Valve Closure Research Articles

Equivalence method and transient flow characteristics of the integrated valve

As a new kind of built-in control rod drive technology, the control rod hydraulic drive system (CRHDS) is applied to the 200 MW nuclear heating reactor (NHR-200). The integrated valve (IV) is the key flow control component of CRHDS, realizing the stepping function of control rod. During operation, the rapid action of IV can trigger the water hammer, which can lead to system vibration, noise and instrument damage. Therefore, it is necessary to investigate the transient flow process. The composition and working principle of IV were presented, and the transient flow experiments were conducted. An equivalence method was proposed innovatively, and the transient flow model of IV was established, whose results were in good agreement with the experimental data. Finally, the model was applied to variable parameter conditions. The analysis results show that: IV can be simplified as flow capacitance, flow resistance, internal connecting pipe and closing valve. The water hammer pressure fluctuation amplitude decreases with the increase of valve closing time, cavity volume and system pipe diameter. The water hammer period increases with the increase of cavity volume and system pipe length. The research results provide guidance for the optimization and engineering application of CRHDS.

Dynamics of large cavity induced by valve closure in an undulating pipeline

The dynamics of large cavity and the accompanied water column separation and rejoining induced by fast closing of a butterfly valve in an undulating pipeline system are investigated in this study. The three-dimensional computational fluid dynamics numerical simulations are performed using a newly developed interfacial surface tension-based model (ISTM) that accounts for the surface tension effect on large cavities. The applicability of the ISTM model is validated with the experimental data, showing better accuracy in predicting pressure fluctuations and cavity evolutions than three typical cavitation models. Differences in cavitation characteristics are observed between upstream and downstream of the valve. Upstream the valve, cavitation primarily appears at the pipe top, with the vapor volume fraction varying sharply due to the rarefaction pressure waves (maximum value of 0.0073). Downstream the valve, the complete water-column separation occurs, and vapor volume fraction changes slowly correspond with the growth and collapse of the large cavity (maximum value of 0.647). The maximum length of the large cavity can reach about six times the pipe diameter, with a minimum water vapor interface angle of 16°. The cavitation evolution displays a transition from a clustered inception to a sheet-like growth and collapse pattern. These findings contribute to the design and operation guidance for complex hydraulic systems during transient processes.

Mechanocardiography detects improvement of systolic function caused by resynchronization pacing.

Objective.Cardiac resynchronization therapy (CRT) is commonly used to manage heart failure with dyssynchronous ventricular contraction. CRT pacing resynchronizes the ventricular contraction, while AAI (single-chamber atrial) pacing does not affect the dyssynchronous function. This study compared waveform characteristics during CRT and AAI pacing at similar pacing rates using seismocardiogram (SCG) and gyrocardiogram (GCG), collectively known as mechanocardiogram (MCG).Approach.We included 10 patients with heart failure with reduced ejection fraction and previously implanted CRT pacemakers. ECG and MCG recordings were taken during AAI and CRT pacing at a heart rate of 80 bpm. Waveform characteristics, including energy, vertical range (amplitude) during systole and early diastole, electromechanical systole (QS2) and left ventricular ejection time (LVET), were derived by considering 6 MCG axes and 3 MCG vectors across frequency ranges of >1 Hz, 20-90 Hz, 6-90 Hz and 1-20 Hz.Main results.Significant differences were observed between CRT and AAI pacing. CRT pacing consistently exhibited higher energy and vertical range during systole compared to AAI pacing (p< 0.05). However, QS2, LVET and waveform characteristics around aortic valve closure did not differ between the pacing modes. Optimal differences were observed in SCG-Y, GCG-X, and GCG-Y axes within the frequency range of 6-90 Hz.Significance.The results demonstrate significant differences in MCG waveforms, reflecting improved mechanical cardiac function during CRT. This information has potential implications for predicting the clinical response to CRT. Further research is needed to explore the differences in signal characteristics between responders and non-responders to CRT.

