1,721,005 research outputs found
Measured and Predicted Particle Number and Mass Emissions from Spark-Ignition Engines
No full textModern engine technologies are subject to increasingly tighter emission standards and recent number-based regulations have become a new challenge, since historically only a mass-based regulation needed to be met. This evolution derives from the need to control the emissions of very fine particles, that are believed to cause more damage than larger ones.
The aim of the present work is to provide further guidance in understanding the mechanisms of particle emission processes in Spark-Ignition (SI) engines. By means of both numerical and experimental investigations, it tries to answer some still open questions related to this complex topic. Different fuels are considered, such as gasoline and other promising cleaner alternatives for the future, including natural gas.
3-D Computational Fluid Dynamics simulation are used as useful additional tool to investigate the fuel-related soot emissions and help explain the experimental-derived results. The modified version of the KIVA-3V code, developed at the Engine Research Center (ERC) of the University of Wisconsin-Madison, is used for the present modeling work. It includes improvements in its ignition, combustion and emission models. In particular, a semi-detailed soot model and a chemical kinetic model, including Poly-Aromatic Hydrocarbon formation, are coupled with a SI model and the G equation flame propagation model for the engine simulations and for predictions of soot mass and particulate number density. The present work improves and extends the laminar flame speed correlations for several fuels of practical use in order to assure the correct prediction of combustion phasing and in-cylinder pressure evolution.
The effects of a load increase achieved by pure oxygen addition in gasoline SI engines, as well as, the influence of natural gas composition on combustion are investigated. Furthermore, additional extensive experimental investigations provide more insights about the effects of lubricant oil on particle emissions from both gasoline and natural gas SI engines. In this last case both Port Fuel and Direct Injection mode are considered.
The experimental tests were performed at the �Istituto Motori CNR�, Italy
Sliding spool design for reducing the actuation forces in direct operated proportional directional valves: Experimental validation
Full text linkThis paper presents the experimental validation of a new methodology for the design of the spool surfaces of four way three position direct operated proportional directional valves. The proposed methodology is based on the re-design of both the compensation profile (the central conical surface of the spool) and the lateral surfaces of the spool, in order to reduce the flow forces acting on the spool and hence the actuation forces. The aim of this work is to extend the application range of these valves to higher values of pressure and flow rate, thus avoiding the employment of more expensive two stage configurations in the case of high-pressure conditions and/or flow rate. The paper first presents a theoretical approach and a general strategy for the sliding spool design to be applied to any four way three position direct operated proportional directional valve. Then, the proposed approach is experimentally validated on a commercially available valve using a hydraulic circuit capable of measuring the flow rate as well as the actuation force over the entire spool stroke. The experimental results, performed using both the electronic driver provided by the manufacturer and a manual actuation system, show that the novel spool surface requires remarkably lower actuation forces compared to the commercial configuration, while maintaining the same flow rate trend as a function of the spool position
Experimental and numerical analysis of cavitation in hydraulic proportional directional valves
No full textThis paper evaluates the effects of cavitation upon the performance of a hydraulic, proportional, directly-operated, directional valve by means of thorough experimental and numerical investigations. The experimental campaign is performed to estimate how cavitation changes the performance curves of the valve; in particular, the experimental equipment assembled to control the cavitation phenomenon inside the proportional valve is described, and the influence of cavitation on the flow rate and the flow coefficient as a function of the spool position is assessed. In addition, a full three-dimensional mixture model of the flow field within the valve is developed to accurately predict cavitation within the flow path for several spool positions. The accuracy of the numerical model is proven by previous experiences and by comparing the numerical results with the experimental data. After their validation, the numerical predictions are employed to analyse the characteristics of cavitation that cannot be experimentally evaluated, such as the volume of vapour, and to identify the zones where cavitation occurs. The numerical simulations are finally employed to predict how the variation in cavitation intensity influences the driving forces required to move the sliding spool and to calculate the minimum cavitation number for which the effects of cavitation are negligible
A novel piezoelectric double-flapper servovalve pilot stage: Operating principle and performance prediction
