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The results of diagnostic tests under steady-state speed conditions of an unloaded engine do not fully reflect the emissivity of vehicles adapted to run on natural gas. Therefore, it is reasonable to pay attention to the emissions performance of these vehicles under dynamic conditions. In this regard, the tests were carried out on a chassis dynamometer with the engine fueled by gasoline and natural gas. Due to the area of operation of natural gas vehicles being usually limited to urban areas, the urban phases of the NEDC (New European Driving Cycle) and WLTC (Worldwide harmonized Light-duty vehicles Test Cycle) were adapted. While CO2 emissions are lower when fueled by natural gas, CH4 emissions can be high, which is related to momentary changes in the composition of the combustible mixture. Although CH4 emissions are higher when the engine runs on natural gas, the CO2eq value is, depending on the driving cycle, about 15–25% lower than when running on petrol. Additionally, studies have shown that in engines adapted to run on CNG (compressed natural gas), it is advisable to consider the use of catalytic converters optimized to run on natural gas, as is the case with vehicles which are factory–adapted to run on CNG. [ABSTRACT FROM AUTHOR]

Electric cars, like internal combustion vehicles, emit particulate pollution from non-exhaust systems, i.e., tires and brakes, which is included in the Euro 7 emission standard planned for implementation. Tests conducted on chassis dynamometers are accompanied by particulate emissions from non-exhaust systems, which are introduced into the ambient air on the test bench. Particulate emissions tests from non-engine systems on chassis dynamometers are mainly aimed at measuring the mass or number of particulates from tires and brakes. In contrast, little attention is paid to the immission of particulate matter from tires and brakes on the dynamometer during tests, which in the case of electric cars include, for example, measurements of energy consumption or range. Therefore, in order to draw attention to the problem of these emissions, the authors carried out measurements of PM2.5 and PM10 immissions into the air in the climatic chamber during tests of an electric car on a chassis dynamometer. The car tests were carried out in accordance with the WLTC (Worldwide harmonized Light duty Test Cycle) and at constant speed. Based on the test results, a model was proposed for the immission of particulate matter in laboratory air from tire and brake abrasion, taking traffic parameters into account. The results and the developed model show that air quality, in terms of particulate content, deteriorates significantly during testing. [ABSTRACT FROM AUTHOR]

The problem of poor air quality in urban areas has a negative impact on the health of residents. This is especially important during periods of smog. In Poland, as in other countries, the problem of poor air quality, especially during the winter season, is associated with a high concentration of particulate pollutants in ambient air (PM10, PM2.5). Sources of particulate emissions, in addition to solid-fuel boilers, include means of transportation, especially those equipped with diesel engines. In turn, during periods of strong sunshine (spring and summer), the problem of photochemical smog, whose precursors are nitrogen oxides NOX, arises in urban areas. Their main sources of emissions are internal combustion engines. Therefore, to improve air quality in urban areas, changes are being made in the transport sector, among which is upgrading the fleet of urban transport vehicles to low- or zero-emission vehicles, which are more environmentally friendly. In addition, measures that reduce the harmfulness of the transportation sector to air quality include the introduction of clean transportation zones, as well as park-and-ride (P&R) systems. The purpose of this article is to present the results in terms of PM10, PM2.5, and NOx emission reductions, implemented over a period of two years (2021–2022) in the area of the Rzeszow agglomeration, related to the modernization of the suburban bus fleet and the implementation of a P&R system for passenger cars. The results of the study were compared with the value of estimated emissions from coal-fired boilers used for residential heating and hot water, which also contribute to smog. Thanks to the implementation of the project, i.e., the replacement of 52 old buses with new buses of the Euro VI emission class and the construction of new P&R spaces, the total average annual reduction in emissions amounted to approximately 703.6 kg of PM10, approximately 692.7 kg of PM2.5, and a reduction of approximately 10.4 tons of NOX. [ABSTRACT FROM AUTHOR]

Differences between the results obtained in laboratory and road tests of vehicles depend on a number of factors. Among the most important of these are driving cycle and road load. These parameters also affect the hybrid drive control, including the combustion engine operation or driving in electric mode. In most studies, tests carried out on chassis dynamometers concern type approval cycles (NEDC—New European Driving Cycle, WLTC—World-wide harmonized Light duty Test Cycle, FTP— Federal Test Procedure), which differ from real on-road tests. Consequently, the different driving cycles do not allow for results similar to those obtained during on-road driving, especially as the actual cycles on the road are unrepeatable. It is also important to determine the effect of the motion resistance function adopted for chassis dynamometer tests on exhaust emissions and fuel consumption. For this purpose, the authors tested a hybrid car under road and laboratory conditions for the same driving cycle. The analysis was conducted for an example urban road cycle in Rzeszow (URRC). The purpose of the study was to determine the differences in the results of gaseous emissions (THC, CO, CO2, NOx) and fuel consumption (energy) of a hybrid car under road conditions, with the results of tests conducted on a chassis dynamometer, for the same cycle and three functions of resistance. [ABSTRACT FROM AUTHOR]

This study deals with the wall resolved Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation of boundary layer flow separation over a circular hump model and its active control. An array of Synthetic Jet Actuators (SJAs) is implemented in the hump model to introduce a train of vortex rings into the boundary layer to control flow separation. The OpenFOAM solver is used to numerically simulate and analyze the fluid flow using the k–ω shear stress transport model. Hot wire anemometry and particle image velocimetry measurements are carried out to evaluate the accuracy of the URANS technique as well as the effectiveness of SJAs by comparing numerical predictions to experimental data. The time-averaged results are in a good agreement with experimental results and demonstrate a successful application of SJAs to delay the flow separation by the interactions of vortical structures with the separated shear flow. The three-dimensional simulation also reveals that near wall coherent flow structures (streamwise and spanwise vortices) are responsible for the wall shear stress components. The results can be used to better understand the performance of SJAs and to further improve future actuator configurations. [ABSTRACT FROM AUTHOR]

The COVID pandemic has caused a major exodus of passengers who chose urban and suburban transport. In many countries, especially in the European Union, there is a tendency to choose individual means of transport, causing damage to the environment and contributing significantly to greenhouse gas emissions. One method to promote urban transport is replacing bus fleets with newer ones, thus making public transport more attractive and reducing the emission of harmful exhaust fume components into the atmosphere. The aim of this study was to show a methodology for calculating CO2e for bus fleets. When determining CO2e, the principal greenhouse gases, such as CO2, CH4, and N2O, are usually considered. However, CO emissions also have indirect effects on climate through enhanced levels of tropospheric O3 and increased lifetime of CH4; therefore, CO2, CH4, N2O, and CO emissions were determined for CO2e emission calculations. Two bus fleet variant scenarios were analysed; the first non-investment variant assumed passenger transport using the old fleet without any P&R parking zones. The second scenario was based on the current state, which includes the purchase of new low-emission buses and the construction of P&R infrastructure. The calculations were performed using the COPERT emission model with real data from 52 buses running on 13 lines. For the analysed case study of the Rzeszow agglomeration and neighbouring communes, implementing the urban and suburban transport modernisation project resulted in a reduction in estimated CO2e emissions of about 450 t. The methodology presented, which also considers the impact of CO emissions on the greenhouse effect, is a new element of the study that has not been presented in previous works and may serve as a model for other areas in the field of greenhouse gas emission analyses. The future research scope includes investigation of other fuels and powertrain supplies, such as hydrogen and hybrid vehicles. [ABSTRACT FROM AUTHOR]

