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Heat Transfer Modeling of Hydrogen-Fueled Spark Ignition Engine
Full text linkCurrently, green hydrogen, generated through renewable energy sources, stands out as one of the best substitutes for fossil fuels in mitigating pollutant emissions and consequent global warming. Particularly, the utilization of hydrogen in spark ignition engines has undergone extensive study in recent years. Many aspects have been analyzed: the conversion of gasoline engines to hydrogen operation, the combustion duration, the heat transfer, and, in general, the engine thermal efficiency. Hydrogen combustion is characterized by a smaller quenching distance compared to traditional hydrocarbon fuels such as gasoline or natural gas and this produces a smaller thermal boundary layer and consequently higher heat transfer. This paper presents findings from experimental trials and numerical simulations conducted on a hydrogen-powered CFR (cooperative fuel research) engine, focusing specifically on heat transfer with combustion chamber walls. The engine has also been fueled with methane and isooctane (two reference fuels); both the engine compression ratio and the air/fuel ratio have been changed in a wide range in order to compare the three fuels in terms of heat transfer, combustion duration, and engine thermal efficiency in different operating conditions. A numerical model has been calibrated with experimental data in order to predict the amount of heat transfer under the best thermal efficiency operating conditions. The results show that, when operated with hydrogen, the best engine efficiency is obtained with a compression ratio of 11.9 and an excess air ratio (lambda) of 2
Performance and combustion analysis of a supercharged double-fuel spark ignition engine
No full textIn order to increase fuel economy and reduce pollutant emissions in the last decades light duty spark ignition (SI) engines have become smaller, supercharged and equipped with direct injection. A suitable alternative to oil derived fuel is represented by gaseous fuels, such as Natural Gas (NG) and Liquefied Petroleum Gas (LPG), whose higher knock resistance and better mixing capabilities substantially improve vehicle fuel economy and pollutant emissions. The simultaneous combustion of gasoline and gaseous fuel (Double-Fuel operation, DF) in a naturally aspirated SI engine has already been investigated in the past also by the same authors, proving remarkable results in terms of engine efficiency increment and exhaust emissions reduction. In this paper the authors present the results of a new methodical experimental study aimed to investigate engine performance, efficiency and pollutant emissions obtained on a supercharged SI engine operated in double fuel mode, with comparison to the use of "reference" pure fuels (i.e. gasoline and NG). A detailed heat release analysis is also performed with the aim to highlight the effect of fuel mixture composition (i.e. the proportion between gasoline and NG) and of charging pressure on the combustion speed
Efficiency advantages of the separated electric compound propulsion system for CNG hybrid vehicles
Full text linkAs is widely known, internal combustion engines are not able to complete the expansion process of the gas inside the cylinder, causing theoretical energy losses in the order of 20%. Several systems and methods have been proposed and implemented to recover the unexpanded gas energy, such as turbocharging, which partially exploits this energy to compress the fresh intake charge, or turbo-mechanical and turbo-electrical compounding, where the amount of unexpanded gas energy not used by the compressor is dedicated to propulsion or is transformed into electric energy. In all of these cases, however, maximum efficiency improvements between 4% and 9% have been achieved. In this work, the authors deal with an alternative propulsion system composed of a CNG-fueled spark ignition engine equipped with a turbine-generator specifically dedicated to unexpanded exhaust gas energy recovery and with a separated electrically driven turbocompressor. The system was conceived specifically for hybrid propulsion architectures, with the electric energy produced by the turbine generator being easily storable in the on-board energy storage system and re-usable for vehicle traction. The proposed separated electric turbo-compound system has not been studied in the scientific literature, nor have its benefits ever been analyzed. In this paper, the performances of the analyzed turbo-compound system are evaluated and compared with a traditional reference turbocharged engine from a hybrid application perspective. It is demonstrated that separated electric compounding has great potential, with promising overall efficiency advantages: fuel consumption reductions of up to 15% are estimated for the same power output level
A regenerative braking system for internal combustion engine vehicles using supercapacitors as energy storage elements - Part 1: System analysis and modelling