No full textThis paper proposes a novel architecture for the pilot stage of electro-hydraulic two-stage servovalves that does not need a quiescent flow and a torque motor as well as a flexure tube to operate. The architecture consists of two small piezoelectric valves, coupled with two fixed orifices, which allow variation of the differential pressure at the main stage spool extremities in order to move it with high response speed and accuracy. Each piezoelectric valve is actuated by a piezoelectric ring bender, which exhibits much greater displacement than a stack actuator of the same mass, and greater force than a rectangular bender. The concept is intended to reduce the influence of piezoelectric hysteresis. In order to assess the validity of the proposed configuration and its controller in terms of spool positioning accuracy and dynamic response, detailed simulations are performed by using the software Simscape Fluids. At 50% amplitude the -90? bandwidth is about 150Hz
Full simulation of a piezoelectric double nozzle flapper pilot valve coupled with a main stage spool valve
Full text linkThis paper develops a detailed simulation model, realized by the software Simscape, which can be a powerful tool to analyze the performance of a double nozzle flapper valve actuated by a piezoelectric ring bender. The particularity of this valve is that the use of the torque motor and flexure tube is avoided, thus reducing the complexity, manufacturing time and cost of the valve assembly. The model accounts for all the real phenomena present in the valve, such as fluid compressibility and fluid viscosity. The viability of the valve concept is validated by step tests simulated at different valve openings. It is shown that the response time obtained for a supply pressure of 210 bar and necessary to reach 90% of the maximum opening degree (corresponding to a maximum spool position of 1mm and maximum flow rate of 60 l/min) is only 6 ms, which is comparable with typical commercially available double nozzle flapper valves, but with the advantage of having removed critical components such as the torque motor and the flexure tube
Overview on recent developments in energy storage: Mechanical, electrochemical and hydrogen technologies
Full text linkEnergy production is changing in the world because of the need to reduce greenhouse gas emissions, to reduce the dependence on carbon/fossil sources and to introduce renewable energy sources. Despite the great amount of scientific efforts, great care to energy storage systems is necessary to overcome the discontinuity in the renewable production. A wide variety of options and complex characteristic matrices make it difficult and so in this paper the authors show a clear picture of the available state-of-the-art technologies. The paper provides an overview of mechanical, electrochemical and hydrogen technologies, explaining operation principles, performing technical and economic features. Finally a schematic comparison among the potential utilizations of energy storage systems is presented
Towards the Development of the In-Cylinder Pressure Measurement Based on the Strain Gauge Technique for Internal Combustion Engines
No full textA simple, cheap and effective way of measuring the pressure inside the cylinders of internal combustion engines is proposed in this paper. It is well known that the in-cylinder pressure is one of the most significant variables describing the combustion status in internal combustion engines; therefore, if the measured value of the actual pressure in the combustion chamber is used as a feedback variable for closed loop monitoring and control techniques, it will be possible both to improve engine performances and to reduce fuel consumptions and emissions. However, to date such a pressure-based control strategy has been limited by costs, reliability and lifetime of commercially available cylinder pressure sensors.To overcome these limitations, the present paper proposes a very simple and low cost experimental device for measuring the pressure inside the combustion chamber, developed for engine control and monitoring applications. The sensor exploits the strain measurements of the external walls of engine cylinders, which are indicative of the pressure information during the combustion process. The measurement is carried out by means of strain gauges attached to the external wall of the cylinders inside the water channels of the cylinder block. This location has been selected because it minimizes the temperature variations induced by different loads and engine speeds.This study presents a feasibility analysis of the system. Preliminary tests were initially conducted on a hydraulic cylinder and subsequently on an internal combustion engine. The analysis shows that the proposed method has the potential to predict the internal cylinder pressure accurately, thus representing an interesting contribution for the development of low-cost engine management systems. The robustness of the proposed solution has the potential to be very high, as the concept is based on strain gauges. Forthcoming experimental investigations on a fired engine under regular engine operating conditions will aim at assessing the capability of the proposed method over various loads, frequencies and thermal conditions
Optical device for measuring the injectors opening in common rail systems
