vacuum environment for rapid low temperature dehydration that produces high quality products has long been recognized. Microwave vacuum drying is a dehydration process that uses microwave radiation to generate heat in the absolute pressure (chamber pressure) range from above the triple point of water to less than atmospheric pressure (0.61–101.33 kPa). The earliest related applications involved using a combination of radio frequency energy and vacuum. Potatoes and cabbage were reported to be rapidly dehydrated using this technique, and penicillin was dried using radio frequency energy (28 MHz) in combination with a vacuum to prevent the thermal degradation of the antibiotic. While the radiation used in these applications was below microwave frequency, these examples embody the concept of converting electromagnetic energy to heat inside a material rather than relying on conduction and convection for heat transfer and of using vacuum to maintain a low product temperature, resulting in improved product quality.

Lean Partially Premixed Combustion Investigation of Methane Direct-Injection Under Different Characteristic Parameters

Abstract: The effects of hydrogen addition, diluent addition, injection pressure, chamber pressure, chamber temperature and turbulence intensity on methane–air partially premixed turbulent combustion have been studied experimentally using a constant volume combustion chamber (CVCC). The fuel–air mixture was ignited by centrally located electrodes at given spark delay times of 1, 5, 40, 75 and 110 milliseconds. Experiments were performed for a wide range of hydrogen volumetric fractions (0% to 40%), exhaust gas recirculation (EGR) volumetric fractions (0% to 25% as a diluent), injection pressures (30–90 bar), chamber pressures (1–3 bar), chamber temperatures (298–432 K) and overall equivalence ratios of 0.6, 0.8, and 1.0. Flame propagation images via the Sclieren/Shadowgraph technique, combustions characteristics via pressure derived parameters and pollutant concentrations were analyzed for each set of conditions. The results showed that peak pressure and maximum rate of pressure rise increased with the increase in chamber pressure and temperature while changing injection pressure had no considerable effect on pressure and maximum rate of pressure rise. The peak pressure and maximum rate of pressure rise increased while combustion duration decreased with simultaneous increase of hydrogen content. The lean burn limit of methane–air turbulent combustion was improved with hydrogen addition. Addition of EGR increased combustion instability and misfiring while decreasing the emission of nitrogen oxides (NOx).Copyright © 2013 by ASME

Investigation of Effect of Diaphragms on the Efficiency of Hybrid Rockets

Abstract: This paper describes computational fluid dynamics applied to the analysis of a hybrid rocket motor with a diaphragm in the combustion chamber to enhance rocket performance. This work follows the last author’s experiments: An engine was tested with nitrous oxide and paraffin wax as propellants. Several of the tests have been used as references for numerical simulations. The following approximations have been made: steady-state conditions, eddy dissipation model with one-step reaction, gaseous injection of fuel and oxidizer, and no droplets entrainment (typical of a paraffin grain). First of all, a single geometry without a diaphragm has been analyzed with different turbulence models (k-ω, k-ω shear stress transport, k-e, k-e renormalization group). It has been shown that the k-ω model predicts a lower flame temperature and chamber pressure than the k-e model. Then, five geometries have been studied to compare two different types of diaphragms (one hole and four holes) in two positions (24 and 33% of the to...

Combustion Stability Characteristics of the Project Morpheus Liquid Oxygen / Liquid Methane Main Engine

Abstract: The project Morpheus liquid oxygen (LOX) / liquid methane (LCH4) main engine is a Johnson Space Center (JSC) designed ~5,000 lbf-thrust, 4:1 throttling, pressure-fed cryogenic engine using an impinging element injector design. The engine met or exceeded all performance requirements without experiencing any in- ight failures, but the engine exhibited acoustic-coupled combustion instabilities during sea-level ground-based testing. First tangential (1T), rst radial (1R), 1T1R, and higher order modes were triggered by conditions during the Morpheus vehicle derived low chamber pressure startup sequence. The instability was never observed to initiate during mainstage, even at low power levels. Ground-interaction acoustics aggravated the instability in vehicle tests. Analysis of more than 200 hot re tests on the Morpheus vehicle and Stennis Space Center (SSC) test stand showed a relationship between ignition stability and injector/chamber pressure. The instability had the distinct characteristic of initiating at high relative injection pressure drop at low chamber pressure during the start sequence. Data analysis suggests that the two-phase density during engine start results in a high injection velocity, possibly triggering the instabilities predicted by the Hewitt stability curves. Engine ignition instability was successfully mitigated via a higher-chamber pressure start sequence (e.g., ~50% power level vs ~30%) and operational propellant start temperature limits that maintained \cold LOX" and \warm methane" at the engine inlet. The main engine successfully demonstrated 4:1 throttling without chugging during mainstage, but chug instabilities were observed during some engine shutdown sequences at low injector pressure drop, especially during vehicle landing.