Abstract Design and optimisation of a co-axial travelling-wave thermoacoustic cooler (TWTC) powered by a standing-wave thermoacoustic engine (SWTE) is conducted based on the linear thermoacoustic theory. The target application is storage of medical supplies in rural communities of developing countries with no access to electricity grid, where waste heat from cooking can be used as energy input. The design is guided by construction simplicity and low cost. Thus the SWTE/TWTC coupling is enclosed in a constant-diameter resonator which accommodates a compact co-axial configuration of the TWTC. Following earlier experiments, working fluid is air at 10 bar, and operating frequency is 50 Hz. Parameters such as the ratio of the cross-sectional area of the cooler to feedback inertance and stack and regenerator geometries, have been optimised for maximum system efficiency. Here, at the target input power of 600 W a drive ratio of 7.75% can be obtained, leading to the cooling load of 133 W at 250 K. This corresponds to the SWTE thermal-to-acoustic efficiency of 17% and TWTC COP of 1.9, and the combined efficiency of 22.2%. The simulations are to inform the build of an enhanced prototype of the proposed device. A detailed discussion and guidelines for practical builds are provided. Highlights • Numerical optimisation of coupled thermoacoustic engine-refrigerator is conducted. • Standing wave engine drives a co-axial travelling wave refrigerator. • Working fluid and frequency are air at 10 bar and 50 Hz, respectively. • 133 W of cooling load (at 250 K) can be generated for 600 W thermal input. • Combined engine-cooler efficiency of 22.2% is obtained with cooler COP of 1.9 [ABSTRACT FROM AUTHOR]

Highlights • Low-cost approach to thermoacoustic electricity generator for rural communities. • Numerical study of two-stage system with loudspeaker as linear alternator made. • Laboratory demonstrator producing ca. 14 W of electricity tested experimentally. • Demonstrated waste heat recovery from cooking activities through use of hot air. Abstract Thermoacoustic heat engines convert thermal power into acoustic power with no-moving parts, while the latter can be converted to electricity using linear alternators. Such thermoacoustic electricity generators can be a means of providing inexpensive electricity to developing countries using the simplest fabrication approaches. This paper shows a detailed study of a prototype waste-heat-driven, two-stage, looped-tube, travelling-wave thermoacoustic electricity generator with a branched linear alternator and tuning stub for acoustic impedance matching purposes. The generator was modelled and designed using DeltaEC. To keep the costs down, the working medium was atmospheric air, many resonator components were made of PVC pipes and fittings, heat exchangers were made of automotive parts, while the linear alternator was a commercially available loudspeaker. The prototype generated 14.2 W of electrical power to a load of 9 Ω. The effects of matching stub length, variable resistive loads and heat inputs were investigated. The simulations and measurement results are presented and discussed in detail. [ABSTRACT FROM AUTHOR]

• CVCC method was used in the investigation. • Derived cetane numbers for RME and 1-butanol were determined. • Ignition and combustion delay for 1-butanol–biodiesel blends were measured. • Tests of auto-ignition were realized for different combustion chamber temperatures. In this article, the auto-ignition properties of blends of high cetane rape methyl esters (RME) as biodiesel and 1-butanol were investigated, with 1-butanol fractions of up to 25% by volume. The tests were performed using the constant volume combustion chamber (CVCC) method to determine the combustion chamber temperature effect (between 550 °C and 650 °C) on the ignition delay (ID) and combustion delay (CD) periods of the verified blends. The research of the auto-ignition properties was complemented with the derived cetane number (DCN) and the calorific properties of the fuels tested. The results uncovered several properties relating to such blends and also showed that the periods of ID and CD increase with an increase in the 1-butanol fraction in the 1-butanol–biodiesel fuel blend (1-BBF). The work also shows that an increase in the temperature of the combustion chamber into which the fuel is supplied causes delay periods to shorten to varying degrees. For fractions of 5–25% by volume in 1-butanol, for each addition of a 5% fraction of 1-butanol, the cetane number for 1-BBF decreases by an average of 4.2 units. [ABSTRACT FROM AUTHOR]

Conventional measurement techniques used to investigate the internal fluid flow processes in gas-solids fluidized beds are known to introduce disturbances to the flow. Two non-intrusive methods: pressure fluctuation measurement and electrical capacitance tomography (ECT) techniques have been usually used separately to study the complex two phase flow phenomena in fluidized beds. However, no systematic study has been carried out to compare these two methods in terms of their capabilities to reveal the hydrodynamic characteristics of fluidized beds. This paper presents a comparative study between these two non-intrusive measurement techniques within a bench-scale fluidized bed. Experiments were carried out using two alternative test sections (one equipped with pressure transducers, one with ECT sensor) for the same operating conditions. The performance of these two methods was evaluated against some important hydrodynamic parameters within fluidized beds, such as the determination of the minimum fluidization velocity, the minimum slugging velocity, dominant frequency and bubble rise velocity. The results demonstrate that the two measurement techniques can both provide broadly consistent results, although ECT tends to be more reliable with respect to estimating bubble rise velocity. [ABSTRACT FROM AUTHOR]

The high reliability and long lifespan of thermoacoustic generators (TAG) make them ideal for waste heat recovery applications. However, the size and weight of these generators is still a challenge. This paper introduces a traveling-wave thermoacoustic generator that is free from a wavelength long loop. The new generator consists of an acoustic driver (linear motor), thermoacoustic engine and a linear alternator. The linear motor introduces the initial acoustic power into the thermoacoustic engine which amplifies it, then the amplified acoustic power is converted into electricity through the linear alternator. The electric power obtained from the alternator exceeds the initial input ("seed") power consumed by the motor to kick-start the thermoacoustic amplification, thus providing the net power gain. The advantage lies in decoupling the operation from the reliance on the acoustic resonance. A two-stage engine can be built with half a meter length, while a three-stage engine can be less than a meter long including a coiled inertance pipe. The three-stage TAG can generate 120.5 W of electricity, at a thermal to acoustic efficiency of 34.2% and a total efficiency of 20.5%. • Thermoacoustic engine free from resonance length. • Linear motor and linear alternator matching to a thermoacoustic engine. • Cascade traveling wave thermoacoustic engine. • Passive control of phase difference using inertance tube. • Modelling of thermoacoustic engines using DeltaEC. [ABSTRACT FROM AUTHOR]

Electrical capacitance tomography (ECT) has been developed as a non-invasive and non-intrusive measurement technique to investigate the internal hydrodynamic characteristics of gas-solids systems in fluidized beds. This paper describes an investigation, in which a customized twin-plane ECT sensor was designed and constructed to study the fluid flow processes within a bench-scale gas-solids fluidized bed. A detailed calibration process was conducted using hollow plastic balls of different diameters to derive the reference grey level cut-off values for determining the bubble diameter. In addition, numerical simulations were carried out to investigate the plastic ball wall effect on measured capacitance values. Bubble diameters were estimated by means of the individual reference cut-off values and their linear and second-order fitted curves. Linear back-projection (LBP) and iterative LBP image reconstruction algorithms were compared with respect to estimating the bubble diameter. A number of approaches were investigated to estimate the bubble rise velocity including three methods based on cross-correlation techniques and the detailed signal analysis. Bubble diameters were also obtained using a new approach based on “back-calculation” of the bubble rise velocity through widely accepted empirical correlations from the existing literature. [ABSTRACT FROM AUTHOR]

