3D Computational Fluid Dynamics Model Research Articles

Aerodynamic limits of gas turbine compressor during high air offtakes for minimum load extension

Renewable energy sources (RES) have become a favoured alternative to fossil fuel energy generation that has been driven by environmental concerns. Their intermittent nature has meant that gas turbines have remained relevant to support them as a backup. Current grid operation requires gas turbines to operate at as low power as possible when their demand drops, and also ramp-up quickly when power generation from renewables declines. Air extraction from a gas turbine compressor can address the first requirement, as this mechanism reduces the load or power of the engine while storing the air for further pressurised reinjection, related to ramp-up rate improvements. This study demonstrates the aerodynamic implications and the limits to air extraction behind the last stage of the compressor, to achieve further minimum load reduction. To achieve this, a zero-dimensional (0D) analytical model of an engine at design and off-design conditions (air extraction) has been used to determine the boundary conditions for a 3D compressor Computational Fluid Dynamics (CFD) model. The multi-stage CFD model shows the aerodynamic implications of low to high air extractions that are limited by choke, high flow separation, and loss in the pressure at the hub region of OGV and last stage stator. As such, the back of the compressor was more affected than the earlier stages. Based on these, the limit of flow extraction is 18% (of the compressor discharge). The compressor of the analytical engine model showed similarity in trends for comparable conditions with the stand-alone 3D compressor, however, more optimistic than the latter. The work has shown that the compressor is capable of high airflow extractions to reduce the minimum load further.

A numerical methodology for thermo-fluid dynamic modelling of tyre inner chamber: towards real time applications

The characterization and reproduction of tyre behaviour for vehicle modelling is a topic of particular interest both for real-time driver in the loop simulations and for offline performance optimization algorithms. Since the accuracy of the tyre forces and moments can be achieved by the accurate physical modelling of all the phenomena concerning the tyre-road interaction, the link between the tyre thermal state and the tyre frictional performance turns into a crucial factor. An integrated numerical methodology, allowing to couple the full 3D CFD (Computational Fluid Dynamics) flux within the internal chamber of the tyre with an equivalent discrete 3D structure model, is proposed with the aim to completely represent the tyre thermodynamic convective behaviour in the steady-state operating conditions. 3D CFD model enables the evaluation of the internal distribution of the gas temperature and of the thermal powers exchanged at each sub-wall in detail. This allows to increase the reliability of the tyre thermodynamic modelling with a particular reference to the proper managing of the aero-thermal flow of the brake disc impact on the rim temperature and therefore on the internal gas dynamics in terms of temperature and pressure, being able to optimize the tyre overall dynamic performance in both warm-up and stabilized thermal conditions. The steady RANS (Reynolds Averaged Navier–Stokes) simulations have been performed employing the 3D CFD model in a wide range of angular velocities with the aim to calculate the convective thermal flux distributions upon rim and inner liner surfaces. The simulation results have been then exploited to derive the convective heat transfer coefficients per each sub domain to be employed within the real-time tyre physical thermal model, with the peculiar advantage of an enhanced model reliability for thermal characteristics. To validate the proposed methodology, the tyre thermal model outputs, in terms of temperatures of internal and external layers, have been validated towards the acquired ones within the specific routine performed on tyre force and moment test bench, confirming an excellent agreement with the experimental data in the entire range of operating conditions explored.

Performance and Losses Analysis for Radial Turbine Featuring a Multi-Channel Casing Design

