Department of Mechanical engineering
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Item Numerical Investigation on Optimisation of the Mass of PCM in a Hybrid Battery Thermal Management System(Springer, 2023-04) Verma, SaketA hybrid thermal management system for lithium-ion batteries, with convectional and Phase Change Material (PCM) based cooling is proposed. The thermal performance of the battery pack during the constant heat generation condition has been numerically analyzed based on a two-dimensional heat transfer model. The investigation is performed for the following cooling methods: natural convection, PCM plus natural convection, forced convection, and Hybrid cooling with air as the medium. It is found that the maximum temperature exceeds the optimal temperature range without a thermal management system. It is also found that thermal uniformity and maximum temperature can be maintained with only PCM (with thickness 3 to 5 mm) and hybrid cooling methods except in the case of 1 mm thickness. Furthermore, it is found that variable thickness of PCM can be used to optimize the weight and hence cost factors. Variable PCM thickness of 1mm for the first cell and 2 mm for the other 5 cells are found suitable, where both the thermal factors are not compromised at the optimized condition, up to 95.4% reduction in the mass is possible with variable PCM thicknessItem Degradation Estimation of Polymer Electrolyte Fuel Cell under Different Cycling Load Profiles(Springer, 2023-04) Verma, SaketPolymer electrolyte fuel cells (PEFC) finds a suitable application in automotive vehicles as the prime mover. During its lifetime operation, a PEFC is subjected to various types of loading conditions, most of which is cyclic in nature. However, cyclic loading has been found to adversely affect the Pt catalyst cathode of a PEFC by dissolution and agglomeration of the Pt particles. It results in reduction of active electrochemical surface area, and hence reduced performance of the PEFC. In the present study, the degradation estimation of Pt catalyst cathode of a PEFC under various cyclic load profiles has been studied. Rectangular and trapezoidal load profiles have been selected with different duty cycles. The degradation estimation is based on the Pt agglomeration model, which can predict the electrochemical surface area (ECSA) at the end of set number of cycles. It was found that different voltage profile can affect the ECSA degradation in the PEFC. Degradation effect is evaluated based on the change in the electrochemical surface area, which renders to performance degradation. The Ostwald ripening effect for the Pt particles with operating time is also studied. It was concluded that Ostwald ripening lead to growth of Pt particles, which further inversely affect the ECSA and causes performance degradation.Item An experimental study on gas-to-liquids and biogas dual fuel operation of a diesel engine(Inder Science, 2021-10) Verma, SaketIn the present configuration, GTL replaces diesel, and biogas is used as gaseous fuel in the dual fuel (DF) operations. The effects of this substitution have been evaluated from the perspectives of second-law of thermodynamics. The results are compared with the diesel single-fuel, GTL single-fuel and GTL-biogas DF operations. Also, engine out emissions have been compared to understand the environmental impact of these fuel combinations. The results show that DF operation offers up to 80% pilot liquid fuel replacement by biogas, however, some reductions in energy and exergy efficiencies are observed.Item Advances in the Utilization of Biogas in Diesel Engines: An Exergy Based Approach(Springer, 2022-01) Verma, SaketIn order to reduce the use of fossil fuels in the transportation sector, various alternatives have been explored in the past. Biogas is an interesting candidate in this context with its large potential in countries like India, which can be utilized for vehicular as well as decentralized power generation applications. Biogas is a renewable fuel that is produced from organic waste materials through anaerobic digestion process. The produced raw biogas contains methane as the fuel; however, carbon dioxide is also present in considerable amount. This inert gas reduces the flame speed and heating value of biogas and eventually deteriorates engine performances. The auto-ignition temperature of biogas is high enough that it cannot be directly utilized in the diesel engines. One of the easiest and flexible ways to utilize biogas in diesel engines is through ‘Dual Fuel (DF)’ technique. In this technique biogas is used as the main gaseous fuel and another liquid fuel (commonly diesel) is used as the pilot fuel. In this way, existing diesel engines can use biogas as the fuel with minimum engine modifications. Nevertheless, the performance of biogas DF engine