Publications
243 results found
Merla Y, Wu B, Yufit V, et al., 2018, An easy-to-parameterise physics-informed battery model and its application towards lithium-ion battery cell design, diagnosis, and degradation, Journal of Power Sources, Vol: 384, Pages: 66-79, ISSN: 0378-7753
Accurate diagnosis of lithium ion battery state-of-health (SOH) is of significant value for many applications, to improve performance, extend life and increase safety. However, in-situ or in-operando diagnosis of SOH often requires robust models. There are many models available however these often require expensive-to-measure ex-situ parameters and/or contain unmeasurable parameters that were fitted/assumed. In this work, we have developed a new empirically parameterised physics-informed equivalent circuit model. Its modular construction and low-cost parametrisation requirements allow end users to parameterise cells quickly and easily. The model is accurate to 19.6 mV for dynamic loads without any global fitting/optimisation, only that of the individual elements. The consequences of various degradation mechanisms are simulated, and the impact of a degraded cell on pack performance is explored, validated by comparison with experiment. Results show that an aged cell in a parallel pack does not have a noticeable effect on the available capacity of other cells in the pack. The model shows that cells perform better when electrodes are more porous towards the separator and have a uniform particle size distribution, validated by comparison with published data. The model is provided with this publication for readers to use.
Palenschat T, Mueller M, Rajoo S, et al., 2018, Steady-State Experimental and Meanline Study of an Asymmetric Twin-Scroll Turbine at Full and Unequal and Partial Admission Conditions, WCX World Congress Experience
© 2018 SAE International. All Rights Reserved. The use of twin-scroll turbocharger turbines has gained popularity in recent years. The main reason is its capability of isolating and preserving pulsating exhaust flow from engine cylinders of adjacent firing order, hence enabling more efficient pulse turbocharging. Asymmetrical twin-scroll turbines have been used to realize high pressure exhaust gas recirculation (EGR) using only one scroll while designing the other scroll for optimal scavenging. This research is based on a production asymmetrical turbocharger turbine designed for a heavy duty truck engine of Daimler AG. Even though there are number of studies on symmetrical twin entry scroll performance, a comprehensive modeling tool for asymmetrical twin-scroll turbines is yet to be found. This is particularly true for a meanline model, which is often used during the turbine preliminary design stage. This study presents the development of a generalized meanline model for a twin-scroll turbine, which can be used in the early design stages, concentrating on asymmetrical scrolls. The improvements from the previous meanline model, i.e., the inlet duct and interspace model, in order to enable asymmetrical scroll prediction is described. The latter is based on the popular theory of turbomachinery wakes mixing, adopted from literature. The model is validated against experimental cold gas stand data under equal and unequal-admission conditions. Comparison between the model and experiments indicates the importance of the inlet duct and interspace model between the scrolls in obtaining satisfactory predictions across different admission conditions, due to the non-symmetrical features between the scrolls.
Padzillah MH, Rajoo S, Martinez-Botas RF, 2018, A Detailed Comparison on the Influence of Flow Unsteadiness Between the Vaned and Vaneless Mixed-Flow Turbocharger Turbine, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, Vol: 140, ISSN: 0742-4795
Palenschat T, Cortell JF, Newton P, et al., 2018, Numerical study of the quasi-steady approach applied to an asymmetric twin-scroll volute turbocharger turbine for a heavy duty diesel engine under realistic boundary conditions, Pages: 443-458
This paper presents a numerical study on the validity of the quasi-steady approach with respect to an asymmetric twin-scroll turbocharger heavy duty diesel engine under realistic boundary conditions. The motivation of using the quasi-steady approach in this context is the possibility to speed up the evaluation process in early design steps while already taking into account boundary conditions more suitable than equal admission. As transient 3D CFD is computationally very expensive, the quasi-steady approach is used to reduce computational time drastically. However, the validity of the quasi-steady approach is widely discussed and does not hold for the volute. Furthermore, it has never been evaluated for an asymmetric twin-scroll turbine and unequal admission. A 3D CFD model is built in this paper using the Ansys tool chain. The computational model is validated against experiments carried out at the cold-gas turbocharger test facility of Imperial College London. The boundary conditions for the analysis are selected based upon the real load conditions of a Mercedes-Benz lorry on a given route and take into account equal and unequal admission between the two scrolls. A set of steady computations is performed using the unequal and equal boundary admission conditions of the discretised pulsations. The cycle efficiency is computed in order to find a metric to compare the steady and unsteady approaches. Following, unsteady computations are performed with unsteady boundary conditions to capture the real pulsating boundary conditions resulting from the engine. Steady as well as unsteady computations are compared in order to evaluate the validity of the quasi-steady approach. Finally, the same comparison is also shown based on experimental data.