Abstract A novel control technique for radial turbines is under investigation for providing turbine performance controllability, especially in turbocharger applications. This technique is based on replacing the traditional spiral casing with a multi-channel casing (MC). The MC divides the turbine rotor inlet circumferentially into a certain number of channels. Opening and closing these channels controls the inlet area and, consequently, the turbine performance. The MC can be distinguished from other available control techniques in that it contains no movable parts or complicated control mechanisms. Within the casing, this difference makes it practical for a broader range of applications. In this investigation, a turbocharger featuring a turbine with MC has been tested on a hot gas test stand. The experimental test results show a reduction in the turbine operating efficiency when switching from full to partial admission. This reduction increases when reducing the admission percentage. To ensure the best performance of the turbine featuring MC while operating at different admission configurations, it becomes crucial to investigate its internal flow field at both full and partial admission to understand the reasons for this performance reduction. A full 3D computational fluid dynamics (CFD) model of the turbine was created for this investigation. It focuses on identifying the loss mechanisms associated with partial admission. Steady and unsteady simulations were performed and validated with available test data. The simulation results show that operating the turbine at partial admission results in highly disturbed flow. It also detects the places where aerodynamic losses occur and which are responsible for this performance reduction. This operation also shows flow unsteadiness even when operating at steady conditions. This unsteadiness depends mainly on the admission configuration and percentage.

Evaluation of different personalized ventilation air terminal devices: Inhalation vs. clothing-mediated exposures

Human exposure to particles indoors occurs through direct inhalation or indirectly through deposition on clothes that release them in other spaces. Ventilation systems are installed to decrease direct exposure but little is known about their effect on clothing-mediated exposures. This work weighs the effect of personalized ventilation (PV) systems on decreasing inhalation exposure to indoor particles versus their contribution to clothing contamination by particle deposition. To conduct this work, a 3D computational fluid dynamics model was developed for an office conditioned by mixing ventilation and common PV air terminal devices: computer mounted panel (CMP), vertical desk grill (VDG) and round movable panel (RMP). Typical particle sources were considered: furniture resuspension and human breathing. The model was validated experimentally in a climatic chamber by comparing real-time particle mass concentration near a thermal manikin. Results showed that CMP delivering 5 l/s reduced total inhalation exposure by 27% and deposition by 72% compared to standalone mixing ventilation. Increasing the flow to 10 l/s led to reductions of 89% in exposure and 56.5% in deposition. A VDG delivering 5 l/s reduced exposure by 33% while deposition reduction was negligible at 3%. Increasing the flow rate to 10 l/s reduced exposure by 91% and slightly increased deposition by 12%. The RMP at 5 l/s and 10 l/s reduced exposure by 89% and 97% respectively and increased deposition by 70% and 80% respectively. Among the three ATDs, the CMP offered the best compromise between reducing inhalation exposure and clothing-mediated exposures at all possible flow rates.

Reliability-based retrofit assessment of coastal bridges subjected to wave forces using 3D CFD simulation and metamodeling

ABSTRACT This paper proposes a comprehensive analysis framework, combining three-dimensional (3D) numerical modelling and metamodeling, to investigate the probabilistic performance of retrofit actions on coastal bridges subjected to extreme wave forces. Specifically, a 3D Computational Fluid Dynamics (CFD) model is developed to calculate extreme wave load on the bridge superstructure. The established 3D model is validated by laboratory experiments. The characteristics of wave forces are parametrically investigated, and an Artificial Neural Network (ANN) metamodel is utilised to quantify the loading effects with multiple surge and wave parameters. Such a numerical-based ANN metamodel could predict wave forces under variable scenarios accurately, and significantly reduce the high computational cost of the 3D numerical model. Based on the numerical and metamodeling results, the bridge fragility curve is derived by considering uncertainties associated with structural demand, capacity, and hurricane hazard. Long-term failure risk is assessed under different climate change scenarios. Furthermore, different retrofit methods to improve structural performance and reduce failure risk are examined according to the proposed framework, including inserting air venting holes, enhancing connection strengths, and elevating bridge structures. The proposed framework could facilitate the optimal and robust design and maintenance of coastal infrastructures under hurricane effects in a long-term time interval.

