Varying Chamber Pressure Research Articles

Effect of Using Fractals as Grain Configuration on the Performance of Solid Rocket Motors

Grain design is a very crucial consideration for determining the performance of solid propellant rocket motors. A rocket’s performance and combustion characteristics (thrust profile, chamber pressure variation, propellant mass flow rate, and sliver among other important performance parameters) depend very strongly on the grain configuration. We propose fractal shapes (Koch star, Koch snowflake, Gosper, and Cesaro) as new port geometries and theoretically predict their performance using simulations based on the fast-marching method implemented in the open-source software Open-Motor. The initial thrust for fractal geometry grains was found to be significantly higher than the commonly used industry standard BATES and Finosyl ports. The fractal grains also showed a significant decrease in sliver as compared to the Finocyl port that is generally used to increase performance as compared to the circular BATES ports. Especially, The Koch snowflake port had a drastically lower sliver. These new grain geometries proposed in this work can be used for applications in which low initiation and ignition times along with high initial thrust are crucial. Moreover, these geometries can improve the performance of the solid rocket motor (SRM) owing to their better regression characteristics which promise complete utilization of the entire grain web.

Simulation based analysis to study the effect of compression ring crown height in ring liner assembly on the performance of four stroke petrol engine

Among different piston rings of an Internal Combustion Engine (IC), the top compression ring-liner assembly shared a momentous amount of the total frictional losses, particularly at the Top Dead Center (TDC) and Bottom Dead Center (BDC) where boundary lubrication subsists. In the present study, the lubrication mechanism in piston ring cylinder liner conjunction for top compression ring using one dimensional Reynolds equation assuming axisymmetric contact was studied. The hydrodynamic and mixed lubrication regimes were taken during the study. Gumbel boundary conditions were used for Reynolds equation solution. For boundary pressure calculation, first, combustion chamber pressure variation was determined, then, interring pressure was calculated assuming orifice volume method by solving mass flow rate through crevice volumes using Runge-Kutta 4th order method. The Reynolds equation was solved using finite difference method. Whole solution process was repeated for different engine speed and crown height of top compression ring to study the effect of them in wear and power loss. First, the solution was found for 3000, 5000 and 7500 RPM keeping constant crown height of 10 µm. Average power loss was found to be increased with the increasing engine speed. There was increased in oil film thickness around mid-stroke with the increased engine speed, but there was no significant change in film thickness with the engine speed at the TDC and BDC positions. Then, the solution was again repeated for different RPM varying the crown height. The compression ring with lower crown height showed the better wear performance by increasing the minimum film thickness in critical zones of engine cycle for all RPM. The crown height of 5,7 and 9 µm gave the minimum power loss (77.89, 163.47 and 297.33 W) for 3000, 5000 and 7500 rpm. Moreover, the power loss in the range of 5-9 µm had no significant differences.

Etching of photon energy into binding energy in depositing carbon films at different chamber pressures

A hot filament chemical vapor deposition is an attractive technique to deposit carbon films of different applications. In this technique, it is also feasible to study the influence of chamber pressure in the deposition of carbon films. In the deposition chamber, having dissociated from the methane precursor, gaseous carbon atoms first convert into the graphite state atoms and then into the diamond state atoms. An increase in the chamber pressure changes the morphology and structure of the deposited carbon films. The growth rate of the deposited carbon film increases by increasing the chamber pressure from 3.3 kPa to 8.6 kPa. The rate of converting gaseous carbon atoms into diamond atoms also increases. At 11.3 kPa and 14 kPa chamber pressure, gaseous carbon atoms convert into graphite state atoms at a high rate. The gas activation and gas collision processes vary broadly at varying chamber pressure. The morphology and structure of carbon films got deposited at different growth rates. The dissociation of molecular hydrogen into atomic hydrogen varies by varying the chamber pressure. Atomic hydrogen etched the photons released from the hot filaments. Thus, bits of differently shaped energy result. Gaseous carbon atoms convert into graphite and diamond state atoms under suitably shaped bits of energy. Graphite state atoms bind under the same involved bits, which is not the case when the diamond state atoms bind. The study sets a new trend in depositing, characterizing, and analyzing carbon films.

