Exhaust Port Research Articles

Flow-field evolution and vortex structure characteristics of a high-temperature buoyant jet

High-temperature buoyant jets generally exist at the exhaust port during the casting process. Canopy hoods are employed to capture these jets in industrial plants. However, because of the lack of flow-field evolution and vortex structure characteristics of the buoyant jets, the optimal design of canopy hood is lack of guidance. In this study, the effects of different initial temperatures (T0) of buoyant jets on the evolution of the temperature, velocity, and vorticity magnitude fields and vortex structure characteristics were studied by large-eddy simulation. The results showed that for 100–1200 °C buoyant jets, the contracted section, which is useful in determining the preferred canopy hood installation position, is generated within 0.7–2 times the source diameter from the nozzle (Z/D). As T0 increases, the position of the contracted section tends to come closer to the nozzle, and the space height for temperature attenuation in the core region is reduced. The contracted section formation results from the rupture of the vortex ring. Because the vortex ring can restrict the diffusion of the buoyant jet, the initial temperature has little effect on the diffusion angle within 4 Z/D. In addition, the spiral vortex structure entrains a large quantity of ambient air, which causes the exhaust flow rate to increase sharply. These conclusions may guide for the design of the exhaust hood installation height for high-temperature buoyant jets to achieve energy savings.

Characteristics of helicopter engine exhaust through scaled experiments using stereoscopic particle image velocimetry

Helicopter engines are often mounted atop the fuselage to keep the aircraft footprint small and optimal for operations. As a result, hot gases produced by the engines may inadvertently impinge upon the tail boom or dissipate inefficiently that compromises on operation safety. In this study, a scaled fuselage model with a hot air blower was used to simulate hot exhaust gases. The velocity field immediately outside the exhaust port was measured through stereoscopic particle image velocimetry to capture the trajectory and flow behaviour of the gases. Two cases were considered: freestream to exhaust velocity ratios of 0 (no freestream velocity) and 0.46 (co-flowing free stream), respectively. The formation of a counter-rotating vortex pair was detected for both cases but were opposite in the rotational sense. For the case without freestream, the plume formed into a small “kidney” shape, before expanding and dissipating downstream. For the case with freestream, the plume formed into a slenderer and more elongated “reversed-C” shape as compared to the case without freestream. It also retained its shape further downstream and maintained its relative position. These observations on the trajectory and shape of plume provide basis to understanding the nature and interaction of the plume with its surroundings.

Transient flow field and performance analysis of a claw pump for FCVs

The claw-type hydrogen pump has been applied in fuel cell vehicles (FCVs) because of its compact structure, high reliability, and oil-free quality. In this study, a three-dimensional transient computational fluid dynamics (CFD) modelling of a claw-type hydrogen pump used in FCVs was established. Hexahedral structured grids were generated and updated at an increment of 3° in rotating angle to ensure the mesh quality of the whole solving process. The leakage of radial clearance (RC) and axial clearance (AC) was considered. The presented modelling and simulation methods were validated by operating a claw pump at different pressure ratios. The pressure and velocity vector fields in both AC and middle plane, along with the mechanism of the fluid field distribution were analyzed in detail. The in-depth relationship amongst the fluctuation of discharge pressure, outlet mass flow rate and discharge area during the whole working process was revealed. P-θ and V-θ diagram of the whole operating cycle were analyzed. The influence of AC and RCs respectively on the volumetric efficiency of a claw pump was compared and evaluated. It is concluded that back flow in suction pipe happened near 360° as part of the discharge chamber was cut off from the exhaust port and high pressure gas from carryover flowed back into the inlet pipe. The pressure increase during the displacement process, theoretically zero, is actually significant and even comparable to the pressure increase during the compression and discharge process. In addition, volumetric efficiency is most sensitive to axial clearance, followed by radial clearance between rotor and casing, while radial clearance between the rotors has the least influence.

Effect of the exhaust thermal insulation on the engine efficiency and the exhaust temperature under transient conditions

As well as new advances in the after-treatment systems are required to achieve the new pollutant emission requirements, new designs of the exhaust line can be considered in order to increase the engine efficiency and the after-treatment effectiveness. In the present work, a one-dimensional gas dynamic model has been used to carry out a simulation study comparing several exhaust insulation solutions. This solutions include the insulation of the exhaust ports, the exhaust manifold, the internal surface of the turbine volute, the turbine external housing, as well as different combinations of these solutions. A transient analysis has been done in order to evaluate the increment in the exhaust gases temperature, fuel economy and pollutant emission levels over the WLTC (Worldwide harmonized Light vehicles Test Cycle) at three different temperature conditions. As a conclusion, a 12% increment in the turbine outlet gas enthalpy can be achieved by insulating both the exhausts ports and the exhaust manifold. Moreover, more than 30% less pollutant emissions are released to the environment with this setup.