Travelling-wave thermoacoustic heat engine is capable of converting heat to acoustic power which in turn can be used to generate electricity by a linear alternator. The thermoacoustic heat engine can work in a wide range of heat quality, giving it the ability to be used for waste heat recovery. In this paper, a new configuration of looped-tube travelling wave thermoacoustic engine is proposed, which consists of two identical stages each having a power extraction point, and the linear alternator connecting these two points working in “push-pull” mode. This enables a more effective acoustic impedance matching compared to the use of multiple linear alternators known in the literature. The laboratory demonstrator has been designed, built and tested. The applied heat source temperature is similar to that of the internal combustion engine exhaust gases in order to explore the potential of using the device for waste heat recovery from road or marine transport. In experiments, the maximum electric power of 48.6 W at thermal-to-electric efficiency of around 6% was achieved with helium at 28 bar as working fluid and 297 K temperature difference across the regenerator. The performance of the device has been analysed and compared to modelling performed using DeltaEC simulation tool. [ABSTRACT FROM AUTHOR]

Due to increasing fuel consumption in various industries, especially in road transport, interest in increasing the market participation of renewable fuels is growing. One such fuel is ethanol. The raw materials for its production include sugar beets, sugar cane, potatoes and many other starch-containing plants. Ethanol can be used as a pure fuel in positive-ignition engines that have undergone relatively minor technical modifications. However, in compression-ignition engines, due to factors such as a very low cetane number and lubricity, ethanol cannot be used as a pure fuel. Therefore, increasing attention is being paid to fuel consisting of blends of diesel fuel with certain concentrations of ethanol. Diesel fuel containing up to 15% (v/v) ethanol is sometimes referred to as e-diesel or oxygenated diesel. In this paper, the lubricity of blends of conventional diesel fuel and ethanol, with ethanol content up to 14% (v/v), were tested. The HFRR ( High-Frequency Reciprocating Rig ) method was used for the research, which is a normative method of determining the lubricity of diesel fuel. For individual fuel samples, microscopic photographs of wear scar caused on test balls, along with the designation of areas that have been considered when measuring the diameters of wear scars, were presented. The obtained values of WSD ( Wear Scar Diameter ) were compared to the regulatory requirements for diesel fuels. Further measurements of kinematic viscosity, density and water content were conducted for individual fuel samples. The results showed that in the range of up to 14% (v/v), the proportion of ethanol in diesel fuel causes hardly any changes to its lubricity as determined by HFRR, and in addition, diesel fuel with up to 14% (v/v) added ethanol still meets the standard requirements in terms of lubricity. [ABSTRACT FROM AUTHOR]

• Transient simulations of standing wave thermoacoustic engine developed • Non-linear behaviour of high pressure amplitude thermoacoustic engine studied • Hypothesis of "Distributed fluidic pump" developed • Mechanisms behind having higher mean pressure than the charge pressure identified This article deals with the numerical study of the nonlinear features of oscillatory flow in a high pressure amplitude standing wave thermoacoustic heat engine. The overall performance of thermoacoustic devices can deteriorate due to nonlinearities caused by their operation at high pressure amplitudes. Acoustic mass streaming is one of these nonlinearities that can influence the performance of thermoacoustic systems by an undesirable convective heat transfer. Therefore, understanding the nonlinear phenomena within thermoacoustic devices is of fundamental and practical importance. The Navier‐Stokes and energy equations are solved on the structured meshes by resolving thermal and viscous boundary layers utilizing the open-source modelling software OpenFOAM. In particular, the paper looks in more detail at the causes of a non-uniform distribution of mean pressure along the resonator reported previously by both experimental and numerical studies. This is explained by an analogy to a "distributed fluidic pump" manifesting itself through the pumping effects of streaming patterns. Also, the non-linear regime of the mean dynamic pressure shows interesting start-up instabilities which can be influential on achievable efficiencies. [Display omitted] [ABSTRACT FROM AUTHOR]

Due to increasing fuel consumption in various industries, especially in road transport, interest in increasing the market proportion of renewable fuels is growing. One of such fuels is ethanol. The raw materials for production of ethanol may include sugar beets, sugar cane, potatoes and many other plants containing starch. Ethanol can be used as a self-contained fuel in positive-ignition engines, which undergo relatively minor technical modifications. However, in diesel engines with compression ignitions, due to, e.g., a very low cetane number, this fuel cannot be used. Therefore, more attention is given to fuels consisting of mixtures of diesel fuel with certain proportions of ethanol. In this paper, the properties of autoignition mixtures of conventional diesel and ethanol, with ethanol content of up to 14% (v/v), were examined. A combustion chamber of constant volume was used in the study. The effect of injection pressure in the range of 80 MPa–140 MPa on the period of ignition delay and the period of combustion delay was determined in the study. In addition, for each mixture of diesel fuel and ethanol, the value of derived cetane number was examined. The studies have shown that with increasing proportions of ethanol, the ignition and combustion delays periods increase and the increase in fuel injection pressure in varying degrees shortens those periods. It was also shown that in the range of 14% ethanol, for every 2% increase in the proportion of ethanol, the derived cetane number of the mixture of diesel and ethanol is reduced by an average of 1.7 units. [ABSTRACT FROM AUTHOR]

• Time-dependent numerical models of standing wave thermoacoustic engine developed. • Start-up behaviour of the SW engine investigated vs. various boundary conditions. • Nonlinear flow behaviour and time-dependent flow fields studied in steady state. • Acoustic streaming patterns demonstrated in characteristic SW engine locations. • Mechanisms behind limiting SW engine performance due to streaming identified. Understanding of transient fluid flow and heat transfer characteristics within thermoacoustic devices is crucial to improve their start up processes and subsequently the achievable efficiencies. The present numerical study investigates the transient features of a standing-wave quarter-wavelength thermoacoustic heat engine composed of hot and cold heat exchangers, a stack, and a resonator. The non-linear fluid dynamical as well as energy equations are solved on the structured grids by resolving viscous and thermal boundary layers using OpenFOAM software. Full discretization of governing equations captured nonlinear features of flow at high pressure amplitudes which are typically ignored by the linear theory. The results show the existence of acoustic streaming phenomenon in the system due to the interaction of Stokes boundary layer adjacent to the solid regions which can lead to undesirable convective heat transport and as a result the reduction of the system efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Fluid dynamical mechanisms of flow control using SJAs investigated. • Identification of optimum position, velocity ratio and waveform conducted. • Quantitative velocity and vorticity field investigation carried out by PIV and HWA. • Reduction in the size of recirculation zone quantified (up to 44%) and explained. This research investigates the effectiveness of a spanwise array of synthetic jet actuator (SJA) for the control of boundary layer separation over a circular "hump" model. The influence of geometrical and operational parameters – including actuator position, velocity ratio (i.e., the ratio of the peak exit jet velocity of actuators to the freestream velocity of cross flow, VR) and the actuation waveform – on the flow separation control are investigated using hot-wire anemometry (HWA) and particle image velocimetry (PIV) techniques. The effect of the position of SJA array on flow separation control has been studied experimentally over a considerable length of the hump chord (from the "apex" of the model to near the "trailing edge") for the first time. The investigation looks in more detail into the mechanisms behind the alleviation of adverse pressure gradient as a key factor controlling the flow separation. The investigation of the effect of VR on the performance of SJAs shows the importance of the momentum injection in the mitigation of the momentum deficiency as another important factor in turbulent boundary layer flow separation. A holistic overview of the control parameters allowed to reveal a considerable change in the separation flow patterns. The results show that the best performance of SJA array from the viewpoint of separation control occurs at the velocity ratio of 1.85 with a reduction of the length of recirculation region of around 42.6 and 44.2% by using sine and square waves excitation of SJAs, respectively. [ABSTRACT FROM AUTHOR]

