Showing papers on "Chamber pressure published in 2022"

Visualization of Pre-Chamber Combustion and Main Chamber Jets with a Narrow Throat Pre-Chamber

Abstract: <div class="section abstract"><div class="htmlview paragraph">Pre-chamber combustion (PCC) has re-emerged in recent last years as a potential solution to help to decarbonize the transport sector with its improved engine efficiency as well as providing lower emissions. Research into the combustion process inside the pre-chamber is still a challenge due to the high pressure and temperatures, the geometrical restrictions, and the short combustion durations. Some fundamental studies in constant volume combustion chambers (CVCC) at low and medium working pressures have shown the complexity of the process and the influence of high pressures on the turbulence levels. In this study, the pre-chamber combustion process was investigated by combustion visualization in an optically-accessible pre-chamber under engine relevant conditions and linked with the jet emergence inside the main chamber. The pre-chamber geometry has a narrow-throat. The total nozzle area is distributed in two six-hole rows of nozzle holes. A novel optical pre-chamber assembly was designed and tested on an optical engine, with combustion only in the pre-chamber volume, using methane (99.5% purity CH₄) as fuel. A separate measurement was carried out using a metal pre-chamber assembly to study the emergence of the pre-chamber jets into the main chamber to assess the difference between the pre-chambers. The combustion process was captured using a broadband camera and pressure transducers in both chambers (pre- and main chamber). The combustion inside the pre-chamber starts at the spark location; the flame propagates along the cone and subsequently propagates fast inside the throat. The broadband combustion luminosity exhibited a non-proportional relation with the heat release rate (HRR) due to the CO₂* chemiluminescence. An HSV-model (Hue Saturation Value) analysis revealed the predominance of premixed combustion during the first stage of the process, followed by infrared flame radiation. Finally, although the optical pre-chamber assembly showed a faster pressure increase, the combustion process is similar to the metal pre-chamber assembly on a mass burnt scale.</div></div>

Effect of Combustion Chamber Geometrical Parameters on the Decomposition and Combustion Characteristics of an ADN-Based Thruster

Abstract: In this paper, numerical simulations were used to study the decomposition and combustion processes inside the 0.2 N-class ADN-based thruster, and the effects of two geometrical parameters (length and diameter) of the combustion chamber on the combustion performance were evaluated. The decomposition and combustion processes of the thruster were simulated using a reduced chemical reaction mechanism with 22 components and 20 reactions steps. According to the distribution of the basic physical fields, the variation patterns of the pressure field, velocity field, temperature field, and key component parameters caused by different combustion chamber geometrical parameters were observed and analyzed. The results show that the specific impulse and thrust of the thruster increased and then decreased with the increase of the combustion chamber diameter. When the combustion chamber diameter is 7.9 mm, the specific impulse reaches the maximum value of 206.6 s. Additionally, the specific impulse increased from 186 s to 206 s when the combustion chamber length was changed from 7 mm to 11 mm; the specific impulse increased gradually but not significantly, and the growth trend started to flatten out. The results from the paper can serve as a reference for the design and vacuum testing of an ADN-based thruster.

Controlled Deposition of Nanostructured Hierarchical TiO2 Thin Films by Low Pressure Supersonic Plasma Jets

Abstract: Plasma-assisted supersonic jet deposition (PA-SJD) is a precise technique for the fabrication of thin films with a desired nanostructured morphology. In this work, we used quadrupole mass spectrometry of the neutral species in the jet and the extensive characterization of TiO2 films to improve our understanding of the relationship between jet chemistry and film properties. To do this, an organo–metallic precursor (titanium tetra–isopropoxide or TTIP) was first dissociated using a reactive argon–oxygen plasma in a vacuum chamber and then delivered into a second, lower pressure chamber through a nozzle. The pressure difference between the two chambers generated a supersonic jet carrying nanoparticles of TiO2 in the second chamber, and these were deposited onto the surface of a substrate located few centimeters away from the nozzle. The nucleation/aggregation of the jet nanoparticles could be accurately tuned by a suitable choice of control parameters in order to produce the required structures. We demonstrate that high-quality films of up to several µm in thickness and covering a surface area of few cm2 can be effectively produced using this PA-SJD technique.

