Vahid Esfahanian

University of Tehran | UT · Vehicle, Fuel and Environment Research Institute, School of Mechanical Engineering

Wet steam flow in the low-pressure stage of a steam turbine reduces efficiency and causes blade erosion due to the formation of water droplets. To enhance efficiency and lifetime, shape optimization is a suitable method, but it requires computationally expensive numerical simulations of non-equilibrium condensation in 3D viscous flow. This study in...

The improvement of existing turbines requires time-consuming computations that often limit the number of parameters that can be optimized. To address this challenge, this study uses through-flow code, which is about 200 times faster than 3D Computational Fluid Dynamics (CFD), to optimize a two-stage axial turbine with 112 geometrical parameters usi...

Air pollution has many harmful effects and leads to various damages. In this research, the amount of social costs caused by air pollution in Tehran metropolis for PM, NOx, SOx, CO and VOC pollutants has been met. For this purpose, first, the emission rate of this pollutant has been determined based on the reports of the Environmental Protection Org...

An object-oriented PIC-DSMC numerical code using the C++ programing language was developed to predict the grid erosion and lifetime of the multi-grid and, in particular, the dual-stage ion thrusters. The code was developed for hybrid parallel processing on both the CPU and GPU. The extractor grid effects on the thruster lifetime were studied by com...

The main contributions of this study are, first, developing an efficient reduced-order model (ROM) to fast and accurately simulate the temperature rise and electrochemical behavior of a lead-acid cell during discharge and, second, presenting a comprehensive analysis for the dominant thermal modes of the cell. For this purpose, the governing transpo...

Plug-in hybrid electric buses are a viable solution to increase the fuel economy. In this framework, precise estimation of optimal state-of-charge trajectory along the upcoming driving cycle appears to play a pivotal role in the way to approach the globally optimal fuel economy. This paper aims to conduct a parametric study on the key factors affec...

The ultra-battery is a hybrid energy storage system, which can be used to operate in the high rate partial state of charge (HRPSOC) mode. In this study, the electrochemical model of the ultra-battery is implemented to simulate the interaction of double-layer capacitance and deposited lead on carbon surfaces, which can be operative at the carbon par...

Long charging time is one of the main disadvantages of lead–acid batteries. Although the higher charging voltage can shorten the charging time, it is limited in order to avoid thermal instability. In the present research, the charging time has shortened using a higher charging voltage while the stability of the system has remained the same through...

The present study aims to provide a modified model for analysing the longitudinal dynamics of ground vehicles. Bearing in mind that an inevitable tire slip occurs under the transmission of driving torque to the drive wheels, the pure rolling assumption employed in many previous works is modified in this research. This paves the way through the deve...

Owing to current status of global energy consumption and greenhouse gases emission, investigation of energy demand in different sectors seems to be necessary. Meanwhile, International Energy Agency (IEA)’s reports imply that a considerable share of global energy use is consumed in transport sector. Thus, conducting the vehicle energy demand and inf...

Unsteady fluid systems are nonlinear high-dimensional dynamical systems that may exhibit multiple complex phenomena in both time and space. Reduced Order Modeling (ROM) of fluid flows has been an active research topic in the recent decade with the primary goal to decompose complex flows into a set of features most important for future state predict...

Unsteady fluid systems are nonlinear high-dimensional dynamical systems that may exhibit multiple complex phenomena both in time and space. Reduced order modeling (ROM) of fluid flows has been an active research topic in the recent decade with the primary goal to decompose complex flows to a set of features most important for future state predictio...

Unsteady fluid systems are nonlinear high-dimensional dynamical systems that may exhibit multiple complex phenomena both in time and space. Reduced order modeling (ROM) of fluid flows has been an active research topic in the recent decade with the primary goal to decompose complex flows to a set of features most important for future state predictio...

Plasma sheath, as ion injection boundary of accelerator system, has direct effect on ion beam characteristics and consequently on ion thruster performance and lifetime. In most of numerical simulations of accelerator system of electrostatic ion thrusters, the effects of electrons on upstream plasma and plasma sheath's shape are simulated by treatin...

