Spark-ignition engines are still a competitive solution in a great number of applications. European manufacturers are all involved in the effort of improving fuel economy, at least at some engine ...operating points while meeting, of course, the pollutant emission standards.
The EGR technique, since a long time adopted in reducing the NO
x
formation rate, could be an effective system for fuel economy improvement. Mainly, a de-throttle effect and decreased heat losses to the walls can be obtained in this way. Furthermore, lower exhaust gas temperatures can be reached thus avoiding damages to the noble metals of catalytic converters.
In this paper, the EGR technique has been widely investigated by carrying out an experimental analysis of a small, naturally aspirated, spark-ignition engine. In particular, at full or high load operation, attention has been paid to the combustion development and the influence of EGR rate on the values of spark advance, at knock onset limit, tolerated by the engine has been assessed. Due to lower temperature levels within the combustion chamber, the obtained results show a decreased octane requirement, thus an optimal choice of spark advance is possible. Hence a significant increase of engine efficiency has been obtained.
•Realistic experimental representation of mangroves.•Long mangrove forest.•Effect of seaward slope in fringe mangrove forest.•Effect of flume bottom and walls friction.•New method for direct ...measurement of forces.•Realistic assessment of mangrove attenuation capacity.•Realistic assessment of forces on mangroves.•Implications on predictive models: formulation, calibration and validation.
With the aim of better understand and parameterize the physical processes involved in flow-mangrove interaction, wave attenuation and drag forces along a 1:6 scale fringe Rhizophora mangrove forest are studied experimentally. The 26 m long forest is composed by 135 models built reproducing mature Rhizophora mangrove trees with 24 prop roots. Hydrodynamic conditions are scaled using Froude similarity based on values collected in nature. Regular and random waves are tested and three water depths are considered to account for the influence of variable mangroves frontal area along the vertical. Wave decay analysis highlights the importance of considering the effect of flume bottom and walls friction. Neglecting this additional damping can result in a high overestimation of the mangrove dissipation capacity. It is proven that water depth, and the associated mangroves frontal area, and wave height are the dominant variables driving wave attenuation for short waves. The slope seaward the forest induces wave shoaling leading to an increase of wave steepness. Accordingly, the exerted forces on the mangroves also increase along the first 3–4 m of the forest. Smaller forces are recorded further into the forest where wave decay formulations fit well to the recorded wave heights. In general, analytical drag forces obtained by using mangrove trees induced damping coefficients compare well to the forces measured within the forest. However, analytical drag forces can lead to overestimations of up to double in some cases. This aspect is very important when experimental results are used to feed numerical or analytical models based on the introduction of a drag force in the momentum equation. These models should be calibrated using, whenever possible, direct force measurements.
•All the walls curve toward the fire and the walls made with structural bricks exhibit a reverse arch after a landing in the lateral displacement.•The walls with higher applied loads changed the ...failure criterion, consequently, the fire resistance time of the wall.•The temperatures on the face of the wall not exposed to fire were similar for ceramic brick as well as the laying mortar, with a difference of no more than 40 °C.
Ceramic brick masonry construction systems have long been used in civil construction. Understanding their performance at high temperatures is important, as several fires have occurred in recent years in these types of buildings. Therefore, in this study, the structural performances of 16 ceramic brick masonry walls under typical service and fire loads were experimentally analyzed. Parameters, such as the type of ceramic bricks (non-structural common and structural with horizontal and vertical perforations, respectively), the type of test (at room temperature and fire resistance test), load level, and laying mortar were tested. Walls with structural ceramic bricks exhibited low resistance capacities under ambient conditions, which were below normative values and close to practical service load levels. In the event of a fire, the walls constructed with common brick exhibited low fire resistance (FR), not reaching the 30-min class. Structural ceramic brick walls exhibited better fire performance, reaching the 150-min class, but higher loads considerably reduced this time.
•A novel cylindrical geometry 1kW MCFC is analysed.•A description of the considered experimental set-up is provided.•The results of a suitable experimental campaign are discussed.•The MCFC is fed by ...hydrogen, landfill gas and different mixtures of them.•A comparative analysis of the so fuelled MCFC performance results is performed.
