Ujjwal K. Saha

Review of experimental investigations into the design, performance and optimization of the Savonius rotor:

The Savonius rotor is a drag-based vertical axis wind turbine and is used as an alternative source in small-scale energy generation. Design simplicity, low-cost, easy installation, good starting ability, relatively low operating speed and independent to wind directions are the main advantages of this rotor. However, because of its low efficiency and high negative torque produced by the returning blade, this rotor concept rarely gained popularity. Over the last few decades, although a number of investigations around the world have reported performance gains of the Savonius rotor, the available technical design is still not able to fulfill the demand of efficient small-scale wind energy converter at low wind speeds. Until now, various design changes have been proposed to meet a growth in power output through optimization of influencing variables like aspect ratio, overlap ratio, blade material, and so forth. Investigations have also been carried out by installing additional devices like curtain design, deflector plate, nozzle and ducts, multi-staging, guide-box tunnel and windshields. Installation of these devices considerably reduced the negative torque as well as improved the starting performance of the rotor. As a result, the power output of the rotor is also improved. Several researchers have reported increased power coefficients for various rotor designs based on their different testing parameters. Power coefficients for the conventional Savonius rotors have been mostly reported in the range of 0.12–0.18 and by optimizing its design, it can reach as high as 0.38. This article attempts to discuss the various influencing parameters as well as the augmentation techniques. This would offer an overall idea on the progress that has taken place to improve the design and performance of the Savonius rotor.

Influence of Emulsified Palm Biodiesel as Pilot Fuel in a Biogas Run Dual Fuel Diesel Engine

This study attempts to explore the influence of emulsified palm biodiesel as a pilot fuel in a biogas run dual fuel engine. The intention is to achieve diesel-equivalent performance from a diesel engine, together with a reduction in engine emissions, with complete replacement of fossil diesel with renewable fuels. The results of this study are compared to those for a neat biodiesel (Jatropha)-biogas dual fuel engine run at identical engine settings. For baseline comparison, the results are also compared with a standard diesel run. The results show that with the presence of biogas, emulsified biodiesel as a pilot fuel can present a better dual fuel efficiency (41%) and a lower energy consumption (38%) than neat biodiesel in a piloted study. Also, the presence of a microexplosion of emulsified biodiesel was found to reduce the pilot fuel consumption with the presence of biogas, especially at lower loads, where the burning rate of biogas usually slows down due to the lean gas-air mixture and cooler charge temperature. In addition, emulsified palm biodiesel successfully brings the peak cylinder pressure (PCP) closer (8 degrees ATDC) to top dead center (TDC). This elevates the magnitude of the PCP, which increases the expansion ratio and hence improves engine efficiency. With the presence of emulsified biodiesel, the supply of biogas is found to get reduced, especially at higher loads, which in turn reduces the hydrocarbon emission. However, other emission characteristics are not as exciting, and hence emulsified biodiesel in biogas dual fuel mode needs to be further explored at various engine-operating characteristics in order to obtain a superior emission performance

Theoretical Route toward the Estimation of Second Law Potential of an Emulsified Palm Biodiesel Run Diesel Engine

AbstractThe application of biodiesel as an alternative to diesel is well recognized. However, having a lesser calorific value than diesel, it results in a lower power and efficiency. This can suitably be improved by emulsifying biodiesel with water. However, the properties of biodiesel emulsions are not similar to that of diesel. Hence, the energy and availability distribution of a biodiesel emulsion–run engine will not be identical to that of a diesel-run engine at standard diesel settings. To enlighten this ambiguous fact of literature, an energy-exergy analysis has been performed for a water-in-biodiesel emulsion run diesel engine for a set of compression ratios (CRs) and injection timings (ITs) at full engine load. The biodiesel considered for the study is palm oil methyl ester (POME). The parameters analyzed are the energy and exergy potential of fuel input, shaft work, cooling water, exhaust gas, and exergy destruction. Side by side, the effects of the variation of CR and IT on peak pressure, peak h...