Road transport contributes to almost a quarter of carbon dioxide emissions in the EU. To analyze the exhaust emissions generated by vehicle flows, it is necessary to use specialized emission models, because it is infeasible to equip all vehicles on the road in the tested road sections with the Portable Emission Measurement System (PEMS). However, the currently used emission models may be inadequate to the investigated vehicle structure or may not be accurate due to the used macroscale. This state of affairs is especially related to full hybrid vehicles, since there are none of the microscale emission models that give estimated emissions values exclusively for this kind of drive system. Several automakers over the past decade have invested in hybrid vehicles with great opportunities to reduce costs through better design, learning, and economies of scale. In this work, the authors propose a methodology for creating a CO2 emission model, which takes relatively little computational time, and the models created give viable results for full hybrid vehicles. The creation of an emission model is based on the review of the accuracy results of methods, such as linear, robust regression, fine, medium, coarse tree, linear, cubic support vector machine (SVM), bagged trees, Gaussian process regression (GPR), and neural network (NNET). Particularly in the work, the best fit for the road input data for the CO2 emission model creation was the GPR method. PEMS data was used, as well as model training data and model validation. The model resulting from this methodology can be used for the analysis of emissions from simulation tests, or they can be used for input parameters for speed, acceleration, and road gradient. [ABSTRACT FROM AUTHOR]

Among the solutions that make it possible to reduce CO2 emissions in the transport sector, particularly in urban traffic conditions, are hybrid vehicles. The share of driving performed in electric mode for hybrid vehicles is highly dependent on motion resistance. There are different methods for determining the motion resistance function during chassis dynamometer testing, leading to different test results. Therefore, the main objective of this study was to determine the effect of the chassis dynamometer load function on the energy demand and CO2 emissions of a full-hybrid passenger car. Emissions tests according to the New European Driving Cycle (NEDC) were carried out on a chassis dynamometer for three different methods of determining the car's resistance to motion. The study showed that adopting the motion resistance function according to different methods, results in differences in CO2 emissions up to about 35% for the entire cycle. Therefore, the authors suggest that in the case of tests carried out with chassis dynamometers, it is necessary to also provide information on the chassis dynamometer loading function adopted for the tests. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a novel concept of a travelling-wave thermoacoustic electricity generator, which employs a looped-tube travelling-wave thermoacoustic engine to convert thermal energy into acoustic power, an ultra-compliant alternator within the engine loop to extract and convert the engine acoustic power to electricity and an acoustic stub matching technique to match the alternator to the engine. In addition, a carefully designed cold heat exchanger acts as a phase shifting inertance to improve the performance. A simple model has been developed to capture and demonstrate the physics of this new concept, while the whole system has been investigated in detail numerically by using a specialized design tool DeltaEC. Based on the current concept, a prototype has been designed, constructed and tested. It uses atmospheric air as the working fluid, a commercially available audio loudspeaker as the electro-dynamic transducer, and inexpensive standard parts as the acoustic resonator. The experimental results have verified the simplified model and the numerical simulations of the practical build. The small-scale inexpensive prototype generator produced 11.6W of electrical power, which shows the potential for developing cheap thermoacoustic electricity generators for energy recovery from waste heat sources. It is concluded that such concept could be very attractive provided that inexpensive ultra-compliant alternators based on the standard technology used in audio loudspeakers could be developed. Finally, some guidelines have been discussed and proposed for developing such alternators. [Copyright &y& Elsevier]

Abstract: This paper considers the role of acoustic impedance, flow resistance, configuration and geometrical dimensions of regenerators on the power produced in travelling-wave thermoacoustic engines. The effects are modelled assuming a pure travelling-wave and ideal gas, which allows defining a pair of dimensionless factors based on the “net” acoustic power production. Based on the analysis provided, the acoustic power flow in the regenerators is investigated numerically. It is shown that impedance essentially reflects the proportion between the acoustic power produced from heat energy through the thermoacoustic processes and the acoustic power dissipated by viscous and thermal-relaxation effects in the regenerators. Viscous resistance of the regenerator mainly determines the magnitude of the volumetric velocity and then affects the magnitude of acoustic impedance. High impedance and high volumetric velocity are both required in the regenerators for high power engines. The results also show that the optimum transverse dimension of the gas passage exists, but depends on the local acoustic impedance. In principle, it is possible to obtain an optimum combination between these two parameters. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to provide a comprehensive review of the current measurement technologies available for on-line monitoring of the performance of the gas/oil/water separators, which are commonly used as the first stage of crude oil processing. Firstly, a short overview is given of the fluid physics governing the separation processes and the design of separation vessels. Simple theoretical models of separation physics are briefly reviewed and the process challenges outlined. This is followed by the description of existing measurement systems, those entering the market and likely future developments. The measurement systems are broadly divided into three categories: (1) those based on the assumption of a complete phase separation within the vessel; (2) those based on the concept of an array of sensors distributed across the heterogeneous layers, hence not requiring any assumptions regarding the actual phase distribution; and (3) more complex systems enabling cross-sectional imaging in the industrial process tomography sense. [Copyright &y& Elsevier]

Abstract: This paper considers an entrance flow into the channels formed by a stack of parallel plates, placed in an acoustic resonator that provides oscillatory flow forcing. Interesting complex flow phenomena around the extremity of the stack are observed, essentially due to the introduction of cross-sectional discontinuities: vortex formation and shedding during the fluid ejection from the channels and development of an entrance flow during the suction phase, when the fluid enters the channels from outside. It is the latter that is of particular interest in this study. Particle image velocimetry (PIV) is used to investigate the flow structures in the “entrance region”. Velocity profiles are measured as a function of phase angle within an oscillation period and the distance from the stack end into the channel. Using the data obtained, an “entrance length” defined by analogy with existing fluid mechanical definitions, is estimated. The experiments are supplemented by CFD calculations to improve the understanding of such entrance flows. [Copyright &y& Elsevier]

