Hollow Chamber Research Articles

Propagation and stabilization properties of rotating detonation waves in a hollow combustion chamber with heated air inflow

The application of rotating detonation to conventional engine poses challenges such as high-temperature inflow conditions. In this study, experiments were conducted to discuss the propagation and stabilization properties of rotating detonation waves within a hollow rotating detonation combustor using pure heated air/ethylene as propellant. The temperature and equivalence ratio are varied to explore the boundary of detonative limits. The results show that the pressure of detonation waves is influenced by temperature fluctuations, whereas changes in air temperature have minimal impact on velocity losses. In addition to detonation, the deflagration zone is observed within the combustor. When the air temperature is increased, the deflagration zone expands gradually. The static temperature of air increases from 304 to 618 K, resulting in an increase in the area of the glowing zone from 17.7% to 60.0%. The expansion of the zone indicates a rise in deflagration percentage, and a stable single-wave mode is achieved mainly under fuel-rich conditions. The detonative equivalence ratio range is narrowed with increasing heated temperature at 484–618 K. Unstable propagation modes, characterized by sawtooth waves, are frequently observed at detonative lower limit, where the equivalence ratio is around 1.

Soft pneumatic actuators for pushing fingers into extension

BackgroundCompliant pneumatic actuators possess many characteristics that are desirable for wearable robotic systems. These actuators can be lightweight, integrated with clothing, and accommodate uncontrolled degrees of freedom. These attributes are especially desirable for hand exoskeletons, where the soft actuator can conform to the highly variable digit shape. In particular, locating the pneumatic actuator on the palmar side of the digit may have benefits for assisting finger extension and resisting unwanted finger flexion, but this configuration requires suppleness to allow digit flexion while retaining sufficient stiffness to assist extension.MethodsTo meet these needs, we designed an actuator consisting of a hollow chamber long enough to span the joints of each digit while sufficiently narrow not to inhibit finger adduction. We explored the geometrical design parameter space for this chamber in terms of shape, dimensions, and wall thickness. After fabricating an elastomer-based prototype for each actuator design, we measured active extension force and passive resistance to bending for each chamber using a mechanical jig. We also created a finite element model for each chamber to enable estimation of the impact of chamber deformation, caused by joint rotation, on airflow through the chamber. Finally, we created a prototype hand exoskeleton with the chamber parameters yielding the best outcomes.ResultsA rectangular cross-sectional area was preferable to a semi-obround shape for the chamber; wall thickness also impacted performance. Extension joint torque reached 0.33 N-m at a low chamber pressure of 48.3 kPa. The finite element model confirmed that airflow for the rectangular chamber remained high despite deformation resulting from joint rotation. The hand exoskeleton created with the rectangular chambers enabled rapid movement, with a cycle time of 1.1 s for voluntary flexion followed by actuated extension.ConclusionsThe developed soft actuators are feasible for use in promoting finger extension from the palmar side of the hand. This placement utilizes pushing rather than pulling for digit extension, which is more comfortable and safer. The small chamber volumes allow rapid filling and evacuation to facilitate relatively high frequency finger movements.

Experimental study on upstream pressure characteristics of rotating detonation engine with methane and oxygen-enriched air

The interaction mechanism between the rotating detonation engine (RDE) and its upstream is one key issue that needs to be explored when considering its application. In this study, experimental tests with methane and 50% oxygen-enriched air are conducted to investigate the relationship between upstream pressure characteristics and the detonation wave. As a result of operational considerations, a hollow chamber and a rear ignitor are used and the initiation process is discussed. Upstream pressure characteristics are analyzed under varied injection pressures and equivalence ratios. Stable modes including single-wave and double-wave modes are recorded in most cases. Notably, two unstable modes are also captured at low injection pressure in which the detonation quenches quickly. The results highlight that significant feedback pressure pulsations synchronize with the rotation frequency of detonation waves after ignition due to the upstream oblique shock wave (UOSW). But the inherent frequency of injection should also be emphasized at elevated injection pressure. The detonation wave can also cause injection blockage, particularly at low injection pressure, leading to the bifurcation of unstable mode. Such unstable is attributed to an inadequate upstream pressure increase after ignition, which hinders the injection reconstruction. Further analysis reveals that higher injection pressures or lower equivalence ratios diminish the differential between the detonation wave and upstream pressure, and consequently, the pulsation amplitude. An increase in the detonation wave number can also reduce the pulsation amplitude, which can even be lower than 10% in a double-wave mode. The results are beneficial for integrating RDE and its upstream components.

