Imperial College London

DrAaronCostall

Faculty of EngineeringDepartment of Mechanical Engineering

Lecturer in Thermofluids
 
 
 
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Contact

 

+44 (0)20 7594 7186a.costall Website

 
 
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Location

 

605City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
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32 results found

Hazizi K, Ramezanpour A, Costall A, Asadi Met al., 2019, Numerical analysis of a turbocharger compressor, XII International Conference on Computational Heat, Mass and Momentum Transfer (ICCHMT 2019), Publisher: EDP Sciences, Pages: 1-8

The automotive industry is under obligation to meet regulations for emission control that has resulted in further use of turbochargers in passenger cars to enable downsizing and increase engine power density. In this study, a set of numerical simulations are conducted along two turbocharger compressor speed lines of 150,000 rpm and 80,000 rpm to analyse and validate the results against experimental data. The domain includes the full compressor stage comprising intake, impeller as a Multiple Reference Frame, diffuser and outlet. The k-omega SST turbulence model with three different mesh sizes is used tosolve the compressible flow using ANSYS Fluent software. Three points on each speed-line are selected:one point each in regions close to surge and choke and a point in the stable zone of the compressor map. The simulations predict compressor performance in terms of the total–to–total pressure ratioand total–to–total efficiency. Results reveal the predicted pressure ratio error is in the range of 1-6%. At 150,000 rpm the pressure ratio is underpredicted for the point close to the surgebut overpredicted for the point close to the choke. However, the pressure ratio results are within 1% difference for 80,000 rpm. In all cases, the predicted efficiency increased when a finer mesh is used.While results are close to the experimental data in both the surge and stable areas of the map, the efficiency wasoverpredicted up to 20% in the region close to the choke. In conclusion, the finer mesh leads to higher pressure ratio and efficiency values that overpredict the performance, especially for the pointclose to choke.

Conference paper

Kapoor P, Costall AW, Sakellaridis N, Hooijer J, Lammers R, Tartoussi H, Guilain Set al., 2018, Adaptive turbo matching: radial turbine design optimization through 1D engine simulations with meanline model in-the-loop, SAE WCX World Congress Experience 2018, Publisher: SAE International, ISSN: 0148-7191

Turbocharging has become the favored approach for downsizing internal combustion engines to reduce fuel consumption and CO 2 emissions, without sacrificing performance. Matching a turbocharger to an engine requires a balance of various design variables in order to meet the desired performance. Once an initial selection of potential compressor and turbine options is made, corresponding performance maps are evaluated in 1D engine cycle simulations to down-select the best combination. This is the conventional matching procedure used in industry and is passive' since it relies on measured maps, thus only existing designs may be evaluated. In other words, turbine characteristics cannot be changed during matching so as to explore the effect of design adjustments. Instead, this paper presents an adaptive' matching methodology for the turbocharger turbine. By coupling an engine cycle simulation to a turbine meanline model (in-the-loop'), adjustments in turbine geometry are reflected in both the exhaust boundary conditions and overall engine performance. Running the coupled engine-turbine model within an optimization framework, the optimal turbine design evolves. The methodology is applied to a Renault 1.2 L turbocharged gasoline engine, to minimize fuel consumption over given full- and part-load operating points, while meeting performance constraints. Despite the current series production turbine being a very good match already, and with optimization restricted to a few turbine geometric parameters, the full-load case predicted a significant cycle-averaged BSFC reduction of 3.5 g/kWh, while the part-load optimized design improved BSFC by 0.9 g/kWh. No engine design parameters were changed, so further efficiency gains would be possible through simultaneous engine-turbocharger optimization. The proposed methodology is not only useful for improving existing designs; it can also develop a bespoke turbine geometry in new engine projects where there is no previously available mat

Conference paper

Ioannou E, Costall AW, Khairuddin U, Ramasamy P, Haigh Eet al., 2018, Turbocharger turbine aerodynamic optimization for reduced fuel consumption and CO<inf>2</inf> emissions from heavy-duty diesel engines: Experimental validation and flow field analysis, Pages: 373-388

© The author(s) and/or their employer(s), 2018. This paper describes aerodynamic optimization of the high pressure turbine in a two-stage heavy-duty diesel engine air system. A genetic algorithm generates designs that reduce fuel consumption and CO2 emissions by maximizing turbine efficiency, while meeting boost and packaging requirements. Scaling the baseline 47 mm diameter turbine to 83.6 mm permits on-design testing. Optimization of the scaled baseline predicts a 2.1%-point on-design benefit, confirmed by experiments which measure a 2.6%-point efficiency gain. This validates both the CFD model and the optimization process. CFD flow field analysis reveals the aerodynamic loss in the blade tip region is significantly improved by the optimized design.

