Showing papers by "Ujjwal K. Saha published in 2019"

Application potential of vegetable oils as alternative to diesel fuels in compression ignition engines: A review

Abstract: Vegetable oils have been identified as the promising alternative source to replace fossil based fuel in the compression ignition (CI) engine. It is renewable and possesses characteristics that is similar to that of the diesel. Biodiesel, transesterifiedform of vegetable oil (VO), is now being commercially used in CI engines. However, biodiesel production from VO involves use of alcohols and chemicals which results the need of skilled labor and investment for its production. In view of this, many studies are also being carried out on the direct use of VO in the engine. The direct use of VO oil in engine is as good as that of the diesel. The superior quality of diesel however makes it better performance in engine as compared to the vegetable oil. Preheating and blending of VO are found to be the most common solution to overcome its inferior properties. The use of preheated and blended VO is found to improve the engine overall performance. This paper is focused exclusively on the one-to-one basis of study pertaining to the effect of neat, preheated and blended vegetable oils on diesel engine performance and emission through supplementation of illustrative figures from the various experimental studies.

Evolution and Progress in the Development of Savonius Wind Turbine Rotor Blades Profiles and Shapes

Abstract: The blade profiles and blade shapes of vertical-axis Savonius wind turbine rotors have undergone a series of changes over the past three decades. Wind turbine aerodynamicists have carried out numerous computational and experimental research to arrive at a suitable rotor blade design configuration so as to harvest maximum energy from the available wind. In most of the studies, the geometric and aerodynamic aspects of the rotor blade design have been reported. Interestingly enough, a couple of review papers got published in the area of Savonius rotors during the last one decade. However, there is not a single piece of literature that gives a comprehensive and a systematic review of Savonius rotor blade profiles and shapes. This paper aims to collate all the research findings related to these blade profiles/shapes and makes an attempt to highlight their features together with future recommendations.

Examining the Aerodynamic Drag and Lift Characteristics of a Newly Developed Elliptical-Bladed Savonius Rotor

Abstract: The elliptical-bladed Savonius wind turbine rotor has become a subject of interest because of its better energy capturing capability. Hitherto, the basic parameters of this rotor such as overlap ratio, aspect ratio, and number of blades have been studied and optimized numerically. Most of these studies estimated the torque and power coefficients (CT and CP) at given flow conditions. However, the two important aerodynamic forces, viz., the lift and the drag, acting on the elliptical-bladed rotor have not been studied. This calls for a deeper investigation into the effect of these forces on the rotor performance to arrive at a suitable design configuration. In view of this, at the outset, two-dimensional (2D) unsteady simulations are conducted to find the instantaneous lift and drag forces acting on an elliptical-bladed rotor at a Reynolds number (Re) = 0.892 × 105. The shear stress transport (SST) k–ω turbulence model is used for solving the unsteady Reynolds averaged Navier–Stokes equations. The three-dimensional (3D) unsteady simulations are then performed which are then followed by the wind tunnel experiments. The drag and lift coefficients (CD and CL) are analyzed for 0–360 deg rotation of rotor with an increment of 1 deg. The total pressure, velocity magnitude, and turbulence intensity contours are obtained at various angles of rotor rotation. For the elliptical-bladed rotor, the average CD, CL, and CP, from 3D simulation, are found to be 1.31, 0.48, and 0.26, respectively. The average CP for the 2D elliptical profile is found to be 0.34, whereas the wind tunnel experiments demonstrate CP to be 0.19.

Effect of Capped Vents on Torque Distribution of a Semicircular-Bladed Savonius Wind Rotor

Abstract: To address the problem of the imminent energy crisis, pollution from fossil fuels, and global warming, it is necessary to incorporate renewable technologies. In that context, the drag-based Savonius wind turbine has tremendous potential to extract wind energy and can be operated as a standalone system at remote areas where the conventional electricity cannot be provided. The present study primarily focuses on the performance evaluation of a conventional semicircular-bladed Savonius rotor with capped vents (CVs) or nozzle chamfered vents. The rotor blades having vent ratios of 7%, 14%, and 21% are tested in a wind tunnel, and subsequently, their performances are compared with a rotor without CVs under identical test conditions. Computational fluid dynamics (CFD) simulations have also been carried out to compliment the surprising experimental results and also to analyze the flow physics around the rotor blades. From the understanding of torque distribution, it has been noticed that the performance of the rotor with CV deteriorates compared with the conventional semicircular-bladed rotor. The vents are found to decrease the positive torque and increase the negative torque by disturbing the pressure distribution of the conventional semicircular-bladed Savonius rotor.