Liu H, Romagnoli A, Ismail MI, et al., 2018, Multi-injection turbine housing: A novel concept for performance improvement in radial turbines, Pages: 291-308
Secondary flow injection is a way which allows for the efficiency of a turbomachine to be increased further, after blade design optimizations have already been performed. In this paper, a novel method for improving turbine performance using secondary flow injection through an injection slot over the turbine shroud is investigated. Numerical simulations were conducted on a mixed flow turbocharger turbine to test the effectiveness of secondary flow injection. An optimization using Genetic Algorithm was performed at peak efficiency at 50% turbine design speed to determine the injection set up which gives the highest turbine efficiency. The final optimized point gave an increase in efficiency of 2.6 percentage points compared to the baseline turbine. Flow analysis shows that injection partially blocks the flow passage near the blade tip, forcing turbine passage flow to migrate towards the hub. This apparently weakens the hub suction side separation vortex and reduces entropy generation from the vortex. However, entropy generation near the blade tip is increased, and the tip leakage vortex structure has become a counter-rotating vortex pair. Overall, injection reduces the entropy generation in the turbine by 10.7% at the optimized point. The optimized set of injection parameters was then used across 4 different speed lines to generate the turbine performance maps. The turbine maps show an overall increase in turbine efficiency, but a slight decrease in mass flow parameter and increased back pressure. The turbine maps are then used in an engine simulation to predict engine performance with and without injection. Engine performance at full load and part load conditions are simulated at 4 different engine speeds. The engine simulation results show that injection increases the turbocharger boost pressure. As a result, the brake specific fuel consumption (BSFC) of the engine is reduced throughout the engine speeds tested. The greatest reduction in BSFC is at 1050 rpm, where f
Barrera-Medrano ME, Martinez-Botas R, Tomita I, et al., 2018, On the effect of engine pulsations on the performance of a turbocharger centrifugal compressor, Pages: 101-125
In an IC engine, the centrifugal compressor is placed upstream of the inlet manifold and therefore, it is exposed an unsteady flow regime caused by the inlet valves of the cylinder arrangement. This valve motion sets a pulsating state at the compressor exit, having greater influence when the operation is near the surge margin of the compressor; it may therefore limit further the engine minimum flow rate. This paper presents the experimental results of the evaluation of the surge dynamics on a compressor with induced downstream pulsating flow. Different pulsation levels are achieved by the variation of four different parameters on the induced pulse: pulse frequency, amplitude, the presence of a storage volume (plenum) and pulse location. Each of the four pulse parameters was evaluated independently in order to assess its effect on the compressor stability limit. The main effect on the surge margin of the compressor has been found to be due to the presence of a volume in the system for all cases, whether steady or unsteady/pulsating condition, and at all frequencies. It was found that the magnitude of the pulse frequency determines the hysteresis behaviour of the system that leads to a phase difference between the convected terms (volume flow) and the acoustic dominated terms (pressure), and therefore this affects the onset of flow instability, surge, in the compression system under study. Based on these results, the compressor performance, and particularly its stability limit, is strongly influenced by the downstream conditions of the system where the compressor is placed. The nature of downstream conditions influences the compressor characteristic curve, and in some cases the compressor "feels" like another machine just by means of varying the downstream state at the compressor exit. The presence of a pulsating state at the compressor outlet increases the inertia of the compression system and thus it affects the compressor transient response. The outlet pu
Xue YX, Yang MY, Deng KY, et al., 2018, Performance and flow analysis of a mixed flow turbine with twin-entry nozzled volute, Pages: 425-441
This paper studies the performance and detailed flow field of a nozzled turbine with twin-entry volute (developed by Imperial College London) at different admission conditions via experimentally validated numerical method. Two partial admissions are analysed which are the admission near hub side (referring as HI) and near shroud side (referring as SI), respectively. Results manifest that the efficiency of the case of HI is moderately higher than that of SI although their flow capacity is the same. The performance of unequal admission is bounded by that of the full admission and the partial admission. The breakdown of the flow loss in turbine components shows that significant discrepancies exist among different admissions. The flow loss in the volute Is nearly the same for two cases. However, the loss is moderately higher in the nozzle for SI at all turbine loadings, but notably lower in the rotor for this case when compared with its counterpart. This is caused by the load-dividing between these two cases: the more expansion is divided to the rotor for HI, while more expansion is divided to the nozzle for SI. Flow analysis shows that higher entropy is generated in the nozzle for SI due to strong flow separation on the suction surfaces near the leading edge because of large incidence angle. On the other hand, the flow aligns well with the vane angle for HI near the hub, but a large size vortex rolls up near the shroud side which corresponds to the high entropy generation. Downstream the nozzle, a 'tornado' vortex is developed in the rotor passages for the case HI, which leads to higher entropy generation and hence higher flow loss in rotor. This studyunveils the flow mechanism of performance distinctions at different admission conditions for the turbine with twin-entry nozzled volute, which may enlighten performance improvement of the turbine and hence the internal combustion engine.