Effect of Structural Materials on Monopropellant Thruster Propulsion Performance in Micro Scale

This paper reports on the effect of structural materials on heat loss-associated propulsion performance degradation of monopropellant thrusters in the micro scale. In order to address the effect of fabrication materials on heat loss, propellant flow characteristics, and propulsion performance, a conjugate heat transfer numerical study has been conducted considering several practical substrate candidates for microthrusters. The results were analyzed with respect to the thermal diffusivity of the materials, which revealed different propulsion performance characteristics and inner nozzle flow characteristics due to varying amounts of heat loss, depending on the microfabrication materials used and propellant enthalpies. Regardless of propellant enthalpies, however, there was a dramatic degradation in the amount of the thrust produced with respect to thermal diffusivity, particularly in the range of low thermal diffusivity. Glass, among the material types compatible with fabrication processes in regard to microthrusters, exhibited a 4% degradation in thrust performance for the 50 mN class microthruster considered, with the least degradation, while copper, with 7% degradation, exhibited the greatest amount of degradation among the materials considered. With varying chamber pressure and Mach number at the nozzle exit depending on structural materials, the results also indicated the necessity of heat loss consideration in a microthruster design process.

Nonlinear oscillations of a collapsible tube subjected to unsteady external pressure

The non-linear dynamics of an extremely thin-walled collapsible tube with internal flow subjected to a time-varying external pressure are studied experimentally and theoretically. For the constant chamber pressure case, we observe the existence of a fixed-point attractor, period-1 attractor, and quasiperiodic attractor. The period-1 limit cycle oscillations are essentially relaxation oscillations with up-down asymmetry in the time domain, and as the Reynolds number increases, the asymmetry becomes greater. With the forcing (varying chamber pressure), the system has no fixed points; its response can be period-n, quasiperiodic, or chaotic, depending upon the Reynolds number, driving amplitude, and frequency. For the forced system, at a low Reynolds number, the external forcing dominates the self-excited oscillations and symmetric oscillations are observed; at a higher Reynolds number, the reverse is true. In experiments and theory, aperiodic oscillations for the forced system are always observed in regimes beyond the Hopf bifurcation point of the unforced system. Distended and collapsed cases, under forcing, exhibit only 1:1 synchronous oscillation. These suggest that a natural oscillation timescale of the system must be present for the external forcing to induce aperiodicity. In the experiments, the forced system exhibits signs of quasiperiodic route to chaos at lower driving amplitude, while period-doubling route to chaos at higher driving amplitude. When the system is forced near its natural frequency, an aperiodic response is totally suppressed.

Experimental study of position tracking control and pressure variation analysis on electrohydraulic system in open loop

This paper studies on the variable displacement electro-hydrostatic actuation system to control the position of hydraulic actuator with the used of bidirectional swashing variable displacement axial piston pump. The pump control system is more efficient than valve control system. The paper is focused on the experiment of position tracking of a symmetric linear hydraulic actuator in an open loop control, the demand of actuator is sinusoidal with frequencies of 0.10 to 0.25 Hz, amplitude of 0.1 m and offset of demand 0.1 m. The effective pressure force of the actuator depends on the chamber pressure variation of the actuator, the nature of pressure variation measured which played decisive role to control the position of the actuator. In industrial application, the role of the electrohydraulic system with accurate control is quite evident, the present experimental work emphasis to control the hydraulic actuator position.

Differences of chamber pressure variations during stage separation between flight and detonation-shock-tube-based ground tests

Interstage separation is a key link in the flight process of a solid rocket; however, the ground test often cannot cover the environmental conditions of the flight state during interstage separation. Therefore, it is necessary to master the difference between flight and ground tests during this process for the ground test results to reflect the flight environment effectively. With the new detonation-shock-tube-based ground test technology as the research background, combined with a theoretical model and numerical simulation, this paper studies the similarity law of pressure variation in the chamber and the difference of the effect of initial pressure and density conditions between flight and ground tests. In addition, it illustrates the requirement for equivalent-simulating stage separation through the detonation shock tube.

Highly selective and vertical etch of silicon dioxide using ruthenium films as an etch mask

Highly selective and vertical profile etching of thermally grown SiO2 films using thin metallic Ru mask films was investigated in a commercial inductively coupled plasma etcher. The effects of varying chamber pressure, substrate bias, and gas composition on etch performance were all investigated. Selectivities (measured as the SiO2 etch rate divided by the Ru etch rate) ranging from 50 to as high as 370 were measured under various process conditions without compromising the etch profile quality. It was found that fluorocarbon gas mixtures (CF4/CHF3 and CF4/C4F8) gave the best results. The addition of SF6 to the gas mixture dramatically reduced selectivity, resulting in significant Ru mask faceting and necking in the etched pillars and is not recommended for use in a standard Ru/SiO2 etch process.