Performance improvement of turbocharged SI engine by post-oxidation enhancement in exhaust gas in-homogeneity

In this research, the improvement of mixing and pulsation in exhaust manifold with a design and implementation of bypass adapter at exhaust port were deeply investigated. This in-turn can improve the post-oxidation phenomena and hence emissions and engine performance could be enhanced. This research investigation includes 1-D, 3-D simulations and experimental validation on a 4-cylinder turbocharged spark ignition (SI) engine. Firstly, the 1-D and 3-D simulation models were developed and calibrated with the experimental results. Then, the simulations were used for the detailed investigation of mixing and pulsation in exhaust manifold with and without bypass adapter. Thereafter, experimental test for the post-oxidation were conducted with and without consideration of the bypass adapter and results were compared. From the simulation and experimental results, it was proven that by using bypass adapter at the exhaust port, the mixing of exhaust gas species was observed to be significantly improved to some extent. Also, the unbalance between exhaust port and turbocharger upstream gas species were reduced. This also reduced the exhaust gas pulsation. By the improvement of mixing between scavenged O2 and unburned gas species, the post-oxidation reaction was also noted to have improved and consequently the emissions and turbo-speed were found to be better that led to an improved IMEP and thermal efficiency of the engine.

Study of low load performance on a two-stroke direct injection spark ignition aero-piston engine fuelled with diesel

Purpose The purpose of this paper is to investigate power performance, economy and hydrocarbons (HC)/carbon monoxide (CO) emissions of diesel fuel on a two-stoke direct injection (DI) spark ignition (SI) engine. Design/methodology/approach Experimental study was carried out on a two-stroke SI diesel-fuelled engine with air-assisted direct injection, whose power performance and HC/CO emissions characteristics under low-load conditions were analysed according to the effects of ignition energy, ignition advance angle (IAA), injection timing angle and excess-air-ratio. Findings The results indicate that, for the throttle position of 10%, a large IAA with adequate ignition energy effectively increases the power and decrease the HC emission. The optimal injection timing angle for power and fuel consumption is 60° crank angle (CA) before top dead centre (BTDC). Lean mixture improves the power performance with the HC/CO emissions greatly reduced. At the throttle position of 20%, the optimal IAA is 30°CA BTDC. The adequate ignition energy slightly improves the power output and greatly decreases HC/CO emissions. Advancing the injection timing improves the power and fuel consumption but should not exceed the exhaust port closing timing in case of scavenging losses. Burning stoichiometric mixture achieves maximum power, whereas burning lean mixture obviously reduces the fuel consumption and the HC/CO emissions. Practical implications Gasoline has a low flash point, a high-saturated vapour pressure and relatively high volatility, and it is a potential hazard near a naked flame at room temperature, which can create significant security risks for its storage, transport and use. The authors adopt a low volatility diesel fuel for all vehicles and equipment to minimise the number of different devices using various fuels and improve the potential military application safety. Originality/value Under low-load conditions, the two stroke port-injected SI engine performance of burning heavy fuels including diesel or kerosene was shown to be worse than those of gasoline. The authors have tried to use the DI method to improve the performance of the diesel-fuelled engine in starting and low-load conditions.

Plasma exhaust in a sheared-flow-stabilized Z pinch

The fusion Z-pinch experiment device produces a 0.3 cm radius by 50 cm-long Z pinch between the end of the inner electrode of a coaxial plasma gun and an end wall 50 cm away. The plasma column is stabilized for thousands of instability growth times by an embedded radially sheared axial plasma flow. To investigate the effect of end wall design on Z-pinch plasma behavior, the solid end wall with a central exhaust port is replaced with a spoked end wall with a solid hub. While the Z-pinch plasma behavior was largely unaffected, the plasma exhausted from the Z-pinch provides an experimental platform to study magnetic confinement and detachment. Current and density signals are compared between two cases: a low energy and a high energy case. Plasma is found to be frozen-in flux in the Z-pinch assembly region. The exhaust of plasma from the flux conserving region is found to be dependent on the ratio of plasma ram and thermal pressures to the local magnetic pressure, calculated from an equilibrium model at the end wall. Plasma exhaust is observed to increase with the spoked end wall only for the high energy conditions as its ratio of ram and thermal pressures to the magnetic pressure increases.