Abstract: This paper presents a preliminary study of a previously unreported phenomenon of the “gas driven granular jump”, observed in the gas–solids flow within the pneumatic conveying system. From the phenomenological point of view, it resembles the already known processes such as hydraulic jumps in shallow water or granular jumps in granular flows in chutes or avalanches (although it seems most appropriate to explain it by analogy to a propagating granular bore). Clearly, unlike in classical phenomena of this type, the flow itself is driven by the aerodynamic forces related to the gas flow and the behaviour of the front of the “jump” is modified significantly by their presence. A series of high-speed camera visualisations are presented, which focus on this unusual behaviour of the flow on the border-line between cluster and stratified flow regimes in a horizontal pipe. Some similarities are drawn between the observed phenomenon and the broader class of problems exhibiting transition between super- and sub-critical flows. The fluid dynamical aspects and possible mechanisms behind the new phenomenon are discussed and the results obtained are compared quantitatively with simple theoretical models. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental study to investigate the suitability of thick-film ultrasonic transducers for composition measurements in heterogeneous mixtures. Following on from earlier developments [G. Meng, A.J. Jaworski, T. Dyakowski, J.M. Hale, N.M. White, Design and testing of a thick-film dual-modality sensor for composition measurements in heterogeneous mixtures, Meas. Sci. Technol. 16(4) (2005) 942–954], focused on the design and preliminary testing of the transducers for mixtures of vegetable oil and salty water, the current paper looks in more detail into their application to industrially relevant fluids, namely crude oil and process water, which are common in oil and gas extraction and petrochemical industries. The measurements are based on the time-of-flight of the ultrasonic pressure wave in order to obtain the speed of sound. The results, showing the variation of the speed of sound with the volume fraction of crude oil, for three different temperatures, are compared with five theoretical models available in the existing literature. It is shown that the models proposed by Urick [R.J. Urick, A sound velocity method for determining the compressibility of finely divided substances, J. Appl. Phys. 18 (1947) 983–987] and by Kuster and Toksöz [G.T. Kuster, M.N. Toksöz, Velocity and attenuation of seismic waves in two-phase media. Part I. Theoretical formulations, Geophysics 39 (1974) 587–606] provide a relatively accurate prediction for the speed of sound in the media studied. Interestingly, the model developed by Povey and co-workers [V.J. Pinfield, M.J.W. Povey, Thermal scattering must be accounted for in the determination of adiabatic compressibility, J. Phys. Chem. B 101 (1997) 1110–1112] only agrees with experiment when its thermal scattering features are neglected. Overall, the results obtained demonstrate that the slim-line and compact thick-film transducers can be considered as a viable means for the composition measurements in the process conditions. [Copyright &y& Elsevier]

Abstract: This paper provides an overview of research activities conducted and results obtained within an industrially driven research programme managed through UMIST (currently The University of Manchester) over the recent years. Its main objective was to design, construct and demonstrate new instrumentation technologies which could allow reliable measurement of the separation process in the oil and gas extraction industries with the view of transferring the technology developed in academia into the oilfield environment. The paper describes the developments starting from the early work, which aimed at the laboratory qualification of the distributed electrical capacitance sensors embedded in the parallel-plate interceptor of the transparent oil–water separator located at the university Pilot Plant. This is followed by the description of the design, analysis and industrial evaluation of the pre-prototype capacitance probe, containing 24 distributed sensors, in the live oilfield conditions of the BP Exploration facility at Wytch Farm, Dorset, UK. Finally, the most recent advances, including industrial tests of the prototype multi-electrode capacitance probe carried out in the National Engineering Laboratory in Glasgow are reported. The probe was designed and built to include a mechanical deposit prevention system and to meet the flame proof standards of the oil and gas extraction industry. The three case studies presented demonstrate the process of evolution of the measurement technology, which originally stemmed from ECT, and its transfer into the live process environment. [Copyright &y& Elsevier]

This paper presents a novel approach to designing sensors and instrumentation for monitoring and controlling multiphase processes. It is based on the use of distributed sensor arrays, embedded within vital plant components, which provides an enhanced method of monitoring multiphase phenomena in both the spatial and temporal sense. This can be of particular importance for a more efficient extraction of fossil fuels and improved energy management in manufacturing sector. Two case studies are provided. First example shows the use of the concept in the separation processes in oil and gas extraction sector, while the second relates to nylon polymerization in the chemical industry. [ABSTRACT FROM AUTHOR]

The gas–solids flows in the dense pneumatic conveying exhibit many interesting features related to their three-dimensional and unsteady nature. The dominant characteristic in this type of flows is the appearance of discrete flow instabilities commonly known as ‘slugs’ and ‘plugs’. These are investigated by two techniques: a high-speed video camera and a twin-plane electrical capacitance tomography (ECT), and the results obtained are discussed. Data extracted from tomographic measurements can be processed and presented in several different ways to enable a better understanding of the flow behaviour. Several examples are given, including body shape type information, internal structure of the flow instabilities, their propagation velocity and frequency characteristics. A short case study, focused on measurements of bidirectional flow in a vertical channel, is presented. [Copyright &y& Elsevier]

Due to the increasing consumption of fuels in heavy industries, especially in road transportation, significant efforts are being made to increase the market participation of renewable fuels, including ethanol. In diesel engines, however, ethanol cannot be used as a pure fuel, primarily due to its very low cetane number and lubricity. For this reason, greater attention is being paid to blended fuels containing diesel and varying percentages of ethanol. Tests of lubricating properties carried out in accordance with the standard HFRR (high frequency reciprocating rig) method for ethanol–diesel fuel blends have long durations, which leads to ethanol evaporation and changes in the composition of the tested fuel sample under elevated temperatures. Therefore, this study presents an alternative lubricity assessment criterion based on the measurement of the scuffing load with a four-ball machine. Lubricity tests of blends of typical diesel fuel and ethanol, with ethanol volume fractions up to 14% (v/v), were conducted using a four-ball machine with a continuous increase of the load force of the friction node. In this method the lubrication criterion was the scuffing load of the tribosystem. The obtained results provided insights into the influence of the addition of ethanol to diesel fuel on lubricating properties, while limiting the ethanol evaporation process. The results also showed that an increase in the fraction of ethanol up to 14% (v/v) in diesel fuel resulted in a decrease in the scuffing load and a corresponding deterioration in the lubricating properties of the diesel–ethanol blend. For an ethanol volume fraction of 6–14%, the changes in the scuffing load were smaller than in ethanol volume fractions of 0–6%. [ABSTRACT FROM AUTHOR]

The problem of global warming and the related climate change requires solutions to reduce greenhouse gas emissions, in particular CO2. As a result, newly manufactured cars consume less fuel and emit lower amounts of CO2. In terms of exhaust emissions and fuel consumption, old cars are significantly inferior to the more recent models. In Poland, for instance, the average age of passenger cars is approximately 13 years. Therefore, apart from developing new solutions in the cars produced today, it is important to focus on measures that enable the reduction in CO2 emissions in older vehicles. These methods include the adaptation of used cars to run on gaseous fuels. Natural gas is a hydrocarbon fuel that is particularly preferred in terms of CO2 emissions. The article presents the results of research of carbon oxides emission (CO, CO2) in the exhaust gas of a passenger car fueled by petrol and natural gas. The emissions were measured under the conditions of the New European Driving Cycle (NEDC) test and in real road tests. The test results confirm that compared to petrol, a CNG vehicle allows for a significant reduction in CO2 and CO emissions in a car that is several years old, especially in urban traffic conditions. [ABSTRACT FROM AUTHOR]