Coupled Heat Transfer Analysis in Regeneratively Cooled Thrust Chambers

Abstract: The coupled hot gas–wall–coolant environment that occurs in regeneratively cooled liquid rocket engines is studied by a computational procedure able to provide a quick and reliable prediction of thrust chamber wall temperature and heat flux as well as coolant flow characteristics, like pressure drop and temperature gain in the regenerative circuit. The coupled analysis is performed by means of a computational fluid dynamics solver of the Reynolds-averaged Navier–Stokes equations for the hot gas flow and by a simplified quasi-two-dimensional approach, which widely relies on semiempirical relations, for the coolant flow and wall structure heat transfer in the cooling channels. Coupled computations of the space shuttle main engine main combustion chamber are performed and compared with available literature data. Results show a reasonable agreement in terms of coolant pressure drop and temperature gain with nominal data, whereas the computed wall temperature peak is closer to hot-firing test data than to the ...

Experimental Investigation of an Alternative Rocket Configuration for Rocket-Based Combined Cycle Engines

Abstract: Experimental tests are conducted to evaluate two rocket exhaust configurations within an Rocket-Based Combined Cycle engine model. Each configuration uses a single rocket chamber but expands the rocket exhaust to a different geometry. One configuration uses two traditional circular rocket nozzles whereas the other uses two annular exhaust geometries based on the Exchange Inlet design. Wall pressure data are collected along the length of each configuration to evaluate the air entrainment. The annular configuration is shown to increase the entrainment ratio by as much as 28% over the traditional circular rocket design. The annular configuration is also shown to choke the incoming airflow at a lower rocket chamber pressure more uniformly across the engine cross section. Total pressure measurements are also obtained at the engine exit plane, which show that the annular configuration yields an average Mach number 57% higher than the circular configuration under conditions close to those for maximum air entrain...

Accuracy and applicable range of a reconstruction technique for hybrid rockets

Abstract: Accuracy of a reconstruction technique assuming a constant characteristic exhaust velocity (c*) efficiency for reducing hybrid rocket firing test data was examined experimentally. To avoid the difficulty arising from a number of complex chemical equilibrium calculations, a simple approximate expression of theoretical c* as a function of the oxidizer to fuel ratio (ξ) and the chamber pressure was developed. A series of static firing tests with the same test conditions except burning duration revealed that the error in the calculated fuel consumption decreases with increasing firing duration, showing that the error mainly comes from the ignition and shutdown transients. The present reconstruction technique obtains ξ by solving an equation between theoretical and experimental c* values. A difficulty arises when multiple solutions of ξ exists. In the PMMA-LOX combination, a ξ range of 0.6 to 1.0 corresponds to this case. The definition of c* efficiency necessary to be used in this reconstruction technique is different from a c* efficiency obtained by a general method. Because the c* efficiency obtained by average chamber pressure and ξ includes the c* loss due to the ξ shift, it can be below unity even when the combustion gas keeps complete mixing and chemical equilibrium during the entire period of a firing. Therefore, the c* efficiency obtained in the present reconstruction technique is superior to the c* efficiency obtained by the general method to evaluate the degree of completion of the mixing and chemical reaction in the combustion chamber.

A novel experimental hypoxia chamber for cell culture.

Abstract: Tissue hypoxia is a common pathophysiological process. Since 1990s, numerous studies have focused on investigating cellular adaptation to experimental hypoxia. A modular incubator chamber made of solid materials has frequently been used in the experiments that require hypoxic conditions. Here, we introduce a novel and inflatable chamber for hypoxia experiments. In experiments detecting hypoxia-induced accumulation of hypoxia-inducible factor 1α (HIF-1α) and hypoxia-induced expression of HIF-1-regulated genes, the new chamber yielded reproducible and comparable results as the modular incubator chamber did. The new chamber did not create inner chamber pressure during its use. Other properties of the new chamber were low-cost, easy to use, and leakage-free. Moreover, the size of the new chamber was adjustable, and the smaller one could be placed onto an inverted microscope for real-time studies. The successful examples of real-time studies included the real-time recording of GFP-HIF-1α fusion nuclear translocation and endothelial cell tubular formation.