Abel M, Newton P, Martinez-Botas RF, et al., 2018, 3D COMPUTATIONAL ANALYSIS OF A COMPRESSOR FOR HEAVY DUTY TRUCK ENGINE TURBOCHARGERS, ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
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- Citations: 1
Ardani MI, Patel Y, Siddiq A, et al., 2017, Combined experimental and numerical evaluation of the differences between convective and conductive thermal control on the performance of a lithium ion cell, Energy, Vol: 144, Pages: 81-97, ISSN: 0360-5442
Testing of lithium ion batteries is necessary in order to understand their performance, to parameterise and furthermore validate models to predict their behaviour. Tests of this nature are normally conducted in thermal/climate chambers which use forced air convection to distribute heat. However, as they control air temperature, and cannot easily adapt to the changing rate of heat generated within a cell, it is very difficult to maintain constant cell temperatures. This paper describes a novel conductive thermal management system which maintains cell temperature reliably whilst also minimising thermal gradients. We show the thermal gradient effect towards cell performance is pronounced below operating temperature of 25 °C at 2-C discharge under forced air convection. The predicted internal cell temperature can be up to 4 °C hotter than the surface temperature at 5 °C ambient condition and eventually causes layers to be discharge at different current rates. The new conductive method reduces external temperature deviations of the cell to within 1.5 °C, providing much more reliable data for parameterising a thermally discretised model. This method demonstrates the errors in estimating physiochemical paramet ers; notably diffusion coefficients, can be up to four times smaller as compared to parameterisation based on convective test data.
Abas MA, Salim WSW, Ismail MI, et al., 2017, Fuel consumption evaluation of SI engine using start-stop technology, JOURNAL OF MECHANICAL ENGINEERING AND SCIENCES, Vol: 11, Pages: 2967-2978, ISSN: 2289-4659
Salim WSIW, Mahdi AAM, Ismail MI, et al., 2017, Benefits of spark-ignition engine fuel-saving technologies under transient part load operations, JOURNAL OF MECHANICAL ENGINEERING AND SCIENCES, Vol: 11, Pages: 3027-3037, ISSN: 2289-4659
Tan FX, Chiong MS, Rajoo S, et al., 2017, Analytical and Experimental Study of Micro Gas Turbine as Range Extender for Electric Vehicles in Asian Cities, Joint Conference of the World Engineers Summit / Applied Energy Symposium and Forum - Low Carbon Cities and Urban Energy (WES-CUE), Publisher: ELSEVIER SCIENCE BV, Pages: 53-60, ISSN: 1876-6102
Romagnoli A, Manivannan A, Rajoo S, et al., 2017, A review of heat transfer in turbochargers, RENEWABLE & SUSTAINABLE ENERGY REVIEWS, Vol: 79, Pages: 1442-1460, ISSN: 1364-0321
Padzillah MH, Yang M, Rajoo S, et al., 2017, Experimental Work on the Characterization of the Hysteresis Behavior of the Vaned and Vaneless Mixed-Flow Turbocharger Turbine, JOURNAL OF ENERGY ENGINEERING, Vol: 143, ISSN: 0733-9402
Andwari AM, Pesiridis A, Rajoo S, et al., 2017, A review of Battery Electric Vehicle technology and readiness levels, RENEWABLE & SUSTAINABLE ENERGY REVIEWS, Vol: 78, Pages: 414-430, ISSN: 1364-0321
Ding Z, Zhuge W, Zhang Y, et al., 2017, A one-dimensional unsteady performance model for turbocharger turbines, ENERGY, Vol: 132, Pages: 341-355, ISSN: 0360-5442
Abas MA, Zainal Abidin SF, Rajoo S, et al., 2017, Evaluation between Engine Stop/Start and Cylinder Deactivation Technologies under Southeast Asia Urban Driving Condition, WCX™ 17: SAE World Congress Experience
Copyright © 2017 SAE International. Engine stop/start and cylinder deactivation are increasingly in use to improve fuel consumption of internal combustion engine in passenger cars. The stop/start technology switches off the engine to whenever the vehicle is at a stand-still, typically in a highly-congested area of an urban driving. The inherent issue with the implementation of stop/start technology in Southeast Asia, with tropical climate such as Malaysia, is the constant demand for the air-conditioning system. This inevitably reduces the duration of engine switch-off when the vehicle at stop and consequently nullifying the benefit of the stop/start system. On the other hand, cylinder deactivation technology improves the fuel consumption at certain conditions during low to medium vehicle speeds, when the engine is at part load operation only. This study evaluates the