Demystifying theoretical concerns involving respirators with exhalation valves during COVID-19 pandemic

Demystifying theoretical concerns involving respirators with exhalation valves during COVID-19 pandemic

Using gas dynamic models to improve exhaust system design for large-bore, two-stroke engines

It is vital to have accurate predictions of the gas exchange behavior of an engine in order to reliably study engine performance and emissions using engine simulation models. There are a multitude of factors, both upstream and downstream of the engine cylinder, which influence its gas exchange characteristics. Quite often these influences are interconnected in a non-linear manner that results in complicated feedback loops, which can introduce significant errors in the computed thermodynamic state of the post-breathing cylinder mixture. The effects of such bi-directional movement of pressure pulses are particularly pronounced in two-stroke engines. This study investigates the importance of exhaust system design on the scavenging characteristics of a piston-scavenged, cross-flow, two-stroke engine. A validated one-dimensional predictive model is used to study the effects of changing the exhaust port timing, exhaust system length, and exhaust port efficiency on the breathing performance of the engine, along with the consequent effects on the thermal efficiency and NOx emissions. Exhaust pressure waves and mass flows across ports are used to understand and explain the observed changes. The results show that while making design changes, thermodynamic efficiency considerations can act as a barrier to improving the scavenging efficiency of the engine; in addition, a trade-off between the two has to be considered in the design process to meet engine performance targets. The effects of such a trade-off on the NOx production are analyzed and two exhaust system modifications are discussed.

Engine exhaust manifold with thermoelectric generator unit

Thermal energy recovery systems are subject of intensive research activities in automotive engineering. They are becoming appealing because of the energy savings, low maintenance requirements and compact designs. Another element is the increase in working temperature ranges over the previous maximum of 400 °C. This was limiting the positioning of these devices to mid and rear locations of the exhaust systems. They also contained a specially designed cooling system for the cold side of the thermoelectric generator unit, which effectively preformed the requirements of the cold junction point (Seebeck effect) between the “P” and “N” semiconductors. Currently, thermoelectric generator manufacturers are producing devices that could operate at the temperatures over 850 °C which is opening up different research and application opportunities. This research report shows a continuation of previous research work carried out, to test 850 °C thermoelectric generator units, using the performance specifications and measurements conducted in our labs. We have extrapolated and predicted power output further. In the research, we covered the concept of placing high-temperature thermoelectric generator units directly into the exhaust port of the engine, just outside the cylinder head. Novel development solution is presented, where a new thermoelectric generator unit is designed to be adaptable to the profile of the exhaust port. Computational fluid dynamics analysis was conducted on a real-world engine and concept models, confirming consistent thermal heat transfer from the combustion chamber of the engine into the exhaust manifold thermoelectric generator unit assembly. Cooling of the device is achieved by direct coolant flow from the cylinder head. It could also be realized using an external cooling system.

A novel inline PEEP valve design for differential multi-ventilation

BackgroundVentilator sharing is one option to emergently increase ventilator capacity during a crisis but has been criticized for its inability to adjust for individual patient needs. Newer ventilator sharing designs use valves and restrictors to control pressures for each patient. A key component of these designs is an inline Positive End Expiratory Pressure (PEEP) Valve but these are not readily available. Creating an inline PEEP valve by converting a standard bag-valve-mask PEEP valve is possible with the addition of a 3D printed collar. MethodsThis was a feasibility study assessing the performance and safety of a method for converting a standard PEEP valve into an inline PEEP valve. A collar was designed and printed that covers the exhaust ports of the valve and returns exhaled gases to the ventilator. ResultsThe collar piece was simple to print and easily assembled with the standard PEEP valve. In bench testing it successfully created differential pressures in 2 simulated expiratory limbs without leaking to the atmosphere at pressures greater than 60 cm of H2O. ConclusionOur novel inline PEEP valve design shows promise as an option for building a safer ventilator sharing system.