Numerical investigation of calcification effects on aortic valve motions and ambient flow characteristics

The pathogenesis and progression of calcific aortic stenosis pose a significant challenge in medical science due to the intricate nature of blood fluid dynamics. To better understand this crucial phenomenon, this study investigates the physiological behaviors of aortic valves with varying degrees of lesions and ambient flow conditions using an in-house CFD solver, CgLES-Y code. The code is validated by simulating two-dimensional valve opening and closure, followed by the extension to three-dimensional symmetrically simplified valve dynamics. The simulation results exhibit great agreement with other numerical, experimental and clinical data. Patient-specific models of the aortic root and inner valve geometries are developed based on CT images. Analysis of fluid dynamics traits, configuration properties and leaflet stress is performed for both normal and calcified aortic valves during the systolic and diastolic periods. The study further examines the impact of calcium deposition on abnormal flow fields and leaflet motion, which indicates that calcium deposition increases the tensional burden on healthy leaflets, therefore, the microcosmic increase in valve modulus leads to global damage extending from the root to the tip, whereas macroscopic calcification primarily induces damage in the vicinity of the calcium compound. Additionally, the generation of additional vortices on the valve surface and sinus lumen heightens the likelihood of calcium accumulation.

Experimental Investigation of Column Separation Using Rapid Closure of an Upstream Valve

In this study, the phenomenon of column separation that occurs in the downstream pipeline of a rapid closure valve is experimentally investigated. Special attention is paid to the dynamic behavior of the formation, growth, and collapse processes of cavities, which are observed using a high-speed camera. Synchronized images of cavity patterns and measured pressure histories are analyzed to elucidate the process of water column separation, the mechanism of column separation events, and the influence of parameters on the transient flow. Experimental results indicate that during the collapse process of vapor cavities, a superposition phenomenon involving a positive pressure wave and collapse wave occurs, resulting in a nearly three times rise of Joukowsky pressure. In all test cases, the maximum pressure of the pipeline exceeded 150 times the reservoir static pressure. A new classification for a water hammer combined with cavitation (four types of pressure oscillation patterns) is proposed based on whether the duration of column separation decreases sequentially and the maximum pipeline pressure follows the first collapse of cavities at the valve. As the initial flow velocity increases, there is generally an increase in maximum pressure; however, this trend may be scattered under certain operation conditions.

THE INFLUENCE OF VALVE TIMING ON IN-CYLINDER PRESSURE SPARK IGNITION ENGINES PERFORMANCE CHARACTERISTICS

The performance of the engine depends on many factors. One of the factors is valve timing known to be the timing of opening and closing of valves that has a significant effect on the in-cylinder performance. However, there is less information in the study about valve timing effect on single cylinder engine performances. In this study, the focus is to analyze in-cylinder pressure characteristics on a single piston fuel injection for a spark-ignition engine. This can be done by simulating the effects of valve timing on in-cylinder pressure. The methodology of this project will be simulation-based by using commercial one-dimensional software. The research results are engine performance parameters which are volumetric efficiency, brake torque, brake power, and cylinder pressure in 1000 to 5500 RPM engines. The results show a positive increment in engine performance from the baseline model (CTA240) which is 9.06% for brake power, 2.85% for brake torque, and 13.09% for volumetric efficiency. At low engine speed, it was also found improvement in cylinder pressure when advancing the intake valve timing opening (IVO) by 20 to 25 degrees bTDC. For high speed, the cylinder pressure was found to improve once the retardation of intake valve timing closing (IVC) was done between 40 to 45 degrees aBDC by comparing it with the baseline results. The result highlights the importance of intake valve timing setup by varying the opening and closing of the intake valve to give better output for engine performance.

