The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Sam Akehurst - One of the best experts on this subject based on the ideXlab platform.
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Observations on and Potential Trends for Mechanically Supercharging a Downsized Passenger Car Engine: a Review
Proceedings of the Institution of Mechanical Engineers Part D: Journal of Automobile Engineering, 2016Co-Authors: Bo Hu, Sam Akehurst, Chris Brace, James Turner, Colin CopelandAbstract:Engine downsizing is a proven approach for achieving a superior fuel efficiency. It is conventionally achieved by reducing the swept volume of the engine and by employing some means of increasing the specific output to achieve the desired installed engine power, usually in the form of an exhaust-driven Turbocharger. However, because of the perceptible time needed for the Turbocharger system to generate the required boost pressure, a characteristic of turbocharged engines is their degraded driveability in comparison with those of their naturally aspirated counterparts. Mechanical supercharging refers to the technology that compresses the intake air using the energy taken directly from the engine crankshaft. It is anticipated that engine downsizing which is realised either solely by a supercharger or by a combination of a supercharger and a Turbocharger will enhance a vehicle’s driveability without significantly compromising the fuel consumption at an engine level compared with the downsizing by turbochargi...
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Novel approaches to improve the gas exchange process of downsized turbocharged spark-ignition engines: A review
International Journal of Engine Research, 2015Co-Authors: Bo Hu, Sam Akehurst, Christian J. BraceAbstract:Engine downsizing, which is the use of a smaller engine that provides the power of a larger engine, is now considered a mega-trend for the internal combustion engine market. It is usually achieved using one or more boosting devices including a supercharger or a Turbocharger. Although supercharging is beneficial for engine’s transient response, turbocharging technology is more widely adopted considering its advantages in fuel efficiency. Compared to turbocharged compression ignition engines, turbocharged spark-ignition engines tend to be more challenging with respect to the gas exchange process mainly due to their higher pumping loss, the need for throttling and the fact that spark-ignition engines demand more controllability due to the mitigation of knock, particularly with regard to minimizing trapped residuals. These challenges encourage the entire gas exchange process of turbocharged spark-ignition engines to be regarded as a complete air management system instead of just looking at the boosting system...
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Review of Turbocharger Mapping and 1D Modelling Inaccuracies with Specific Focus on Two-Stag Systems
SAE Technical Paper Series, 2015Co-Authors: Calogero Avola, Sam Akehurst, Colin Copeland, Tomasz Duda, Richard Burke, Christian J. BraceAbstract:The adoption of two stage serial Turbochargers in combination with internal combustion engines can improve the overall efficiency of powertrain systems. In conjunction with the increase of engine volumetric efficiency, two stage boosting technologies are capable of increasing torque and pedal response of small displacement engines. In two stage serial turbocharges, a high pressure (HP) and a low pressure (LP) Turbocharger are connected by a series of ducts. The former can increase charge pressure for low air mass flow typical of low engine speed. The latter has a bigger size and can cooperate with higher mass flows. In serial configuration, Turbochargers are packaged in a way that the exhaust gases access the LP turbine after exiting the HP turbine. On the induction side, fresh air is compressed sequentially by LP and HP compressors. By-pass valves and waste-gated turbines are often included in two stage boosting systems in order to regulate Turbochargers operations. One-dimensional modelling approaches are considered for investigating the integration of boosting systems with internal combustion engines. In this scenario, Turbocharger behaviour are input in the powertrain models through previously measured compressor and turbine maps in Turbocharger gas stands. However, this procedure does not capture all the effects that occur on engine application such as heat transfer, friction and flow motion that influence the Turbochargers operations. This is of particular importance for two stage serial Turbochargers where the LP compressor may induce a swirling motion to the flow at the entry of the HP compressor. In addition, flow non-uniformities caused by bends between the two compressors can make the HP compressor perform differently. In this paper, a review of the available literature containing approaches to quantify the effects of heat transfer on Turbocharger efficiency and the flow influence in the prediction of two stage serial Turbochargers performance is explored.