ARTICLE INFO The work involved a fundamental study of auto-ignition under unusually high knock intensities for an optical spark ignition engine. The single-cylinder research engine adopted included full bore overhead optical access capable of withstanding continuous peak in-cylinder pressures of up to 150 bar. A heavy knock was deliberately induced...

Wind turbines have been used to harvest clean energy for many years. However, wind turbine simulation is extremely expensive as it requires a high computational cost. Consequently, many studies have proposed different methods to reduce the computational time of wind turbine simulation. Reduced Order Methods (ROMs) show their capability to predict t...

Lithium-ion batteries (LIBs) have drawn attention in research due to their broad range of applications. To achieve low-cost and high reliable batteries, researchers have worked on a variety of degradation phenomena. Among them, the Solid Electrolyte Interphase (SEI) layer is the most important degradation phenomenon and causes the cell to capacity...

Dynamic Mode Decomposition (DMD) is a data-driven reduced order method, which is known for its power to capture the basic features of dynamical systems. In fluid dynamics, modal analysis of unsteady fluid flows over moving structures is significant in terms of state estimation and control. However, the underlying algorithm of the DMD requires a fix...

Fields of hybrid electric vehicles (HEVs) and renewable energies require energy storage systems operating in a partial state of charge (PSOC). The ultra-battery combines an asymmetric supercapacitor and a lead-acid battery in a unit cell and is compatible with the PSOC mode. In this study, a mathematical model is presented for numerical simulation...

The present study aims to investigate the effect of hydrogen enrichment of the methane jet fuel on the formation of pollutants and greenhouse gases and exergy efficiency of a burner working on flameless MILD combustion mode for different amounts of oxygen present in the hot air co-flow stream using computational fluid dynamics coupled with detailed...

High energy density lithium-air batteries are ideal storage systems for future transportation like electric vehicles. The theoretical energy density of lithium-oxygen batteries is more than ten times greater than the energy density of lithium-ion batteries which are currently used in electric vehicles. In spite of high energy density of lithium-oxy...

Development of a fast and accurate tool for simulation of batteries is greatly interested in the applications which require real-time estimation of the battery operating status, e.g., battery monitoring, online prognostics, and control. This study proposes three lumped model for the real-time simulation of Lead-acid batteries. The first one, named...

Real‐time fast simulation of lead‐acid battery (LAB) plays an important role in monitoring, control, optimization, and many other engineering fields. Hence, any improvement toward a reduction in computational time of LAB simulation while maintaining the accuracy of results is of practical interest. Reduced‐order modeling (ROM) is one of the promisi...

The importance of energy efficiency, as one of the most crucial issues in automotive industry, has grown more rapidly considering the global energy crisis and climate change in recent years. This paper aims to introduce a method to increase the powertrain efficiency based on the minimization of tire power loss. Slip resistance is taken into account...

A wavelet-based power management system is proposed in this paper with a combination of the battery and ultracapacitor (UC) hybrid energy storage system (HESS). The wavelet filter serves as a frequency-based filter for distributing the power between the battery and UC. In order to determine the optimal level of wavelet decomposition as well as the...

Lithium-ion batteries (LIB) have been prevalently used as an energy storage system in numerous devices. Real-time, highly accurate numerical simulation of lithium batteries is a crucial prerequisite for many applications such as battery online state monitoring and controlling, optimization, and uncertainty quantification. The pseudo-two-dimensional...

In the present study, the effects of Organic Rankine Cycle (ORC) and turbo-compound (T/C) system integration on a heavy-duty diesel engine (HDDE) is investigated. An inline six-cylinder turbocharged 11.5 liter compression ignition (CI) engine employing two waste heat recovery (WHR) strategies is modelled, simulated, and analyzed through a 1-D engin...

Battery State of Power (SoP) estimation is one of the most crucial tasks of the battery management system in electric and hybrid electric vehicles. The inevitable error in estimates of battery State of Charge (SoC) and State of Health (SoH) is a cause of inaccuracies towards estimating the SoP for an aged battery. To overcome this, the present stud...

Faster charging of lead-acid batteries is one of the main challenges of researchers in the field of electric vehicles. The increase of the charging voltage can cause to thermal instability in addition to the reduction of the charging time. In the present study, the thermal stability of lead-acid batteries is analyzed, linearly. The governing equati...