Transient characteristics of a typical vacuum ejector—An experimental study

Abstract: Using simultaneous measurements of unsteady pressures in conjunction with time-resolved Schlieren images and oil flow visualization, we investigate the characteristics of a typical vacuum ejector's starting transient, steady-state, and shut-down transient. With varying primary jet chamber pressure, the pressure evolution in the secondary chamber shows smooth, perturbed, rapid, and steady evacuation stages, as well as hysteresis and rapid filling stages. It is noticed that the evacuation in the secondary chamber is improved during stopping transient just before the unstart event. By using oil flow images, we illustrate the separation bubble characteristics during each stage of the vacuum ejector operation and their influence on the pressure evolution. Through cross correlation, it has been determined that the primary jet flapping during the starting transient causes the jet to attach to one of the diffuser walls. We also demonstrate that the primary jet undergoes both longitudinal and lateral oscillations in the starting transient, the former having a major effect on unsteadiness in the secondary chamber using proper orthogonal decomposition and spectral proper orthogonal decomposition algorithms and power spectral density (PSD). Simultaneous acquisition of unsteady pressures and high-speed Schlieren images allow us to correlate the frequency peaks (PSD spectra) in the flow. Using magnitude-squared coherence and cross correlation analyses, we confirm communication of unsteadiness and its direction of propagation between the secondary chamber and the diffuser. In this study, we demonstrate that a high ramping rate of primary jet chamber pressure reduces the unsteadiness in the secondary chamber during the transient starting phase.

Investigation of a Marine Water-Breathing Hybrid Ram-Rocket Motor

Abstract: This work presents theoretical and experimental performance studies and a general scheme of an innovative concept for propelling marine high-speed underwater vehicles, a water-breathing hybrid ram rocket. The water-augmented hybrid ram rocket enables obtaining superior performance relatively to a standard rocket and improved performance relatively to a parallel water–augmented solid ram rocket. In addition, it demonstrates improved safety and controllability due to the hybrid motor characteristics. The theoretical model incorporated data from a thermochemical program. The experimental investigation was based on static firing tests of hybrid rocket motors augmented by the addition of water during combustion. The study focused on the use of a non-water-reactive propellant combination, cured polyester as fuel and gaseous oxygen as oxidizer. Wide ranges of oxidizer-to-fuel and water-to-propellant ratios were considered. The experimental results showed a significant improvement (up to 70%) in specific impulse, relatively to a non-water-augmented hybrid rocket, in good accordance with the theoretical results. It is concluded that for standard chamber pressure of 6.9 MPa, corresponding to the ram pressure for cruising at , a specific impulse greater than 400 s can be achieved by a water-augmented hybrid ram rocket using a non-hydro-reactive fuel.

Dynamic Numerical Simulation of Hybrid Rocket Motor with HTPB-Based Fuel with 58% Aluminum Additives

Abstract: The addition of aluminum (Al) to the fuel is an effective way to increase the regression rate of hybrid rocket motors (HRMs). Due to its high regression rate, the impact of the regression of combustion surface on the performance of HRMs cannot be ignored. Therefore, it is significant to establish a dynamic numerical simulation model to predict the performance of HRMs. In this study, the dynamic simulation model was established based on dynamic mesh technology and was verified by a firing test. The results show that the simulation results agree well with the experimental results, and the errors of the average thrust and combustion chamber pressure are 3.4% and 1.4%, respectively. The dynamic simulation shows that with the regression of the combustion surface, the vortex of the pre-combustion chamber is divided into two vortices. The vortex near the front of the grain will increase the regression rate downstream. The results show that the addition of Al can obviously improve the regression rate of HRMs. The fuel containing 58% Al can improve the regression rate by 88.8% compared with the fuel with pure hydroxyl-terminated polybutadiene (HTPB). Moreover, due to the higher combustion temperature and the scouring of metal particles, the ablation rate of the nozzle with carbon ceramic materials reaches 0.16 mm/s. This investigation provides a valuable reference for HRMs design and simulation.