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experimental and analytical investigation of implementing a ball bearing Turbocharger on a production diesel engine
11th International Conference on Turbochargers and Turbocharging#R##N#13–14 May 2014, 2014Co-Authors: Qingning Zhang, Sam Akehurst, Chris Brace, Tomasz Duda, Richard Burke, Geoff Capon, Peter G Dowell, Peter DaviesAbstract:Ball bearing Turbocharger technology has started to be adopted for mass-production engines due to the potential benefit in transient performance and fuel consumption. Compared to the conventional journal bearing, the low friction of the ball bearing allows the Turbocharger to accelerate faster so that the engine can be supplied with boost pressure more quickly following a transient torque request and under steady state offers reduced engine back pressure, which can reduce engine fuel consumption. In this study, the benefits of using a ball bearing Turbocharger compared to a conventional journal bearing Turbocharger were identified first in simulation and then validated in a back to back comparison of two otherwise identical Turbochargers through extensive experimental analysis.
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1 d simulation study of divided exhaust period for a highly downsized turbocharged si engine scavenge valve optimization
SAE International journal of engines, 2014Co-Authors: Sam Akehurst, Colin Copeland, Chris Brace, J W G TurnerAbstract:Fuel efficiency and torque performance are two major challenges for highly downsized turbocharged engines. However, the inherent characteristics of the turbocharged SI engine such as negative PMEP, knock sensitivity and poor transient performance significantly limit its maximum potential. Conventional ways of improving the problems above normally concentrate solely on the engine side or Turbocharger side leaving the exhaust manifold in between ignored. This paper investigates this neglected area by highlighting a novel means of gas exchange process. Divided Exhaust Period (DEP) is an alternative way of accomplishing the gas exchange process in turbocharged engines. The DEP concept engine features two exhaust valves but with separated function. The blow-down valve acts like a traditional turbocharged exhaust valve to evacuate the first portion of the exhaust gas to the turbine. While the scavenge valve feeding the latter portion of the exhaust gas directly into the low resistant exhaust pipe behaves similarly to valves in a naturally aspirated engine. By combining the characteristics of both turbocharged and naturally aspirated engines, high backpressure between the turbine inlet and the exhaust port is maintained in the blowdown phase while significant reduction of the backpressure could be achieved in the latter displacement phase. This is directly beneficial for pumping work and residual gas scavenging. Combustion phasing & stability and Turbocharger efficiency could also benefit from such concept. This simulation study was carried out using a validated 1D model of a highly downsized SI engine. Two degrees of freedom including the lift and the duration of the scavenge valve were optimized to achieve minimum BSFC. The potential for higher attainable BMEP was also briefly investigated at low engine speed.
J W G Turner - One of the best experts on this subject based on the ideXlab platform.
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1 d simulation study of divided exhaust period for a highly downsized turbocharged si engine scavenge valve optimization
SAE International journal of engines, 2014Co-Authors: Sam Akehurst, Colin Copeland, Chris Brace, J W G TurnerAbstract:Fuel efficiency and torque performance are two major challenges for highly downsized turbocharged engines. However, the inherent characteristics of the turbocharged SI engine such as negative PMEP, knock sensitivity and poor transient performance significantly limit its maximum potential. Conventional ways of improving the problems above normally concentrate solely on the engine side or Turbocharger side leaving the exhaust manifold in between ignored. This paper investigates this neglected area by highlighting a novel means of gas exchange process. Divided Exhaust Period (DEP) is an alternative way of accomplishing the gas exchange process in turbocharged engines. The DEP concept engine features two exhaust valves but with separated function. The blow-down valve acts like a traditional turbocharged exhaust valve to evacuate the first portion of the exhaust gas to the turbine. While the scavenge valve feeding the latter portion of the exhaust gas directly into the low resistant exhaust pipe behaves similarly to valves in a naturally aspirated engine. By combining the characteristics of both turbocharged and naturally aspirated engines, high backpressure between the turbine inlet and the exhaust port is maintained in the blowdown phase while significant reduction of the backpressure could be achieved in the latter displacement phase. This is directly beneficial for pumping work and residual gas scavenging. Combustion phasing & stability and Turbocharger efficiency could also benefit from such concept. This simulation study was carried out using a validated 1D model of a highly downsized SI engine. Two degrees of freedom including the lift and the duration of the scavenge valve were optimized to achieve minimum BSFC. The potential for higher attainable BMEP was also briefly investigated at low engine speed.
Antonio Garcia - One of the best experts on this subject based on the ideXlab platform.