No full textSince the needle displacement exerts a fundamental influence on the operation of Common Rail injection systems, accurate measurements of the control piston position can be crucial for a more thorough analysis of the behaviour of injectors, in particular when multiple injections are employed. Eddy current sensors have traditionally been used in lab activities to measure the control piston position inside injectors; apart from the high cost, the scientific literature clearly shows their inadequacy, which is mainly due to the presence of electromagnetic disturbance: the current pulse, which controls the opening of the injector, generates electromagnetic fields which strongly affect the acquisition of data. Many attempts have recently been made either to solve the interference occurring during such measurements or to propose alternative displacement transducers whose operation is not influenced by electromagnetic interference. In this paper, a new device for measuring the injector opening is proposed: it is an optical transducer characterized both by simple and very cheap construction and by a reliable physical principle for measuring the control piston lift. The reliability of the proposed sensor is assessed by a thorough experimental campaign and by comparing the experimental results with the numerical predictions achieved by a Common Rail injector model. Since the assembly of the optical sensor does not affect the injector operation, it can efficiently be used both for experimental tests and for on-board diagnosis and monitoring of the injector operation
Thermodynamic analysis of small-scale externally fired gas turbines and combined cycles using turbo-compound components for energy generation from solid biomass
No full textThis paper proposes the implementation of cost-effective commercially available automotive components in small-scale power plants for the energy generation from carbon-neutral biomass. Specifically, a turbocharger and a power turbine of turbo-compound systems are proposed to be coupled with an external combustor and a high temperature heat exchanger in order to obtain a cheap externally fired gas turbine capable of producing about 30 kW of electrical power from the combustion of pruning residues. The externally fired gas turbine cycle can be combined either with a final heat exchanger to generate useful thermal power or with a bottoming cycle to generate useful thermal power and an additional electrical power of about 15 kW. Two plant configurations are proposed for the bottoming cycle: the first is a water Rankine cycle employing the “green steam turbine” as the steam expander, whereas the second is an organic Rankine cycle using an axial turbine and toluene as the working fluid. The results of the simulations, obtained through a detailed thermodynamic model, show that the use of a combined cycle is fundamental to maximize the primary energy savings of the power plant. In the case of negligible pressure losses, the use of a bottoming water Rankine cycle leads to a maximum second law efficiency of about 0.25 and maximum primary energy savings of about 0.23. Instead, a bottoming organic Rankine cycle employing a single stage turbine can increase the second law efficiency and the primary energy savings up to about 0.27 and 0.26, respectively. It is also demonstrated that the use of a two-stage turbine for the organic Rankine cycle can further enhance the plant performance. The effects of the pressure drops in the system are investigated in detail to point out that the minimization of the pressure losses is fundamental to improve the performance parameters of all the proposed configurations. © 2018 Elsevier Lt
Measured and Predicted Soot Particle Emissions from Natural Gas Engines
No full textDue to the new challenge of meeting number-based regulations for
particulate matter (PM), a numerical and experimental study has been
conducted to better understand particulate formation in engines
fuelled with compressed natural gas. The study has been conducted
on a Heavy-Duty, Euro VI, 4-cylinder, spark ignited engine, with
multipoint sequential phased injection and stoichiometric
combustion. For the experimental measurements two different
instruments were used: a condensation particle counter (CPC) and a
fast-response particle size spectrometer (DMS) the latter able also to
provide a particle size distribution of the measured particles in the
range from 5 to 1000 nm. Experimental measurements in both
stationary and transient conditions were carried out. The data using
the World Harmonized Transient Cycle (WHTC) were useful to
detect which operating conditions lead to high numbers of particles.
Then a further transient test was used for a more detailed and deeper
analysis. Finally 3-D Computational Fluid Dynamics (CFD)
simulations were performed and the numerical results obtained were
compared to particle size distributions (PSDs) derived from the
experimental measurements carried out in stationary conditions. In
this way the influences of engine load and regime on particle size
distribution (PSD) were determined. A semi-detailed soot model and
a chemical kinetic model, including poly-aromatic hydrocarbon
(PAH) formation, were coupled with a spark ignition model and the
G equation flame propagation model for the SI engine simulations
and for predictions of soot mass and particulate number density.
Qualitative agreements of in-cylinder particle distributions were
obtained and results are helpful to understand particulate formation
processes
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