Closed-Loop Precision Throttling of a Hybrid Rocket Motor

Abstract: A closed-loop throttle controller for a laboratory-scale N2O and hydroxyl-terminated polybutadiene hybrid rocket motor is presented. Closed-loop throttling was achieved using commercial off-the-shelf valve hardware and a commercially available motor case adapted for hybrid rocket testing. Multiple and open- and closed-loop tests were performed to demonstrate that closed-loop control can significantly reduce the run-to-run burn variability typical of hybrid rocket motors. Closed-loop proportional/integral control algorithms featuring thrust or pressure feedback were used to track prescribed step and linear ramp profiles. Because the relationship between the selected throttle control valve position and the effective valve flow area was highly nonlinear, the effect of valve position on motor thrust/chamber pressure was measured open loop and curve fit to allow direct command of either total thrust or chamber pressure. Control law gains were tuned a priori using a numerical model and then adjusted using the a...

Assessment of primary energy conversions of oscillating water columns. II. Power take-off and validations

Abstract: This is the second part of the assessment of primary energy conversions of oscillating water columns (OWCs) wave energy converters. In the first part of the research work, the hydrodynamic performance of OWC wave energy converter has been extensively examined, targeting on a reliable numerical assessment method. In this part of the research work, the application of the air turbine power take-off (PTO) to the OWC device leads to a coupled model of the hydrodynamics and thermodynamics of the OWC wave energy converters, in a manner that under the wave excitation, the varying air volume due to the internal water surface motion creates a reciprocating chamber pressure (alternative positive and negative chamber pressure), whilst the chamber pressure, in turn, modifies the motions of the device and the internal water surface. To do this, the thermodynamics of the air chamber is first examined and applied by including the air compressibility in the oscillating water columns for different types of the air turbine PTOs. The developed thermodynamics is then coupled with the hydrodynamics of the OWC wave energy converters. This proposed assessment method is then applied to two generic OWC wave energy converters (one bottom fixed and another floating), and the numerical results are compared to the experimental results. From the comparison to the model test data, it can be seen that this numerical method is capable of assessing the primary energy conversion for the oscillating water column wave energy converters.

Optimization of dry etching parameters for fabrication of polysilicon waveguides with smooth sidewall using a capacitively coupled plasma reactor.

Abstract: In this paper, we demonstrate the optimization of a capacitively coupled plasma etching for the fabrication of a polysilicon waveguide with smooth sidewalls and low optical loss. A detailed experimental study on the influences of RF plasma power and chamber pressure on the roughness of the sidewalls of waveguides was conducted and waveguides were characterized using a scanning electron microscope. It was demonstrated that optimal combination of pressure (30 mTorr) and power (150 W) resulted in the smoothest sidewalls. The optical losses of the optimized waveguide were 4.1±0.6 dB/cm.

Analysis of Coolant Mass Flow Requirements for Transpiration Cooled Ceramic Thrust Chambers

Abstract: The long-term development of ceramic rocket engine thrust chambers at the German Aerospace Center (DLR) culminates in compact designs of transpiration-cooled fibre-reinforced ceramic rocket engine chamber structures Achievable benefits of the transpiration cooled ceramic thrust chamber are the reduction of engine mass and manufacturing cost, as well as an increased reliability and higher lifetime due to thermal cycle stability The transpiration cooling principle however reduces the engine performance Due to the transpiration cooling the characteristic velocity decreases with increasing coolant ratio The goal of the chamber development is therefore to minimize the required coolant mass flow The wall temperature can be calculated using known heat transfer correlations, for example given by Bartz, and employing a model given in literature for the reduction of the heat transfer coefficient based on coolant mass flow By this method the required coolant mass flow ratio for different chamber diameters and pressure levels can be calculated This paper discusses the application potential of DLR's ceramic thrust chamber technology for high performance engines Parametric variations of engine sizing (such as chamber pressure and diameter) are performed For large diameters and high chamber pressures the required coolant ratio is below 1%

Nylon 66 nanofibers prepared by CO2 laser supersonic drawing

Abstract: Nylon 66 nanofibers were prepared by irradiating as-spun nylon 66 fibers with radiation from a carbon dioxide (CO2) laser while drawing them at supersonic velocities. A supersonic jet was generated by blowing air into a vacuum chamber through the fiber injection orifice. The fiber diameter depended on the drawing conditions used, such as laser power, chamber pressure, laser irradiation point, and fiber supply speed. A nanofiber obtained at a laser power of 20 W and a chamber pressure of 20 kPa had an average diameter of 0.337 μm and a draw ratio of 291,664, and the drawing speed in the CO2 laser supersonic drawing was 486 m s−1. The nanofibers showed two melting peaks at about 257 and 272°C. The lower melting peak is observed at the same temperature as that of the as-spun fiber, whereas the higher melting peak is about 15°C higher than the lower one. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40015.