Controlling Thermal Diffusivity, Residual Stress and Texture in W/Cu Nano-Multilayers by Magnetron Chamber Pressure Variation

The effect of magnetron deposition pressure during manufacture of W/Cu nano-laminates on their thermal diffusivity, residual stress depth profiles and texture was analysed. A strong correlation between these properties and the Ar working pressure was confirmed experimentally via a combination of Transient Grating Spectroscopy, Focused Ion Beam ring drilling, and cross-sectional high resolution SEM and EDX characterisation. The underlying mechanisms controlling thermal diffusivity and residual stress can be related to the defect evolution during sputter deposition, which is largely controlled by the interaction of the working gas and the sputtered metal atoms.

Influence of chamber pressure variations of plasma nitriding on surface hardness and micro structure of Al 6061

Aluminium 6061 is a material that is widely applied in industrial and automotive parts. The corrosion resistance and surface hardness of Al 6061 can be improved by using plasma nitriding. Plasma nitriding is the process of treating the surface of a material by inserting nitrogen in the material through the plasma, i.e. nitrogen gas was converted in the form of plasma before being inserted into the material. This research was conducted using experimental research methods by directly observing the plasma nitriding process. This research used aluminium alloy 6061 as a specimen, variations in chamber pressure of plasma nitriding 100 mTorr, 200 mTorr, and 300 mTorr, constant temperature of 150 °C, constant power input of 40 watts, and holding time for 2 hours. Hardness testing was carried out using a micro-Vickers hardness tester, whereas microstructure testing used SEM (Scanning Electron Microscope) and EDAX. Experimental results showed the highest surface hardness value of Al 6061 was 276.5 VHN. This condition occurred at a chamber pressure of 200 mTorr, temperature of 150 °C, the input power of 40 watts and a holding time of 2 hours. Based on composition and microstructure analysis using EDAX and Scanning Electron Microscope shown that the lowest surface hardness 179.4 VHN had a nitrogen content of 1.225% and this occurred at a chamber pressure of 300 mTorr.

Controlling Thermal Diffusivity, Residual Stress and Texture in W/Cu Nano-Multilayers by Magnetron Chamber Pressure Variation

Controlling Thermal Diffusivity, Residual Stress and Texture in W/Cu Nano-Multilayers by Magnetron Chamber Pressure Variation

LyoPRONTO: an Open-Source Lyophilization Process Optimization Tool

This work presents a new user-friendly lyophilization simulation and process optimization tool, freely available under the name LyoPRONTO. This tool comprises freezing and primary drying calculators, a design-space generator, and a primary drying optimizer. The freezing calculator performs 0D lumped capacitance modeling to predict the product temperature variation with time which shows reasonably good agreement with experimental measurements. The primary drying calculator performs 1D heat and mass transfer analysis in a vial and predicts the drying time with an average deviation of 3% from experiments. The calculator is also extended to generate a design space over a range of chamber pressures and shelf temperatures to predict the most optimal setpoints for operation. This optimal setpoint varies with time due to the continuously varying product resistance and is taken into account by the optimizer which provides varying chamber pressure and shelf temperature profiles as a function of time to minimize the primary drying time and thereby, the operational cost. The optimization results in 62% faster primary drying for 5% mannitol and 50% faster primary drying for 5% sucrose solutions when compared with typical cycle conditions. This optimization paves the way for the design of the next generation of lyophilizers which when coupled with accurate sensor networks and control systems can result in self-driving freeze dryers.

The influence of dynamic swash plate vibration on outlet flow ripple in constant power variable-displacement piston pump