Conference paper

Costall AW, Khairuddin UB, Aerodynamic Optimization Of The High Pressure Turbine And Interstage Duct In A Two-Stage Air System For A Heavy-Duty Diesel Engine, Journal of Engineering for Gas Turbines and Power, ISSN: 0742-4795

Turbochargers reduce fuel consumption and CO2 emissionsfrom heavy-duty internal combustion engines by enablingdownsizing and downspeeding through greater power density.This requires greater pressure ratios and thus air systemswith multiple stages and interconnecting ducting, allsubject to tight packaging constraints. This paper considersthe aerodynamic optimization of the exhaust side of a twostageair system for a Caterpillar 4.4-litre heavy-duty dieselengine, focusing on the high pressure turbine wheel and interstageduct. Using current production designs as a baseline,a genetic algorithm-based aerodynamic optimizationprocess was carried out separately for the wheel and ductcomponents to evaluate seven key operating points. Whileefficiency was a clear choice of cost function for turbinewheel optimization, different objectives were explored for interstageduct optimization to assess their impact. Optimizeddesigns are influenced by the engine operating point, so eachdesign was evaluated at every other engine operating point,to determine which should be carried forward. Prototypes ofthe best compromise high pressure turbine wheel and interstageduct designs were manufactured and tested against thebaseline to validate CFD predictions. The best performinghigh pressure turbine design was predicted to show an effi-ciency improvement of 2.15 percentage points, for on-designoperation. Meanwhile, the optimized interstage duct contributeda 0.2 and 0.5 percentage-point efficiency increasefor the high and low pressure turbines, respectively.

Journal article

Mason A, Costall AW, McDonald JR, 2017, The sensitivity of transient response prediction of a turbocharged diesel engine to turbine map extrapolation, ICE 2017 - 13th International Conference on Engines & Vehicles Sector:, Publisher: Society of Automotive Engineers, ISSN: 0148-7191

Mandated pollutant emission levels are shifting light-duty vehicles towards hybrid and electric powertrains. Heavy-duty applications, on the other hand, will continue to rely on internal combustion engines for the foreseeable future. Hence there remain clear environmental and economic reasons to further decrease IC engine emissions. Turbocharged diesels are the mainstay prime mover for heavy-duty vehicles and industrial machines, and transient performance is integral to maximizing productivity, while minimizing work cycle fuel consumption and CO2 emissions. 1D engine simulation tools are commonplace for "virtual" performance development, saving time and cost, and enabling product and emissions legislation cycles to be met. A known limitation however, is the predictive capability of the turbocharger turbine sub-model in these tools. One specific concern is accurate extrapolation of turbine performance beyond the narrow region populated by supplier-measured data to simulate non-steady conditions, be it either to capture pulsating exhaust flow or, as is the focus here, engine transient events. Extrapolation may be achieved mathematically or by using physics-based correlations, sometimes in combination. Often these extrapolation rules are the result of experience. Due to air system dynamic imbalance, engine transients force instantaneous turbine mass flow and pressure ratio into regions well away from the hot gas bench test data, necessitating great trust in the extrapolation routine. In this study, a 1D heavy-duty turbocharged diesel engine model was used to simulate four transient events, employing a series of performance maps representing the same turbine but with increasing levels of extrapolation, using commonly-adopted methodologies. The comparison was enabled by measuring real turbine performance on the dynamometer at Imperial College London. This testing generated a wide baseline dataset which was used to produce corresponding transient response predic

Conference paper

Gharaibeh K, Costall AW, 2017, A flow and loading coefficient-based compressor map interpolation technique for improved accuracy of turbocharged engine simulations, ICE 2017 - 13th International Conference on Engines & Vehicles, Publisher: Society of Automotive Engineers, ISSN: 0148-7191