Effects of inner cone length on continuous rotating detonation in a variable cross-section combustor

A variable cross-section combustion chamber with different inner cone length L is designed, composing of an annular part with divergent width and a cylinder part without inner cone. Ethylene-air and hydrogen-air continuous rotating detonation (CRD) experimental tests are conducted. The results show that the ethylene-air CRD wave can be achieved in the variable cross-section combustor with the short inner cone. The propagation velocity of ethylene-air CRD wave can be 1661.37 m/s with the equivalence ratio of 0.91 and L of 10 mm. With L increasing from 0 mm to 30 mm, the combustion mode varies in the single wave mode, the sawtooth wave mode, and the hybrid mode. The combustor width is not the main factor leading to the failure of detonation in this study. The acceleration of propellent mixture caused by the expansion of the annulus channel, and the downstream movement and reduction of recirculation zone around the inner cone both increase the difficulty in CRD realization. While the hydrogen-air CRD can self-sustain with the intensive reaction zone in the annular part in the critical configuration of ethylene-air CRD. This study will contribute to the understandings of self-sustaining mechanism of CRD in the divergent combustor and the combustor design of the hollow chamber.

Barrel effect in an air-cooled proton exchange membrane fuel cell stack

The performance of a single cell affects the proton exchange membrane fuel cell (PEMFC) stack's overall output performance, and the barrel effect occurs in PEMFC stacks. This research presents strategies to alleviate single-cell performance degradation in an air-cooled PEMFC stack. Results show that the poorest cell performance is caused by location-related issues. By embedding a copper plate in the position of cell-1, a hollow chamber replaces the cell-1 flow field. The stack equipped with an embedded copper plate achieved its peak power at 2151.22 W under a current of 40 A, signifying an 8.6 % enhancement in performance compared to the original stack. The incorporation of carbon paper and copper plates contributes to the establishment of a uniform stress distribution within the stack, consequently resulting in enhanced voltage consistency, characterized by a minimal variance value of approximately 0.033. Furthermore, the output performance of cell-1 increased by 0.101 V in the stack with copper plate compared to the original stack under 30 A current loading. By introducing a copper plate, the hollow gas chamber replaces the low pressure-drop cells position, effectively resolving the barrel effect in the PEMFC stack, and alleviating the single-cell degradation problem.

Preparation and Performance Analysis of 3D Thermoformed Fluidic Polymer Temperature Sensors for Aquatic and Terrestrial Applications.

Employing a combination of Polyethylene terephthalate (PET) thermoforming and 3D-printed cylindrical patterns, we carefully engineer a linear resistive temperature sensor. This intricate process involves initial PET thermoforming, yielding a hollow cylindrical chamber. This chamber is then precisely infused with a composite fluid of graphite and water glue. Ensuring electrical connectivity, both ends are affixed with metal wires and securely sealed using a hot gun. This cost-effective, versatile sensor adeptly gauges temperature shifts by assessing composite fluid resistance alterations. Its PET outer surface grants immunity to water and solubility concerns, enabling application in aquatic and aerial settings without extra encapsulation. Rigorous testing reveals the sensor's linearity and stability within a 10 °C to 60 °C range, whether submerged or airborne. Beyond 65 °C, plastic deformation arises. To mitigate hysteresis, a 58 °C operational limit is recommended. Examining fluidic composite width and length effects, we ascertain a 12 Ω/°C sensitivity for these linear sensors, a hallmark of their precision. Impressive response and recovery times of 4 and 8 s, respectively, highlight their efficiency. These findings endorse thermoforming's potential for fabricating advanced temperature sensors. This cost-effective approach's adaptability underscores its viability for diverse applications.