has been found to be much poor than the standard diesel engine, especially at the low loads. It has been shown that there are many engine parameters, e.g. engine load, type and quantity of biogas, injection timing of the pilot fuel etc., which can affect the performance and emission characteristics of a DF engine. This article presents an overview of these effects on a biogas operated DF engine and suggests various techniques to enhance the performance of the engine.Item An Experimental Comparison of Enriched Biogas and CNG on Dual Fuel Operation of a Diesel Engine(IOP, 2019) Verma, SaketIn the present work CNG and enriched biogas (93% CH4 by vol.) have been experimentally compared for performance and emission characteristics in a dual fuel diesel engine. The diesel is used as the pilot fuel, which is directly injected into the engine cylinder. The CNG and biogas are used as the main fuels, which are inducted with the intake air in the intake manifold. The experimental observations are taken for steady state conditions at varying engine loads for maximum pilot fuel substitution conditions. The performance of the engine is evaluated based on energy and exergy analyses. The emission characteristics are shown for oxides of nitrogen (NOx), hydrocarbon (HC), carbon monoxide (CO) and smoke emissions. It was found that enriched biogas showed the performance similar to that with CNG, whereas slight variations in the emissions were observed. The exergy efficiencies of 27.8% and 26.9% were calculated for CNG and biogas dual fuel operations respectively at the full load. Similarly, maximum pilot fuel substitutions were found 73.4% and 71.4% for the above conditions respectivelyItem Experimental analysis on the effect of hydrogen supply systems in a diesel dual fuel engine(ISEES, 2019) Verma, SaketAn experimental investigation on dual fuel (DF) operation of a diesel engine with hydrogen as the main fuel and diesel as the pilot fuel has been performed. The focus has been made on gaseous fuel delivery system for performance enhancement during DF operations. Two techniques of hydrogen delivery namely, manifold port induction and manifold port injection are compared in the DF engine. In the case of manifold induction, the gas is introduced with the help of a gas mixture in the intake manifold, whereas in the case of manifold injection, the gas is introduced with the help of an injector. The injector is located close to the intake valve and its timing is controlled through an electronic control unit. It was found that hydrogen manifold injection improves the diesel substitution and thermal efficiency of the DF engine as compared to manifold induction technique. The diesel substitution was improved by 2.3% and 1.5% at low and high loads respectively. Similarly, the brake thermal efficiency was improved by 0.4% and 0.5% at low and high loads respectively.Item Exergy Analysis of Hydrogen-Fueled Spark Ignition Engine Based on Numerical Investigations(Springer, 2017-02) Verma, SaketHydrogen fuelled IC engines (H2ICEs) have been considered as one of the most promising systems for pollution free transportations and their performance and combustion merits have been extensively discussed in the literature. However, studies related to these discussions have largely been linked to first-law analysis. On other hand, second-law of thermodynamics coupled with first-law, also known as exergy analysis, can give better insight into the engine performances. Bearing it in mind, this work presents second-law quantification of hydrogen engine processes and sub-processes, which helps to understand its true potential to deliver the output and simultaneously estimates various losses. This study quantifies different process inefficiencies in terms of irreversibilities thereby identifying the gaps to be addressed for further improvements. A computational fluid dynamics model has been prepared to simulate hydrogen-fueled spark-ignition engine (H2SIE) operations and second-law equations have been coupled to ascertain different exergy terms. Present study shows that combustion process is the biggest source of irreversibility in IC engines. It has also been found that the level of irreversibility for a hydrogen-operated engine is substantially lesser as compared to that with gasoline engine under identical ranges of operating conditions. Combustion irreversibilities for H2SIE and gasoline engine were found to be 15% and 23.6% of the total input fuel exergy respectively. Moreover, significant increase in second-law efficiency for H2SIE as 44.4% compared to 36.8% that for gasoline engines has been found. Another important conclusion from this work includes exergy distribution for H2SIE, which is considerably diverse from gasoline engine operation. It indicates that optimization and improvements of different H2SIE