1,721,076 research outputs found
Influence of driving cycles on Euro-3 Scooter emission levels
No full textThis study derives from the need to evaluate the impact on the urban air quality of two-wheeler vehicular class. Mopeds and motorcycles, in fact, are increasingly used in recent years, representing a great share of motor-powered vehicles in urban environment. This paper is finalized at the examination of the emissions of the last generation motorcycles, contributing broadly to extend knowledge of two- wheeler emission behavior, with reference to cold and hot operating conditions. For this aim, an experimental investigation was performed on a medium-size motorcycle belonging to the Euro-3 statutory category, evaluating the exhaust emissions of regulated pollutants. This scooter was tested on a dynamometer bench both on a type approval test cycle and on real-world test cycles in order to study the influence of driving cycles on the emission levels. The statistical processing results of the experimental data were compared with recent emission models for estimating emissions from road traffic
Hybrid Propulsion in SI Engines for New Generation Motorcycles: A Numerical-Experimental Approach to Assess Power Requirements and Emission Performance
No full textEnergy Performance and Fluid Leakage in Rotary Volumetric Machines at Off-Design Operating Conditions
No full textThe main purpose of the present paper is to establish a thermodynamic model to examine the energy advantages of rotary machines when used as volumetric expanders. The screw expander is a particular volumetric machine which can exploit energy in working fluids of high temperature and pressure to produce mechanical power without high fluid velocities. In this research, to describe the real expansion process of the screw expander, a part-load numerical model is investigated also considering all the energy losses which affect thermodynamic performance at off-design working conditions (including fluid leakage losses). An energetic assessment of the part-load behavior is then performed to predict best working conditions of the screw expander
THERMODYNAMIC ANALYSIS OF SCREW EXPANDERS AT PART-LOAD WORKING CONDITIONS: ENERGY LOSSES, FLUID LEAKAGE AND OVERALL EFFICIENCY
No full textThis research provides fundamental principles to study the thermodynamic performance of the screw expander at part-load working conditions. Screw expanders are rotary-type volumetric machines which can convert thermal to mechanical energy with a satisfactory efficiency even for low-grade heat sources and when expanding fluid in two-phase conditions, unlike standard dynamic expanders which are unable to handle with liquid droplets. However, since screw expanders operate at off-design condition in most situations, calculating expander efficiency under fluctuating working conditions appears to be a crucial issue. Hence, in this study, a part-load thermodynamic model on the real expansion process of the screw expander is investigated considering all the energy losses affecting actual working conditions, also including variable fluid leakage losses. Therefore, in relation to the part-load behavior of this volumetric power machine, the optimum working conditions together with the resultant best global efficiencies are defined and shown. Lastly, the predicted energy performance is compared with experimental data, so obtaining a good agreement between the calculated and measured overall efficiency of screw expanders
Local high-frequency vibration therapy following eccentric exercises reduces muscle soreness perception and posture alterations in elite athletes
No full textPURPOSE:
Exercise-induced muscle damage produces painful sensations (delayed onset of muscle soreness, DOMS). DOMS causes compensatory postural adaptations, which in turn affect athletes' walking and running gait biomechanics. It is still debated whether the postural changes are due to impaired proprioception or pain perception. To disambiguate between these two contrasting hypotheses, we designed a study that tested post-exercise postural adjustments in two groups of athletes: a group who was administered a vibration therapy (VT), to attenuate pain perception, and a control group.
METHODS:
Thirty professional futsal players were tested on five different occasions: baseline, eccentric exercises (EE) session day, 24, 48 and 72 h after EE. Vibration therapy (120 Hz) was applied on legs muscles for 15 min in the experimental group, while no vibration was applied in the control group. The measurements included: isokinetic evaluation, stabilometric test, perceived soreness evaluation and serum levels of creatine kinase, and lactate dehydrogenase.
RESULTS:
48 h after EE, the control group showed changes in biomechanical parameters (antero-rotations of pelvis, p < 0.05). A substantial alteration in the hip kinematics was found, associated to a reduced contractile force (p < 0.01) and soreness perception. On the contrary, the VT group did not show any change in posture and pain perception. High-intensity VT decreases EE effects on muscle strength and DOMS.
CONCLUSIONS:
DOMS significantly changes athletes' posture; but postural changes disappear following a VT therapy that decreases pain perception. It is concluded that soreness perception is the main cause of postural changes and that its effects can be counteracted using VT therapy
Modeling and energetic-exergetic evaluation of a novel screw expander-based direct steam generation solar system
No full textThis paper proposes an innovative solar electricity generation system based on the steam Rankine cycle, which
employs screw expanders and parabolic trough collectors, with water as heat transfer and working fluid. Owing
to its good efficiency at low-medium heat source temperatures, the solar generation system can meet the need to
design renewable energy power plant with simple technical requirements in heat storage and collection. Screw
expander-based solar thermal electricity systems have further advantages: avoidance of overheating, satisfactory
applicability in energy conversion with liquid-steam mixtures, low operating pressure and good applicability for
distributed power generation. In this paper a thermodynamic mathematical model on the polytropic expansion
process is first investigated, revealing variation of isentropic efficiency with the operating pressure ratio and
built-in volume ratio of the screw expander. Basic criteria are then provided to evaluate the energetic and
exergetic benefits of such a power plant, developing a macro balance to define optimum operating conditions.
