Ricardo Martinez-botas | Imperial College London (original) (raw)

Papers by Ricardo Martinez-botas

Journal of Turbomachinery, 2013

This paper presents a method for prediction of the unequal admission performance of a double entr... more This paper presents a method for prediction of the unequal admission performance of a double entry turbine based on the full admission turbine maps and a minimal number of unequal admission points. The double entry turbine has two separate inlet ports which feed a single turbine wheel: this arrangement can be beneficial in a turbocharger application; however the additional entry does add complexity in producing a complete turbine map which includes unequal admission behavior. When a double entry turbine is operated under full admission conditions, with both entries feeding the turbine equally, this will act effectively as a single entry device and the turbine performance can be represented by a standard turbine map. In reality a multiple entry turbine will spend the majority of time operating under varying degrees of unequal admission, with each entry feeding the turbine different amounts; the extent of this inequality can have a considerable impact on turbine performance. In order ...

CFD Letters

EGR extraction from one side of the exhaust manifold creates imbalance of mass flow in a double e... more EGR extraction from one side of the exhaust manifold creates imbalance of mass flow in a double entry turbine. To overcome this problem, the asymmetric double entry turbine was introduced. The performance maps of this turbine were obtained through extensive test configurations in both steady and unsteady flow conditions at Imperial College cold flow test rig. Two main configurations were investigated; nozzleless and nozzle vane setting. Nevertheless, no attempt has been made to compare the performance of asymmetric double entry turbine to that of the symmetric counterpart. One way to make comparison between these two double entry turbine volutes, is by using numerical simulation. This is achieved by using ANSYS CFX tool in this paper. A symmetric double entry volute CAD model is developed using the same A/R ratio as the asymmetric counterpart, adopting the same mixed flow rotor, inlet and exit ducts. The steady state numerical investigation was conducted at two turbine speeds, 30k R...

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy

This paper describes the results of the simulation of a mixed flow turbine under pulsating inlet ... more This paper describes the results of the simulation of a mixed flow turbine under pulsating inlet conditions. The volute casing of the turbine is simulated as a tapered duct with one-dimensional unsteady flow analysis applied to this duct, while one-dimensional steady flow analysis is used in a quasi-steady manner to simulate the flow through the rotor of the turbine. The physical model of the turbine is an improved version of that described by Chen and Winterbone (1), and its predictive capability is evaluated against experimental data of the turbine performance obtained in the Imperial College's unsteady flow turbocharger rig.

Journal of Engineering for Gas Turbines and Power, 2016

It is well known that compressor surge imposes a significant limit on the flow range of a turboch... more It is well known that compressor surge imposes a significant limit on the flow range of a turbocharged internal combustion engine. The centrifugal compressor is commonly placed upstream of the inlet manifold, and hence, it is exposed to the intermittent flow regime of the inlet valves. Surge phenomena have been well studied over the past decades, and there still remains limited information with regard to the unsteady impact caused by the inlet valves. This study presents an experimental evaluation of such a situation. Engine representative pulses are created by a downstream system comprising a large volume, two rotating valves, a throttle valve, and the corresponding pipe network. Different pulsation levels are characterized by means of their frequency and the corresponding amplitude at the compressor inlet. The stability limit of the system under study is evaluated with reference to the parameter B proposed by Greitzer (1976, “Surge and Rotating Stall in Axial Flow Compressors—Part...

2016 IEEE 13th International Conference on Wearable and Implantable Body Sensor Networks (BSN), 2016

Body sensor networks are increasingly popular in healthcare, sports, military and security. Howev... more 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 implanted devices is a promising alternative. This paper presents an airflow energy harvester to harness human motion energy from footstep. 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-strike. A ducted radial-flow turbine is employed to generate electrical energy from airflow. The design parameters of the turbine rotor, including blade number, the inner diameter of the blades, were optimized using computational fluid dynamics (CFD). A prototype was developed and tested with footsteps from a 65 Kg person. The peak output power of the harvester was first measured with different resistors. The value was 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 energy was stored in the circuit from 165 footsteps, which means 89.7 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.

Journal of Power Sources, 2016

A novel electrical circuit analogy is proposed modelling electrochemical systems under realistic ... more A novel electrical circuit analogy is proposed modelling electrochemical 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.

The Aeronautical Journal, 2004

Direct optimisation techniques using different methods are presented and compared for the solutio... more Direct optimisation techniques using different methods are presented and compared for the solution of two common flows: a two dimensional diffuser and a drag minimisation problem of a fixed area body. The methods studied are a truncated Newton algorithm (gradient method), a simplex approach (direct search method) and a genetic algorithm (stochastic method). The diffuser problem has a known solution supported by experimental data, it has one design performance measure (the pressure coefficient) and two design variables. The fixed area body also has one performance measure (the drag coefficient), but this time there are four design variables; no experimental data is available, this computation is performed to assess the speed/progression of solution. In all cases the direct search approach (simplex method) required significantly smaller number of evaluations than the generic algorithm method. The simplest approach, the gradient method (Newton) performed equally to the simplex approach...