No full textIn this two-part work, an electric kinetic energy recovery system (e-KERS) for internal combustion engine vehicle (ICEV) is presented, and its performance evaluated through numerical simulations. The KERS proposed is based on the use of a supercapacitor as energy storage, interfaced to a brushless machine through a properly designed power converter. In part 1, the system is described and analysed, and the mathematical model used for the simulations is presented. For each component of the KERS, the real efficiency, and the power or energy limitations are adequately considered. In part 2, the energetic and economic advantages attainable by the proposed KERS are evaluated using MATLAB Simulink, considering a widely diffused passenger car and two reference driving cycles (ECE-15 and Artemis Urban). Energy savings of the order of 20% were found, with a slight increase in vehicle weight (+2%) and with an overall commercial cost that would be compensated in 5 years thanks to the fuel economy improvement, to which corresponds an equal reduction of CO2 emissions. The low complexity of the system, never proposed for ICEV, the moderate weight of its components, and their availability on the market, make the solution presented ready for the introduction in current vehicle production
A regenerative braking system for internal combustion engine vehicles using supercapacitors as energy storage elements - Part 2: Simulation results
No full textIn this two-part work, an electric kinetic energy recovery system (e-KERS) for internal combustion engine vehicle (ICEV) is presented and its performance evaluated through numerical simulations. The KERS proposed is based on the use of a supercapacitor as energy storage, interfaced to a brushless machine through a properly designed power converter. In Part 1, the system is described and analysed, and the mathematical model used for the simulations is presented. For each component of the KERS, the real efficiency and the power or energy limitations are adequately considered. In Part 2, the energetic and economic advantages attainable by the proposed KERS are evaluated using MATLAB Simulink, considering a widely diffused passenger car and two reference driving cycles (ECE-15 and Artemis urban). Energy savings of the order of 20% were found, with a slight increase in vehicle weight (+2%) and with an overall commercial cost that would be compensated in 5 years thanks to the fuel economy improvement, to which corresponds an equal reduction of CO2 emissions. The low complexity of the system, never proposed for ICEV, the moderate weight of its components, and their availability on the market, make the solution presented ready for the introduction in current vehicle production
A six legs buck-boost interleaved converter for KERS application
Full text linkThis paper addresses the design of a bi-directional DC/DC power converter to interface a supercapacitor bank and a motor-generator unit. The design is based on an interleaved six legs topology in which the current is shared among six inductors to minimize their weight and cost, allowing, besides, a low switching frequency to lessen switching losses. The converter is conceived to be employed in an electric Kinetic Energy Recovery System for Internal Combustion Engine Vehicles. The system makes use of a supercapacitor as a storage system, and a motorgenerator unit connected to the drive shaft for vehicle acceleration and braking. The system uses available commercial devices, thus obtaining a cheap and high-efficiency conversion chain. It is shown how the design criteria differ from traditional interleaved converters. The same topology allows minimizing the input and output ripple and improving the reliability in case of fault as well. Losses are reduced both by sharing the currents and by a suitable control strategy, which allows more converters to be connected in parallel to increase the delivered power. Results, given in simulation, assess the stability and dynamic performance of the conversion circuit, showing a low current and voltage ripple in all operating conditions. © 2020, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved
Detailed Combustion Analysis of a Supercharged Double-Fueled Spark Ignition Engine
Full text linkThe main goal of researches in the field of automotive engineering is to obtain a large-scale implementation
of low- or zero-emissions vehicles in order to substantially reduce air pollution in urban
areas. A fundamental step toward this green transition is represented by the improvement of current
internal combustion (IC) engines in terms of fuel economy and pollutant emissions. The spark ignition
(SI) engines of modern light-duty vehicles are supercharged, down-sized, and equipped with direct
injection. Gaseous fuels, such as liquefied petroleum gas (LPG) or natural gas (NG), proved to be a
valid alternative to gasoline in order to reduce pollutant emissions and increase fuel economy. In
previous works the authors investigated the simultaneous combustion, in an SI engine, of gasoline
and a gaseous fuel (referred to as Double-Fuel operation, DF) both in the naturally aspirated and
supercharged version; a significant increment of engine efficiency and a great reduction of pollutant
emissions were obtained with respect to pure gasoline operation, with almost unchanged performance.
This article is a development of the previous work and shows the results of a detailed heat
release analysis, performed on the DF supercharged engine fueled with mixtures of gasoline and
NG in order to highlight the effects of engine speed, charging pressure, and fuel mixture composition
(the proportion between gasoline and NG) on the combustion speed.