Modelación mediante dinámica de fluidos computacional 3D de temperatura y humedad en un invernadero con humidificación

Introduction: Medium and low technology greenhouses use natural ventilation as a method of temperature and humidity control. However, at certain times of the year, this is insufficient to extract excess heat inside the greenhouse, so devices such as hydrophanes (humidifiers) have been implemented to reduce the temperature. It is necessary to know the behavior of temperature and humidity, since both factors influence the development of crops and, therefore, their yield. Objective: To develop a computational fluid dynamics (CFD) model of a naturally ventilated zenithal greenhouse equipped with hydrophanes to understand the spatial and temporal distribution of temperature and humidity inside the greenhouse. Methodology: The experiment was carried out in a greenhouse equipped with hydrophanes and grown with bell pepper. Temperature and humidity measurements were performed from March 7 to 25, 2014. The ANSYS Workbench program was used for the 3D CFD modeling. Results: The CFD model satisfactorily described the temperature and humidity distribution of the greenhouse, with an error of 0.11 to 3.43 °C for temperature, and 0.44 to 10.80 % for humidity. Limitations of the study: Numerical modeling using CFD is inadequate to model the temporality of the variables. Originality: There are few studies that model humidity behavior with CFD and the use of hydrophanes in Mexico. Conclusions: The CFD model allowed visualizing the distribution of temperature and air humidity inside the greenhouse.

LANDSLIDE-GENERATED TSUNAMIS: A NUMERICAL ANALYSIS OF THE NEAR-FIELD

There are coastal areas which are particularly prone to landslide-generated tsunami risk. The destructive effects caused by the impulsive waves, generated by landslide sources, can be strongly magnified by the characteristics of the so-called "confined geometries" (e.g. bays, reservoirs, lakes, volcanic islands, fjords, etc.). Complicated physical phenomena (e.g. trapping mechanisms, edge waves, wave runup, etc.) take place as a consequence of the interaction between the generated waves and the local bathymetry and control the tsunami propagation and interaction with the coast, often causing devastating consequences. Many past events of landslide-generated tsunamis testify this reality (e.g. Lituya Bay, Alaska, Fritz et al., 2009; Stromboli Island, Italy, Tinti et al., 2005; Anak Krakatau, Indonesia, Grilli et al., 2019). To reduce and mitigate the tsunami risk a proper comprehension, and modelling, of such complicated phenomena is crucial. Landslide-generated tsunamis have been largely studied by exploiting experimental, analytical and numerical modelling. Experimental tests are often time and money consuming, especially if 3D models are considered. Large facilities, as well as complicated experimental configurations and sophisticated measurement systems (e.g. Romano et al. 2016), are often needed. Furthermore, not always it is possible to explore in detail the influence of all the involved parameters, in particular those related to the landslide triggering mechanisms and rheology, that have a considerable influence on the wave characteristics in the so-called "near-field". To this end, numerical modelling can provide a valuable assistance. The new tools offered by the Computational Fluid Dynamics (CFD) methods represent a valuable means for shedding light on the unresolved aspects. In particular, the 3D CFD modelling techniques appear to be crucial as far as the tsunami characteristics in the near-field, induced by landslide sources, are concerned. Indeed, the accurate reproduction of the energy transfer between the landslide and the water is essential to model the tsunami generation and propagation mechanisms, allowing to explore a large variety of landslide triggering mechanisms and rheology. In this paper we present a numerical study of the landslide-generated tsunamis in the near-field.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/liUdiV2qXPg

CFD Modeling and Experimental Validation of an Alkaline Water Electrolysis Cell for Hydrogen Production

Although alkaline water electrolysis (AWE) is the most widespread technology for hydrogen production by electrolysis, its electrochemical and fluid dynamic optimization has rarely been addressed simultaneously using Computational Fluid Dynamics (CFD) simulation. In this regard, a two-dimensional (2D) CFD model of an AWE cell has been developed using COMSOL® software and then experimentally validated. The model involves transport equations for both liquid and gas phases as well as equations for the electric current conservation. This multiphysics approach allows the model to simultaneously analyze the fluid dynamic and electrochemical phenomena involved in an electrolysis cell. The electrical response was evaluated in terms of polarization curve (voltage vs. current density) at different operating conditions: temperature, electrolyte conductivity, and electrode-diaphragm distance. For all cases, the model fits very well with the experimental data with an error of less than 1% for the polarization curves. Moreover, the model successfully simulates the changes on gas profiles along the cell, according to current density, electrolyte flow rate, and electrode-diaphragm distance. The combination of electrochemical and fluid dynamics studies provides comprehensive information and makes the model a promising tool for electrolysis cell design.