Pressure Calibration of Large-Volume Press: A Case Study of Hinged 6-8 Type Large-Volume High-Pressure Apparatus

Abstract: In this study, methods for the pressure calibration of 6–8 static high-pressure apparatus were investigated. The relationship between the pressure of DS 6 × 1,400 t pressing oil and the chamber pressure was calibrated using water, ZnTe, ZnS, and GaAs at room temperature. Also, the relationship between the pressure of the DS 6 × 1,400 t pressing oil and the chamber pressure was calibrated by the phase transition experiments using KCl, LiCl, KCl + LiCl, and quartz-coesite at high temperatures. We found a linear relationship between the chamber pressure and the oil pressure at room temperature. However, when the temperature and pressure increased to certain values, the chamber pressure and the oil pressure deviated from the linear relationship.

Slip Flow Analysis in an Experimental Chamber Simulating Differential Pumping in an Environmental Scanning Electron Microscope

Abstract: This paper describes the combination of experimental measurements with mathematical–physical analysis during the investigation of flow in an aperture at low pressures in a prepared experimental chamber. In the first step, experimental measurements of the pressure in the specimen chamber and at its outlet were taken during the pumping of the chamber. This process converted the atmospheric pressure into the operating pressure typical for the current AQUASEM II environmental electron microscope at the ISI of the CAS in Brno. Based on these results, a mathematical–physical model was tuned in the Ansys Fluent system and subsequently used for mathematical–physical analysis in a slip flow regime on a nozzle wall at low pressure. These analyses will be used to fine-tune the experimental chamber. Once the chamber is operational, it will be possible to compare the results obtained from the experimental measurements of the nozzle wall pressure, static pressure, total pressure and temperature from the nozzle axis region in supersonic flow with the results obtained from the mathematical–physical analyses. Based on the above comparative analyses, we will be able to determine the realistic slip flow at the nozzle wall under different conditions at the continuum mechanics boundary.

A review of vaporization models as design criterion for bipropellant thrust chambers

Abstract: In the beginning of liquid propellant rocket engine development, the thrust chamber sizes were obtained, mainly, empirically. With the technological advancements over the years, several approaches have been developed in order to optimize its sizes and predict more accurately the performance. Besides the clear contribution in predicting efficiencies, the use of accurate vaporization models to optimize combustion chambers decreases losses and the number of required tests. To increase efficiencies, the chamber must be optimized. In case the chamber is too small, incomplete combustion is achieved and combustion instability may occur. In case the chamber is too large, losses due to weight and heat transfer increase and the vehicle becomes larger (leading to more drag losses). Additionally, the number of tests is reduced since models were experimentally validated and less experimental iterations are required in order to obtain the optimized design. Although there are many models, all of them reach similar conclusions, such as an increase in chamber pressure, a decrease in injected droplet size and velocity, and others, lead to a decrease in the required chamber size. Nowadays, with the advancements in computing budget, more complex and accurate models have be developed. Some of these models account for chemical reactions, turbulence effects, droplet collisions and interactions, two- and three-dimensional modeling, and others. Also, the use of CFD codes provides relevant contributions to the analytical and numerical models, especially in validating them, and, additionally, decreases the amount of required experimental tests. The main propulsive parameter that rules this phenomenon is the characteristic length, which accounts the required chamber size for the propellants to be injected, atomized, vaporized, mixed and combusted. Most of the available models neglect the atomization, mixing and combustion of the propellant, since those phenomena occur much faster compared with the vaporization. This work provides a review of those vaporization models, focusing on the main used models worldwide. Such review is of great importance in order to supply enough information and comparison between models, making possible for the researcher/engineer to choose the model that better fit its necessities, requirements and limitations.

Effects of orifice diameter of pre-chamber jet ignition on the combustion characteristics and pressure oscillations in a kerosene-fueled engine