Performance investigation of tempered glass based photovoltaic panel integrated with back cooling hollow chamber

ABSTRACT At present, the whole world is facing a huge fuel crisis and those who adopt the extraction of energy from renewable sources are getting much benefit both environmentally and economically. Photovoltaic systems are the most mature and scaled renewable energy generation systems worldwide. However, the optimal condition for maximizing the output from Photovoltaic (PV) panels is characterized by low temperatures and high irradiation levels. With the increasing temperature and irradiation, the solar panel becomes warmer and thus the efficiency drops. Hence, by cooling the PV panels, the efficiency can be increase. Various thermal collector designs and different water flowing methods (Top cooling & Back cooling) has been employed to cool the panels. In this research study, an experiment of building a new PVT panel attached to a hollow chamber (Thermal Collector) at the back of the panel is carried out. In hollow chamber the warm water was kept inside and release that when the water was hot enough. This experiment was conducted in various outdoor conditions. On average, the electrical efficiency was measured 8.7 to 9.9% higher than the simple PV system. Maximum overall efficiency was recorded as 76%. The experiment also figured out due to low irradiation in cloudy weather the output power drops significantly.

Experimental Study on the Propagation Characteristics of Rotating Detonation Wave with Liquid Hydrocarbon/High-Enthalpy Air Mixture

Rotating detonation engines (RDEs) are a promising propulsion technology featuring high thermal efficiency and a simple structure. To adapt the practical engineering applications of ramjet RDEs, rotating detonation combustion using a liquid hydrocarbon and pure air mixture will be required. This paper presents an experimental study on the propagation characteristics of rotating detonation waves with a liquid hydrocarbon and high-enthalpy air mixture in a hollow cylindrical chamber. The parameters, such as the equivalence ratio and inlet mass flux, are considered in this experiment. The frequency and the propagation velocity of rotating detonation combustion are analyzed under typical operations. The experimental results show that the peak pressure and propagation velocity of the rotating detonation wave are close to the C-J theoretical values under the inlet mass flux of 400 kg/(m2s). Both the propagation velocity and peak pressure of the rotating detonation wave decrease as the mass flux and equivalence ratio are reduced while the number of detonation wavefronts increases. Detonation wave instability tends to occur when the inlet mass flux decreases. There is a transition progress from thermo-acoustic combustion to rotating detonation combustion in the experiment under the condition of mass flux 350 kg/(m2s) and the equivalent ratio 0.8. The static pressure in the chamber is higher during detonation combustion than during thermo-acoustic combustion. These experimental results provide evidence that rotating detonation waves have the potential to significantly improve propulsion performance. The findings can serve as a valuable reference for the practical engineering application of rotating detonation engines.

Analysis on the radial structure of rotating detonation wave in a hollow combustor

This experimental study discusses the radial structure of the rotating detonation wave (RDW) in a hollow chamber. The head chamber wall could be fabricated with quartz glass for high-speed visualizations or metal cover for high-frequency pressure measurement. The entire radial-stratified reaction zone was directly and continuously captured. The wall-attached bright zone indicated that the main reaction zone propagated along the chamber wall, but some deflagration was still observed in the inner zone. Based on the phase-averaged CH* chemiluminescence image, the radial thickness of the reaction zone was determined to be about 15–20 mm. The diminishing pressure peaks and deteriorating waveforms of the high-frequency pressure signals proved that the intensity of shock waves decreased along the chamber radius. The structure of RDW was reconstructed using radially distributed pressure sensors. Due to the compression effect of the concave chamber wall, a Mach reflection of detonation wave might occur. The detonation wave was connected to a diffracted shock, which stretched in the radial direction with decreasing intensity. The central angles calculated with the time-difference analysis demonstrated that the entire RDW bent forward in the inner zone of the chamber. Moreover, the radial thickness of the reaction zone and the curvature of shock waves increased with decreasing nozzle contraction ratio, which mainly attributed to the increasing expansion effect. This study demonstrated the distribution of reaction zone and the radial structures of shock waves for the RDW in a hollow combustor, contributing to the exploration of the flow and combustion process in a rotating detonation engine.