Experimental and numerical investigation on dynamic characteristic of nozzle check valve and fluid-valve transient interaction

Check valves play an important role in multiple systems within nuclear power plants. This study focuses on the valve closing process and investigates the dynamic characteristics, valve disc motion, and flow field of a nozzle check valve under different spring stiffness and fluid deceleration rates using experimental and numerical simulation methods. Experimental tests were conducted on a DN300 annular disc-type nozzle check valve with a spring stiffness of 3000 N/m, and the dynamic characteristic curve of the check valve was obtained. The curve exhibits a small maximum slope (0.0454), indicating good dynamic performance of the check valve. Numerical simulations were performed using the dynamic mesh method and RNG k-ε turbulence model to study the effects of different spring stiffness and fluid deceleration rates on the maximum reverse flow velocity, disc motion process, disc impact velocity, and internal flow field of the valve. The maximum reverse flow velocity was also corrected, and the resulting dynamic characteristic curve agrees well with experimental values. This study analyzes the influence of spring stiffness and fluid deceleration rate on various parameters during the dynamic closing process of the check valve. This study contributes to the optimization design of check valves and provides guidance for more accurate calculation of the dynamic characteristic curve of check valves through numerical simulations.

Design of a Drag-reducing System for Smart Bar Conveying Chain Plate

This paper presents a solution to the issue of high frictional resistance between the chain plate and guide rail in cigarette conveying systems, which can result in chain plate failure. The proposed solution is an intelligent drag reduction system that incorporates lubrication and automatic dust removal. The system includes a conveyor chain plate, supporting roller assembly, air knife dust removal assembly, chain plate lubrication assembly, and controller. The controller manages the dust removal assembly's air source output and the lubrication of the chain plate assembly through the opening and closing of an electromagnetic valve, which controls the oil output to decrease resistance. Experimental testing of the system shows that it effectively reduces the chain plate's frictional resistance in the cigarette conveying line, resulting in improved system efficiency.

Insights into CFD Modelling of Water Hammer

A problem with 1-D water hammer modelling is in the application of accurate unsteady friction. Moreover, investigating the time response of fluid dynamics and unsteady turbulence structures during the water hammer is not possible with a 1-D model. This review article provides a summary of 1-D modelling using the recent finite volume approach and the discussion extends to a quasi-2-D model and historical developments as well as recent advancements in 3-D CFD simulations of water hammer. The eddy viscosity model is excellent in capturing pressure profiles but it is computationally intensive and requires more computational time. This article reviews 3-D CFD simulations with sliding mesh, an immersed solid approach, and dynamic mesh approaches for modelling valve closures. Despite prediction accuracy, a huge computational time and high computer resources are required to execute 3-D flow simulations with advanced valve modelling techniques. Experimental validation shows that a 3-D CFD simulation with a flow rate reduction curve as a boundary condition predicted accurate pressure variation results. Finally, a brief overview of the transient flow turbulence structures for a rapidly accelerated and decelerated pipe flow using DNS (Direct numerical simulation) data sets is presented. Overall, this paper summarises past developments and future scope in the field of water hammer modelling using CFD.

Natural shear wave measurements detect changes in operational stiffness induced by mechanical ventilation in sheep