Effect of new simple breathing apparatus on oxygen therapy in patients with severe and critical coronavirus disease 2019

To make a new simple respirator and observe the oxygen therapy effect of the respirator on patients with severe and critical coronavirus disease 2019 (COVID-19). Based on the infectivity and hospital requirements of COVID-19, a new simple respirator was designed by the medical staff of the Department of Anesthesiology of the Second Affiliated Hospital of Nanchang University, which was applied on the 22 patients with severe and critical COVID-19 who needed oxygen therapy admitted to the Cancer Center of Tongji Medical College of Huazhong University of Science and Technology from February 15th to March 15th in 2020. The new simple respirator contained two National Utility Model Patents (a respirator: ZL 2015 2 0410623.6, a fluid switch and oxygen suction device: ZL 2017 2 0873509.6), which was mainly composed of anesthesia mask and filter, L-shaped connecting tube, soft breathing bladder, connecting tube and elastic fixing belt. When in use, the anesthesia mask was fixed to the patient's mouth and nose with elastic straps, the connecting tube was inserted into the oxygen meter interface, the oxygen flow was adjusted to 6-10 L/min, and the L-shaped connecting tube was opened immediately after the soft breathing bag was full. The carbon dioxide and excess oxygen in the body was discharged from exhaust port. The oxygen flow was lowered to 2-3 L/min, the patient's respiratory rate (RR) was observed through the soft breathing bag fluctuations, and the oxygen flow was adjusted at any time. The changes of pulse oxygen saturation (SpO2), RR and heart rate (HR) before and after application of new simple respirator were observed, and the blood gas test results of part of the patients were collected. Twenty-two patients with severe and critical COVID-19 had significantly higher SpO2 at 10 minutes after application of the new simple ventilator than before application (0.994±0.007 vs. 0.952±0.017, P < 0.01), and RR was significantly lower than that before application (times/min: 27.59±3.63 vs. 29.64±3.81, P < 0.01); after 1 day of application, each index was further improved. All 13 patients who received blood gas analysis indicated no carbon dioxide accumulation. The new simple respirator can significantly improve the oxygen therapy effect of patients with severe and critical COVID-19. At the same time, 2019 novel coronavirus (2019-nCoV) can be filtered through the filter to reduce the formation of aerosol and protect the medical staff and patients.

Research on Design Method of High Speed and High Dynamic Pressure Separation Structure

The inter-stage separation scheme has always been the focus and difficulty of low-altitude high-speed aircraft design. The separation reliability of low altitude high-speed aircraft is required to be higher. Experts and scholars have carried out design research on different forms of separation schemes. In this paper, two typical kind of inter-stage separation schemes are introduced. For aircraft A, a point cold separation scheme is adopted, which is connected by four explosive bolts, and two piston push rods provide separation impulse. For aircraft B, exhaust ports are opened on both sides of the rear of the transition section. The tail section is equipped with four “X” full-motion rudders for flight control. In addition, two horizontal stabilizers were added to improve stability. Based on the comparison and analysis of different inter-stage separation schemes for The separation reliability of low altitude high-speed aircraft is required to be higher. Experts and scholars have carried out design research on different forms of separation schemes. two different types of aircraft A and aircraft B, a new high reliability interstage separation scheme is proposed, the feasibility of the scheme is verified by simulation analysis, and the design of the stage separation structure under high dynamic pressure and high speed with compact layout is realized.

Numerical Study of the Maximum Impact on Engine Efficiency When Insulating the Engine Exhaust Manifold and Ports during Steady and Transient Conditions

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;In the present work, a study about the impact on engine performance, fuel consumption and turbine inlet and outlet temperatures with the addition of thermal insulation to the exhaust ports, manifold and pipes before the turbocharger of a 1.6L Diesel engine is presented. First, a 0D/1D model of the engine was developed and thoroughly validated by means of an extensive testing campaign. The validation was performed by means of steady state and transient running conditions and in two different room temperatures: 20°C and -7°C. Once the validation was complete, in order to evaluate the maximum gain by means of insulating materials, the exhaust air path before the turbine was simulated as adiabatic. Results showed that the thermal insulation proved to have a great potential in regard to T4 increase that would lead to a reduction of the warm up time of the aftertreatment systems. However, its impact on engine efficiency was limited in both steady and transient conditions.&lt;/div&gt;&lt;/div&gt;

A Thermal Exhaust Port on the Death Star of Plasmodium falciparum-Infected Erythrocytes

Eliciting reliable and effective immunity against Plasmodium falciparum parasites remains an elusive goal in malaria control. Raj and colleagues recently described a naturally occurring human antibody response to a parasite antigen that initiates apoptosis-like cell death of parasites, adding fascinating insight into host-pathogen dialog that may furnish actionable targets for antiparasite therapies or vaccines.