In this paper the results of an on-site experimental analysis carried out on a Molten Carbonate Fuel Cell (MCFC) fed by different fuels (hydrogen, landfill gas and different mixtures of them) are presented. The examined MCFC is one of the experimental devices of an innovative power plant located at the urban landfill of Giugliano in Campania (Naples, Italy). Here, electricity is produced through four cogenerative reciprocating engines and one cogenerative gas turbine fed by landfill gas, operating since 2003. At the same site, two different fuel cells are installed for scientific purposes.
During the considered experimental campaign, the MCFC is initially supplied by hydrogen for testing the system at the best operating conditions. Afterward, the fuel cell is fed by mixtures of different ratios of hydrogen and reformed landfill gas. For this reason, the system is equipped with an external reformer and a suitable gas cleaning. In order to analyse the system energy performance under varying electricity loads (obtained through an electronic device), several tests were carried out. In addition, several stress tests were also performed aiming at analysing the system endurance when fed by landfill gas. The experimental results concerning the produced electric currents and voltages show satisfactory performance of the system, while the obtained operating temperatures and cell reliability still need to be improved.
One of the important mechanisms in CO2 storage is dissolution trapping. The dissolution of CO2 in aquifer brines increases the brine density and leads to hydrodynamic instabilities, formation of ...CO2‐rich fingers, and a desirable acceleration of the CO2 dissolution. In recent decades, there has been an intensive effort to identify suitable deep aquifers for CO2 sequestration. Despite reports that background horizontal flow exists in many of these aquifers, few numerical studies have addressed whether background flow affects the dissolution process. These studies had no available measurements to support their results. Here, we report on laboratory experiments, using a dyed mixture of methanol and ethylene‐glycol (MEG) as a CO2 analog. The effect of an imposed horizontal water flow was investigated by injecting MEG from above into a cell filled with glass beads. An imaging system was used to provide concentration maps, which were analyzed to calculate dissolution rates and to evaluate the characteristics of the convective fingers. The results show that background flow leads to suppression of the fingers' formation, a fivefold decrease of the fingers' wave number, and a twofold decrease in their propagation rate. Therefore, it was expected that the dissolution rate would also be suppressed, consistent with previous numerical results. However, our results show that the dissolution rate was hardly affected by the background flow. We postulate that the horizontal flow results in a trade‐off between the suppression of the convective flux and the enhancement of dispersive fluxes, resulting in negligible net influence on the dissolution rate.
Key Points
Although background flow exists in many aquifers that are considered for CO2 storage, its impact on CO2 dissolution was mostly ignored
We found experimentally that while background flow reduces the number and propagation speed of the fingers, dissolution rate was unaffected
The result is explained by a trade‐off between the suppression of the convective flux and the enhancement of dispersive fluxes
The use of the two-phase closed thermosyphons (TPCTs) is increasing for many heat transfer applications. This paper reviews the most recent published experimental and theoretical studies on the TPCT. ...After a description of the TPCT operating principle and the performance characteristics, the heat transfer analysis in condenser and evaporator sections that depends on the complex two-phase process are described. The influence of the affecting parameters on the performance of TPCTs such as the geometry (diameter, shape and length), the inclination angle, the filling ratio (FR), the working fluid, the operating temperature and pressure analyzed by various researchers is discussed. The various operating limits occurring in a thermosyphon includes viscous, sonic, dryout, boiling and flooding are also analyzed. Considering the application of TPCTs, the paper presents a review of experimental tests and applications. This paper can be used as the starting point for the researcher interested in the TPCTs and their renewable energy applications.
•The performance of an open-drive single-screw expander is presented.•A total of 102 steady-state points with R245fa and SES336 have been collected.•The maximum overall isentropic efficiency of 64.7% ...was achieved with SES36.•Internal losses and potential design improvements have been analyzed.•Experimental data and the expander semi-empirical model are made available.
This paper focuses on the experimental and numerical characterizations of a single-screw expander for waste heat recovery organic Rankine cycle (ORC) applications. A down-scaled industrial ORC test-rig has been tested with two different working fluids, R245fa and SES36. The hot source inlet temperature has been set to 125°C and the maximum expander inlet pressure was limited to 1200kPa. A total of 102 steady-state points have been collected by varying the expander pressure ratio between 3 and 9 with rotational speeds in the range from 2000rpm to 3300rpm. The experimental results allowed to assess the relationship between internal built-in volume ratio and imposed expansion ratio at different rotational speeds with respect to shaft and overall isentropic efficiency as well as volumetric performance in terms of filling factor. Results showed that while R245fa allowed approximately a 10% higher power output, the single-screw expander was performing at higher isentropic efficiency with SES36 due to higher pressure ratio achievable under the given working conditions and system limitations which also led to a better matching between ORC system and volumetric expander performance. A semi-empirical model has been developed and calibrated to break down the expander internal losses in the case of R245fa. The model has been exercised to investigate the effect of potential design improvements on the overall performance. The friction losses played a major role in the total loss count followed by suction pressure drops and leakages. As a consequence, the effect of lubrication should be further investigated to reduce leakages and friction. This study demonstrates the potential of single-screw technology as volumetric expander for ORC applications.