Analysis of Throttle Opening Variation Impact on a Diesel Engine Performance Using Second Law of Thermodynamics

The fuel efficiency of a modern diesel engine has decreased due to the recent revisions to emission standards. For an engine fuel economy, the engine speed is to be optimum for an exact throttle opening (TO) position. This work presents an analysis of throttle opening variation impact on a multi-cylinder, direct injection diesel engine with the aid of Second Law of thermodynamics. For this purpose, the engine is run for different throttle openings with several load and speed variations. At a steady engine loading condition, variation in the throttle openings has resulted in different engine speeds. The Second Law analysis, also called ‘Exergy’ analysis, is performed for these different engine speeds at their throttle positions. The Second Law analysis includes brake work, coolant heat transfer, exhaust losses, exergy efficiency, and airfuel ratio. The availability analysis is performed for 70%, 80%, and 90% loads of engine maximum power condition with 50%, 75%, and 100% TO variations. The data are recorded using a computerized engine test unit. Results indicate that the optimum engine operating conditions for 70%, 80% and 90% engine loads are 2000 rpm at 50% TO, 2300 rpm at 75% TO and 3250 rpm at 100% TO respectively.Copyright

Effect of compression ratio and injection timing on the performance characteristics of a diesel engine running on palm oil methyl ester

Diesel fuel has a limited resource, and concerns over environmental pollution are leading to the use of ‘bio-origin fuels’ as they are renewable and environmentally benign. Palm oil methyl ester, an esterified biofuel, has an excellent cetane number and a reasonable calorific value. Besides, palm oil methyl ester (C18.07H34.93O2) has around 11.25% of oxygen bonded in its molecular structure which increases its burning intensely. Thus, it closely resembles the behavior of diesel. However, being a fuel of different origin, the standard design limits of a diesel engine is not suitable for palm oil methyl ester. Therefore, in this work, a set of design and operational parameters are studied to find out the optimum performance of a palm oil methyl ester run diesel engine. The parameters varied are the compression ratio (CR) and injection timing (IT) along with load in a variable compression ratio diesel engine. The palm oil methyl ester run engine is investigated for its performance, combustion and emission characteristics. The combination of CR = 18 and IT = 20°BTDC improves the efficiency by 8% and cuts the exhaust gas temperature by 5%. Moreover, the palm oil methyl ester run engine lowers the ignition delay which further gets reduced by 7% and 12% with CR augmentation and IT retardation, respectively. The increase in CR trims down carbon monoxide by 40%, nitrogen oxides by 46% and hydrocarbon by 40%; however, it increases carbon dioxide emission by 19%. The IT retardation reduces the carbon dioxide emission by 16%.

Aerodynamic Performance Evaluation of a Novel Savonius-Style Wind Turbine Under an Oriented Jet

The Savonius-style wind turbine, a class of vertical axis wind turbines, can be a viable option for small scale off-grid electricity generation in the context of renewable energy applications. A better self-starting capability at low wind speeds is one of the major advantages of this turbine. However, as reported in open literature, the power coefficient of the conventional design is found to be inferior as compared to its counterparts. In this regard, a new blade design has been developed. In the present investigation, the aerodynamic performance of this newly designed turbine is assessed under an oriented jet. This is affected by installing deflectors upstream of the turbine blades. The intention of this study is to maximize the utilization of wind energy at the exhaust systems of several practical applications. Experiments are carried out in a low speed wind tunnel at a wind speed of 6.2 m/s. The gradual loads applied to the turbine, and the corresponding rotational speeds are recorded. Power and torque coefficients are calculated at various mechanical loads. Further, all the estimated data are corrected by a suitable correction factor to account for the wind tunnel blockage effects. The results obtained are compared with the experimental data of modified Bach and conventional designs. The results have shown a significant improvement in the performance of newly designed Savonius-style wind turbine under the concentrated and oriented jet.Copyright

On the Attainment of Optimum Injection Timing of Pilot Fuel in a Dual Fuel Diesel Engine Run on Biogas