Volume 6: Turbo Expo 2005, Parts A and B, 2005

This paper describes the Computational Fluid Dynamic (CFD) numerical optimization of a modern cen... more This paper describes the Computational Fluid Dynamic (CFD) numerical optimization of a modern centrifugal compressor impeller with a ported shroud for increased surge margin. The vent configuration selected was a full circumference, constant-width slot. A multiblock, steady flow three dimensional (3D) viscous RANS model (ADPAC) is used with parallel processing capability to increase computational speed. Grid generation is performed in an automated fashion to enable the timely optimization of the ported shroud configuration. A designed experiment (DoE) approach is used to minimize the number of vent configurations to be modeled, to ensure that factor interaction effects are captured, and to facilitate the definition of an optimum vent configuration. The DoE is a 2 factor, 2 level full factorial experiment with a center point included to detect possible curvature in the solution surface. The factors optimized are slot width and the flow-wise location of the slot. The numerical techniq...

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2015

Currently, industrial applications to monitoring, simulation and optimization of compressors empl... more Currently, industrial applications to monitoring, simulation and optimization of compressors employ empirical models that are either data-driven or based on the manufacturer performance maps. This paper proposes the use of one-dimensional aerodynamic models for industrial applications such as simulation and monitoring. The physical model establishes causality relationships among input and output variables that are tuned to match the real compressor by using operation data. The application of the method is shown using data from an industrial multistage centrifugal compressor with interstage coolers and variable inlet guide vanes. This is a more complex but more relevant case study for process industry, as opposed to the single-stage variable speed compressors, which is the common example in the literature.

Energy Conversion and Management, 2015

ABSTRACT Turbo-compounding is an effective way to recover waste heat from engine exhaust and redu... more ABSTRACT Turbo-compounding is an effective way to recover waste heat from engine exhaust and reduce fuel consumption for internal combustion engine (ICE). The characteristics of two-stage turbine, including turbocharger turbine and power turbine, have significant effects on the overall performance of turbo-compound engine. This paper investigates the interaction between two turbines in a turbo-compound engine and its impact on the engine performance. Firstly an analytical model is built to investigate the effects of turbine equivalent flow area on the two-stage turbine characteristics, including swallowing capacity and load split. Next both simulation and experimental method are carried out to study the effects of high pressure variable geometry turbine (HP VGT), low pressure variable geometry turbine (LP VGT) and combined VGT on the engine overall performance. The results show that the engine performance is more sensitive to HP VGT compared with LP VGT at all the operation conditions, which is caused by the larger influences of HP VGT on the total expansion ratio and engine air–fuel ratio. Using the HP VGT method, the fuel reductions of the turbo-compound engine at 1900 rpm and 1000 rpm are 3.08% and 7.83% respectively, in comparison with the baseline engine. The corresponding optimum values of AR are 2.0 and 2.5.

10th International Conference on Turbochargers and Turbocharging, 2012

The present disclosure relates to the analysis of battery performance. In particular, but not exc... more The present disclosure relates to the analysis of battery performance. In particular, but not exclusively, the disclosure concerns the provision of battery managements systems that enable users of battery powered devices or systems to be provided with information regarding battery characteristics.

Volume 8: Turbomachinery, Parts A, B, and C, 2012

ABSTRACT In order to extract maximum amount of energy possible from the automotive reciprocating ... more ABSTRACT In order to extract maximum amount of energy possible from the automotive reciprocating engine exhaust gas, the turbocharger usually installed closely downstream the exhaust valve thus exposing it to highly pulsating flow conditions. This condition induces highly complex flow field within the turbocharger stage and significantly impact its performance characteristics which is not fully understood. The main objective of this paper is to provide understanding of unsteady flow feature using a Computational Fluid Dynamics (CFD) approach validated with experimental data. Despite focusing on unsteady feature of the flow, this research also emphasizes the importance of accurately modelled geometry in the early section of the paper. A steady state validation against experimental data is performed prior to unsteady calculations. The effect of different phase shifting methods is described and the relationship of instantaneous efficiency with incidence angle is established. In the final section of this paper, the turbocharger stage is sectioned where its instantaneous performance is evaluated individually in each section. The unsteady simulation is performed at fixed 30 000 RPM with 20Hz pulsing flow.