There is generally limited guidance available on the optimum clamping method for the diaphragms used in the synthetic jet actuators (SJAs). This paper describes the effects of clamping methods (O-rings, neoprene rubber washers and metal-to-metal clamping) on the actuator diaphragm displacement using Polytec scan vibrometer (PSV). Once the clamping type was implemented, an optimization study to examine the effect of geometrical parameters for three designs of synthetic jet actuators in quiescent conditions--in particular the number of orifices per cavity, the space between them, and their effects on the jet velocity--was performed. It has also been shown that with use the Helmholtz resonance of the cavity and amplitude modulation of the excitation signal, the actuator can exhibit a more significant "blowing" velocity at a reduced power input. [ABSTRACT FROM AUTHOR]

This work involved the simulation of both a multiphase gas–liquid flow and the electromagnetic field representing a two-electrode capacitance sensor in a circular pipe. The simulation investigates in particular the sensitivity of the sensor orientation around the pipe (i.e., top-to-bottom or side-to-side) that best capture the induced flow patterns. The presented numerical work is a simplified simulation by COMSOL multi-physics which was validated by a systematic and an extensive experimental work, using (a) a specially designed simple capacitance sensor (i.e., concave two electrodes), (b) different gas–liquid superficial velocity combinations, (c) different flow section inclinations, and (d) high-speed camera images. The numerical modelling capacitance values were validated against the experimentally measured values which shows a satisfactory level of agreement with a deviation of less than ±2%. The quantity of finite points was between 280,000 and 340,000, which was influenced by the simulated flow pattern. The simulated cases captured the generated flow patterns and their variation inside the pipe, which was in a good agreement when compared to the experimental work as time-dependent values. It was found that the best orientation for the utilized two-electrode capacitance sensor was the top-to-bottom configuration. This is because the sensor's electrical field distribution was more sensitive, and capable of detecting a greater range of capacitance values. The sensitivity of the top-to-bottom configuration was 1.25–1.64 times greater than that of the side-to-side configuration. Therefore, for design purposes and performance optimization, it is recommended to use the top-to-bottom configuration. [ABSTRACT FROM AUTHOR]

This work proposes a method to distinguish between various flow patterns in a multiphase gas–liquid system. The complete discrimination between different flow patterns can be achieved by mapping the corresponding frequency and statistical parameters. These parameters are usually obtained from further analysis conducted on the signal data of the utilized sensor. The proposed technique is based on establishing interrelationships between these parameters, namely the mean (m), the standard deviation ( σ ¯ ), power spectral density (PSD), the width of the characteristic frequency peaks (Δƒ), the skewness ( γ 1 ) and the kurtosis ( γ 2 ). Therefore, a relatively simple electrical capacitance sensor with two electrodes was designed and implemented on a two-phase flow apparatus with a circular pipe. The experimental operating conditions comprised of different combinations of air–water superficial velocities at three inclinations (i.e., horizontal, upward 15° and upward 30°). This research discusses in specific the analysis underlying flow patterns identification method and the rationale for selecting the proposed approach. The results showed that some parameters found to be more valuable than others such as m, σ ¯ and Δƒ. Besides, combining two sets of these statistical graphs which are (a) σ ¯ vs. Δƒ with Δƒ vs. m (or Δƒ vs. total power), (b) Δƒ vs. total power with γ 1 vs. σ ¯ (or γ 2 vs. σ ¯ ), and (c) σ ¯ vs. m with Δƒ vs. m (or Δƒ vs. total power), allowed all flow patterns field to be identified clearly at all inclinations. It is therefore concluded that for any gas–liquid multiphase flow system, the reported approach can be used reliably to discriminate between different generated flow patterns. [ABSTRACT FROM AUTHOR]

Fluid flow and heat transfer processes play an important role in many areas of science and engineering from the planetary scale (e.g., influencing weather and climate) to microscopic scales of enhancing heat transfer by the use of nanofluids; they also underpin the performance of many energy systems understood in the broadest possible sense. "Numerical Study of the Magnetic Field Effect on Ferromagnetic Fluid Flow and Heat Transfer in a Square Porous Cavity" by El-Amin et al. [[17]]; 17 El-Amin M.F., Khaled U., Beroual A. Numerical Study of the Magnetic Field Effect on Ferromagnetic Fluid Flow and Heat Transfer in a Square Porous Cavity. [Extracted from the article]

This paper presents the development and assessment of a two-stage thermoacoustic electricity generator that aims to mimic the conversion of waste heat from the internal combustion engine exhaust gases into useful electricity. The one wavelength configuration consists of two identical stages which allow coupling a linear alternator in a "push-pull" mode because of the 180° out of phase acoustic excitation on two sides of the piston. This type of coupling is a possible solution for the low acoustic impedance of looped-tube traveling-wave thermoacoustic engines. The experimental set-up is 16.1 m long and runs at 54.7 Hz. The working medium is helium at maximum pressure of 28 bar. In practice, the maximum generated electric power was 73.3 W at 5.64% thermal-to-electric efficiency. The working parameters, namely load resistance, mean pressure and heating power, were investigated. System debugging illustrates the effect of local acoustic impedance of the regenerator on the start-up process of the thermoacoustic engine. The additional modelling showed that the feedback loop length can be reduced by using a combination of acoustic inertance and compliance components. [ABSTRACT FROM AUTHOR]

Thermoacoustic engines convert heat into acoustic power without moving parts. Coupling them with electrodynamic transducers – directly converting acoustic power into electricity – enables building simple electricity generators, where the only moving part is the piston of the linear alternator. Integration of such devices with biomass-driven cookstoves widely used in remote and rural areas of developing countries can lead to inexpensive electrical power systems, essentially powered by waste heat from daily cooking activities. In this paper the modelling, design, construction and testing of a laboratory demonstrator of such generator is outlined. A travelling-wave thermoacoustic engine with a looped-tube configuration is modelled using DeltaEC tool and constructed to convert heat input into acoustic power. Flue gas from a propane burner is used as a heat source for demonstration purposes. An audio loudspeaker is connected to a side branch and adopted as the electro-dynamic transducer for electricity production. Atmospheric air is employed as the working fluid to keep the cost of future systems low. The demonstrator produced just under 20 W of electricity with thermal-to-acoustic and thermal-to-electric efficiencies of around 3.5% and 1.9%, respectively, which demonstrates the micro-power source concept. Experimental results and their numerical validation are outlined and analysed. [ABSTRACT FROM AUTHOR]

In a standing wave thermoacoustic refrigerator, heat transport from the “cold” to the “ambient” end of a stack is achieved by means of an oscillatory motion of a compressible fluid undergoing cyclic compression and expansion. However, the stacks can be both costly and impractical to fabricate due to material and assembly costs, which limits the cost benefits of thermoacoustic systems. Some of these problems could be solved by the application of stacks that have irregular geometries, for instance stacks made of “random” materials from metal machining (swarf), which are often considered as waste. In this paper, the thermal performance of stacks made of a few selected materials is determined by carrying out experiments in a standing wave thermoacoustic refrigerator. The reported results will be beneficial for developing low-cost thermoacoustic refrigerators or heat pumps for both domestic and commercial applications. [ABSTRACT FROM AUTHOR]