The vibration of a swash plate is caused by the piston forces and the control actuator acting on the swash plate. An earlier study of the outlet flow ripple of variable-displacement axial piston pumps assumed a fixed swash plate angle; it ignored the influence of swash plate vibration on the outlet flow ripple of the axial piston pump. In this work, a theoretical model of the outlet flow ripple and pressure pulsation was established in a constant power variable-displacement piston pump. The vibration of swash plate, flow leakage, and valve dynamic characteristics are considered in the theoretical model. The computational results of the theoretical model at different external load pressures are verified by comparison with experimental results. The vibration of the swash plate is strongly influenced by both the piston chamber pressure variation and the control actuator mechanism. The study proved the influence of the swash plate vibration on the outlet flow ripple and the pressure pulsation of an axial piston pump. Compared to the case of a fixed swash plate angle, accounting for swash plate vibration is much more suitable for the accurate determination of the outlet flow ripple and pressure pulsation of an axial piston pump. It is also shown that the vibration of the swash plate affects the valve plate design. Accordingly, valve plate optimization based on the theoretical model of the outlet flow ripple was also studied in this work. The amplitude of the instantaneous outlet flow ripple was considered as the optimization objective function. Finally, the optimized design parameters for a constant power variable-displacement swash plate axial piston pump were evaluated.

A study on the development of a numerical model for a rotary vane vacuum pump for brake boosters

A negative pressure is formed inside the brake booster in a running diesel vehicle by using a rotary vane vacuum pump. In vacuum pump design, it is important to reduce the time required to induce the minimum negative pressure required for immediate consecutive braking and to reduce the torque used to drive the pump. In this study, a numerical simulation model to predict the performance of a vacuum pump was developed and experimentally validated by comparing the pump’s drive torque and the time required by a 4 L chamber to reach the target pressure. The housing profile was obtained via 3D scanning, while the check valve, bypass hole, and groove, which significantly affect the pump performance, were mathematically described. The model was validated by comparing the vacuum chamber pressure variation and the average torque. Similarly, the pump performance with respect to changes in major design factors, such as check valve and bypass hole shapes, were compared against the experimental data. In addition, the pump performance was predicted as a function of the housing profile shape, which is difficult to evaluate experimentally, and a new profile shape to improve the performance was proposed.

Dynamic Response of a Dual-Manifold Injector Rocket Engine to Throttling

The capability of a dual-manifold injector rocket engine scheme for deep throttling under extremely fuel-rich condition was demonstrated experimentally. The dynamic response of the rocket engine to throttling was analyzed as well. Under the extremely fuel-rich condition, the response of chamber pressure is sensitive to oxygen adjusting but insensitive to fuel adjusting. Response delay appears at the end of throttling, for both oxygen-adjusting cases and fuel-adjusting cases. The response delay mainly comes from the supply system for oxygen adjusting, whereas the response delay mainly results from the combustion process for fuel adjusting. The antiregulation, which means the chamber pressure variation is opposite to the throttling direction, occurs at the beginning of throttling. It can only be triggered by fuel adjusting, not by oxygen adjusting. It is found that fuel adjusting contributes to the antiregulation, whereas oxygen adjusting suppresses the antiregulation. Furthermore, the effects of oxygen adjusting and fuel adjusting on the antiregulation are positively related with their adjusting rate. The slow evaporation of liquid fuel under extremely fuel-rich condition is identified strongly with the response delay and the antiregulation. First, the evaporation time of liquid fuel is the main reason for response delay after the throttling process is terminated. Second, it is the interval between large amounts of heat absorption and large amounts of vapors released during the evaporation process of droplets that finally results in the antiregulation.

Twin-Fluid Atomized Spray Combustion of Straight Vegetable Oil at Elevated Pressures

The effect of the chamber pressure on combustion of a twin-fluid-atomized spray of straight vegetable oil (VO) in a swirl stabilized combustion system is experimentally studied. A system with high pressure capabilities was developed, and flame and emissions characteristics of VO are investigated at elevated pressures up to about 5 bars, different heat release rates (HRRs), and atomizing air to liquid ratios (ALR) by mass. An image analysis technique was developed to infer flame and soot characteristics from visual images acquired by a digital camera. An increase in the ALR resulted in improved combustion of VO, characterized by blue flames, lower CO and NOx emissions, and minimal soot formation. For a given fuel flow rate, an increase in the chamber pressure resulted in smaller volume flames with lower CO levels but higher NOx emissions. Compared to diesel, as pressure increased, straight VO flames produced lower NOx and more voluminous flames characterized by distributed combustion with less soot formation. Overall, straight VO could be atomized and combusted at elevated pressures using the twin-fluid atomizer of the present study, and the resulting VO flames exhibited less sensitivity to chamber pressure variations.