Tunnel segment uplift model of earth pressure balance shield in soft soils during subway tunnel construction

Abstract: Segment uplift is a frequent problem during the construction of shield tunnels. This article presents a full-scale field test to study the influence factors of segment uplift, such as chamber pressure, advance rate, vertical component force of total thrust and grouting pressure and grout composition. This paper proposes a tunnel segment uplift calculation model of earth pressure balance shield based on a series of in situ tests in the typical soft soil stratum in China. The test results show that grouting pressure and grout composition have significant impacts on the segment uplift. However, the influences of chamber pressure, advance rate and total thrust are insignificant for the uplift. The analysis data based on the calculation model correspond well with the monitoring data in the shield tunnelling construction. By comparison, the deviation rate ranges from −19% to +15%.

Impact of static pressure on transmembrane fluid exchange in high molecular weight cut off microdialysis.

Abstract: With the interest of studying larger biomolecules by microdialysis (MD), this sampling technique has reached into the ultrafiltration region of fluid exchange, where fluid recovery (FR) has a strong dependence on pressure. Hence in this study, we focus on the fluid exchange across the high molecular weight cut off MD membrane under the influence of the static pressure in the sampling environment. A theoretical model is presented for MD with such membranes, where FR has a linear dependence upon the static pressure of the sample. Transmembrane (TM) osmotic pressure difference and MD perfusion rate decide how fast FR increases with increased static pressure. A test chamber for in vitro MD under static pressure was constructed and validated. It can hold four MD probes under controlled pressurized conditions. Comparison showed good agreement between experiment and theory. Moreover, test results showed that the fluid recovery of the test chamber MD can be set accurately via the chamber pressure, which is controlled by sample injection into the chamber at precise rate. This in vitro system is designed for modelling in vivo MD in cerebrospinal fluid and studies with biological samples in this system may be good models for in vivo MD.

Starting Transients in Vacuum Ejector-Diffuser System

Abstract: In this endeavor, the transients persisting in a vacuum ejector system are studied by numerically simulating the flowfield and experimentally validating the steady-state results. An inertial effect is discovered in the study due to the recirculation zone moving forward and backward during the transients, and subsequently the pressure in the secondary chamber oscillates. The flow exhibits damped oscillations in which the direction of the mass flux through the secondary chamber keeps changing and finally settles down to a state in which there is no mass flux into or from the secondary chamber. It is seen that the characteristics of the short transients in pressure and mass flux in the secondary chamber depend highly on the thicknesses of the primary and secondary jets and the secondary chamber volume. The inertial effect reduces with the reduction in thicknesses of both primary and secondary jets. As the volume of the secondary chamber increases, the inertial effect decreases further. It is also seen that t...

An Approach for Predicting the Flow Regime in an Aero Engine Bearing Chamber

Abstract: The paper discusses an approach to predict the two-phase flow regime in an aero engine bearing chamber. In general, one of two distinct flow regimes can occur in a bearing chamber. At lower shaft speeds, the oil flow is only partially affected by the air flow, which is driven by the rotating shaft. At higher shaft speeds, however, the rotating air flow forces the oil film at the chamber walls to rotate, too. Thus, the two flow regimes correspond to two very different oil film distributions inside a bearing chamber presumably with significant consequences for the internal wall heat transfer. In order to determine the driving parameters for the flow regimes and the change between them, experiments were carried out with a bearing chamber test rig. With this test rig all relevant operating parameters as well as the geometry of the bearing chamber could be varied independently. The analysis of the experimental data allowed defining a general parameter which takes into account the chamber pressure, shaft speed, oil viscosity and chamber length. The influence of the oil flow rate and the overall dimensions are assessed qualitatively.Copyright © 2014 by ASME

Method for direct deposition of silicon carbide (SiC) coating on carbon material surface in graphite heat-generating body heating furnace

Abstract: The invention provides a method for direct deposition of a silicon carbide (SiC) coating on a carbon material surface in a graphite heat-generating body heating furnace, and the method comprises the following steps: (1) vacuumizing the graphite heat-generating body heating furnace body as a deposition furnace to a vacuum degree reaching below 10 Pa; (2) raising the temperature of the graphite heat-generating body heating furnace to 1000 to 1200 DEG C; (3) using hydrogen as a carrier gas, using a bubbling method to lead methyltrichlorosilane into a graphite heat-generating body heating furnace chamber, regulating the carrier gas flow rate, according to the furnace body size, to 200 ~ 800ml / min, at the same time, using argon with the flow rate of 200 ~ 800ml / min as a dilution gas, keeping the heating furnace chamber pressure to be 3*10 ~10 Pa for deposition for 20 ~ 50 hours, and cooling to form the silicon carbide (SiC) coating on the carbon material surface. According to the method, no special chemical vapor deposition equipment is needed in a preparation process, and the prepared silicon carbide (SiC) coating is good in quality, and large, flexible and controllable in coating thickness.