fuel economy benefit between the stop/start and cylinder deactivation technologies for the actual Kuala Lumpur urban driving conditions in Malaysia. Malaysia is chosen as a case study to represent a typical urban environment in Southeast Asia. A 1.6 L PFI 4-cylinder engine is modeled in one-dimensional gas dynamics software to predict the fuel consumption. A transient driving profile obtained from the actual road test over the Kuala Lumpur route is simulated and the fuel consumption is compared with New European Drive Cycle (NEDC). The results provide useful insight and enable manufacturers to assess and consider which of the two technologies offers more impact on the fuel economy and the challenges under urban driving in Southeast Asia conditions.
Romagnoli A, Vorraro G, Rajoo S, et al., 2017, Characterization of a supercharger as boosting & turbo-expansion device in sequential multi-stage systems, Energy Conversion and Management, Vol: 136, Pages: 127-141, ISSN: 0196-8904
This paper proposes a detailed performance analysis and experimental characterization of a high-pressure supercharger in a multi-stage boosting system (turbo-super arrangement). Infact, besides the technical challenges associated with achieving adequate tuning, interoperability and driveability of multi-stage boosting systems, another challenge lies in their performance prediction during engine design. Indeed, performance maps of single boosting systems are usually provided by manufacturers and used as look-up tables in 1-D engine models. Tests are usually conducted in a standalone mode, with no information provided on the behaviour and performance of the combination of more than one boosting device. The supercharger was tested with varying inlet pressures and temperatures matching on-engine operating conditions and the results were then used to assess the effectiveness of 1-D engine models performance prediction when dealing with multi-stage boosting systems. An assessment on heat transfer in superchargers was also carried out together with the analysis on the nature of non-dimensional performance maps when dealing with a pressurized inlet. Finally, the analysis also looked into the opportunity to use the superchargers as expanders (‘expansion mode’) in order to cool the air charge entering the engine. The results showed that there is discrepancy between the efficiency values computed by 1-D engine models and those obtained experimentally under pressurized/heated inlet air conditions; the correction of the efficiency maps for heat transfer plays a significant role in the final measured efficiency and the correction of the maps for varying inlet temperatures must be carried out in order to avoid incurring in apparent efficiencies greater than unity. The experiments on the supercharger in ‘expansion mode’ showed that low isentropic efficiencies can be achieved; despite this, 1-D engine simulations showed that it is possible to achieve savings
Jimenez-Arreola M, Dal Magro F, Romagnoli A, et al., 2017, ANALYTICAL INVESTIGATION OF A THERMAL-SUPERCHARGED INTERNAL COMBUSTION ENGINE COMPOUNDED WITH ORGANIC RANKINE CYCLE FOR WASTE HEAT RECOVERY, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
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- Citations: 3
Palenschat T, Newton P, Martinez-Botas RF, et al., 2017, 3-D COMPUTATIONAL LOSS ANALYSIS OF AN ASYMMETRIC VOLUTE TWIN-SCROLL TURBOCHARGER, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
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- Citations: 11
Liu H, Romagnoli A, Martinez-Botas R, et al., 2017, MULTI-INJECTION TURBINE HOUSING: A NOVEL CONCEPT FOR TIP-LEAKAGE IMPROVEMENT IN RADIAL TURBINES, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
Ding Z, Weilin Z, Zhang Y, et al., 2017, INVESTIGATION ON PULSATING FLOW EFFECT OF A TURBOCHARGER TURBINE, ASME Fluids Engineering Division Summer Meeting, Publisher: AMER SOC MECHANICAL ENGINEERS
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- Citations: 2
Hohenberg KG, Newton PJ, Martinez-Botas RF, et al., 2017, DEVELOPMENT AND EXPERIMENTAL VALIDATION OF A LOW ORDER TURBINE MODEL UNDER HIGHLY PULSATING FLOW, ASME Turbine Technical Conference and Exposition (Turbo Expo), Publisher: AMER SOC MECHANICAL ENGINEERS
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- Citations: 3
Barrera-Medrano ME, Newton P, Martinez-Botas R, et al., 2016, Effect of Exit Pressure Pulsation on the Performance and Stability Limit of a Turbocharger Centrifugal Compressor, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, Vol: 139, ISSN: 0742-4795