Water evaporation temperature and condensation pressure were thus optimized with respect to heat-to-power
conversion efficiency, solar thermal power generation efficiency and exergetic efficiency. Our results indicate
that the optimum evaporation temperature ranges from about 204 °C to 276 °C with increasing solar radiation,
whereas the corresponding maximum solar thermal power efficiency and exergetic efficiency are around 12.6%
and 17.8%, respectively
A review on the effects of ethanol/gasoline fuel blends on NOX emissions in spark-ignition engines
No full textEthanol can be used as an alternative fuel for spark-ignition (SI) engines to increase the octane number and oxygen content of ethanol/gasoline blends, thereby reducing dependence on fossil fuels and the exhaust emissions of incomplete combustion products. Although it is widely agreed that ethanol can reduce CO and HC exhaust emissions, the literature on ethanol and NOX emissions is far from conclusive; hence there is a need for an in-depth, updated review of ethanol/gasoline blends in SI engines and the relative production of NOX emissions. In light of that, the present work aims to provide a comprehensive literature review on the current state of ethanol combustion in SI engines to shed definitive light on the potential changes in NOX emissions under various operating conditions. The first part of this paper discusses the feasibility of ethanol as an alternative transportation fuel, including world production and ethanol production processes. The physicochemical properties of ethanol and gasoline are then compared to analyze their effects on combustion efficiency and exhaust emissions. Then, the pathways of NOX formation inside the cylinder of SI engines are discussed in depth. Finally, we review and critically discuss the effects of ethanol concentration in blends and different engine parameters on NOX formation
Exergetic analysis of a new direct steam generation solar plant using screw expanders
No full textScrew expanders are volumetric machines particularly suitable in energy conversion with steam-liquid mixtures and for the exploitation of low temperature heat sources. This study explored the main criteria to evaluate the thermodynamic advantages and exergetic assessment of an innovative solar electricity generation system: Screw expanders are utilized as power machines and parabolic trough collectors as a thermal source. Such a direct steam generation solar system, which is based on the Rankine cycle, offers benefits in comparison with usual power plants with dynamic expanders: The best exploitation of low temperature heat sources, satisfactory thermal effciency with steam-liquid mixtures, lower evaporation pressures, and reduced size. Under real working conditions, screw expanders can work at part-load operating conditions; thus, the chief purpose of the present paper was to analyze the exergetic advantages of the planned solar power system when solar radiation and off-design working conditions fluctuate. Initially, the polytropic expansion phase with a specific numerical model is described to evaluate the energy losses that affect the thermodynamic performance of screw expanders when installed in the planned renewable energy power plant. Subsequently, to explore the exergy harnessing in the exhausted steam at off-design working conditions and then to appraise the maximum exergetic efficiency of the proposed screw expander-based solar thermal electricity plant, numerical optimization was performed in a broad range of evaporation and condensation temperatures
Hybrid Propulsion for Motorcycle Application to Reduce Engine-out Emissions: An Analytical-Experimental Investigation
No full textAll over the world, motorcycles represent an important share of motorized vehicles helping to meet daily urban transport needs, thus, particularly in urban contexts, two-wheelers impact to air pollution is significant. In a previous experimental investigation, emissions of regulated pollutants were measured in the exhaust of a four-stroke motorcycle belonging to the Euro-3 legislative category. Since exhaust emissions and fuel consumption are very sensitive to variations in vehicles instantaneous speed and acceleration, such experimental results are used in this research to recognize the kinematic parameters that cause higher CO and HC emissions. The hybrid electric propulsion is then proposed to reduce exhaust emissions in particular driving conditions which include high levels of acceleration with resultant sudden steep increase in engine speed. In such phases, in fact, an enrichment of the air/fuel mixture is needed which affects the catalyst conversion efficiency. Subsequently, the power requirements and the grade of electrical assistance in such driving situations are estimated by a procedure based on both the measured exhaust emissions and the kinematic parameters that characterize the driving dynamics collected during the experimental tests. Finally, the share of CO and HC emissions that could be saved utilizing a hybrid motorcycle instead of a conventional thermal motorcycle is calculated through an environmental analysis
Direct steam generation solar systems with screw expanders and parabolic trough collectors: Energetic assessment at part-load operating conditions
No full textThis paper explains a numerical optimization of a novel screw expander-based solar thermal electricity plant to evaluate the energetic benefits in specific case studies. In the proposed solar electricity generation system, which is based on the steam Rankine cycle, water is used as working fluid and storage, parabolic trough collectors as a thermal source and screw expander as power machine. Such solar system offers major advantages over conventional power plants adopting steam turbines: low operating pressures, good exploitation of low temperature heat sources, acceptable efficiency in energy conversion with steam-liquid mixtures and reduced size. Since screw expanders can operate at off-design working conditions in several situations when installed in direct steam generation solar plants, the chief purpose of the present study is to develop a thermodynamic model to analyse the energy performance of the planned solar power system when off-design operating conditions befall. To assess maximum efficiency of the whole power plant at part-load operating conditions, numerical optimization is then performed in a specific range of fluctuating evaporation temperatures under fixed condensation pressures
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