The race among the different nations to attain supremacy has given rise to twin crisis: depletion of fossil fuel reserves and degradation of environment. Every nation wants to increase the per capita income by producing more power. In order to achieve this feat, each nation has to burn huge amounts of fossil fuels causing an increase in the emission of greenhouse gases. In this regard, renewable energy can be a panacea to the above mentioned problems. Biogas, one form of biomass energy, has an immense potential as a renewable fuel. This biogas can be used successfully in diesel engines for the generation of power. However, in order to achieve an optimum efficiency, the operating parameters of the biogas run dual fuel engine have to be standardized. In such an engine, injection timing of the pilot fuel is one of the important operational parameters that greatly affects the engine performance. In view of this, in the present paper, an attempt has been made to standardize the injection timing of pilot fuel a biogas run dual fuel diesel engine on the basis of its performance and emission characteristics of. Experimental investigation demonstrates an improvement in efficiency and a reduction in emissions at the injection timing of 29° before top dead centre.Copyright

Numerical Investigation to Assess an Optimal Blade Profile for the Drag Based Vertical Axis Wind Turbine

Rapid depletion rate of fossil fuels with an increasing energy demand and their high emission are imposing the evolution activities in the arena of renewable energy. To meet the future demands of renewable energy sources, wind energy is a very promising concept. In this feature, the drag based vertical axis wind turbines (VAWTs) are suitable for small scale wind energy generation for decentralized locations. However, these turbines have low power and torque coefficients as compared to other wind turbines. Numerous blade shapes have been proposed till now to improve the performance of these turbines. In the present paper, a computational study has been performed to simulate the air-flow over different blade profiles using shear stress transport (SST) k–ω turbulence model. The results obtained are validated with the available experimental data. In the dynamic simulations, the power and torque coefficients are calculated considering the blade arc angle as the variable shape parameter. The effects of drag and lift forces on the variable blade shapes are also studied in static simulations at various angular positions. The present paper tries to demonstrate an effective computational methodology to predict the flow behavior around a drag based VAWT. Through this study, it has been found possible to select an optimal blade shape from the point of its aerodynamic performance.Copyright

Performance analysis of savonius-style wind turbines under concentrated and oriented jets

With the rapid growth of renewable energy sector, vertical axis wind turbines are finding their applications in the small-scale distributed wind energy system, particularly in rural areas. These turbines are simple in construction and easy to install with comparatively lower cost. However, the efficiency of these turbines is not competitive to that of horizontal axis wind turbines. In this paper, an attempt has been made to improve the efficiency of a Savonius-style vertical axis wind turbine under concentrated and oriented jets through installation of deflectors at different positions ahead of the turbine. The aim is to make the major portion of the flow to be incident on the concave part of the blades. Experiments are conducted in a low speed wind tunnel with an open test section facility. For all the experiments, the wind speed in the tunnel is kept constant at 6.2 m/s. The mechanical loads are varied to analyze the performance of the turbine at various tip speed ratios. In each case, both power and torque coefficients are calculated in order to estimate the performance indices of the turbine. Moreover, a suitable operating range of this turbine is specified. The present investigation demonstrates that with the installation of deflectors, the performance of the Savonius-style wind turbines can be sufficiently improved under concentrated and oriented jets. The peak power coefficient of 0.32 is achieved with an optimized position of the deflectors in front of both the advancing and returning blades.Copyright

Characterization and analysis of thermal response of rice husk for gasification applications

Present study involves characterisation and thermal analysis of rice husk as a potential source for gasification. Both the thermogravimetric (TG) analysis and differential scanning calorimetry were used to study the influence of heating rate on the degradation of rice husk. Experiments were carried out at three different heating rates of 10, 30, and 80 K min−1. The kinetic parameters, viz. pre-exponential factor, activation energy, and order of reaction were evaluated for both first and second reaction zones, which are categorized based on the degradation of cellulose, hemicelluloses, and lignin content present in the biomass. The degradation of mass with temperature obtained from TG curve was validated numerically. The thermal response of rice husk undergoing decomposition has also been modelled by using a one dimensional (1-D) transient thermal model with an nth order approximation for the rate of decomposition. Kinetic parameters, heat of decomposition, and thermal properties are taken as input to the ...