Multi-material polyjet printing for more lifelike endodontic practice teeth.

Root canal therapy is a highly technical procedure that has several unique challenges. Extracted human teeth have traditionally been used to train dental students which have come under increased scrutiny in recent years.1 Multiple published studies have demonstrated the value of three-dimensional (3D) printed teeth for dental education.2-5 A limitation common to these publications has been the inability to 3D print using multiple materials simultaneously.3 One strategy for creating a multi-material tooth was to create a tooth with a hollow pulp chamber and cavity preparation that was later filled with impression material and resin composite, respectively.2 Polyjet printing that allows for the use of six materials with different colors and physical properties was used to create endodontic practice teeth that had a white enamel layer, an A2 shaded dentin and root structure as well as a hollow, red pulp chamber full of a water-soluble, gelatinous support material (J5 Dentajet; Stratasys). A cone beam computed tomography (CBCT) radiograph of an extracted maxillary first premolar was made (75 μm, 90 kV, and 10.0 mA). The pulp chamber and canals were segmented from the reconstruction and Standard Tesselation Language files of the pulp chamber and tooth were exported. A 3D modeling program (Meshmixer, Autodesk) was used to further segment the file into an enamel layer, a dentin and root layer, and a hollow pulp chamber (Figure 1). These three files were brought into the printing software (GrabCAD; Stratasys) as an assembly which allows for the selection of different materials to be printed simultaneously in a single object. The enamel layer was printed using a white resin, DEN847 VeroDent PureWhite, an A2 shade resin for the root layer, MED620 VeroGlaze, the hollow pulp layer was printed using a red resin, RGD 852 VeroMagenta-V, and the hollow cavity of the pulp layer was printed with SUP711. Figure 2 shows the three layers assembled into a single item as well as disassembled into its three constituent parts. PolyJet printing was capable of fabricating endodontic practice teeth with multiple textures throughout the printed item. Figure 3 shows the printed teeth in cross-section and whole demonstrating the three solid materials and the gelatinous material filling the pulp chamber and canals. The canals can be filed with endodontic files and the gelatinous support material removed in a similar fashion to the pulp tissue. The initial expense of 3D printing technology can be high as identified by several authors.3 The use of the described technology in this article was able to produce 100 of the practice teeth in an overnight printing cycle for a per-tooth cost of less than half of one US dollar. With the ease of producing segmented files from a CBCT image of a tooth and the low cost of printing, students can be given greater access to standardized practice teeth for endodontic education. This same process has been applied by the author to design and create practice teeth with soft, excavatable carious lesions for a similarly low cost per tooth.

Steady rotation of a Mach shock: experimental and numerical evidences

This experimental and numerical work reports on the dynamical behaviour of a shock in an inert gas at the concave wall of a hollow circular chamber. The gas in the chamber was air or He + $${\rm O}_{2}$$ + 2 Ar at initial pressures $$p_{{\rm c0}}$$ ranging from 2 to 12 kPa and initial temperature T0 =288 K. The shock was generated using a detonation driven shock tube. The shock dynamics were characterized through high-speed shadowgraph recordings and high-resolution numerical simulations. For each gas and $$p_\text {c0}$$ , the experiments evidenced the formation of a Mach reflection along the wall and identified a range of initial pressures for which this configuration rotates with constant stem heights and constant velocities larger than those at the chamber entry. The numerical simulations were capable of capturing the dynamics quantitatively. These results extend to inert gases our previous work with a reactive gas for which we reported on the possibility of a steadily rotating overdriven Mach detonation. The steadiness range is narrower with the inert gases, likely because of the smaller initial pressure ratios at the chamber entry and lower support from the subsonic flow behind the shock. The initial support in the reactive case was more efficient because the discontinuities at the chamber entry were self-sustained Chapman–Jouguet detonations. Further investigations of these Mach rotating regimes should rely only on specific experiments and numerical simulations, for example, on the effect of the chamber dimensions, because of the complex non-dimensional formulation of the problem.