Abstract Shear wave elastography (SWE) has the potential to non-invasively measure myocardial stiffness, based on the propagation speed of shear waves traveling through the myocardium after valve closure. However, shear wave propagation speed (SWS) is related to the operational stiffness of the heart, which is defined by the slope of the end-diastolic stress-strain relationship at the operating volume/pressure. Therefore, operational stiffness can be altered by both changes in intrinsic myocardial stiffness and myocardial loading conditions. We aimed to investigate whether SWE can detect differences in operational stiffness induced by loading changes during mechanical ventilation, and whether SWE combined with respiratory hold manoeuvres could detect an evolution in stiffness during the course of ischemic cardiomyopathy (ICM). We assessed SWS in 8 sedated and mechanically ventilated sheep: 1 healthy control, 3 within 8 weeks, and 4 after at least 16 weeks following left coronary artery ligation (early vs. late ICM). Left ventricular parasternal long-axis views were acquired with a state-of-the-art ultrasound scanner with high frame rate technology (&amp;gt; 1100 Hz). Shear waves after mitral valve closure were considered during an inspiratory hold at 30 cmH2O and 15 cmH2O and expiratory hold at 0 cmH2O (atmospheric pressure). We used linear regression to assess the trend of the SWS during ventilation manoeuvres per animal and a two-tailed Student’s T-test to assess changes between ICM stages and their respective response to ventilation manoeuvres. In all but one sheep, SWS declined with higher inspiratory pressures (see fig. 1), possibly due to a reduction in preload at higher inspiratory pressures resulting in a shift towards a reduced slope on the myocardial stress-strain relation. The sheep with a positive slope was excluded from further analyses. SWS during expiratory hold at atmospheric pressure was 3.4 m/s in the healthy control and was significantly lower in early vs. late ICM (mean±SD 4.0±0.6 vs. 9.0±1.7 m/s; p=0.007). Furthermore, the change in SWS was larger in late vs. early ICM (slope of regression line -0.16 vs. -0.05 m/s/cmH2O; p=0.03). These observations suggest loading on a steeper part of the end-diastolic stress strain relationship in late ICM. In conclusion, our results suggest that SWE is able to detect differences in operational stiffness induced by mechanical ventilation. Secondly, SWE appears to distinguish between different time points in the course of ICM based on the magnitude of the SWS during expiratory hold at atmospheric pressure, but also on the magnitude of the SWS change during loading alterations induced by mechanical ventilation. Further work should assess whether SWE combined with respiratory hold manoeuvres could contribute to differentiate intrinsic from hemodynamic stiffening, and to exploit its full potential as a non-invasive bedside method for the assessment of operational stiffness.

Unsupervised machine learning model for predicting anomalies in subsurface safety valves and application in offshore wells during oil production

Predicting oil well behavior regarding the integrity of its equipment during production and anticipating behavioral changes and anomalies are among the main challenges in oil production. In this context, this study focuses on the development of predictive models for real-time monitoring of well behavior using sensor data from production wells. An unsupervised Novelty and Outlier Detection model has been introduced with a specific focus on predicting instances of unexpected subsurface safety valve closures in subsea wells. This model effectively classifies anomalies observed in these systems by leveraging real-world pressure and temperature data sourced from published literature. The methodology involves the implementation of a floating window for assembling training and test sets. Additionally, a comprehensive investigation is conducted into the impact of hyperparameters and the model’s threshold value (cp threshold). The results highlight the effectiveness of the developed model, observed through the accuracy achieved around 99.9% in predicting spurious closure events of the Downhole Safety Valve. On the same dataset, previous works reported 99.9% accuracy by using long short-term memory (LSTM) autoencoder, 87.1% by using random forest, and 60% with the Decision Tree method. Looking at F1-SCORE values, the developed model performs the best, followed by the LSTM model, both of which are significantly superior to the Decision Tree and random forest models. Furthermore, the model’s applicability is validated through testing in ultradeep water subsea wells within the pre-salt area of the Santos Basin. The significance lies in the potential for this research to enhance anomaly prediction in offshore wells, consequently reducing the costly interventions due to equipment malfunctions. Timely detection and corrective actions, facilitated by the model, can mitigate production loss and safeguard well integrity, addressing critical concerns in the oil and gas industry.

Incidence and predictors of the novo significant mitral and tricuspid regurgitation in patients with permanent atrial fibrillation