Heat exchangers play a key role in the overall performance of thermoacoustic devices. Due to the complex nature of oscillatory flows, the underlying mechanism of heat transfer in oscillatory flows is still not fully understood. This work investigates the effect of fin length and fin spacing on the thermal performance of finned-tube heat exchangers. The heat transfer rate between two finned-tube heat exchangers arranged side-by-side in an oscillatory flow was measured over a range of testing conditions. The results are presented in terms of heat transfer coefficient and heat transfer effectiveness. Comparisons are made between experimental results of this work and a number of models, such as the Time-Average Steady-Flow Equivalent (TASFE) model, the Root Mean Square Reynolds Number (RMS-Re) model and the boundary layer conduction model, as well as several empirical correlations in literature. A new empirical correlation is proposed to be used for the prediction of thermal performance for finned-tube heat exchangers in oscillatory flows. The uncertainties associated with the measurement of heat flux are estimated. [ABSTRACT FROM AUTHOR]

Heat exchangers are important components of thermoacoustic devices. In oscillatory flow conditions, the flow and temperature fields around the heat exchangers can be quite complex, and may significantly affect heat transfer behaviour. As a result, one cannot directly apply the heat transfer correlations for steady flows to the design of heat exchangers for oscillatory flows. The fundamental knowledge of heat transfer in oscillatory flows, however, is still not well-established. The aim of the current work is to develop experimental apparatus and measurement techniques for the study of heat transfer in oscillatory flows. The heat transferred between two heat exchangers forming a couple was measured over a range of testing conditions. Three couples of finned-tube heat exchangers with different fin spacing were selected for the experiment. The main parameters considered were fin spacing, fin length, thermal penetration depth and gas displacement amplitude. Their effects on the heat exchanger performance were studied. The results were summarised and analysed in terms of heat transfer rate and dimensionless heat transfer coefficient: Colburn-j factor. In order to obtain the gas side heat transfer coefficient in oscillatory flows, the water side heat transfer coefficient is required. Thus, an experimental apparatus for unidirectional steady test was also developed and a calculation method to evaluate the heat transfer coefficient was demonstrated. The uncertainties associated with the measurement of heat transfer rate were also considered. [ABSTRACT FROM AUTHOR]

Understanding of heat transfer processes between a solid boundary and an oscillatory gas flow is important for the design of internal components such as heat exchangers, regenerators and thermal buffer tubes in thermoacoustic and Stirling thermodynamic machines where the flow oscillations are part of the power production or transfer processes. The heat transfer between the flow and an arrangement of hot and cold plates forming a parallel-plate channel is studied experimentally and numerically. Here, the particular focus is on the processes occurring within the thermal and viscous boundary layers. The measured phase-dependent temperature fields combined with the velocity fields are studied in detail. Near wall temperature minima and maxima of the cross sectional temperature profiles are observed when the gas moves from cold to hot or from hot to cold parts of the channel. They are referred to as "temperature undershoot" and "overshoot", respectively. The existence of these temperature minima and maxima causes large local temperature gradients in the direction normal to the wall, which result in large heat diffusion between gas layers in the direction normal to the wall. It is observed that the flow history has a strong impact on the temperature fields. This invalidates the so-called "Iguchi hypothesis", based on which the heat transfer data for steady flows is being applied to oscillatory flow conditions. General guidelines for the design of heat exchangers used in thermoacoustic devices are discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the feasibility of using commercially available loudspeakers as low-cost linear alternators for thermoacoustic applications, to convert acoustic power to electricity. The design of a purpose built experimental apparatus, in which a high intensity acoustic wave is induced by using a high power woofer, is described. The rig is used to excite loudspeakers (referred here as “alternators”) under test, while a pair of microphones and a laser displacement sensor are used to enable acoustic power measurements. The paper presents a case study in which characteristics of acoustic-to-electric energy conversion of a candidate loudspeaker (alternator) – selected from the viewpoint of general performance, as well as parameters such as: high force factor, low electrical resistance and low mechanical loss – are measured. The measurements of acoustic power absorbed by the alternator and the electric power extracted from it by the load resistor, which allow estimating acoustic-to-electric efficiencies, are presented. The alternator has been tested at different operating frequencies, cone displacements and load resistance values. The measurement results are discussed and compared in detail with the calculations based on the linear acoustics model. [Copyright &y& Elsevier]

Abstract: This paper investigates vortex shedding processes occurring at the end of a stack of parallel plates, due to an oscillating flow induced by an acoustic standing wave. Here the hot-wire anemometry measurement technique is applied to detect the velocity fluctuations due to vortex shedding near the end of the stack. The hot-wire fast time response enables detailed frequency spectra of the velocity signal to be obtained, which can be used for identifying the dominant frequencies associated with vortex shedding, and thus allow calculation of the corresponding Strouhal numbers. By varying the stack configuration (the plate thickness and spacing) and the acoustic excitation level (the so-called drive ratio), the impact of the stack blockage ratio and the Reynolds number on the Strouhal number has been studied in detail. Furthermore, in the range of Reynolds numbers between 200 and 5000 a correlation between the Strouhal number and Reynolds number has been obtained and compared with analogous relationships in the steady flow. Particle Image Velocimetry (PIV) is also used to visualize the vortex shedding processes within an acoustic cycle, phase-by-phase, in particular during the part of the cycle when the fluid flows out of the stack—selected cases are shown for comparisons with hot-wire measurements. [Copyright &y& Elsevier]

Abstract: This paper aims at evaluating three selected low-cost porous materials from the point of view of their suitability as regenerator materials in the design of thermoacoustic travelling-wave engines. The materials tested include: a cellular ceramic substrate with regular square channels; steel “scourers”; and stainless steel “wool”. Comparisons are made against a widely used regenerator material: stainless steel woven wire mesh screen. For meaningful comparisons, the materials are selected to have similar hydraulic radii. One set of regenerators was designed around the hydraulic radius of 200μm. This included the ceramic substrate, steel “scourers”, stainless steel “wool” and stacked wire screens (as a reference). This set was complemented by steel “scourers” and stacked wire screens (as a reference) with hydraulic radii of 120μm. Therefore six regenerators were produced to carry out the testing. Initial tests were made in a steady air flow to estimate their relative pressure drop due to viscous dissipation. Subsequently, they were installed in a looped-tube travelling-wave thermoacoustic engine to test their relative performance. Testing included the onset temperature difference, the maximum pressure amplitude generated and the acoustic power output as a function of mean pressure between 0 and 10bar above atmospheric. It appears that the performance of regenerators made out of “scourers” and steel “wool” is much worse than their mesh-screen counterparts of the same hydraulic radius. However cellular ceramics may offer an alternative to traditional regenerator materials to reduce the overall system costs. Detailed discussions are provided. [Copyright &y& Elsevier]