Internal combustion engines are routinely developed using 1D engine simulation tools. A well-known limitation is the accuracy of the turbocharger compressor and turbine sub-models, which rely on hot gas bench-measured maps to characterize performance. Such discrete map data is inherently too sparse to be used directly in simulation, and so a preprocessing algorithm interpolates and extrapolates the data to generate a wider, more densely populated map. Methods used for compressor map interpolation vary. They may be mathematical or physical in nature, but there is no unified approach, except that they typically operate on input map data in SAE format. For decades it has been common practice for turbocharger suppliers to share performance data with engine OEMs in this form. This paper describes a compressor map interpolation technique based on the nondimensional compressor flow and loading coefficients, instead of SAE-format data. It compares the difference in compressor operating point prediction accuracy when using this method against the standard approach employing dimensional parameters. This is done by removing a speed line from a dataset, interpolating for the removed speed using the two methods, and comparing their accuracy to the original data. Three maps corresponding to compressor diameters of 54, 88, and 108 mm were evaluated. In some cases, the residual sum of squares between the interpolated and original data demonstrated an order of magnitude improvement when using the nondimensional coefficients. When evaluated in a simple engine model, this manifests as a slight shift in interpolated turbocharger speed, resulting in a difference in predicted compressor efficiency of up to 0.89 percentage points. This paper shows how the use of truly nondimensional interpolation techniques can improve the accuracy of processed turbocharger compressor maps, and consequently the value of 1D engine simulations as a reliable performance development tool, at virtually no addi

Conference paper

Khairuddin U, Costall AW, Aerodynamic Optimization of the High Pressure Turbine and Interstage Duct in a Two-Stage Air System for a Heavy-Duty Diesel Engine, ASME Turbo Expo 2017

Conference paper

Chiong MS, Rajoo S, Romagnoli A, Costall AW, Martinez-Botas RFet al., 2016, One-dimensional pulse-flow modeling of a twin-scroll turbine, Energy, Vol: 115, 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.

Journal article

Robertson MC, Costall AW, Newton PJ, Martinez-Botas RFet al., 2016, Radial Turboexpander Optimization Over Discretized Heavy-Duty Test Cycles for Mobile Organic Rankine Cycle Applications, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Winward E, Rutledge J, Carter J, Costall A, Stobart R, Zhao D, Yang Zet al., 2016, Performance testing of an electrically assisted turbocharger on a heavy duty diesel engine, Pages: 363-382

© The author(s) and/or their employer(s), 2016. An electrically assisted turbocharger was designed, built and tested by a consortium consisting of Caterpillar Inc., BorgWarner Turbo Systems, Imperial College London and Loughborough University. The Electric Turbocharger Assist (ETA) device was based on a BorgWarner BV63 variable turbine geometry (VTG™) turbocharger with a bearing housing that was extended to accommodate a switched reluctance (SR) electrical machine. The ETA device was evaluated over a range of steady state and transient engine conditions with the ETA providing electric assist or electric regeneration. The response of the single stage ETA turbocharger matched a production 2-stage turbocharger on the same engine.

Conference paper

Khairuddin U, Costall AW, Martinez-Botas RF, 2015, INFLUENCE OF GEOMETRICAL PARAMETERS ON AERODYNAMIC OPTIMIZATIONOF A MIXED-FLOW TURBOCHARGER TURBINE, ASME Turbo Expo 2015: Turbine Technical Conference and Exposition, Publisher: ASME

This paper describes an optimization procedure to modify the geometry of a mixed-flow turbocharger turbine for improved aerodynamic efficiency. The procedure integrates parameterization of the turbine blade geometry, genetic algorithm optimization, and 3D CFD analysis using a commercial solver.Using a known mixed-flow turbocharger turbine as the baseline, the main features of the blade geometry — the hub, shroud, camberline, leading and trailing edge profiles—were separately adjusted by the genetic algorithm in the direction of better efficiency. Apart from optimizing the subject turbine for the operating point in question, more usefully this permits each geometrical feature to be ranked by their contribution to the change in efficiency. Cases were also run in which the hub and shroud curves were simultaneously adjusted. Analysis of CFD results provides additional insight into the underlying reasons for efficiency changes by examination of the relevant flow field features.The hub and shroud profiles were observed to have the greatest impact on turbine performance, optimization of which leads to an increase of 1.3 percentage points of efficiency. This compares to only 0.2 percentage points improvement following optimization of the outlet geometry.