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hd diesel engine equipped with a bottoming rankine cycle as a waste heat recovery system part 2 evaluation of alternative solutions
Applied Thermal Engineering, 2012Co-Authors: J R Serrano, V Dolz, Ricardo Novella, Antonio GarciaAbstract:Abstract A theoretical investigation has been performed on the feasibility of introducing a waste heat recovery (WHR) system in a two-stage turbocharged HDD engine. The WHR is attained by introducing a Rankine cycle, which uses an organic substance or directly water as a working fluid depending on energetic performance considerations. A previous research was carried out to evaluate the maximum potential of this WHR concept, a conventional layout was used for coupling the Rankine cycle to the thermal engine. The objective of the present research is to broad the scope of the previous analysis by considering new alternative solutions for the problems related to the coupling between the WHR Rankine cycle and the thermal engine. These solutions are based on adapting one of the Turbochargers by removing its turbine and trying to recover the energy by the Rankine cycle. Finally, the turbine of the Rankine cycle supplies the recovered energy directly to the compressor of this Turbocharger. Thus, in these layouts the coupling is simpler as it involves only two turbomachines, which are supposed to share a similar rotating speed. From the results of the global energy balance, these alternative layouts produce slight benefits in fuel consumption but in all cases these benefits are lower compared to those attained with conventional layouts.
Srithar Rajoo - One of the best experts on this subject based on the ideXlab platform.
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Performance evaluation of low-pressure turbine, turbo-compounding and air-Brayton cycle as engine waste heat recovery method
Energy, 2019Co-Authors: Aaron Edward Teo, Ricardo F. Martinez-botas, Meng Soon Chiong, Mo Yang, Alessandro Romagnoli, Srithar RajooAbstract:Abstract This paper presents an equivalent comparison of waste heat recovery method on an internal combustion engine using low-pressure turbine (LPT), turbo compound (TC) & air-Brayton cycle (ABC). A 5.9 L, six cylinders turbocharged diesel engine is used for this case study. All recovery methods are simulated on AVL BOOST where the engine model, Turbocharger and heat exchanger are validated with experimental data. It is found that all three methods cannot work effectively without at least reducing the Turbocharger turbine size to amplify the compressor surplus power. It is done by using a commercially available Turbocharger turbine with smaller area over radius (A/R) volute, hence ensuring the least possible engine hardware change. In all the cases, the engine is ensured to deliver its baseline brake power. It is shown that LPT can recover the most exhaust waste heat (up to 5.40 kW), followed by TC (up to 1.75 kW) and ABC (up to 0.64 kW).
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Aeroacoustics characterization methodology applicable to Turbocharger compressor
ARPN journal of engineering and applied sciences, 2015Co-Authors: Kishokanna Paramasivam, Srithar Rajoo, Danial Mohamed, Alesssandro Romagnoli, Alias Mohd NoorAbstract:Turbochargers have become an important part of modern high efficient engines, and soon will be a standard component. Almost all automotive and industrial diesel engines and most of the high performance SI engines are equipped with Turbocharger. Even though past few decades have seen continuous performance improvement, there is still lack of wide range research on acoustical behavior of Turbochargers. A Turbocharger consists of compressor which is driven by an exhaust turbine. Turbocharger produces high frequency aerodynamic sound due to the high speed rotating blade. The main aerodynamic noise generating mechanisms in turbo-compressors is tonal noise at blade passing frequencies, buzz-saw noise and blade tip clearance noise. The focus will be on tonal noise which occurs due to pressure fluctuation that is related to the rotating speed. The tonal noise is periodic in time where it consists of the blade passing frequency (BPF) and its harmonics. Higher rotating speed will result in a more prominent blade passing noise and its harmonics. The aim of this paper is to offer a methodology on characterizing the tonal noise of Turbocharger based on investigation of high speed turbo machinery, which also has similar acoustical behavior. This study will include results from commercial computational fluid dynamics (CFD) code and experimental with the sound pressure level distribution.
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Variable Geometry-Active Control Turbocharger Turbine
2010Co-Authors: Srithar Rajoo, Ricardo F. Martinez-botasAbstract:This manuscript presents the experimental evaluation of a variable geometry mixed flow Turbocharger turbine under steady and pulsating flow conditions. The variable geometry turbine is tested with two different nozzle vane designs, a conventional nozzle vane with straight-stacking and the newly designed nozzle vane with lean-stacking. The lean stacking design was established based on the lean leading edge geometry of a mixed flow turbine. Comprehensive and scientific elaborations are given on the design process, experimental setup and procedures as well as the extensive performance analysis. Additionally, a novel and patented turbocharging concept is introduced called, Active Control Turbocharger (A.C.T.). It is well established that automotive Turbochargers work under pulsating exhaust flow conditions, however this is not taken into consideration in its design process. A.C.T. provides an added advantage to a variable geometry Turbocharger in adapting to the pulsating exhaust flow, thus improving energy extractions.