A Numerical Simulation of Membrane Distillation Treatment of Mine Drainage by Computational Fluid Dynamics

Membrane distillation (MD) is a promising technology to treat mine water. This work aims to investigate the change in mass and heat transfer in reverse osmosis mine water treatment by vacuum membrane distillation (VMD). A 3D computational fluid dynamics (CFD) model was carried out using COMSOL Multiphysics and verified by the experimental results. Then, response Surface Methodology (RSM) was used to explore the effects of various parameters on the permeate flux and heat transfer efficiency. In terms of the influence degree on the permeation flux, the vacuum pressure > feed temperature > membrane length > feed temperature membrane length, and the membrane length has a negative correlation with the membrane flux. Increasing the feed temperature can also increase the convective heat transfer at the feed side, which will affect the heat transfer efficiency. Furthermore, the feed temperature also has a critical effect on the temperature polarization phenomenon. The temperature polarization becomes more notable at high temperatures.

Heat transfer modeling within the microclimate between 3D human body and clothing: effects of ventilation openings and fire intensity

PurposeThe purpose of this study is to determine the effect of ventilation openings and fire intensity on heat transfer and fluid flow within the microclimate between 3D human body and clothing.Design/methodology/approachOn account of interaction effects of fire and ventilation openings on heat transfer process, a 3D transient computational fluid dynamics model considering the real shape of human body and clothing was developed. The model was validated by comparing heat flux history and distribution with experimental results. Heat transfer modes and fluid flow were investigated under three levels of fire intensity for the microclimate with ventilation openings and closures.FindingsTemperature distribution on skin surface with open microclimate was heavily depended on the heat transfer through ventilation openings. Higher temperature for the clothing with confined microclimate was affected by the position and direction of flames injection. The presence of openings contributed to the greater velocity at forearms, shanks and around neck, which enhanced the convective heat transfer within microclimate. Thermal radiation was the dominant heat transfer mode within the microclimate for garment with closures. On the contrary, convective heat transfer within microclimate for clothing with openings cannot be neglected.Practical implicationsThe findings provided fundamental supports for the ease and pattern design of the improved thermal protective systems, so as to realize the optimal thermal insulation of the microclimate on the garment level in the future.Originality/valueThe outcomes broaden the insights of results obtained from the mesoscale models. Different high skin temperature distribution and heat transfer modes caused by thermal environment and clothing structure provide basis for advanced thermal protective clothing design.

Computational simulation of air-side heat transfer and pressure drop performance in staggered mannered twisted oval tube bundle operating in crossflow

With a high demand for reduced energy consumption, twisted oval tube (TWT) heat exchangers are increasingly convenient for industrial applications. After a comprehensive literature survey, it was found that the literature so far discussed the counterflow efficiency of such heat exchangers, unfortunately, there is minimal emphasis on the thermohydraulic behaviour of the staggered TWT bundle operating in air-water cross-flows. And in particular, there are almost no computational studies to explore the thermal-hydraulic behaviour of staggered TWT bundles operating in crossflow. Further investigations with design optimisation are therefore required for efficient and cost-effective operation. In this study, a three-dimensional (3D) computational fluid dynamics (CFD) model is developed to analyse the air-side heat transfer and pressure drop performances in TWT bundle with staggered layout operating in air-water crossflow (600 < Re < 17,000). The Realizable k-ϵ model is used to evaluate the turbulence effect of the 3D fluid flow. The simulation results is firstly validated against the measured results and then the effects of geometrical parameters on the overall performance were analysed, such as ratio of outer major to outer minor axis (A/B = 1.491, 2.063 and 3.034), twisted pitch length (S = 0.2, 0.3 and 0.4 m), transverse tube pitch, (S1 = 0.033, 0.038 and 0.043 m), longitudinal tube pitch (S2 = 0.050, 0.065 and 0.080 m), diagonal tube pitch (S2/= 0.0527, 0.0671 and 0.0827 m), longitudinal tube rows (Z = 4, 6 and 8), and the number of TWTs (tn = 6, 9 and 12). The air-side overall heat transfer coefficient, h, the Nusselt number, Nu, and pressure drop, ΔP, were observed to be positively correlated to the Reynolds number, Re. As the Re increased, both Nu and ΔP increased with the increase of A/B, S2, and S2/, Z, respectively. However, both Nu and ΔP decreased with the geometric increase in S and S1, respectively. Finally, a generalised Nu correlation (independent of tn) is developed and validated against a recent measurement, offering a useful reference for the design of such heat exchangers.