This research reveals the effect of hybridisation numerically for different advanced fibre (Glass/Carbon/Kevlar) reinforcement in polymer matrix composite on the eigen-characteristics. The ...higher-order displacement polynomial kinematics and curvature effect have been utilized for the modelling of the hybrid composite component including the necessary shear deformation. The adequate solution accuracy of the derived hybrid composite mathematical formulation has been examined by comparing with the first-five modal data considering the effect of aspect ratios, numbers of layers and the fibre types with the experimental data. The eigen-frequency solutions are obtained using an isoparametric linear finite element formulation in association with experimental properties for the hybrid composite. Also, the modal responses are obtained via a simulation model considering the individual layer effects of each fibre through the static-structural module of the commercial package (ANSYS). Finally, the influential structural design parameters (thickness ratio and constraint conditions) affecting the frequency characteristics including the geometrical shape are examined using the present numerical model. The computational results reveal that the numbers of layer and type of fibre affect the frequency parameter due to the variation in their stiffness.
•Experimental post-buckling analysis of elastomeric columns until failure.•Characterization of the hyperelastic material and stored energy function.•Estimate of critical load and imperfection by ...Southwell method including self-weight.•Analysis of evolution of stresses and strains in the pre- and post-buckling regimes.•Experimental results favorably compared with FE 3D simulations.
There has been an increasing amount of research and applications of hyperelastic bars, many of which involving beneficial buckling. However, there is limited information available regarding the stability of hyperelastic structural elements. Therefore, the objective of this study is to investigate experimentally and numerically the pre- and post-buckling behavior of hyperelastic columns until failure. Several constitutive models for hyperelastic incompressible materials undergoing finite deformations are tested. Uniaxial compressive and tensile tests are used to obtain the material constants and identify the most accurate model for the considered material (polyvinyl siloxane). Three-dimensional finite elements simulations are used for comparison. The experimental program is conducted considering different lengths and boundary conditions, covering a wide range of slenderness ratios. The use of a digital image correlation measurement software during the tests allows for an in-depth analysis of the deformation field. The Southwell method is adopted to evaluate the critical load and initial imperfection magnitude. The results are then compared with analytical critical loads and the influence of axial shortening, shear and self-weight is assessed. Results show that the nonlinear equilibrium path is also influenced by axial and shear deformations, self-weight, and anticlastic deformations, even under small strains. Different buckling mechanisms are identified, with some columns exhibiting limit-point instability. Finally, the results demonstrate that the hyperelastic columns can sustain high levels of deformation without damage, crucial in practical applications such as vibration control, energy absorption and harvesting, metamaterial development, bioengineering and medicine and flexible robotics, among others.
With the fast development of 3D data acquisition techniques, topographic point clouds have become easier to acquire and have promoted many geospatial applications. Ground filtering (GF), as one of ...the most fundamental and challenging tasks for the post-processing of large-scale topographic point clouds, has been extensively studied but has yet to be well solved. To reveal future superior solutions, a comprehensive investigation of up-to-date GF studies is essential. However, existing GF surveys are scarce and fail to capture the latest progress and advancements. To this end, this paper not only presents a comprehensive review of up-to-date and advanced GF methods, but also conducts systematic comparative analyses of existing experimental results on public GF benchmark datasets. Moreover, this survey compiles the most recent publicly available resources that can be leveraged for the GF research, including pertinent datasets, metrics, and a range of open-source tools. Finally, the remaining challenges and promising research directions of GF, as well as implications for large-scale 3D geospatial understanding, are discussed in-depth. It is expected that this survey can simultaneously serve as a position paper and tutorial to those interested in GF.
•A comprehensive review of the up-to-date progress on ground filtering is presented.•Experimental results on ground filtering benchmark datasets are systematically compared.•Several promising directions for future ground filtering research are delineated.•Some implications for large-scale 3D geospatial understanding are revealed.