Georges Descombes - One of the best experts on this subject based on the ideXlab platform.
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Experimental identification of Turbocharger mechanical friction losses
Energy, 2012Co-Authors: Michael Deligant, Pierre Podevin, Georges DescombesAbstract:Understanding the friction losses of automotive Turbochargers is a key parameter in assessing properly the mechanical efficiency of these machines. Current Turbochargers are mostly equipped with oil bearings: two journal bearings and one double-acting axial thrust bearing. In order to know on which element improvement efforts have to be focused, it is important to determine their contribution to the total friction losses. This will also make it possible to calibrate the computation models of friction losses of the bearings separately. Measuring the friction losses of a Turbocharger is not easy and existing methods measure only the total losses due to the association of journal and thrust bearings. A novel Turbocharger test bench equipped with a highly accurate torquemeter and a magnetic axial load device has been developed. Measuring methodologies have been fine-tuned to measure the total friction losses, the influence of axial load on the thrust bearing, and the mechanical friction losses of the journal bearings alone. The experimental device and measuring methods are detailed in this paper. Experimental results are presented and analysed. The influence of axial load, oil inlet pressure and the distribution of friction power and oil mass flow between thrust bearing and journal bearings are discussed.
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cfd model for Turbocharger journal bearing performances
Applied Thermal Engineering, 2011Co-Authors: Michael Deligant, Pierre Podevin, Georges DescombesAbstract:Abstract Whether due to the Kyoto protocol or the European regulation to come in 2015, but also due to customer requirements, fuel consumption, and hence CO2 emissions, have become one of the major issues for car manufacturers. One of the most efficient ways to reduce the fuel consumption is to downsize the engine, specifically by increasing the engine-specific power and torque, as well as reducing the engine displacement and using Turbochargers. To achieve this target efficiently, the assembly of an engine and a Turbocharger has to be well tuned. Turbocharger characteristics for low speeds are not provided by Turbocharger manufacturers because compressor maps for low speeds cannot be set up with “ordinary” test benches. Unfortunately, in urban conditions, for engines operating at low speeds (1500 rpm) and low torque, the Turbocharger speed is about 30000 rpm. In order to improve the performance of the turbocharged engine, the knowledge of the whole compressor map is required. The knowledge of compressor performances in the low speed area could be improved by a better understanding of mechanical efficiency. This paper proposes a 3D CFD model to compute power friction losses due to journal bearings. Computations were carried out for various oil entrance temperatures and rotational speeds. Results are presented and discussed, making comparisons with some sets of experiments carried out in the CNAM laboratory using a special Turbocharger test rig equipped with a torque meter.
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influence of the lubricating oil pressure and temperature on the performance at low speeds of a centrifugal compressor for an automotive engine
Applied Thermal Engineering, 2011Co-Authors: Pierre Podevi, Adria Clenci, Georges DescombesAbstract:Abstract Currently, turbocharged common rail high pressure direct injection diesel engines are regarded as state-of-the-art. The use of the turbocharging technique in gasoline engines is also increasing, in order to achieve further fuel consumption reductions via downsizing. As the specific power outputs of both diesel and gasoline engines rise, the low-end torque behavior of such engines and turbo-lag are becoming increasingly critical. This is primarily a result of the specific characteristics of Turbochargers and internal combustion engines themselves. When it comes to matching a Turbocharger to a given engine, the compressor map over the entire operating area has to be known with sufficient accuracy, especially at low Turbocharger speeds corresponding to the engine low part loads (i.e. urban traffic). This map is established assuming the adiabatic behavior of the compressor. While this assumption is acceptable at rather high speeds, it is no longer valid for low speeds, and for that reason, the compressor map in this area is not provided by the Turbocharger manufacturer. Worldwide, there are no standard guidelines for the correct measurement and calculation of Turbocharger maps at low speeds. In collaboration with a French automotive manufacturer, a special method was therefore designed and applied within the laboratory LGP2ES at Cnam Paris in order to obtain the compressor low speed map. A special torquemeter was fitted in a cold Turbocharger test bench, affording measurements from 30,000 rpm to 120,000 rpm. The experimental results presented in this paper show the combined effect of the lubricating oil temperature and pressure on the compressor performance, expressed in terms of compression ratio, compressor power, isentropic efficiency and mechanical efficiency. These results afford a better estimation of the compressor map at low speeds.