Experimental research on the performance of hollow and annular rotating detonation engines with nozzles

• The performance of hollow and annular RDEs with nozzles are compared. • The hollow RDE can reduce the injection pressure loss. • The hollow chamber brings a higher performance loss. Rotating detonation engines (RDEs), which are hoped to achieve significant performance improvements in propulsion systems, have received much attention in recent years. The annular RDE and hollow RDE are two of the major configurations of which the structure is very similar to each other. However, there has been a lack of experimental research discussing the differences in their performance. In the present study, experiments on hollow and annular RDEs are conducted. Four configurations in total are tested at ambient conditions: hollow and annular combustion chambers with two exit throat areas. The gaseous methane and gaseous oxygen are used as propellants. The results reveal that the c*-efficiency of the two hollow combustion chamber configurations is on average 0.7 and 0.79, which is lower than the 0.75 and 0.84 of annular chambers. However, it is exhibited that the hollow RDE can ensure high detonation efficiency at a lower injection pressure ratio. From this perspective, the hollow RDE can be considered a more promising configuration for practical application because it provides a new approach to reducing injection pressure loss. In addition, the analysis of nozzle indicates that the Laval nozzles overperform the aerospike nozzles, which goes against previous studies. The mechanism that accounts for this phenomenon needs further investigation.

Propagation and flow field analysis of wall-detached continuous rotating detonation wave in a hollow combustor

Wall-detached continuous rotating detonation (CRD) was experimentally and numerically achieved in the designed hollow chamber. For this novel CRD wave, the pressure signals measured at the chamber wall showed lower peak pressure but much higher frequency when compared with typical wall-attached CRD. Meanwhile, the high-speed photographs showed that the luminous area (i.e. coupled reaction zone) of this CRD wave always varied within a “wall-detached” cylindrical zone. Experimental results with different ribs further proved that the CRD wave propagated within a cylinder whose diameter was about 44 mm, and the corresponding propagation velocity was very close to that of C-J detonation. A model was proposed to illustrate the flow field structure of this special CRD. According to the annular injection position of propellants, the hollow chamber was divided into two parts, namely, central CRD zone and outer shock wave zone. The detonation wave propagated within the former zone and the induced oblique shock waves stretched in both of the two zones. These two waves rotated synchronously to form the basic flow field structure of this wall-detached CRD. This model was further verified by a premixed numerical simulation case. The wall-detached propellants injection was believed to contribute to the formation and self-sustaining of the detonation wave in the center, and the oblique shock waves were induced on both sides due to the lateral expansion effect. This study shows that the detonation wave could rotate spontaneously and continuously without the support of chamber wall. The analyses on the propagation characteristics as well as the flow field structure of wall-detached CRD contribute to the understanding of self-sustaining mechanism of CRD wave in the hollow chamber.

The effect of external magnetic field on osteogenic and antimicrobial behaviour of surface-functionalized custom titanium chamber with iron nanoparticles. A preliminary research.