Chiong MS, Rajoo S, Romagnoli A, et al., 2016, One-dimensional pulse-flow modeling of a twin-scroll turbine, Energy, Vol: 115, Pages: 1291-1304, ISSN: 0360-5442
This paper presents a revised one-dimensional (1D) pulse flow modeling of twin-scroll turbocharger turbine under pulse flow operating conditions. The proposed methodology in this paper provides further consideration for the turbine partial admission performance during model characterization. This gives rise to significant improvement on the model pulse flow prediction quality compared to the previous model. The results show that a twin-scroll turbine is not operating at full admission throughout the in-phase pulse flow conditions. Instead, they are operating at unequal admission state due to disparity in the magnitude of turbine inlet flow. On the other hand, during out-of-phase pulse flow, a twin-scroll turbine is working at partial admission state for majority of the pulse cycle. An amended mathematical correlation in calculating the twin-scroll turbine partial admission characteristics is also presented in the paper. The impact of its accuracy on the pulse flow model prediction is explored.
Merla Y, Wu B, Yufit V, et al., 2016, Extending battery life: a low-cost practical diagnostic technique for lithium-ion batteries, Journal of Power Sources, Vol: 331, Pages: 224-231, ISSN: 0378-7753
Modern applications of lithium-ion batteries such as smartphones, hybrid & electric vehicles and grid scale electricity storage demand long lifetime and high performance which typically makes them the limiting factor in a system. Understanding the state-of-health during operation is important in order to optimise for long term durability and performance. However, this requires accurate in-operando diagnostic techniques that are cost effective and practical. We present a novel diagnosis method based upon differential thermal voltammetry demonstrated on a battery pack made from commercial lithium-ion cells where one cell was deliberately aged prior to experiment. The cells were in parallel whilst being thermally managed with forced air convection. We show for the first time, a diagnosis method capable of quantitatively determining the state-of-health of four cells simultaneously by only using temperature and voltage readings for both charge and discharge. Measurements are achieved using low-cost thermocouples and a single voltage measurement at a frequency of 1 Hz, demonstrating the feasibility of implementing this approach on real world battery management systems. The technique could be particularly useful under charge when constant current or constant power is common, this therefore should be of significant interest to all lithium-ion battery users.
von Srbik M-T, Marinescu M, Martinez-Botas RF, et al., 2016, A physically meaningful equivalent circuit network model of a lithium-ion battery accounting for local electrochemical and thermal behaviour, variable double layer capacitance and degradation, Journal of Power Sources, Vol: 325, Pages: 171-184, ISSN: 0378-7753
A novel electrical circuit analogy is proposed modellingelectrochemical systems under realistic automotive operation conditions. The model is developed for a lithium ion battery and is based on a pseudo 2D electrochemical model. Although cast in the framework familiar to application engineers, the model is essentially an electrochemical battery model: all variables have a direct physical interpretation and there is direct access to all states of the cell via the model variables (concentrations, potentials) for monitoring and control systems design. This is the first Equivalent Circuit Network-type model that tracks directly the evolution of species inside the cell. It accounts for complex electrochemical phenomena that are usually omitted in online battery performance predictors such as variable double layer capacitance, the full current-overpotential relation and overpotentials due to mass transport limitations. The coupled electrochemical and thermal model accounts for capacity fade via a loss in active species and for power fade via an increase in resistive solid electrolyte passivation layers at both electrodes. The model's capability to simulate cell behaviour under dynamic events is validated against test procedures, such as standard battery testing load cycles for current rates up to 20 C, as well as realistic automotive drive cycle loads.