Computational Modeling of Transport in Porous Media Using an Adaptive Network-Based Fuzzy Inference System.

This investigation is conducted to study the integration of the artificial intelligence (AI) method with computational fluid dynamics (CFD). The case study is hydrodynamic and heat-transfer analyses of water flow in a metal foam tube under a constant wall heat flux (i.e., 55 kW/m2). The adaptive network-based fuzzy inference system (ANFIS) is an AI method. A 3D CFD model is established in ANSYS-FLUENT software. The velocity of the fluid in the x-direction (Ux) is considered as an output of the ANFIS. The x, y, and z coordinates of the node’s location are added to the ANFIS step-by-step to achieve the best intelligence. The number and type of membership functions (MFs) are changed in each step. The training process is done by the CFD results on the tube cross-sections at different lengths (i.e., z = 0.1, 0.2, 0.3, 0.4, 0.6, 0.7, 0.8, and 0.9), while all data (including z = 0.5) are selected for the testing process. The results showed that the ANFIS reaches the best intelligence with all three inputs, five MFs, and “gbellmf”-type MF. At this condition, the regression number is close to 1.

Unraveling the Causes of Excess Lead in Drinking Water Supply Systems of Densely Populated High-Rise Buildings in Hong Kong.

Excess concentrations of lead (Pb) were found in tap water from drinking water supply systems of high-rise buildings in 11 public rental housing (PRH) estates in Hong Kong, posing threats to public health. The copper supply lines are fitted with lead-soldered connections and brass fixtures and faucets. The causes of excess lead are studied through field sampling on occupied households, experiments on prototype supply chains, and 3D numerical modeling. The tap water lead concentration of 129 households in the PRH estates was sampled using a specially designed protocol, revealing the highly variable lead concentration variations induced by sources along the supply chain. Lead concentration variation at consumer tap and its relation with various lead sources are studied in a full-scale test rig. A 3D computational fluid dynamics (CFD) model is successfully developed to interpret the time variation of lead concentrations at the consumer tap. Model predictions of the complex variation of dissolved lead are in good agreement with data and confirm lead solder in copper pipe connections as a major cause of the "lead water" episode in Hong Kong. The CFD calculations demonstrate the importance of turbulent diffusion and shear flow dispersion in the modeling of lead; the use of a "plug flow" approximation can result in significant overestimation of lead concentration. The findings provide a basis for lead risk assessment of different water sampling strategies in densely populated high-rise buildings in Megacities.