Solid Rocket Motor Propellant Optimization with Coupled Internal Ballistic–Structural Interaction Approach

This research aims to optimize the geometric design of slotted propellant grains for solid rocket motors with respect to coupled internal ballistic performance and structural strength criteria. In-house codes such as a zero-dimensional internal ballistic solver and an analytical burnback solver are implemented to compute the variation of chamber pressure and the rocket thrust transiently. Structural analysis of the solid propellant is achieved by using a parametric linear viscoelastic model and a parametric cooldown heat transfer model, both of which are based on the finite element method. The transient temperature distribution data derived from the cooldown process are required inputs for the material properties to be used in the viscoelastic structural analysis. To enable an efficient optimization process, a surrogate heat transfer model that predicts the cooldown time of the system by eliminating expensive iterations is also implemented and validated. Within a coupled analysis approach, the pressure data obtained from the internal ballistic performance analysis are used for the ignition step of the linear viscoelastic analysis. The structural analysis results are evaluated by using a deterministic approach based on the margin of safety with respect to the stress and strain criteria. Finally, the optimum geometrical parameters for a slotted grain subjected to both structural and internal ballistic performance constraints are investigated through multidisciplinary optimization techniques.

Design and control of a 3-chambered fiber reinforced soft actuator with off-the-shelf stretch sensors

The necessity for efficient control of soft actuators has recently resulted in the development of complex physical models that are actuator geometry and material type dependent. In this paper, we address the ability to do closed-loop control with a simplified model independent of material properties and material characteristics of a soft robotic system. We demonstrate this by using a P-controller on a new 3-chambered, fiber-reinforced elastomeric actuator (3CA) that utilizes off-the-shelf stretch sensors. A motion capture system is used to calibrate and generate two different quasi-static models (a general linear regression model and an input dependent model) that map the varying chamber pressure readings with the actuator’s end effector position, effectively represented by the stretch sensor curvature. Simulations using a closed-loop controller, with both models, provide further insight on the quality of the models and corresponding control performance. We use this information in an experimental study that yields comparable performances to the simulated results. Moreover, we demonstrate that the input-dependent model based controller can provide better results than that of the general model based controller. Finally, we demonstrate that our soft actuator can be closed-loop controlled with off-the-shelf stretch sensors with repeatable results. This opens a way to design new control concepts for multi-chambered actuators that can produce more complex motions in the future.

Carbon-conditioned recycled aggregate in concrete production

This paper investigates the use of carbon-conditioned recycled aggregate (RACO2) in concrete production. Experimental work is conducted for RACO2 with varying chamber pressure (0 kPa, 75 kPa, 150 kPa), chamber duration (0 min, 30 min, 90 min) and RACO2 replacement percentages (0%, 30%, 100%) for concrete production. Average of three results on compressive, tensile and flexible strength and modulus of elasticity at 28 curing days are compared. The process of carbon-conditioning refers to the pressurised exposure of recycled aggregate to carbon dioxide (CO2) for a certain period of time before concrete mixing. The entraining of CO2 assists to facilitate the negative properties of recycled aggregate that produces a deprived final recycled concrete as well as providing a superior calcium carbonate chemical reaction. Carbon-conditioning reduces porosity and water absorbency of recycled aggregate. In addition to improve recycled aggregate quality, CO2 emissions from the aggregate also help filling openings in the concrete composition, generating an improved bond matrix from the formation of calcium carbonates (Zhan et al., 2014). These two traits assist in enhancing the recycled concrete properties. This paper demonstrates a great potential in the use of RACO2 in improving physical and mechanical properties of recycled concrete and provides insight for effective use of recycled aggregate for concrete production. The effective use of recycled aggregate can reduce the amount of landfill that is utilised for construction and demolition waste.

Chemical Reaction Effects on Heat Loads of CH4/O2 and H2/O2 Rockets

Cooling of liquid rocket thrust chamber walls to allowable solid material temperatures induces near-wall chemical reactions, which are known to have an important role on the heat transfer from the hot gas to the wall. In this study, the contribution of near-wall chemical reactions to heat flux is investigated and quantified by suitable numerical analyses. Numerical results are first compared to literature experimental data of wall heat flux in subscale calorimetric thrust chambers for both oxygen/methane and oxygen/hydrogen propellant combination. Then, a parametric analysis is carried out varying chamber pressure, wall temperature, and propellant combination. This study highlights that oxygen/methane combustion products are more subject to near-wall recombination phenomena. They provide an increase of wall heat flux between 20 and 30% with respect to the frozen flow model evaluation, whereas in the case of oxygen/hydrogen, the wall heat flux increase due to recombination reactions is between 7 and 14%.