Abstract: This paper investigates vortex shedding phenomena occurring at the end of the parallel-plate thermoacoustic stacks, in oscillatory flow conditions induced by an acoustic standing wave. Phase-locked Particle Image Velocimetry (PIV) measurement technique is used to identify a range of vortex shedding flow patterns within an acoustic cycle, in particular during the “ejection” stage, when the fluid flows out of the stack. As an extension of the earlier work [X. Mao, Z. Yu, A.J. Jaworski, D. Marx, PIV studies of coherent structures generated at the end of a stack of parallel plates in a standing wave acoustic field, Experiments in Fluids 45 (5) (2008) 833–846] this paper reports experimental results obtained for a much wider range of parameters in order to identify detailed relationships between vortex flow patterns and experimental conditions. In addition to the flow patterns observed previously, current results show several new flow phenomena related to the evolution of vortices shed in the ejection stage. This work also attempts to classify systematically the types of the vortex wake patterns using three dimensionless parameters: the Reynolds number (Re), Keulegan–Carpenter number (KC) and Womersley number (Wo). In the (Re, KC) plane (Re is up to 5000, KC is up to 250), four flow pattern regions are defined according to the characteristics of nine types of vortex wake “transitions”. It is proposed that Wo plays an important role in determining the detailed classification of such transitions within each flow pattern region. Furthermore, the physical mechanisms behind different types of wake patterns and their relationship with the dimensionless parameters investigated have been discussed. [Copyright &y& Elsevier]

Abstract: This work aims to develop reliable laser-based measurement techniques to enable fundamental heat transfer and fluid flow studies in thermoacoustic systems. The challenge is to better understand the modes of energy transfer between the key components, such as stacks (or regenerators) and the hot and cold heat exchangers (located on two sides of the stack/regenerator structure), under the oscillatory flow conditions imposed by the acoustic field. The measurement methodologies adopted in this work include combined two-dimensional temperature and velocity field measurements using Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV), respectively. These are investigated around the fins of a pair of mock-up heat exchangers placed side by side in a quarter-wavelength standing-wave acoustic resonator, to mimic the working conditions of a thermoacoustic system. The fins are kept at constant temperatures by means of resistive heating and water cooling, respectively. The velocity and temperature field distributions for 20 phases in the acoustic cycle have been obtained. The impact of the inertial, viscous and thermal effects on the time-dependent local temperature and velocity distributions is discussed. Mutual interaction between both fields is also shown. Future work towards obtaining useful heat transfer correlations in oscillatory conditions is outlined. [Copyright &y& Elsevier]

The development of urban strategies for the reduction of environmental impacts and decarbonization requires ongoing monitoring from the local scale and further deployment of actions to improve transport demand (user characteristics and modal choice) and supply (infrastructure and services). The analysis of pollution sources and the evaluation of possible scenarios are preliminary to the mitigation of impacts. In particular, the study of geometrical and functional characteristics of infrastructures through micro-simulation allows understanding of which schemes can support the reduction of emissions and guarantee high levels of service (LOS), reducing the problem of vehicular congestion in urban areas. The present work focuses on the small-scale analysis of vehicular traffic emissions at a multi-lane roundabout road intersection and the comparison of geometric schemes (current and design) and use with a turbo roundabout scheme as traffic volumes changes. These volumes have plummeted due to the current COVID-19 pandemic. The results show that the geometric-functional modification of the roundabout intersection from a multi-lane to a turbo-roundabout intersection allows a reduction of up to 30% of the emissions considering the current composition of the traffic fleet in the city of Rzeszow in Poland. The proposed comparative analysis methodology can contribute to the drafting of sustainable urban mobility plans (SUMPs) proposing a set of investments for new road works and considering a number of scenarios with interventions that can be implemented in the medium and long term that can provide the incentive to reduce road congestion and vehicular emissions. [ABSTRACT FROM AUTHOR]

Abstract: Thermoacoustic refrigerators work with high amplitude sound waves, which are often created using an acoustic source coupled to a resonator. This coupling can be calculated analytically using linear acoustic equations and a linear model of the loudspeaker. This paper makes a comparison between such a coupling and measurements obtained in a large-scale thermoacoustic resonator constructed at the University of Manchester. The resonator was driven from low to large pressure amplitudes, with drive ratios up to 10%. It is shown that a good agreement is obtained for small amplitudes and this progressively worsens as the amplitude is increased. In the absence of wave harmonics and loudspeaker nonlinearities, the increasing discrepancy is attributed to the presence of minor losses. [Copyright &y& Elsevier]

• Lubricity tests using the HFRR method for the 1-butanol–diesel fuel blends were presented. • Microscopic photographs of the test ball wear scars were presented. • The lubricity tests were conducted at various fuel temperatures. • The results of the lubricity tests were referenced to the standard requirements. It has been shown that 1-butanol cannot be used as a self-contained fuel in typical diesel engines, mainly due to its low propensity for self-ignition and its low lubricity; thus, increasing attention is being paid to 1-butanol–diesel fuel blends (1-BDFs). In turn, considering the durability of fuel injectors, it is important to test the lubrication of fuels at increased temperatures, while varying the conditions under which the lubricating layer is formed. The article evaluates the lubricity of standard diesel fuel and 1-BDFs at temperatures of 30, 60, 90 and 120 °C. Tests were carried out for 1-BDFs at volume fraction of 1-butanol of 5, 15, 25%, using the high-frequency reciprocating rig (HFRR) method. For individual fuel samples, microscopic photos of the wear scar on the test balls are presented, along with the marked areas, which were taken into account when measuring the diameters of the wear scars. The wear scar diameter (WSD) values were adopted as the basic criterion for assessing lubricating properties. The results showed that larger fractions of 1-butanol in a blend contributed to improved lubricity at the highest sample temperature analysed, and the largest differences in lubricating properties at changes in the sample temperature were observed for neat diesel fuel (NDF) and for 1-BDF with a 5% 1-butanol volume fraction. Test results at 60 °C also showed that 1-BDFs with a 1-butanol volume fraction up to 25% meets lubricity requirements specified in EN 590 and ASTM D975. [ABSTRACT FROM AUTHOR]

Urban agglomerations close to road infrastructure are particularly exposed to harmful exhaust emissions from motor vehicles and this problem is exacerbated at road intersections. Roundabouts are one of the most popular intersection designs in recent years, making traffic flow smoother and safer, but especially at peak times they are subject to numerous stop-and-go operations by vehicles, which increase the dispersion of emissions with high particulate matter rates. The study focused on a specific area of the city of Rzeszow in Poland. This country is characterized by the current composition of vehicle fleets connected to combustion engine vehicles. The measurement of the concentration of particulate matter (PM2.5 and PM10) by means of a preliminary survey campaign in the vicinity of the intersection made it possible to assess the impact of vehicle traffic on the dispersion of pollutants in the air. The present report presents some strategies to be implemented in the examined area considering a comparison of current and project scenarios characterized both by a modification of the road geometry (through the introduction of a turbo roundabout) and the composition of the vehicular flow with the forthcoming diffusion of electric vehicles. The study presents an exemplified methodology for comparing scenarios aimed at optimizing strategic choices for the local administration and also shows the benefits of an increased electric fleet. By processing the data with specific tools and comparing the scenarios, it was found that a conversion of 25% of the motor vehicles to electric vehicles in the current fleet has reduced the concentration of PM10 by about 30% along the ring road, has led to a significant reduction in the length of particulate concentration of the motorway, and it has also led to a significant reduction in the length of the particulate concentration for the access roads to the intersection. [ABSTRACT FROM AUTHOR]