Two-stroke cycle engines have always been prominent due to their distinctive advantage incorporating high power-to-weight ratio, however the drawbacks are poor combustion efficiency, fuel short-circuiting and excessive emission of uHC and CO. These problems are apparent at low-load and speed regions and are the major obstacle to their global accept...

High thrust density per thruster area is the most desired achievement in current ion thruster designs. Dual-stage ion thruster concept is introduced to improve the ion beam focusing capability of single-stage thrusters in order to maximize the achievable thrust density for a fixed thruster area. In this paper, a two-grid ion thruster is converted t...

Lead-acid batteries are one of the most applicable electrochemical energy storage technologies which are used in various applications because of their low price, high discharge rate, and recycling. Due to the numerous uncertain parameters in the numerical simulation of a lead-acid battery, it is difficult to determine the importance of these parame...

Considering the important role of verification and validation processes in design and analyses of combustion systems, and the growing role of natural gas as a clean alternative fuel along with the deviation in its composition among different sources, this study aims to investigate the effect of natural gas composition on the correctness of a model’...

The spiral type one is more prominent of which the vertical type ground heat exchange (GHE) is the most common in ground source heat pumps (GSHP) and on the purpose of this study as well. The present paper provides numerical simulation for 1D-3D model of the ground source heat pumps in cooling mode by using COMSOL environment. In contrary to popula...

Increasing of capacity in lead-acid batteries and reducing charging time in lower temperature are considered as some main challenges of designers and manufacturers. Geometrical properties of battery plates such as thickness and maximum activated area are some of effective parameters on battery performance. Thus, determining of optimum values for in...

Investigation of vehicle resistant forces and power losses is of crucial importance owing to current state of energy consumption in transport sector. Meanwhile, considerable portion of resistant forces in a ground vehicle is traced back to tires. Pneumatic tires are known to be a source of energy dissipation as a consequence of their viscoelastic n...

Temperature rise is one of the main problems of battery applications. Thus, preventing the temperature rise in lead–acid batteries is an important research topic. In the present study, the effect of Lewis number on temperature rise is investigated. Moreover, effects of the cell–length (CL), the maximum activated area (Amax) and the newly defined pa...

The increasing number of passenger cars worldwide and the consequent increasing rate of global oil consumption have raised the attention on fuel prices and have caused serious problems to the environment. Nowadays, the demand for reducing fuel consumption and pollutant emissions has paved the way to the development of more efficient power generatio...

This paper focuses on a simulation study of a newly developed high-pressure fuel pump system for small engine. When an engine is operated at high speed in a typical Gasoline Direct Injection (GDI) system, its pump will perform extra pumping requiring continuous engine work. Because it is driven by the engine’s camshaft, the extra pumping action is...

Transport-related pollution as the main source of air pollution must be reduced in Tehran mega-city. The performance of various developed scenarios including BAU (Business As Usual) as baseline scenario, ECV (Elimination of carburetor equipped Vehicle), NEM (New Energy Motorcycles), HES (Higher Emission Standard), VCR (Vehicle Catalyst Replacement)...

The newly developed concept of MILD combustion has paved the way through achievement of high thermal efficiencies with low levels of pollutants and greenhouse gases. High fidelity numerical models play key role in design and optimization of these burners. The present research aims to assess the effect of molecular diffusion and deviations in the am...

Conventional two-stroke cycle engine suffers from typical drawbacks including lower combustion efficiency and excessive emissions of uHC and CO which are largely due to low in-cylinder average charge temperature at low load and speed regions of engine operating conditions. Utilising the hot burned Exhaust Gas Recirculation (EGR) technique can boost...

As concerns of oil depletion and security of supply remain as severe as ever, and faced with the consequences of climate change due to greenhouse gas emissions, Europe is increasingly looking at alternatives to traditional road transport technologies. Battery Electric Vehicles (BEVs) are seen as a promising technology, which could lead to the decar...