The controlled responsive characteristics of iron nanoparticles (FeNp) in magnetic fields make them an attractive prospect in this field. In the presence of a magnetic field, FeNp can significantly impact cell behaviour, leading to breakthroughs in nanotechnology. The aim is to determine the possible applications of iron nano particles (FeNp), and induced magnetic exposure role in osteoconduction and antibacterial activity. The custom-grade IV titanium (Ti)hollow chamber is fabricated, surface treated with FeNp. Each titanium chamber contained neodymium, iron, and boron magnet disc, and the effect of FeNp on osteoblast-like cells (MG63) was evaluated in terms of cell attachment and survivability, morphological characteristics, particle absorption, and antibacterial properties. The effects of cellular uptake of FeNp and their responses to subcellular thrust were studied using fluorescent microscopy. MTT was used to determine cell viability, and von Kossa histochemical staining was used to determine matrix mineralization. In the magnetized Ti chambers group, osteogenic activity and mineralization were considerably greater than in the control groups (p 0.05). With a p value of 0.027, the S. aureus and E. coli were resistant to the antibacterial properties of the FeNp modified titanium custom Ti chamber (MIC: 0.03135mg/mL and 0.02915mg/mL, respectively). The one-of-a-kind, in vitro, conveniently modelled, limited sample study sheds light on the effect of surface-functionalized titanium custom Ti chamber with FeNp on MG63. The use of magnetized FeNp-surfaced implants for long-term strategic bone tissue engineering and bacteriostatic implants.

The nature of sawtooth wave and its distinction from continuous rotating detonation wave

To pinpoint the nature of the sawtooth wave, extensive experiments of methane-air continuous rotating detonation (CRD) are conducted in a hollow chamber around the boundary of the operating range. The time occupancy ratio and the increasing ratio of pressure rise (Δti/ΔTi and ΔPi/Δti) derived from high-frequency pressure data, and the integral of chemiluminescence intensity (ICI) based on self-luminescence images are proposed as quantitative parameters to distinguish the detonation wave and the sawtooth wave. The results show that the sawtooth wave is a critical unstable mode between conventional isobaric combustion and CRD, propagating with high Δti/ΔTi and low ΔPi/Δti. Meanwhile, the reaction zone of sawtooth wave is verified to be stabilized in the center of combustor through the self-luminescence observation. Especially, the multiple transition processes from the sawtooth wave to the CRD wave are accurately captured, and simultaneously represented as the change from single-peak waveform to double-peak waveform on ICI, the rise of ΔPi/Δti, and the reduction of Δti/ΔTi. The significant distinction of the sawtooth wave and the CRD wave in the coupling characteristics is confirmed through Short-Time Fourier Transform processes on ICI and high-frequency pressure. For the CRD wave, the propagation frequency of the reaction zone matches that of the pressure wave, whereas not for the sawtooth wave. It is ascertained that the reaction zone is decoupled with the pressure wave for the sawtooth wave, and the nature of the sawtooth wave is deflagration combined with a weak pressure wave.

Commentary: Changing trends and preferred surgeons' practice for nucleus delivery in manual small-incision cataract surgery-Haven't they changed?

Commentary: Changing trends and preferred surgeons' practice for nucleus delivery in manual small-incision cataract surgery-Haven't they changed?

A fibrin enhanced thrombosis model for medical devices operating at low shear regimes or large surface areas.

Over the past decade, much of the development of computational models of device-related thrombosis has focused on platelet activity. While those models have been successful in predicting thrombus formation in medical devices operating at high shear rates (> 5000 s-1), they cannot be directly applied to low-shear devices, such as blood oxygenators and catheters, where emerging information suggest that fibrin formation is the predominant mechanism of clotting and platelet activity plays a secondary role. In the current work, we augment an existing platelet-based model of thrombosis with a partial model of the coagulation cascade that includes contact activation of factor XII and fibrin production. To calibrate the model, we simulate a backward-facing-step flow channel that has been extensively characterized in-vitro. Next, we perform blood perfusion experiments through a microfluidic chamber mimicking a hollow fiber membrane oxygenator and validate the model against these observations. The simulation results closely match the time evolution of the thrombus height and length in the backward-facing-step experiment. Application of the model to the microfluidic hollow fiber bundle chamber capture both gross features such as the increasing clotting trend towards the outlet of the chamber, as well as finer local features such as the structure of fibrin around individual hollow fibers. Our results are in line with recent findings that suggest fibrin production, through contact activation of factor XII, drives the thrombus formation in medical devices operating at low shear rates with large surface area to volume ratios.