SAE Technical Paper Series, 2015

ABSTRACT Cylinder deactivation has been utilized by vehicle manufacturers since the 80's ... more ABSTRACT Cylinder deactivation has been utilized by vehicle manufacturers since the 80's to improve fuel consumption and exhaust emissions. Cylinder deactivation is achieved by cutting off fuel supply and ignition in some of the engine cylinders, while their inlet and outlet valves are fully closed. The vehicle demand during cylinder deactivation is sustained by only the firing cylinders, hence increasing their indicated power. Conventionally, half the number of cylinders are shut at certain driving conditions, which normally at the lower demand regime. An optimal strategy will ensure cylinder deactivation contributes to the fuel saving without compromising the vehicle drivability. Cylinder deactivation has been documented to generally improve fuel consumption between 6 to 25 %, depending on the type-approval test drive cycle. However, type-approval test has been reported to differ from the “real-world” fuel consumption values. Therefore the documented fuel consumption might not be representable for consumers in their actual driving. The Malaysian authorities have been using the NEDC test to measure the emission and fuel consumption for declaration purposes, which may be misleading. This paper presents the measurement and analysis of an engine operating with cylinder deactivation, tested on a dynamometer in accordance to the actual driving conditions rather than the NEDC. This is to understand the actual benefits of cylinder deactivation in the real world. The regular Malaysian urban driving conditions were previously identified and applied in this analysis. To understand the engine operational behaviour, a piezoelectric sensor was instrumented on the engine to acquire the in-cylinder pressure traces. Test results from this study have shown that cylinder deactivation improves fuel consumption and thermodynamic efficiencies for the actual Malaysian driving conditions. The fuel consumption benefit also correlates well with the improvements on the mean effective pressures. Engine pumping mean effective pressure reduced as much as 19.4% and the thermal efficiency was consistently improved up to 5% during the cylinder deactivated operation. These improvements were achieved while maintaining similar brake mean effective pressures as if when all cylinders are firing. Most importantly, these improvements fall within the regular actual urban driving conditions, thus will be most beneficial for Malaysian drivers. Furthermore, the recorded engine operating characteristics will be the key in determining the correct strategy towards maximizing the benefits of cylinder deactivation for the Malaysian urban driving conditions.

Volume 7: Turbomachinery, Parts A, B, and C, 2010

ABSTRACT A one-dimensional investigation for a mixed-flow turbine turbocharger turbine is describ... more ABSTRACT A one-dimensional investigation for a mixed-flow turbine turbocharger turbine is described in this paper. The main outcome of the research is to develop a validated procedure for turbine performance maps in both steady and pulsating flow. The approach is limited to a simple procedure that can be integrated in wave action codes and thus not requiring 2D or 3D calculations. The mass flow parameter map is used as an input for the investigation, thus requiring some knowledge of either from experiments or from mean line methods calculations. In this paper, the mass flow parameter is experimentally measured at the turbocharger facility in Imperial College. A realistic yet reduced-order model for turbine losses allows the prediction of the steady flow performance; the calibration of the model is performed at peak efficiency of the turbine for a given rotational speed. The loss model for steady flow is then extended for pulsating conditions and for presumed quasi-steady operation. Finally, the predicted turbine performance is compared with experimental data. The comparison between one-dimensional modeling and experimental data for steady flow condition has shown Relative Standard Deviation (RSD) range from 1.62 % to 11.62 %. Meanwhile, a good trend agreement has been achieved for pulsating flow condition.

ABSTRACT Concerns for fuel economy and reduced emissions have focussed the attention of automotiv... more ABSTRACT Concerns for fuel economy and reduced emissions have focussed the attention of automotive internal combustion engine manufacturers on the exhaust system and towards technological developments to both reduce fuel consumption and emissions, as well as account for the still significant levels of waste exhaust energy that can be recovered. The present volume on Automotive Exhaust Emissions and Energy Recovery for both gasoline and diesel engines is, therefore, a timely one. Whereas diesel engines are predominantly turbocharged, only a relatively small percentage of gasoline engines is similarly equipped which has led towards significant efforts by engine manufacturers in recent years to downsize and downspeed these engines. On the other hand, the relative focus in engine development, in terms of emissions and exhaust energy recovery is shifting towards developments beyond the conventional turbocharger, especially in Diesel engines, for enhanced energy recovery and in emissions control technologies to allow the engines of the future to keep up with the twin demand for very low emissions and increasing levels of fuel economy. Automotive Exhaust Emissions and Energy Recovery focuses on the exhaust system and on the technologies and methods used to reduce emissions and increase fuel economy through the use of emissions control technologies and biofuels as well as by capitalizing upon the exhaust gas energy availability either in the form of gas kinetic energy or as waste heat extracted from the exhaust gas. It is projected that in the short to medium term, advances in exhaust emissions and energy recovery technologies will lead the way in internal combustion engine development and pave the way towards increasing levels of engine hybridization until full electric vehicle technology can claim a level of maturity and corresponding market share to turn the bulk of this focus away from the internal combustion engine. The present book is aimed at engine research professionals in the industry and academia as well as students of power train engineering. The collection of articles in this book aims to review both the fundamentals of relevant, recent exhaust system technologies but to also detail recent or on-going projects and to uncover future research directions and possibilities in this area, where relevant.