Conference paper

Ismail MI, Costall A, Martinez-Botas R, Rajoo Set al., 2015, Turbocharger Matching Method for Reducing Residual Concentration in a Turbocharged Gasoline Engine

Copyright © 2015 SAE International. In a turbocharged engine, preserving the maximum amount of exhaust pulse energy for turbine operation will result in improved low end torque and engine transient response. However, the exhaust flow entering the turbine is highly unsteady, and the presence of the turbine as a restriction in the exhaust flow results in a higher pressure at the cylinder exhaust ports and consequently poor scavenging. This leads to an increase in the amount of residual gas in the combustion chamber, compared to the naturally-aspirated equivalent, thereby increasing the tendency for engine knock. If the level of residual gas can be reduced and controlled, it should enable the engine to operate at a higher compression ratio, improving its thermal efficiency. This paper presents a method of turbocharger matching for reducing residual gas content in a turbocharged engine. The turbine is first scaled to a larger size as a preliminary step towards reducing back pressure and thus the residual gas concentration in-cylinder. However a larger turbine causes a torque deficit at low engine speeds. So in a following step, pulse separation is used. In optimal pulse separation, the gas exchange process in one cylinder is completely unimpeded by pressure pulses emanating from other cylinders, thereby preserving the exhaust pulse energy entering the turbine. A pulse-divided exhaust manifold enables this by isolating the manifold runners emanating from certain cylinder groups, even as far as the junction with the turbine housing. This combination of appropriate turbine sizing and pulse-divided exhaust manifold design is applied to a Proton 1.6-litre CamPro CFE turbocharged gasoline engine model. The use of a pulse-divided exhaust manifold allows the turbine to be increased in size by 2.5 times (on a mass flow rate basis) while maintaining the same torque and power performance. As a consequence, lower back pressure and improved scavenging reduces the residual conce

Conference paper

Chiong MS, Rajoo S, Romagnoli A, Costall AW, Martinez-Botas RFet al., 2015, Non-adiabatic pressure loss boundary condition for modelling turbocharger turbine pulsating flow, ENERGY CONVERSION AND MANAGEMENT, Vol: 93, Pages: 267-281, ISSN: 0196-8904

Journal article

Costall AW, Gonzalez Hernandez A, Newton PJ, Martinez-Botas RFet al., 2015, Design methodology for radial turbo expanders in mobile organic Rankine cycle applications, Applied Energy, Vol: 157, Pages: 729-743, ISSN: 1872-9118

Future vehicles for clean transport will require new powertrain technologies to further reduce CO2 emissions. Mobile organic Rankine cycle systems target the recovery of waste heat in internal combustion engines, with the exhaust system identified as a prime source. This article presents a design methodology and working fluid selection for radial turbo expanders in a heavy-duty off-road diesel engine application. Siloxanes and Toluene are explored as the candidate working fluids, with the latter identified as the preferred option, before describing three radial turbine designs in detail. A small 15.5. kW turbine design leads to impractical blade geometry, but a medium 34.1. kW turbine, designed for minimum power, is predicted to achieve an isentropic efficiency of 51.5% at a rotational speed of 91.7. k. min-1. A similar 45.6. kW turbine designed for maximum efficiency yields 56.1% at 71.5. k. min-1. This emphasizes the main design trade-off - efficiency decreases and rotational speed increases as the power requirement falls - but shows reasonable radial turbine efficiencies and thus practical turbo expanders for mobile organic Rankine cycle applications are realizable, even considering the compromised flow geometry and high speeds imposed at such small scales.

Journal article

Chiong MS, Padzillah MH, Rajoo S, Romagnoli A, Costall AW, Martinez-Botas RFet al., 2015, COMPARISON OF EXPERIMENTAL, 3D AND 1D MODEL FOR A MIXED-FLOW TURBINE UNDER PULSATING FLOW CONDITIONS, JURNAL TEKNOLOGI, Vol: 77, ISSN: 0127-9696

Journal article

Chiong MS, Rajoo S, Romagnoli A, Costal AW, Martinez-Botas RFet al., 2015, ASSESSMENT OF PARTIAL-ADMISSION CHARACTERISTICS IN TWIN-ENTRY TURBINE PULSE PERFORMANCE MODELLING, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Shiva Kumar S, Van Leeuwen B, Costall A, 2014, Quantification and sensitivity analysis of uncertainties in turbocharger compressor gas stand measurements using monte carlo simulation, ISSN: 0148-7191