Characteristics of rotating detonation waves in a hollow chamber with different fuel injection positions

Ethylene-air continuous rotating detonation (CRD) was achieved in the hollow chamber with different fuel injection positions. As the injection position moved downstream, the propagation mode of CRD waves appeared in the order of single-wave mode, co-rotating two-waves mode, and lifted-single-wave mode. The axial heat release rate of the former two modes were rapid, indicating that CRD waves propagated near the ethylene orifices. Typically, for CRD wave of single-wave mode, a high peak pressure (about 0.7 MPa) led to a local backflow of propellants in the head recirculation zone. The lifted-single-wave mode was a new propagation mode where the CRD wave was ‘lifted’ from the ethylene orifices. For this mode, the CRD wave propagated with little velocity deficit (8 %) but lower peak pressure (about 0.2 MPa). Besides, the axial heat release rate was much slower in this mode, indicating that the detonation wave propagated in the unburned propellants and the intermediate products of the upstream deflagration. The achieved propagation modes were significantly affected by the ethylene injection position, which was supposed to be related to the variations of matter and energy exchanges between the main stream and the combustion products in the central recirculation zone.

Comparative study of the effects of increasing heat transfer area within compression and expansion chambers in combination with modified pistons in Stirling engines. A simulation approach based on CFD and a numerical thermodynamic model

The aim of this research is to ascertain the potential benefits of increasing heat transfer area in the expansion and compression spaces of Stirling engines. This is achieved, as proposed in an accepted patent, by simultaneously attaching pins or fins to the chamber walls and modifying the geometry of the displacer. Different configurations involving pinned and finned surfaces were proposed for comparison with a hollow cylindrical chamber. In order to compute the heat transfer rate as well as the convective heat transfer coefficient for each suggested geometry, a CFD (Computational Fluid Dynamics) model was run under different temperatures, displacer speeds and pressures. For a selected geometry based on longitudinal cylindrical pins, the computed heat transfer coefficients were correlated with input parameters in order to obtain a simple equation. The equation was subsequently introduced into a three-camera second-order thermodynamic model of a gamma Stirling engine with crankshaft mechanism. Five different cases were evaluated. The models were run for different operational conditions (speed and charge pressure), for a hot wall temperature of 493 K and a cold wall temperature of 293 K. Pressure was varied from 1 to 2.5 atmospheres and the engine rotational speed ranged between 50 and 1000 rpm. Results showed an increase in engine power between 1.3 and 2.5 times when compared to a conventional engine without heat exchangers.

Numerical simulation of flow field characteristics and the improvement of pressure oscillation of rotating detonation engine

Due to the inherent working mode of rotating detonation engine (RDE), the detonation flow field has the characteristics of pressure oscillation and axial kinetic energy loss, which makes it difficult to design nozzle and improve propulsion performance. Therefore, in order to improve the characteristics of detonation flow field, the three-dimensional numerical simulation of annular chamber and hollow chamber is carried out with premixed hydrogen/air as fuel in this paper, and then tries to combine the two chambers to weaken the oscillation characteristics of detonation flow field through the interaction of detonation flow field, which is a new method to regulate the detonation flow field. The results show that there are four states of velocity vectors at the outlet of annular chamber and hollow chamber, which makes RDE be affected by rolling moment and results in the loss of axial kinetic energy. In the external flow field of combined chamber, the phenomenon of cyclic reflection of expansion wave and compression wave on the free boundary is observed, which results in Mach disk structure. Moreover, the pressure monitoring points are set at the external flow field. The pressure signal shows that the high-frequency pressure oscillation at the external flow field of the combined chamber has been greatly weakened. Compared to the annular chamber, the relative standard deviation (RSD) has been reduced from 14.6% to 5.6%. The results thus demonstrate that this method is feasible to adjust the pressure oscillation characteristics of the detonation flow field, and is of great significance to promote the potential of RDE and nozzle design.