It was found that both gasoline content in the DF mixture and supercharging pressure contribute
to increase the combustion speed, which, in some cases, produced engine-indicated efficiency
increments up to 5%. The wide set of experimental data presented in this article allows us to better
understand the combustion behavior of gasoline-NG fuel mixtures and can be also used to calibrate
combustion submodels integrated into engine numerical simulations
Steady State Performance of Spark Ignition Engine with Exhaust Energy Recovery
Full text linkAs is known, internal combustion engines based on Otto or Diesel cycles cannot complete the expansion process of the gas inside the cylinder, thus losing a relevant energy content, in the order of 30% of total. The residual energy of the unexpanded gas has been partially exploited through the use of an exhaust gas turbine for turbocharging the internal combustion engine; further attempts have been made with several compound solutions, with an electric generator connected to the turbocharger allowing to convert into electrical energy the quota power produced by the turbine which is not used by the compressor, or with a second turbine downstream the first to increase the exhaust gas energy recovery. Turbo-compound solutions were also employed in large marine Diesel engines, where the second turbine downstream the first was used to deliver more power to the main propeller shaft. In all these cases the overall efficiency increments remained within 5%. If completely recovered by the use of a properly designed expander-generator unit, the energy content of the unexpanded in-cylinder gas could substantially increase the overall efficiency of the thermal unit. In the present paper the authors evaluate, by means of simple yet effective calculations, the efficiency attainable by a thermal unit composed of a spark ignition engine endowed of an exhaust gas energy recovery expander connected to a proper generator. The proposed thermal unit, which is particularly suitable for hybrid propulsion solutions, has been evaluated both in the naturally aspirated and in the supercharged version. The efficiency of each thermal unit is also compared to reference baseline engine, thus highlighting the real benefit introduced by the adoption of the proposed thermal unit. As result, it was found that the complete and efficient recovery of the unexpanded gas energy has the potential to increase the overall efficiency of the propulsion system by 10-15%, depending on the characteristics of the thermal engine and of the exhaust energy expander-generator unit
The Potential of a Separated Electric Compound Spark-Ignition Engine for Hybrid Vehicle Application
Full text linkIn-cylinder expansion of internal combustion engines based on Diesel or Otto cycles cannot be completely brought down to ambient pressure, causing a 20% theoretical energy loss. Several systems have been implemented to recover and use this energy such as turbocharging, turbomechanical and turbo-electrical compounding, or the implementation of Miller cycles. In all these cases however, the amount of energy recovered is limited allowing the engine to reach an overall efficiency incremental improvement between 4% and 9%. Implementing an adequately designed expander–generator unit could efficiently recover the unexpanded exhaust gas energy and improve efficiency. In this work, the application of the expander–generator unit to a hybrid propulsion vehicle is considered, where the onboard energy storage receives power produced by an expander–generator, which could hence be employed for vehicle propulsion through an electric drivetrain. Starting from these considerations, a simple but effective modeling approach is used to evaluate the energetic potential of a spark-ignition (SI) engine electrically supercharged and equipped with an exhaust gas expander connected to an electric generator. The overall efficiency was compared to a reference turbocharged engine within a hybrid vehicle architecture. It was found that, if adequately recovered, the unexpanded gas energy could reduce engine fuel consumption and related pollutant emissions by 4–12%, depending on overall power output
A life cycle environmental impact comparison between traditional, hybrid, and electric vehicles in the european context
Full text linkGlobal warming (GW) and urban pollution focused a great interest on hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs) as cleaner alternatives to traditional internal combustion engine vehicles (ICEVs). The environmental impact related to the use of both ICEV and HEV mainly depends on the fossil fuel used by the thermal engines, while, in the case of the BEV, depends on the energy sources employed to produce electricity. Moreover, the production phase of each vehicle may also have a relevant environmental impact, due to the manufacturing processes and the materials employed. Starting from these considerations, the authors carried out a fair comparison of the environmental impact generated by three different vehicles characterized by different pro-pulsion technology, i.e., an ICEV, an HEV, and a BEV, following the life cycle analysis methodology, i.e., taking into account five different environmental impact categories generated during all phases of the entire life of the vehicles, from raw material collection and parts production, to vehicle assembly and on‐road use, finishing hence with the disposal phase. An extensive scenario analysis was also performed considering different electricity mixes and vehicle lifetime mileages. The results of this study confirmed the importance of the life cycle approach for the correct determination of the real impact related to the use of passenger cars and showed that the GW impact of a BEV during its entire life amounts to roughly 60% of an equivalent ICEV, while acidifying emissions and par-ticulate matter were doubled. The HEV confirmed an excellent alternative to ICEV, showing good compromise between GW impact (85% with respect to the ICEV), terrestrial acidification, and par-ticulate formation (similar to the ICEV). In regard to the mineral source deployment, a serious concern derives from the lithium‐ion battery production for BEV. The results of the scenario analysis highlight how the environmental impact of a BEV may be altered by the lifetime mileage of the vehicle, and how the carbon footprint of the electricity used may nullify the ecological advantage of the BEV
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