Drag and Lift Characteristics of a Novel Elliptical-Bladed Savonius Rotor With Vent Augmenters

Abstract: Savonius rotor, a class of drag-driven vertical axis wind turbine, has been extensively investigated mainly to calculate the torque and power coefficients (CT and CP) by various investigators. Hitherto, studies related to lift and drag characteristics are very few and have mainly been restricted to a semicircular-bladed rotor. A deeper investigation into the drag and lift coefficients (CD and CL) can result in the better design of rotor blades leading to an increment in CT and CP. In view of this, in the present investigation, CD and CL of an elliptical-bladed rotor with vent augmenters have been studied numerically. Initially, two-dimensional (2D) unsteady simulations using an ansys fluent solver is carried out to estimate the instantaneous CD and CL. The shear stress transport (SST) k–ω turbulence model is selected to solve the Reynolds averaged Navier Stokes (RANS) equations. Finally, three-dimensional (3D) unsteady simulations are carried out for the vented elliptical-bladed rotor. The unsteady simulations are performed for the nonvented elliptical- and semicircular-bladed rotors at the identical condition in order to have a direct comparison. From the unsteady simulations, the average CD for the vented elliptical profile is found to be 1.45; whereas, the average CD for the nonvented elliptical and semicircular profiles is found to be 1.43 and 1.35, respectively.

A Critique on the Research Activities and Potential Benefits of Dual-Fuel Diesel Engines Run on Biogas and Oxygenated Liquid Fuels

Abstract: The dual fuel concept of diesel engines is gaining popularity because of their ability to use alternative renewable gaseous fuels (natural gas, biogas, producer gas) and liquid fuels (biodiesel, alcohol, and others) simultaneously. The dual fuel mode (DFM) not only reduces the consumption of diesel or substitutes the diesel fuel, but there is an advantage of operating the engine in pure diesel mode (PDM) in case of shortage of gaseous primary fuel. The uses of renewable fuels in such engines have the positive impact on green ecosystem in terms of reduction in NOx and smoke emissions; however, there is the engine derating as performance penalty in comparison to engines operating under PDM. The most influential parameters in DFM engines are the type and flow rate of inducted gaseous fuel, fuel–air equivalence ratio (Φglobal), compression ratio (CR), and injection timing (IT). During the last few decades, the researchers have studied the effect of various parameters to improve the overall performance characteristics (performance, combustion, and emission) of DFM engines. This paper makes an in-depth analysis to unveil the physical characteristics of the crucial parameters of DFM engines with specific reference to the use of biogas with ternary blends (TB) of diesel, biodiesel, and ethanol. The paper addresses the issues on how the gaseous fuel flow rate, preheating of the intake charge, compression ratio, injection timing, and the type of oxygenated fuels dominate the overall performance characteristics.

Optimization of Aerodynamic Parameters of an Elliptical-Bladed Savonius Wind Rotor Using Multi-Objective Genetic Algorithms

Abstract: The Savonius wind rotor, a drag-based machine, despite having lesser efficiency has got several advantages such as low price, easy installation, better starting capability independency to wind direction. In order to enhance the performance of such rotor, several design modifications have been built by changing the geometric parameters such as overlap ratio, aspect ratio, tip speed ratio, number of rotor blades and effect of shaft and end plates. Apart from the various geometric parameters, several rotor blades and augmentation techniques has evolved to improve the performance of the Savonius rotor. This has been achieved by using a host of numerical and experimental methods. In the present investigation, the multi-objective genetic algorithms have been used to optimize the incoming velocity, and the torque and lift coefficient for a novel elliptical-bladed profile for maximizing the rotor power coefficient. The multi-physics solver ANSYS direct optimization technique has been used to implement the genetic algorithms. The results obtained from the genetic algorithms have been compared with the established results under identical conditions.