3D CFD Modeling and Optimization of a Cylindrical Porous Bed Reactor for Hydrogen Production using Steam Reforming of Methane

Steam Reforming of Methane, which converts natural gas into products with higher economic value in the presence of a suitable catalyst bed reformer, is the most economical method for hydrogen production in petroleum refineries. This study focuses on developing a Computational Fluid Dynamics (CFD) model of a steam methane reformer. To this purpose, a steady-state heterogeneous 3 Dimensional model that was composed of mass, species, momentum, and energy balances was developed. It compares two different geometrical porous bed reformers with different heating tube configurations for better heat transfer and reforming. Effects of heating tubes inlet temperature, the ratio of inlet CH4/H2O, and the configuration of the heating tube are studied and optimized. The results show that conversion of methane will be promoted by increasing inlet temperature of the heating tube as well as the number of heating tubes in the reformer when CH4/H2O ratio is about 0.2. In this platform, the conversion of methane is not affected by the porosity below 0.35. Also, the simulations results are shown to be in agreement with typical data reported in the literature. So, this study can be used to develop industrial natural gas reformers.

Three-dimensional bioprinting of aneurysm-bearing tissue structure for endovascular deployment of embolization coils

Various types of embolization devices have been developed for the treatment of cerebral aneurysms. However, it is challenging to properly evaluate device performance and train medical personnel for device deployment without the aid of functionally relevant models. Current in vitro aneurysm models suffer from a lack of key functional and morphological features of brain vasculature that limit their applicability for these purposes. These features include the physiologically relevant mechanical properties and the dynamic cellular environment of blood vessels subjected to constant fluid flow. Herein, we developed three-dimensionally (3D) printed aneurysm-bearing vascularized tissue structures using gelatin-fibrin hydrogel of which the inner vessel walls were seeded with human cerebral microvascular endothelial cells (hCMECs). The hCMECs readily exhibited cellular attachment, spreading, and confluency all around the vessel walls, including the aneurysm walls. Additionally, the in vitro platform was directly amenable to flow measurements via particle image velocimetry, enabling the direct assessment of the vascular flow dynamics for comparison to a 3D computational fluid dynamics model. Detachable coils were delivered into the printed aneurysm sac through the vessel using a microcatheter and static blood plasma clotting was monitored inside the aneurysm sac and around the coils. This biomimetic in vitro aneurysm model is a promising method for examining the biocompatibility and hemostatic efficiency of embolization devices and for providing hemodynamic information which would aid in predicting aneurysm rupture or healing response after treatment.

CFD analysis for evaluating and optimizing spatial distribution of CO2 concentration in a strawberry greenhouse under different CO2 enrichment methods

A deeper understanding of the spatial distribution of CO2 concentration inside cultivation facilities (e.g., greenhouses and plant factories) is necessary for the quantitative evaluation and/or the improvement in the performance and efficiency of artificial CO2 enrichment methods. We developed 3D computational fluid dynamics (CFD) models for two CO2 enrichment methods in a strawberry greenhouse – one was for overall greenhouse enrichment, as the usual method, and the other was for localized crop enrichment. We confirmed the model validation by comparing the simulated and measured CO2 concentrations in the greenhouse. With regard to the entire enrichment condition, CO2 accumulated at the upper part of the greenhouse through convection due to the high temperature of CO2 generated while there was low CO2 concentration around the crops. This could be regarded as an ineffectual situation. However, such situation can be alleviated by lowering the temperature of CO2. On the other hand, we found that crop-local enrichment can increase CO2 concentration only around crops albeit with less effect on those at the upper part. Thus, changing the enrichment strategy as well as the equipment could greatly optimize the distribution of CO2 in a greenhouse, thereby improving the efficiency of CO2 enrichment.

Simple mid-depth transverse baffles to improve bacterial disinfection in a shallow maturation pond – performance evaluation and CFD simulation

ABSTRACT Sunlight-mediated disinfection in wastewater treatment ponds is widely recognised as the main role for disinfection, but pathogen removal can be limited by poor light penetration in the water column. The aim of this research is to evaluate a different and simple type of intervention for improving bacterial disinfection, by placing mid-depth transverse baffles perpendicular to the theoretical flow in an existing shallow maturation pond, aiming at increasing the opportunity for bacteria to receive radiation at the upper layers of the pond. In order to understand the hydrodynamic mechanisms and evaluate the effectiveness of the proposed intervention, a 3D Computational Fluid Dynamic (CFD) model was applied, including the transverse baffles and a particle-tracking model. This was complemented by monitoring E. coli in the pond, in the phase before and after inclusion of the transversal baffles. Overall, the transverse baffles increased disinfection efficiency by moulding/re-routing the hydrodynamic flow and increasing microorganism exposure to the sunlight.