In the present study, a new set of dimensionless coefficients is introduced through non-dimensionalization of electrochemical equations of lead-acid batteries. Non-dimensionalization process has been applied to the electrochemical governing equations including conservation of charge in solid and electrolyte, and conservation of species to derive th...

In this study the influence of utilization of two Waste Heat Recovery (WHR) strategies, namely organic Rankine cycle (ORC) and turbocompounding, have been investigated based on the performance of a heavy-duty diesel engine using 1-D simulation engine code (GT-Power) in terms of Brake Specific Fuel Consumptions (BSFC) at various engine speeds and Br...

Fumigation is an important subject in air pollution. In a neutral atmosphere, temperature decreases with the height. However, when there is a transient condition of climate like sunrise in the morning which leads to increase the land surface temperature, temperature profile of stable condition will change. In these conditions, convection of air nea...

The present research aims to propose a new approach to improve the performance of computational codes employing the RANS/LES technique with 2nd order central scheme. To accomplish this, an unsteady compressible 3D coupled RANS/LES solver using two-equation turbulence model is developed. A smart post-processing filter is also embedded as the dissipa...

This study examines the implementation of a waste heat recovery system on an electric hybrid vehicle. The selected waste heat recovery method operates on organic Rankine cycle principles to target the overall fuel consumption improvement of the internal combustion engine element of a hybrid powertrain. This study examines the operational principle...

In this study, the surface vorticity method based on the Biot-Savart law is implemented for analyzing the ducted horizontal axis wind turbine to calculate the aerodynamic performance. The present method requires considerably less computational time than CFD methods. Our goal is to present a method for considering the effects of the duct on the wind...

Several efforts have been performed to improve LBM defects related to its computational performance. In this work, a new algorithm has been introduced to reduce memory consumption. In the past, most LBM developers have not paid enough attention to retain LBM simplicity in their modified version, while it has been one of the main concerns in develop...

Hardware-in-the-loop (HiL) simulation is known as a reliable approach for testing and verification of the control system of hybrid vehicles. In this paper, a low-cost functional HiL test bench is utilised to test and verify the drive motor management software (DMMS) in a series hybrid electric bus. The HiL simulator in the current research is a lap...

One major drawback about premixed charge compression ignition (PCCI) engines is incomplete combustion and producing high levels of carbon monoxide (CO) emission in lean operating conditions. This issue becomes even more serious when fuels with high octane number, e.g. natural gas, are used. In the present work, the combustion process of premixed ch...

This study investigates the effects of hydrogen enrichment on formation of pollutants and greenhouse gases in gas-fueled spark ignition engines. To this end, a previously validated detailed mechanism is embedded with a comprehensive one-dimensional engine model and the results are verified with experimental observations at different compression rat...

The real-time battery monitoring often involves two contradicting requirements, i.e., high accurate modeling and low computational time. The main contribution of this study is developing a reduced order model to accurately simulate a lead-acid battery without any simplification which can be used for real-time monitoring, optimization and control pu...

Thermal management of lithium-ion battery pack in hybrid electric vehicles (HEVs) and electric vehicles (EVs) have become a research focus in recent years because performance, safety and life time of battery have significant dependency on temperature distribution throughout the cell. As the first step in designing a reliable thermal strategy, heat...

Due to high energy and power density, lithium-ion batteries (LIBs) have become one of the most popular choices for electric vehicle (EV) and hybrid electric vehicle (HEV) applications. However, reliability and durability of LIBs are highly affected by the operational and environmental conditions. The Battery Management System (BMS) is responsible f...

Lithium-ion batteries are one of the most common energy storage systems which are widely used as a power source in portable electrical and electronic products, especially in electric and hybrid electric vehicles (HEVs) due to low self-discharge and high energy/power density. However, as a drawback, thermal instability is recognized as one of the ma...

Electric energy storage systems are used considerably in industries and daily applications. The demand for batteries with high energy content has increased because of their use in hybrid vehicles. Lead-acid batteries have wide applications because of their advantages such as high safety factor and low cost of production. The major shortcoming of le...

Ethanol as a renewable and alternative fuel when utilized in homogeneous charge compression ignition (HCCI) has potential to substantially reduce nitrogen oxides (NOx) and particle matter (PM) and can maintain HCCI sustainability. HCCI engine operation is limited between two ringing and misfire regions that too retard and advance combustion phasing...