Bin Mamat AMI, Martinez-Botas RF, Rajoo S, et al., 2016, Design methodology of a low pressure turbine for waste heat recovery via electric turbocompounding, Applied Thermal Engineering, Vol: 107, Pages: 1166-1182, ISSN: 1873-5606
This paper presents a design methodology of a high performance Low Pressure Turbine (LPT) for turbocompounding applications to be used in a 1.0 L “cost-effective, ultra-efficient heavily downsized gasoline engine for a small and large segment passenger car”. Under this assumption, the LPT was designed to recover the latent energy of discharged exhaust gases at low pressure ratios (1.05–1.3) and to drive a small electric generator with a maximum power output of 1.0 kW. The design speed was fixed at 50,000 rpm with a pressure ratio, PR of 1.08. Commercially available turbines are not suitable for this purpose due to the very low efficiencies experienced when operating in these pressure ratio ranges. By fixing all the LPT requirements, the turbine loss model was combined with the geometrical model to calculate preliminary LPT geometry. The LPT features a mixed-flow turbine with a cone angle of 40° and 9 blades, with an inlet blade angle at radius mean square of +20°. The exit-to-inlet area ratio value is approximately 0.372 which is outside of the conventional range indicating the novelty of the approach. A single passage Computational Fluid Dynamics (CFD) model was applied to optimize the preliminary LPT design by changing the inlet absolute angle. The investigation found the optimal inlet absolute angle was 77°. Turbine off-design performance was then predicted from single passage CFD model. A rapid prototype of the LPT was manufactured and tested in Imperial College turbocharger testing facility under steady-state and pulsating flow. The steady-state testing was conducted over speed parameter ranges from 1206 rpm/K0.5 to 1809 rpm/K0.5. The test results showed a typical flow capacity trend as a conventional radial turbine but the LPT had higher total-to-static efficiency, ηt-s in the lower pressure ratio regions. A maximum total-to-static efficiency, ηt-s of 0.758 at pressure ratio, PR ≈ 1.1 was found, no available turbines
Padzillah MH, Rajoo S, Martinez-Botas RF, 2016, PRESSURE DISTRIBUTION ON THE BLADE SURFACE OF AN AUTOMOTIVE MIXED FLOW TURBOCHARGER TURBINE UNDER PULSATING FLOW CONDITIONS, JURNAL TEKNOLOGI, Vol: 78, Pages: 147-153, ISSN: 0127-9696
Fu H, Cao K, Xu R, et al., 2016, Footstep energy harvesting using heel strike-induced airflow for human activity sensing, 13th IEEE International Conference on Wearable and Implantable Body Sensor Networks (BSN), Publisher: IEEE, Pages: 124-129, ISSN: 2376-8886
Body sensor networks are increasingly popular in healthcare, sports, military and security. However, the power supply from conventional batteries is a key bottleneck for the development of body condition monitoring. Energy harvesting from human motion to power wearable or implantable devices is a promising alternative. This paper presents an airflow energy harvester to harness human motion energy from footsteps. An air bladder-turbine energy harvester is designed to convert the footstep motion into electrical energy. The bladders are embedded in shoes to induce airflow from foot-strikes. The turbine is employed to generate electrical energy from airflow. The design parameters of the turbine rotor, including the blade number and the inner diameter of the blades (the diameter of the turbine shaft), were optimized using the computational fluid dynamics (CFD) method. A prototype was developed and tested with footsteps from a 65 kg person. The peak output power of the harvester was first measured for different resistive loads and showed a maximum value of 90.6 mW with a 30.4 Ω load. The harvested energy was then regulated and stored in a power management circuit. 14.8 mJ was stored in the circuit from 165 footsteps, which means 90 μJ was obtained per footstep. The regulated energy was finally used to fully power a fitness tracker which consists of a pedometer and a Bluetooth module. 7.38 mJ was consumed by the tracker per Bluetooth configuration and data transmission. The tracker operated normally with the harvester working continuously.
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