Abstract Introduction Atrial fibrillation (AF) is related to atrial remodeling and annular enlargement, which leads to functional mitral and tricuspid regurgitation. These two entities can derive in heart failure with preserved left ventricular ejection fraction (LVEF), the reason why it is becoming a rising concern in recent years. However, its incidence and predictors have not been well established. Purpose This study aimed to assess the incidence and predictors of significant atrial functional mitral and tricuspid regurgitation in patients with permanent AF. Methods The study population comprised 547 patients from a Spanish health area diagnosed with permanent AF between 2014 and 2019 (CardioCHUVI-AF registry; ClinicalTrials.gov identifier: NCT04364516). Individuals who presented with atrial enlargement at the diagnosis, primary moderate to severe valve disease, previous cardiac surgery (including valve replacement or repair), decreased LVEF, pulmonary hypertension, or right ventricular pacing that could interfere with tricuspid valve closure were excluded. The median age was 78.0 (IQ 70.4-85.6), and men represented 43% of the population (235 patients) compared to women, which represented 57% (312 patients). During a median follow-up of 3.5 years (IQ 2.03-4.95) we assessed the incidence of moderate to severe de novo mitral and tricuspid valve regurgitation and its predictors. Results The development of moderate to severe mitral and tricuspid valve regurgitation was higher after three years of diagnosis. The incidence of mitral regurgitation was 3.8 (3.0-4.9) per 100 persons/year. The incidence of tricuspid regurgitation was 5.5 (4.5-6.8) per 100 persons/year. In addition, multivariate analysis showed an association between the development of mitral regurgitation and older age (HR 1.05 [CI 95% 1.01-1.09]), female sex (HR 1.82 [CI 95% 1.1-3]) and prior admission for HF (HR 2.35 [CI 95% 1.18-4.7]). On the other hand, the development of tricuspid regurgitation did not show an association with age (HR 1.02 [CI 95% 0.97-1.05]), but it did with prior admission for HF (HR 2.11 [CI 95% 1.17-3.79]) and female sex (HR 2.17 [CI 95% 1.43-3.3]). Conclusion Permanent atrial fibrillation was associated with an increased risk of developing atrial functional mitral and tricuspid regurgitation, especially after three years of the diagnosis and in the female sex. Older age was associated with a higher incidence of mitral regurgitation. Prior admission for HF was associated with a higher incidence of tricuspid regurgitation. Based on the preceding, monitoring a specific profile of patients with atrial fibrillation may be especially important in preventing and early treating valve disease that can compromise their prognosis.Incidence of mitral regurgitationIncidence of tricuspid regurgitation

Abstract 17917: Effect of Transcatheter Aortic Valve Replacement (TAVR) on the Dicrotic Notch in Patients With Severe Aortic Stenosis

Background: The dicrotic notch in the aortic pressure waveform is seen around the time of closure of the aortic valve at the end of systole and the beginning of diastole. We aim to study the change in the dicrotic notch post TAVR in patients with severe AS and its impact on clinical outcomes. Methods: We included patients with severe AS who underwent TAVR consecutively between 2019-2020. Central aortic pressure waveforms were reviewed from the SyngoDynamics imaging software (Siemens Healthcare, Malvern, PA) for the invasive hemodynamic data obtained during TAVR. Heights of the systolic, diastolic blood pressure and dicrotic notch waveforms are measured. Dicrotic notch index (DNI) is calculated as the difference between the SBP and dicrotic notch divided by the pulse pressure (see figure 1). The invasive hemodynamics are compared between pre and post TAVR using independent samples t test. Statistical significance was defined as two-tailed p-value less than 0.05. Survival analysis is performed using cox regression. Results: A total of 724 patients (1448 studies) were evaluated. There is significant increase in dicrotic notch pressure (p&lt;0.001) and DNI (p&lt;0.001) post-TAVR in the overall population. Women (n=310) had a higher pre-TAVR and post-TAVR DNI (p&lt;0.001 and p&lt;0.01 respectively). Figure 1 shows hemodynamic characteristics of before and after TAVR. Heart failure hospitalization (HFH) or mortality at 3 years (composite outcome) was present in 146 patients (20.1%). DNI was lower in patients reaching composite outcomes compared to patients surviving without HFH (p&lt;0.001). Conclusion: Higher DNI after TAVR is associated with lower HFH and mortality after TAVR. Simple measurement of DNI offer substantial prognostic value to patients with severe AS undergoing TAVR.