Turbocharger hot gas stand testing is routinely carried out in the industry both to provide an experimental assessment of different designs, and to confirm to automotive OEM customers that the product meets the afore-promised levels of performance and durability. The resulting characteristics, or maps, have a hugely significant role in the correct matching of turbocharger options for engine applications. However, since these are generated from experimentally-determined values of pressure, temperature and mass flow, with each sensed variable having an inherent finite error, the uncertainty in these measured components is variously propagated through to the flow and efficiency characteristics - and the significance of this is not well recognized. This paper addresses this concern by classifying uncertainties according to ISO standards and propagating these through to the standard compressor performance parameters using Monte Carlo simulations, in order to quantify the overall uncertainty present in a turbocharger compressor hot gas test bench. This is followed by a global sensitivity analysis to establish which parameters contribute the highest levels of uncertainty to, for instance, the compressor efficiency characteristic, thereby providing a sensitivity ranking of the most influential measurands. Finally, the analyses are combined to explain the trend in the degree of uncertainty of performance characteristics in different regions of compressor operation. The data presented herein serves as a useful point of reference such that recommendations to improve turbocharger test facilities, either in terms of measurement methods or data acquisition and sensor hardware, can be focused on the most effective areas. Copyright © 2014 SAE International.

Conference paper

Chiong MS, Rajoo S, Costall AW, Salim WS-IBW, Romagnoli A, Martinez-Botas RFet al., 2013, ASSESSMENT OF CYCLE AVERAGED TURBOCHARGER MAPS THROUGH ONE DIMENSIONAL AND MEAN-LINE COUPLED CODES, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Romagnoli A, Copeland CD, Martinez-Botas R, Seiler M, Rajoo S, Costall Aet al., 2013, Comparison Between the Steady Performance of Double-Entry and Twin-Entry Turbocharger Turbines, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME, Vol: 135, ISSN: 0889-504X

Journal article

Chiong MS, Rajoo S, Martinez-Botas RF, Costall AWet al., 2012, Engine turbocharger performance prediction: One-dimensional modeling of a twin entry turbine, ENERGY CONVERSION AND MANAGEMENT, Vol: 57, Pages: 68-78, ISSN: 0196-8904

Journal article

Romagnoli A, Copeland C, Martinez-Botas R, Rajoo S, Seiler M, Costall Aet al., 2012, COMPARISON BETWEEN THE STEADY PERFORMANCE OF DOUBLE-ENTRY AND TWIN-ENTRY TURBOCHARGER TURBINES, ASME Turbo Expo 2011, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1995-2007

Conference paper

Costall AW, Ivanov R, Langley TPF, 2012, ELECTRIC TURBO ASSIST AS AN ENABLER FOR ENGINE DOWNSPEEDING, ASME Turbo Expo 2012, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 511-521

Conference paper

Romagnoli A, Copeland C, Martinez-Botas RF, Rajoo S, Costall A, Seiler Met al., 2012, Comparison Between the Steady Performance of Double-Entry and Twin-Entry Turbocharger Turbines, Journal of Turbomachinery

Journal article

Chiong MS, Rajoo S, Costall AW, Martinez-Botas RFet al., 2011, Inlet boundary condition study for unsteady turbine performance prediction using 1-D modeling, Jurnal Mekanikal, Vol: 33, Pages: 89-104

Journal article

Costall AW, McDavid RM, Martinez-Botas RF, Baines NCet al., 2011, Pulse Performance Modeling of a Twin Entry Turbocharger Turbine Under Full and Unequal Admission, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME, Vol: 133, ISSN: 0889-504X

Journal article

Terdich N, Martinez-Botas RF, Howey DA, Copeland CD, Costall Aet al., 2011, Off-Road Diesel Engine Transient Response Improvement by Electrically Assisted Turbocharging, SAE ICE2011 - 10th International Conference on Engines & Vehicles, Publisher: Society of Automotive Engineers

Conference paper

Costall AW, McDavid RM, Martinez-Botas RF, Baines NCet al., 2009, PULSE PERFORMANCE MODELING OF A TWIN ENTRY TURBOCHARGER TURBINE UNDER FULL AND UNEQUAL ADMISSION, 54th ASME Turbo Expo 2009, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1255-1266

Conference paper

Hakeem I, Su C-C, Costall A, Martinez-Botas RFet al., 2007, Effect of volute geometry on the steady and unsteady performance of mixed-flow turbines, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY, Vol: 221, Pages: 535-550, ISSN: 0957-6509

Journal article

Costall A, Martinez-Botas RF, 2007, Fundamental characterization of turbocharger turbine unsteady flow behavior, 52nd ASME Turbo Expo 2007, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1827-1839

Conference paper

Costall A, Szymko S, Martinez-Botas RF, Filsinger D, Ninkovic Det al., 2006, Assessment of unsteady behavior in turbocharger turbines, 51st ASME Turbo Expo, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1023-1038

Conference paper

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