The present study aims to reduce the computational cost of in-cylinder phenomena simulation under the light of employing Proper Orthogonal Decomposition (POD) technique. The equivalence ratio as the main identifier for soot formation tendency along with temperature and nitrogen oxide fields, are studied inside a gas-fuelled engine. The required cor...

The Energy Storage System (ESS) is an expensive component of an E-bike. The idea of Hybrid Energy Storage System (HESS), a combination between battery and Ultra-Capacitor (UC), can moderate the cost of E-bike ESS. In this paper, a cost function is developed to use for optimal sizing of a HESS. This cost function is consisted of the HESS (battery, U...

In this paper, a new idea for designing the control strategy for the energy management of hybrid powertrains based on the driving cycle type is presented. Here, every instance of an unknown driving cycle is considered to be similar to the reference driving cycles using similarity weights. To determine the control output in the unknown driving cycle...

The wind erosion is the main cause of many environmental phenomena such as desertification, dust haze, sandstorms, and energy balance changes in the atmosphere. Wind erosion occurs when the friction velocity exceeds the threshold friction velocity. Threshold friction velocity depends on many parameters such as surface roughness, heat flux, moisture...

The aneurysm is a complex phenomenon which is affected by different factors, such as the biological diseases and the blood flow parameters. The wall shear stress and pressure are the main factors in the establishment and growth of cerebral aneurysm. The circle of Willis is a prevalent location for aneurysm. On the other hand, the anomalies of circl...

Considering the importance of pollutants and greenhouse gases and the role of internal combustion engines, along with the growing use of compressed natural gas as fuel, this study aims to investigate the effects of hydrogen enrichment on the formation of pollutants and greenhouse gases in gas-fuelled spark ignition engines. To this end, a previousl...

Recently, lattice Boltzmann method (LBM) has drawn attention as an alternative and promising numerical technique for simulating fluid flows. The stability of LBM is a challenging problem in the simulation of compressible flows with different types of embedded discontinuities. This study, proposes a complementary scheme for simulating inviscid flows...

An optimized implementation of a block tridiagonal solver based on the block cyclic reduction (BCR) algorithm is introduced and its portability to graphics processing units (GPUs) is explored. The computations are performed on the NVIDIA GTX480 GPU. The results are compared with those obtained on a single core of Intel Core i7-920 (2.67 GHz) in ter...

In this study, a reduced order model (ROM) based on proper orthogonal decomposition (POD) method has been applied to the coupled one-dimensional electrochemical transport equations in order to efficiently simulate lead-acid batteries, numerically. The governing equations, including conservation of charge in solid and liquid phases and conservation...

Abstract: Hardware-in-the-Loop (HiL) simulation is known as a reliable approach for testing and verification of the control system of hybrid vehicles. In this paper, a low-cost functional HiL test bench is utilized to test and verify the Drive Motor Management Software (DMMS) in a series hybrid electric bus. The HiL simulator in the current researc...

Attempts to simulate compressible flows with moderate Mach number to relatively high ones using Lattice Boltzmann Method (LBM) have been made by numerous researchers in the recent decade. The stability of the LBM is a challenging problem in the simulation of compressible flows with different types of embedded discontinuities. The present study prop...

This paper presents a detailed study on the implementation of Weighted Essentially Non-Oscillatory (WENO) schemes on GPU. GPU implementation of up to ninth-order accurate WENO schemes for the multi-dimensional Euler equations of gas dynamics is presented. The implementation detail is discussed in the paper. The computational times of different sche...

Considering the significance of obtaining higher efficiencies from internal combustion engines (ICE) along with the growing role of natural gas as a fuel, the present work is set to explore the effects of compression ratio (CR hereafter) and air/fuel equivalence ratio (AFER hereafter) on the energy and exergy potentials in a gas-fueled spark igniti...

RANS turbulence models are widely used in industrial applications thanks to their low computational costs. However, they introduce model-form uncertainty originating from eddy-viscosity hypothesis, assumptions behind transport equations of turbulent properties, free parameters in the models, and wall functions. In contrast, DNS provides detailed an...