Abstract 16969: Assessment of the Electromechanical Window in Patients With Conventional Biventricular Pacing as Compared to Patients With Conduction System Pacing

Introduction: The Electromechanical Window (EMW) is a validated measurement reflecting electromechanical coupling of the ventricles, and is defined as the difference between electrical and mechanical ventricular activation times. A larger (more negative) EMW is associated with worse clinical outcomes, especially greater arrhythmic risk, in various clinical conditions such as long QT syndrome, risk of drug-inducd torsade, hypertrophic cardiomyopathy, etc. Cardiac resynchronization therapy (CRT) can be achieved by conventional bi-ventricular pacing (BiVP) or conduction system pacing (CSP). We assessed the EMW in patients undergoing CRT via these 2 modalities. Methods: Total mechanical activation time was measured from the 5 chamber echocardiographic view as the interval (ms) from the onset of the Q wave to aortic valve closure (mean of 3 measurements). Total electrical activation time (QTcBazett interval, ms) was measured from 12 lead ECGs recorded within 24 hours of the echocardiogram. The EMW was calculated as the difference between the QTc and the mechanical ventricular activation time. Results: A total of 60 pts (BiVP=31, CSP=29) were analyzed. There was no significant difference between the heart rates during the ECG and the echocardiogram recorded within 24 hours of each other (74.6 ± 16.5 vs 71.5 ± 12.0 bpm, P=NS). The EMW was significantly more negative in patients with BiVP as compared to CSP (-99.5 ± 70.9 vs -55.2 ± 52.7 ms, P=0.03). When restricting the analysis to patients where the ECG and echocardiographic HRs were within 10 bpm of each other, the difference remained significant (P=0.03). Conclusions: Patients in whom CRT is achieved by CSP have less negative EMWs as compared to patients with BiVP. Based on the known association of more negative EMW with increased arrhythmic risk, these data, if confirmed in larger populations with correlation to clinical outcomes, add to the growing evidence to support CSP as the preferred modality for achieving CRT.

Abstract 12082: Dermatomyositis Associated Pulmonary Fibrosis Masquerading as Severe Aortic Insufficiency

Description of Case: A 56-year-old female with asthma and hypertension presented for two weeks of dyspnea, cough, and fevers. Initial workup revealed bilateral ground glass opacities. TTE revealed severe aortic insufficiency, early mitral valve closure, and a LVEF of 65%. The patient underwent SAVR and was started on diuresis but continued to have significant respiratory distress over the next few months, leading to recurrent hospitalizations and requiring home oxygen therapy. Serial imaging revealed worsening of her pulmonary opacities. Due to persistent musculoskeletal and cutaneous symptoms with an elevated CPK, an alternative diagnosis was considered: dermatomyositis associated pulmonary fibrosis. The patient was started on steroids and immunomodulatory therapy with improvement in her symptoms. Discussion: Dermatomyositis (DM) is an inflammatory myopathy characterized by proximal muscle weakness, rash, and other manifestations including ILD and esophageal dysmotility. Mortality in patients with DM is associated with rapid progression of ILD. Patients may also have myocardial involvement and heart failure. Patients with presumed cardiogenic respiratory failure that does not improve with HF optimization should undergo further workup and consideration of a broader differential diagnosis. Unexplained elevated CPK disproportionate to troponins, and persistent hypoxia in patients with multisystem involvement should trigger an autoimmune work up. If such a process is identified, patients may have a rapid improvement in their symptomatology and excellent prognosis following immunomodulatory therapy. If left undiagnosed, it can cause multi-system failure, including significant myocarditis and heart failure.