3D transient CFD simulation of an in-vessel loss-of-coolant accident in the EU DEMO fusion reactor

Accidental transients in fusion reactors, such as the in-vessel loss-of-coolant accident (LOCA) considered here, are generally analyzed using system-level codes. However, because of their lumped nature, such tools cannot predict local pressure and temperature values, which are instead of interest to assess the integrity of the vacuum vessel (VV) structures. It is then fundamental to prove that the system-level tools’ predictions are at least conservative. In this work, we analyze the helium flow inside the VV following a LOCA in the helium-cooled blanket of the EU DEMO, using a 3D transient computational fluid-dynamics (CFD) model implemented in the commercial STAR-CCM+ code. In view of the large pressure ratio, a hypersonic flow regime (Ma > 5) develops, with the formation of shock fronts requiring a high time and space resolution. The model is applied to compute the evolution of the pressure distribution inside the VV and then to compare it with the information provided by the system-level GETTHEM model. The predictions by the two models of the intervention time of the VV pressure suppression system are compared, showing that the 0D model is conservative.

A Numerical Investigation on De-NOx Technology and Abnormal Combustion Control for a Hydrogen Engine with EGR System

The combustion emissions of the hydrogen-fueled engines are very clean, but the problems of abnormal combustion and high NOx emissions limit their applications. Nowadays hydrogen engines use exhaust gas recirculation (EGR) technology to control the intensity of premixed combustion and reduce the NOx emissions. This study aims at improving the abnormal combustion and decreasing the NOx emissions of the hydrogen engine by applying a three-dimensional (3D) computational fluid dynamics (CFD) model of a single-cylinder hydrogen-fueled engine equipped with an EGR system. The results indicated that peak in-cylinder pressure continuously increased with the increase of the ignition advance angle and was closer to the top dead center (TDC). In addition, the mixture was burned violently near the theoretical air–fuel ratio, and the combustion duration was shortened. Moreover, the NOx emissions, the average pressure, and the in-cylinder temperature decreased as the EGR ratio increased. Furthermore, increasing the EGR ratio led to an increase in the combustion duration and a decrease in the peak heat release rate. EGR system could delay the spontaneous combustion reaction of the end-gas and reduce the probability of knocking. The pressure rise rate was controlled and the in-cylinder hot spots were reduced by the EGR system, which could suppress the occurrence of the pre-ignition in the hydrogen engine.

Thermal Modeling Approaches for a LiCoO2 Lithium-ion Battery—A Comparative Study with Experimental Validation

Temperature prediction of a battery plays a significant role in terms of energy efficiency and safety of electric vehicles, as well as several kinds of electric and electronic devices. In this regard, it is crucial to identify an adequate model to study the thermal behavior of a battery. This article reports a comparative study on thermal modeling approaches by using a LiCoO2 26650 lithium-ion battery, and provides a methodology to characterize electrothermal phenomena. Three approaches have been implemented numerically—a thermal lumped model, a 3D computational fluid dynamics model, and an electrochemical model based on Newman, Tiedemann, Gu and Kim formulation. The last two methods were solved using ANSYS Fluent software. Simulations were validated with experimental measurements of the cell surface temperature at constant current discharge and under a highway driving cycle. Results show that the three models are consistent with actual temperature measurements. The electrochemical method has the lower error at 0.5C. Nevertheless, this model provides the higher error ( 1.3∘C) at 1.5C, where the maximum temperature increase of the cell was 18.1∘C. Under the driving cycle, all the models are in the same order of error. Lumped model is suitable to simulate a wide range of battery operating conditions. Furthermore, this work was expanded to study heat generation, voltage and heat transfer coefficient under natural convection.