Savonius Wind Turbine Blade Profile Optimization by Coupling CFD Simulations With Simplex Search Technique

Abstract: The Savonius rotor, a drag-based vertical axis wind turbine, is characterized by its design simplicity, low noise level, self-starting ability at low wind speed and low cost. However, its low performance is always a major issue. One of the remedies of this issue is to design an optimized rotor blade profile, which has mostly been developed through trial and error approach in the literature. In this paper, an optimum blade profile is obtained by maximizing its power coefficient (CP) by coupling CFD simulations of rotor blade profile with the simplex search technique. Since the blade profile is symmetric about its axis, half of the blade geometry is created through natural cubic spline curve using three points. Two of them are kept fixed, whereas the other one is changed through optimization technique in its every iteration using MATLAB platform. In every iteration, the blade profile is meshed using ANSYS ICEM CFD. The analysis of the blade profile is performed through ANSYS Fluent by using shear-stress transport k-ω turbulence model. A finite volume method based solver is used to solve the transient 2D flow around the wind turbine. The optimum profile of the blade is compared with the conventional profile over a wide range of tip speed ratios (TSRs) in order to check its feasibility for practical applications. The optimum blade profile is found to be better than the semicircular blade in the range of TSR=0.6 – 1.

A Differential Evolution-Based Inverse Method to Optimize Blade Configurations in Elliptical-Bladed Savonius Wind Turbines

Abstract: It is well-known that elliptical-bladed Savonius wind turbine yields relatively better performance than conventionally used semicircular-bladed turbines. This is mainly due to lesser tip loss and delayed flow separation that allow the elliptical turbine to acquire higher rotational speeds than semicircular turbine under a given wind load. In this work, an experimentally-validated inverse analysis is done to determine the optimum blade configurations involving the chord length, turbine height, aspect ratio, and the necessary overlap ratio to derive a required power and torque from elliptical-bladed Savonius wind turbines. Due to obvious advantages of evolutionary metaheuristic optimizers in general, here differential evolution (DE) search algorithm is used to solve the inverse problem through a least-squares minimization of the relevant objective function. The objective function is further subjected to feasible bounds of the unknown design variables. The effects of blockage corrections are duly considered and the variations of the design variables along with the objective function are studied over a range of iterations of the DE algorithm. Through comprehensive analysis, it is highlighted from the present study that for harvesting a given performance, rotor swept area can be reduced by 6.25% with respect to the available experimental data under identical operating conditions of the wind turbine. Multiple blade configurations can be acquired, all of which invariably satisfy the required performance criterion. This study also highlights that amongst various dimensional parameters, turbine height and aspect ratio play more prominent role than chord length and overlap ratio and the blade chord influences only the torque but not markedly the power. The results obtained from the present work are proposed to facilitate the concerned designer to explore various feasible blade designs and determine the suitable one, thereby avoiding valuable time elapsed in repetitive fabrication and testing of various designs.

Analyzing the Effect of Shaft and End-Plates of a Newly Developed Elliptical-Bladed Savonius Rotor From Wind Tunnel Tests

Abstract: In recent times, drag-based vertical-axis wind turbine rotors have gained increasing interests in offshore applications because of their performance potential and reliability. Their advantages like simplicity, easier manufacture and lower maintenance cost have attracted the researcher’s attention toward improving their design further. However, this type of rotor is still suffering from lower efficiency than the lift-based Darrius and the horizontal-axis wind turbine rotors. A recently developed elliptical-bladed Savonius rotor has shown its potential to harvest wind energy more efficiently. However, the geometric parameters of this rotor such as aspect ratio, overlap ratio, number of blades, shaft and end plates, the aerodynamic parameters such as Reynolds number, lift and drag coefficients are needed to be optimized for further improvement of its performance. In the present investigation, the wind tunnel tests have been conducted to analyze the effect of shaft and end-plates of a newly developed elliptical-bladed vertical-axis Savonius wind turbine rotor. Experiments have been conducted over a range of tip speed ratios to find the torque and power coefficients of a two-bladed rotor system for two individual cases viz., the rotor with a shaft and the rotor with end-plates. In order to have a direct comparison, the experimental data are also obtained for the same rotor without the shaft and without the end-plates. The wind tunnel tests have demonstrated an improvement of power coefficient by 26.31% for the rotor with the end plates.