Abstract 17322: Closing the Loop: Use of Amplatzer PFO Occluder Device in Case of LVAD-Associated Aortic Insufficiency

Description of Case: A 72-year-old woman with destination therapy Heartmate 3 left ventricular assist device (LVAD) presented with NYHA Class III symptoms. Review of her echocardiograms since LVAD implantation revealed progressive central aortic insufficiency (AI) with subsequent LV dilatation, managed with reduction in LVAD speed. Patient declined surgical aortic valve replacement and/or repair. After a multidisciplinary discussion, the patient opted to pursue percutaneous aortic valve closure. Cardiac CT demonstrated no aortic valve thrombus and identified appropriate anatomy for closure with an 18x25 mm Amplatzer PFO Occluder device (Graphic 1). Preoperative TEE revealed LV ejection fraction of 15% with moderate to severe AI and fibrosis of the aortic valve commissures with no aortic valve movement. The aortic valve was closed with the Amplatzer PFO Occluder with an 18mm disk that sat on the LV side of the aortic valve within the AV annulus and the 25mm disk sitting on the aortic side of the aortic valve within the sinus of Valsalva. TEE and intracardiac echocardiography demonstrated excellent device placement with two residual trace AI jets at the non-left and left-right commissure. Following LVAD speed increase, the degree of AI remained unchanged and she was discharged with improved symptoms. Discussion: Moderate-severe AI develops in about 15-25% of patients within 1 year of LVAD implantation. There are previous reports of LVAD-associated AI closure with an Amplatzer cribiform device. We describe the first known use of the Amplatzer PFO Occluder device for the management of LVAD-associated AI. While transcatheter aortic valve replacement (TAVR) is an attractive option to treat LVAD-associated AI, securing the transcatheter heart valve in the absence of calcifications remains a challenge.

Canister valve and actuator deposition in metered dose inhalers formulated with low-GWP propellants

A challenge in pressurised metered-dose inhaler (pMDI) formulation design is management of adhesion of the drug to the canister wall, valve and actuator internal components and surfaces. Wall-material interactions differ between transparent vials used for visual inspection and metal canister pMDI systems. This is of particular concern for low greenhouse warming potential (GWP) formulations where propellant chemistry and solubility with many drugs are not well understood. In this study, we demonstrate a novel application of X-ray fluorescence spectroscopy using synchrotron radiation to assay the contents of surrogate solution and suspension pMDI formulations of potassium iodide and barium sulphate in propellants HFA134a, HFA152a and HFO1234ze(E) using aluminium canisters and standard components. Preliminary results indicate that through unit life drug distribution in the canister valve closure region and actuator can vary significantly with new propellants. For solution formulations HFO1234ze(E) propellant shows the greatest increase in local deposition inside the canister valve closure region as compared to HFA134a and HFA152a, with correspondingly reduced actuator deposition. This is likely driven by chemistry changes. For suspension formulations HFA152a shows the greatest differences, due to its low specific gravity. These changes must be taken into consideration in the development of products utilising low-GWP propellants.

A method to quantify the advantages of a variable valve train for CI engines

Today’s CI engines are subject to strict regulations of pollutant emissions and ambitious fuel consumption targets. Therefore, the interaction between the engine and the exhaust aftertreatment system (ATS) has become increasingly important. Numerous studies have shown that a variable valve train (VVT) improves the interaction between engine and ATS. However, most of these studies either quantify the advantage on a specific engine or only present complex CFD models, such that the results are not easily transferable to different engines. Thus, engine manufacturers cannot directly use these results to assess the advantage of various VVT strategies for their engines. In this paper, we propose a cycle-discrete cylinder model based on first principles which allows to simulate various VVT strategies. In contrast to present methods based on CFD, the proposed cylinder model can be realized with the equations presented. Furthermore, the model is identified with measurement data of an engine without a VVT. A separate engine, which is retrofitted with a fully VVT, is used to validate the proposed modeling approach. Using the identified model in combination with a mean-value model of the air path, we are able to simulate the effects of early intake valve closing, early exhaust valve opening, and cylinder deactivation for a complete CI engine that has no VVT installed. The model is then used to highlight the advantage of a VVT for two scenarios at part-load operation. At cold start, where the temperature of the ATS must be increased quickly, variable valve timing achieves higher enthalpy flows to the ATS while also lowering engine-out NOx emissions when compared to a standard engine strategy. If the ATS is at the operating temperature, cylinder deactivation achieves significantly higher enthalpy flows which prevents the ATS from cooling down. In addition, cylinder deactivation also lowers fuel consumption and engine-out NOx emissions.