Numerical investigation the effects of the twin-spark plugs coupled with EGR on the combustion process and emissions characteristics in a lean burn natural gas SI engine

Abstract In this study, the single-spark natural gas (NG) SI engine was simulated by using the CFD coupled with detailed combustion mechanism, and validated against with the experiment data. Additionally, the axisymmetrically twin-spark plugs were placed diametrically opposite to each other in the combustion head of the NG SI engine, and fired simultaneously during the simulation cases to trigger two independent spark kernels. The results indicated that twin-spark plugs yielded approximate combustion phasing and better fuel conversion efficiency. Interestingly, in the early stages of flame propagation triggered by the twin-spark plugs configuration, two independent spark kernels looked remarkably similar to the iconic of “Taiji” diagram of the Chinese Taoism, and two independent flame kernels were obviously moved along with the flow. The strong flow pushed the flame front close to the side of the intake port of the NG SI engine equipped with the single-spark plug. While two independent flame fronts of the NG SI engine equipped with the twin-spark plugs were located separately at the intake and exhaust ports in the combustion chamber. Furthermore, two independent flame fronts mutually collided with each other, and generated more independent combustion block areas in the center of the combustion chamber.

Aerodynamic performance change of exhaust passage in steam turbine under low-load conditions

The exhaust passage is a passage which connect the exhaust port of steam turbine to the inlet of condenser. With the increase of new energy power generation, the coal-fired power units of greater capacity are demanded to participate in peak load regulation, so the steam turbine usually operates under low-load conditions. However, there are lack of literatures that comprehensive analysis aerodynamic performance of exhaust passage under low-load conditions. So in this paper, an exhaust passage coupling with the whole last-stage was numerically simulated by CFX software. The k-ω SST turbulence model and phase transformation model considering the spontaneous condensation flow of wet steam were used. The results show that the inlet swirl flow intensity of exhaust passage increases with the decrease of load. At the 10% turbine heat acceptance(THA) condition, the swirl angle which is more than 90° hold the range of 0% - 64% in blade height. Under low-load conditions, there are six different types of reverse vortices increasing the energy loss of exhaust passage. The total pressure drop of exhaust passage reaches to the maximum of 1671.24 Pa at 10% THA condition. Below the 50%THA condition, the static pressure recovery coefficient cannot be used as the indicator for evaluating the aerodynamic performance of exhaust passage.

Considerations for Pediatric Heart Programs During COVID-19: Recommendations From the Congenital Cardiac Anesthesia Society.

Considerations for Pediatric Heart Programs During COVID-19: Recommendations From the Congenital Cardiac Anesthesia Society.

Experimental and numerical study the effect of EGR strategies on in-cylinder flow, combustion and emissions characteristics in a heavy-duty higher CR lean-burn NGSI engine coupled with detail combustion mechanism

In order to study the effects of exhaust gas recirculation (EGR) strategies on in-cylinder flow, performance, combustion and emissions characteristics in a heavy-duty higher compression ratio (CR) lean-burn natural gas spark ignition (NGSI) engine. In the first stage, a detailed three-dimensional (3-D) full-scale cylinder part (including detailed intake port and exhaust port) is established based on the actual combustion chamber. Then some cases were simulated by commercial CFD code coupled with the detailed combustion mechanism and validated against the measured data. In the second stage, a sensitivity analysis of the EGR rate on in-cylinder temperature, emissions under different crank angles in 3-D, and performance of a heavy-duty higher CR (13.6) engine fueled with 99% methane content is discussed. The results show that the production of NOx is related to the mass fraction of high-temperature gas in a specific section of the cylinder. The larger the mass fraction of high-temperature gas, the more NOx emissions are generated. Besides, NOx is generated on the flame front and continuing to be generated inside the flame surface. The faster the temperature inside the flame surface decreases, the smaller the amount of NOx generation is. Furthermore, the model and these data in the paper can be applied to evaluate and optimize the energy distribution by changing different technologies or strategies in the future. In addition, 3-D data can provide a basis for the quantitative relationship between the EGR rate and combustion rate, NOx generation in the format of 1-D.

Endovascular Therapy for Patients With Acute Ischemic Stroke During the COVID-19 Pandemic: A Proposed Algorithm.

Endovascular Therapy for Patients With Acute Ischemic Stroke During the COVID-19 Pandemic: A Proposed Algorithm.