Method for operating high pressure pump of combustion engine fuel supply system, involves detecting chamber pressure by elevation and lowering of compression unit, and determining whether pump is operated with fuel with unacceptable quality

Abstract: The method involves providing a pump body (101) forming a compression chamber (105). An inlet valve (110) i.e. pre stroke control valve, is connected between an inlet passage (108) and the chamber. An exhaust valve (120) is connected between the chamber and an outlet passage (109). Fuel with high pressure is contained in the chamber. A pressure sensor (102) is arranged in the chamber. Chamber pressure is detected by elevation and lowering of a compression unit (106) i.e. pump piston. A determination is made whether a pressure pump (100) is operated with fuel including unacceptable quality. An independent claim is also included for a high pressure pump for a fuel supply system of a combustion engine.

Two-Phase Flow Heat Transfer and Pressure Drop in Horizontal Scavenge Pipes in an Aero Engine

Abstract: In modern aero-engines, the lubrication system plays a key role due to the demand for high reliability. Oil is used not only for the lubrication of bearings, gears, or seals but it also removes large amounts of the generated heat. Also, air from the compressor at elevated temperature is used for sealing the bearing chambers and additional heat is introduced into the oil through radiation, conduction, and convection from the surroundings. The impact of excessive heat on the oil may lead to severe engine safety and reliability problems which can range from oil coking (carbon formation) to oil fires. Coking may lead to a gradual blockage of the oil tubes and subsequently increase the internal bearing chamber pressure. As a consequence, oil may migrate through the seals into the turbomachinery and cause contamination of the cabin air or ignite and cause failure of the engine. It is therefore very important for the oil system designer to be capable to predict the system’s functionality. Coking or oil ignition may occur not only inside the bearing chamber but also in the oil pipes which carry away the air and oil mixture from the bearing chamber. Bearing chambers usually have one pipe (vent pipe) at the top of the chamber and also one pipe (scavenge pipe) at the bottom which is attached to a scavenge pump. The vent pipe enables most of the sealing air to escape thus avoid over-pressurization in the bearing compartment. In a bearing chamber, sealing air is the dominant medium in terms of volume occupation and also in terms of causing expansion phenomena. The scavenge pipe carries away most of the oil from the bearing chamber but some air is also carried away. The heat transfer in vent pipes was investigated by Busam (2004, “Druckverlust und Warmeuebergang im Entlueftungssystem von Triebwerkslagerkammern (Pressure Drop and Heat Transfer in the Vent System in an Aero Engine’s Bearing Chamber),” Ph.D. thesis, Logos Verlag, Berlin, Germany) and Flouros (2009, “Analytical and Numerical Simulation of the Two Phase Flow Heat Transfer in the Vent and Scavenge Pipes of the CLEAN Engine Demonstrator,” ASME J. Turbomach., 132(1), p. 011008). Busam has experimentally developed a Nusselt number correlation for an annular flow in a vent pipe. For the heat transfer predictions in scavenge pipes, no particular Nusselt number correlation exist. This paper intends to close the gap in this area. As part of the European Union funded research programme ELUBSYS (Engine Lubrication System Technologies), an attempt was done to simplify the oil system’s architecture. In order to better understand the flow in scavenge pipes, high speed video was taken in two sections of the pipe (vertical and horizontal). In the vertical section, the flow was a wavy annular falling film, whereas the flow in the horizontal section was an unsteady wavy stratified/slug flow. Heat transfer has been investigated in the horizontal section of the scavenge pipe, leaving the investigation on the vertical section for later. Thanks to the provided extensive instrumentation, the thermal field in, on, and around the pipe was recorded, evaluated, and also numerically modeled using ansys cfx version 14. Brand new correlations for two-phase flow heat transfer (Nusselt number) and for pressure drop (friction coefficient) in horizontal scavenge pipes are the result of this work. The Nusselt number correlation has been developed in such a way that smooth transition (i.e., no discontinuity) from two-phase into single phase flow is observed.