Study of single and split injection strategies on combustion and emissions of hydrogen DISI engine

Hydrogen energy shows excellent potential as an alternative fuel for internal combustion engines (ICE) in terms of cleanliness and efficiency. However, the specificity of hydrogen density and diffusion rate leads to further optimization of the working process of the hydrogen direct injection spark ignition (DISI) engines. In this study, the effects of single injection and split injection strategies on the combustion and emissions of a hydrogen DISI engine were investigated at medium/low load. The specific results showed that premature hydrogen injection could trigger pre-ignition events, and it was appropriate to set the earliest hydrogen injection timing to 180° CA BTDC after the intake valve closing. For the single injection strategy, the brake thermal efficiency (BTE) increased first and then decreased with the delay of the start of injection (SOI). When SOI = 100° CA BTDC, the optimal BTE (36.1 %) could be obtained, and nitrogen oxide (NOx) emissions could still be limited to less than 0.1 g/(kW·h). For the split injection strategy, Delaying the secondary end of injection (SEOI) beyond 30° CA BTDC rapidly worsened NOx emissions to over 1.5 g/(kW·h). Delaying SEOI achieved higher efficiency but slightly worse the coefficient of variation COVIMEP than the single injection strategy. In addition, increasing the secondary injection mass fraction (SIMF) to 30 % could achieve an 18 % higher peak heat release rate than a single injection and shorter combustion duration. However, over 20 % SIMF resulted in an increase of NOx emissions to over 4 g/(kW·h). The energy distribution indicated that adjusting the injection strategy to increase BTE was mainly achieved by reducing power of heat loss (PHL).

Electromechanical Window and Spontaneous Ventricular Tachyarrhythmias in Takotsubo Syndrome

QT interval prolongation is common in patients hospitalized with Takotsubo syndrome (TTS), however, only a minority experience ventricular tachyarrhythmias. Our aim was to characterize the electromechanical window (EMW) in patients with TTS and to evaluate its association with ventricular tachyarrhythmias. We preformed aretrospective analysis of 84 patients hospitalized with TTS in the Tel-Aviv Medical Center between 2013 and 2022. All patients underwent a comprehensive echocardiographic evaluation and the EMW was calculated by subtracting the QT interval from the QRS onset to the aortic valve closure obtained from a continuous-wave Doppler for the same beat. Of the 84 patients with TTS, 74 (88%) were female and the mean age was 70 ± 11 years. The mean left ventricular ejection fraction was 42 ± 8%. The EMW was negative in 81 patients (96%), and the mean EMW was -69 ± 50 ms. Ventricular tachyarrhythmias occurred in 7 patients (8%). The EMW of patients who experienced ventricular tachyarrhythmias was more negative than patients who did not (-133 ± 23 ms vs -63 ± 48 ms, p = 0.001). In the univariate analysis, EMW and QT were associated with ventricular tachyarrhythmias (univariate odds ratio [OR]EMW1.03, 95% confidence interval [CI] 1.01 to 1.05, p = 0.003 and univariate ORQTc1.02, 95% CI 1.01 to 1.03, p = 0.02); however, only EMW remained significant in the multivariate analysis (OREMW1.03 95% CI 1.03 to 1.05, p = 0.023). EMW was more effective than corrected QT interval in identifying patients who had ventricular tachyarrhythmias (AUCEMW: 0.89, 95% CI 0.82 to 0.97 vs AUCQTc0.77, 95% CI 0.61 to 0.93, p = 0.02), and a cut-off value of -108 ms was predictive of ventricular tachyarrhythmias with a sensitivity of 86% and a specificity of 79%. In conclusion, EMW is negative in patients with TTS and is associated with increased risk for ventricular tachyarrhythmias. The role of EMW in the risk stratification of patients with TTS warrants further investigation.