Abstract: Jet orifice diameter directly impacts the combustion process of the pre-chamber jet ignition (PJI) engine and the optimized diameter is varied with the fuel properties. However, research on the optimization of the jet orifice diameter based on aviation kerosene fuel has not been reported. So, this work investigates the effect of orifice diameter on combustion, pressure oscillation, and performance based on a kerosene-fueled single-cylinder test engine. Two pressure sensors are respectively fitted in the main combustion chamber and the pre-chamber, which can capture the pressure change process and pressure oscillations phenomenon at the two positions, respectively. The result demonstrates that the throttling of the jet orifice leads to a significant three-stage pressure imbalance between the combustion chambers. With the reduction of the orifice diameter, the combustion acceleration of PJI is enhanced, resulting in an advanced combustion phase, improved combustion stability, and enhanced knock. The time-frequency analysis proves that the pressure oscillation propagation to the pre-chamber is frequency-selective and related to the orifice diameter. By matching the pre-chamber Helmholtz resonance frequency with the main-chamber resonance frequency, strong pressure oscillations can be excited in the pre-chamber. Meanwhile, the pressure oscillation energy can be absorbed by the pre-chamber, which may help reduce the engine's combustion noise. Moreover, the PJI with an orifice diameter between 2 ~ 4 mm can improve the combustion stability with the ISFC reduced by 4.7~5.6% and the IMEP increased by 1.2~ 2.6%.

Estimation of Ignition Pressure in Ammunition

Abstract: This paper presents the experimental estimation of the ignition pressure value produced by a primer in small arms ammunition. Investigations were performed using a chamber of the capacity equal to the capacity of the 12.7 mm ammunition case. The inner volume of the chamber was adjusted to the free volume in the cartridge by inserting a sleeve or glass balls of a diameter of 2 or 4 mm. The pressure values were measured inside the chamber after the action of the primer. The maximum pressure value was used as an estimation of the ignition pressure value. Depending on the nature of the filling, considerably different values were obtained; they were compared with the values of pressure measured inside the case at the live firing. A considerable difference between the ignition pressure values measured inside the case and those measured in the model setup was detected. Based on these results, a discussion concerning the choice of the starting pressure in interior ballistics lumped parameters models was carried out.

[Effects of chamber characteristics on CO2 and CH4 flux at the water-air interface measured by the chamber method].

Abstract: The chamber method is widely used to measure CO2 and CH4 flux in inland water. However, the designs of chamber used in various studies are different and lack unified standards, which would affect the observation results. To clarify the impacts of chamber characteristics, including light transmittance, air pressure difference inside and outside the chamber, and gas mixing degree in the chamber, on CO2 and CH4 flux measurements at the water-air interface, we compared the effects of transparent/opaque chamber, the chamber with/without air pressure equalizing device and fan on CO2 and CH4 flux measurements in the aquaculture pond, based on the multi-channel closed dynamic chamber system. The results showed that, during the daytime in summer, compared with the transparent chamber which could measure the actual CO2 flux, when CO2 was emitted from the pond, the opaque chamber overestimated the CO2 flux by 90%; when CO2 was absorbed by the pond, the opaque chamber underestimated the CO2 flux by 50%. The CH4 diffusion flux measured by the opaque chamber was 40% lower than that measured by the transparent chamber. There was no significant difference between CO2 and CH4 flux measured by the chamber with and without air pressure equalizing device. CO2 flux observed by the chamber without fan had poor representativeness, being 20% higher than that observed by the chamber with fan. Moreover, CH4 flux emitted through different pathways could not be distinguished using the chamber without fan. Therefore, when the chamber method was used to observe the CO2 and CH4 flux at the water-air interface, the chamber shall be transparent and be installed with fan.

Measurement of the regression rate in a hybrid rocket motor by acquiring the helmholtz frequency in the combustion chamber

Abstract: Low thrust values obtained with a hybrid rocket motor (HRM) are a consequence of the difficulty in quickly mixing the fuel and oxidizer, which is characterized by a low regression rate of the fuel grain. Therefore, the measurement of this parameter is of great importance in studies that aim at solutions for this deficiency in HRM. Several studies calculate a reliable value of the average regression rate over time by measuring the total mass of fuel before and after each burn. A method to measure instantaneous regression rate is by acquiring the Helmholtz resonance frequency in the combustion chamber. This work uses a piezoelectric pressure transducer to obtain the Helmholtz frequency mode of the combustion chamber in a laboratory scale test bench with high-density polyethylene (HDPE) and gaseous oxygen, and is based on the principle that this frequency is inversely proportional to the square-root of the chamber volume. With the chamber volume variation, the port diameter of the grain variation is obtained. In conclusion, the calculated variation of port diameter agreed well with the correlation for average regression rate, determined from mass loss during operation.