Transition control is of the great significance in laminar flows since determination of aerodynamics coefficients as well as heat transfer magnitude is strongly affected by accurate prediction and control of this phenomenon. Transition is severely dependent on space and time such that various microscopic and macroscopic scales can convert to each o...

Considering the importance of high-order schemes implementation for the simulation of shock-containing turbulent flows, the present work involves the assessment of a shock-detecting sensor for filtering of high-order compact finite-difference schemes for simulation of this type of flows. To accomplish this, a sensor that controls the amount of nume...

In this paper a package for designing, modelling and simulation of three hybrid powertrains are presented. These powertrains are Electric hybrid, Hydraulic hybrid and Flywheel hybrid. The differences among the proposed hybrid powertrains include the energy storage system components, the secondary power converter and also the powertrain configuratio...

The stability of the lattice Boltzmann model (LBM) is a challenging problem in the simulation of compressible flows with different types of embedded discontinuities. This study, proposes a complementary scheme for simulation of inviscid compressible flows by the lattice Boltzmann models using the numerical filters to improve the stability. The adva...

Finite-element based CFD solvers like the family of Discontinuous Galerkin (DG) solvers suffer severely from inaccurate boundary reconstruction. In this matter, developing an accurate and flexible strategy is highly demanded to provide high-order curved boundary representation in DG simulations. In this paper, a general framework is introduced to d...

In this paper, a real time simulator of the engine-generator for a series hybrid electric bus is designed which can be used for hardware in the loop testing of the hybrid bus control unit. As an important step for designing a hardware in the loop simulator, messages that the engine and generator receive from the vehicle control unit are identified....

Due to the complexity in the control system of hybrid vehicles, the electronic control units should go through extensive testing before getting installed in a prototype vehicle. In the first stages of the development process, Hardware-in-the-Loop (HiL) simulation can not be performed because the hardware components of the vehicle are not yet availa...

Fluid-structure interaction (FSI) problems in microchannels play a prominent role in many engineering applications. The present study is an effort toward the simulation of flow in microchannel considering FSI. The bottom boundary of the microchannel is simulated by size-dependent beam elements for the finite element method (FEM) based on a modified...

Design parameters of a battery should be examined carefully to provide the optimum capacity. In this study, a lead-acid electrochemical cell has been simulated numerically in the ANSYS/FLUENT commercial software package. The governing equations including conservation of charge in solid and liquid phases, conversation of species and conversation of...

The market demand for developing new gas engines in stationary and automotive applications is increasing due to its advantageous situation concerning resources and its potential to meet strict engine emission regulations. On the other hand, the changes in carbon content and combustion characteristics due to the diversity in composition of CNG, make...

Due to the complexity in the design and cost involved with the testing of automotive control systems, Hardware-in-the-Loop (HiL) simulation plays a pivotal role in the development of such control units. To perform a HiL simulation, a vehicle simulator is needed which can virtually emulate the real vehicle in response to commands from the control un...

The investigation of design parameters is very helpful for optimizing the capacity of an electrochemical cell, which can be done by both experimental and numerical methods. In this study, a lead-acid battery has been simulated numerically using the CFD commercial software package FLUENT. The governing equations, including conservation of charge in...

Background. In order to reduce the mortality risk of aneurysm rupture, a timely diagnosis and treatment are vital. There are different reasons for aneurysm, such as hypertension, arteriosclerosis, and heredity. An efficient and cost-effective method to study the generation, development, and rupture of aneurysm and also analysis of treatment methods...

Fluid-structure interaction (FSI) problems in microchannels play prominent roles in many engineering applications. The present study is an effort towards the simulation of flow in microchannel considering FSI. Top boundary of the microchannel is assumed to be rigid and the bottom boundary, which is modeled as a Bernoulli-Euler beam, is simulated by...

Interaction of freestream disturbances with high-speed inviscid flow over a blunt nose is simulated utilizing a shock-fitted spectral collocation method. The unsteady flow computations are made through solving the 2D Euler equations by virtue of such a dissipation-free numerical algorithm for precise unsteady flow simulations. A shock-fitting techn...