processes require specific attentions; nevertheless, show much better ability to deliver.Item An experimental investigation of biodiesel-biogas dual-fuel engine based on energy and exergy analysis(Inder Science, 2018-06) Verma, SaketIn the present work, exergy analysis has been performed on the biodiesel-biogas dual fuel (DF) engine. The DF operation has been studied with biodiesel (Jatropha curcas) as the pilot fuel to ignite the main fuel (biogas). The experiments were performed at a constant engine speed of 1500 rpm with varying engine loads and optimised injection timings for both diesel and DF modes. The results indicate that DF operation at low load produces poor performance and emission characteristics, however, no significant variations were observed between diesel-DF and biodiesel-DF operations. At 23% of engine load, exergy efficiencies were found to be 8.53% and 8.4% for diesel-DF and biodiesel-DF operations respectively; compared to 12.57% for pure diesel operation. Nevertheless, at higher loads, exergetic performances of DF operations were significantly improved. Furthermore, oxides of nitrogen (NOx) emissions from DF operations were significantly reduced compared to that with diesel operation.Item Spark Advance Modeling of Hydrogen-Fueled Spark Ignition Engines Using Combustion Descriptors(ASME, 2018-08) Verma, SaketIn-cylinder pressure-based combustion descriptors have been widely used for engine combustion control and spark advance scheduling. Although these combustion descriptors have been extensively studied for gasoline-fueled spark ignition (SI) engines, adequate literature is not available on use of alternative fuels in SI engines. In an attempt to partially address this gap, present work focuses on spark advance modeling of hydrogen-fueled SI engines based on combustion descriptors. In this study, two such combustion descriptors, namely, position of the pressure peak (PPP) and 50% mass fraction burned (MFB) have been used to evaluate the efficiency of the combustion. With a view to achieve this objective, numerical simulation of engine processes was carried out in computational fluid dynamics (CFD) software ANSYS fluent and simulation data were subsequently validated with the experimental results. In view of typical combustion characteristics of hydrogen fuel, spark advance plays a very crucial role in the system development. Based on these numerical simulation results, it was observed that the empirical rules used for combustion descriptors (PPP and 50% MFB) for the best spark advance in conventional gasoline fueled engines do not hold good for hydrogen engines. This work suggests revised empirical rules as: PPP is 8–9 deg after piston top dead center (ATDC) and position of 50% MFB is 0–1 deg ATDC for the maximum brake torque (MBT) conditions. This range may vary slightly with engine design but remains almost constant for a particular engine configuration. Furthermore, using these empirical rules, spark advance timings for the engine are presented for its working range.Item Effect of Hydrogen Enrichment Strategy on Performance and Emission Features of Biodiesel-Biogas Dual Fuel Engine Using Simulation and Experimental Analyses(ASME, 2020-12) Verma, SaketIn the present work, hydrogen enrichment in biogas is studied as a potential approach to improve the performance and emission features of a biodiesel-biogas dual fuel engine. A single-cylinder diesel engine is modified to operate in dual fuel mode using Jatropha curcas biodiesel as the pilot fuel and biogas as the main fuel. An electronic control unit is developed in-house to study 5−20% hydrogen enrichment in biogas using the timed manifold injection (TMI) technique. A three-dimensional computational fluid dynamics-based simulation methodology is presented for optimal selection of TMI parameters to ensure efficient and safe operation of the engine. Subsequently, the optimized injection conditions are used for the experimental evaluations, which are performed for performance and emission characteristics of the engine at low and high engine loads. Engine performance is analyzed based on energy and exergy analyses, whereas hydrocarbon (HC), carbon monoxide (CO), oxides of nitrogen (NOx), and smoke emissions are analyzed for emission characterization. The simulation results show that the injection angle and injection pressure influence in-cylinder mixture formation and hydrogen accumulation in the intake manifold. A combination of injection angle = 60 deg and injection pressure = 150 kPa offers good mixture formation. Experimental results show that at 20% hydrogen enrichment, exergy efficiencies of the dual fuel engine are increased from 8.4% to 10.1% at low load and 23.3% to 25.5% at high load. However, maximum reductions in HC and CO emissions of 35.6% and 50.0%, respectively, are calculated at low load