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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28 results found

Gharaibeh K, Costall AW, 2017, A Flow and Loading Coefficient-Based Compressor Map Interpolation Technique for Improved Accuracy of Turbocharged Engine Simulations

Copyright © 2017 SAE International. 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 performan

CONFERENCE PAPER

Khairuddin U, Costall AW, 2017, Aerodynamic optimization of high pressure turbine and interstage duct in a two-stage air system for a heavy-duty diesel engine

Copyright © 2017 ASME. Turbochargers are a key technology for reducing the fuel consumption and CO 2 emissions of heavy-duty internal combustion engines by enabling greater power density, which is essential for engine downsizing and downspeeding. This in turn raises turbine expansion ratio levels and drives the shift to air systems with multiple stages, which also implies the need for interconnecting ducting, all of which is subject to tight packaging constraints. This paper considers the challenges in the aerodynamic optimization of the exhaust side of a two-stage air system for a Caterpillar 4.4-litre heavy-duty diesel engine, focusing on the high pressure turbine wheel and interstage duct. Using the current production designs as a baseline, a genetic algorithm-based aerodynamic optimization process was carried out separately for the wheel and duct components in order to minimize the computational effort required to evaluate seven key operating points. While efficiency was a clear choice for the cost function for turbine wheel optimization, the most appropriate objective for interstage duct optimization was less certain, and so this paper also explores the resulting effect of optimizing the duct design for different objectives. Results of the optimization generated differing turbine wheel and interstage duct designs depending on the corresponding operating point, thus it was important to check the performance of these components at every other operating point, in order to determine the most appropriate designs to carry forward. Once the best compromise high pressure turbine wheel and interstage duct designs were chosen, prototypes of both were manufactured and then tested together against the baseline designs to validate the CFD predictions. The best performing high pressure turbine design, wheel A, was predicted to show an efficiency improvement of 2.15 percentage points, for on-design operation. Meanwhile, the optimized interstage duct contributed a 0.2 and

CONFERENCE PAPER

Mason A, Costall AW, McDonald JR, 2017, The Sensitivity of Transient Response Prediction of a Turbocharged Diesel Engine to Turbine Map Extrapolation

Copyright © 2017 SAE International. 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 produc

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, Pages: 1291-1304, ISSN: 0360-5442

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

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

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

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

Khairuddin U, Costal AW, Martinez-Botas RF, 2015, INFLUENCE OF GEOMETRICAL PARAMETERS ON AERODYNAMIC OPTIMIZATION OF A MIXED-FLOW TURBOCHARGER TURBINE, 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

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

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 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

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

Copeland CD, Martinez-Botas R, Seiler M, 2011, Comparison Between Steady and Unsteady Double-Entry Turbine Performance Using the Quasi-Steady Assumption, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME, Vol: 133, ISSN: 0889-504X

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

Turbocharged diesel engines are widely used in off-road applications including construction and mining machinery, electric power generation systems, locomotives, marine, petroleum, industrial and agricultural equipment. Such applications contribute significantly to both local air pollution and CO 2 emissions and are subject to increasingly stringent legislation. To improve fuel economy while meeting emissions limits, manufacturers are exploring engine downsizing by increasing engine boost levels. This allows an increase in IMEP without significantly increasing mechanical losses, which results in a higher overall efficiency. However, this can lead to poorer transient engine response primarily due to turbo-lag, which is a major penalty for engines subjected to fast varying loads. To recover transient response, the turbocharger can be electrically assisted by means of a high speed motor/generator. When the engine load is increased, the electrical machine acts as a motor to accelerate the turbocharger so that the torque demand can be met rapidly. Conversely, when boost delivery exceeds demand the electrical machine can act as a generator to recover energy that would otherwise be wastegated. This paper presents a model for the transient response of the electrically-assisted turbocharged engine when subjected to a step increase of torque demand. The base model is representative of a 7-litre turbocharged intercooled diesel engine and has been implemented in Matlab-Simulink and calibrated against test bed data. The model is used for the analysis of the dynamic behaviour of the engine with different levels of electric assist to the turbocharger. The results show that while turbocharger response improves with electric assist, compressor surge can occur in generating mode and that limitations on electric assist power are present. Copyright © 2011 SAE International.

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

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

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, 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

Costall A, Martinez-Botas RF, Palfreyman D, 2005, Detailed study of pulsating flow performance in a mixed flow turbocharger turbine, 50th ASME Turbo-Expo, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1415-1433

CONFERENCE PAPER

Costall AW, Martinez-Botas RF, Palfreyman D, 2005, Detailed study of pulsating flow performance in a mixed flow turbocharger turbine, ASME Turbo Expo 2005: Power for Land, Sea and Air, Pages: 1415-1433

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

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