COMPARISON OF FLOW FIELD BETWEEN STEADY AND UNSTEADY FLOW OF AN AUTOMOTIVE MIXED FLOW TURBOCHARGER TURBINE

Global decarbonizing efforts in transportation industry have forced the automotive manufacturers to opt for highly downsized high power-to-weight ratio engines. Since its invention, turbocharger remains as integral element in order to achieve this target. However, although it has been proven that a turbocharger turbine works in highly pulsatile environment, it is still designed under steady state assumption. This is due to the lack of understanding on the nature of pulsating flow field within the turbocharger turbine stage. This paper presents an effort to visualize the pulsating flow feature using experimentally validated Computational Fluid Dynamics (CFD) simulations. For this purpose, a lean-vaned mixed-flow turbine with rotational speed of 30000 rpm at 20 Hz flow frequency, which represent turbine operation for 3-cylinder 4-stroke engine operating at 800 rpm has been used. Results indicated that the introduction of pulsating flow has resulted in more irregular pattern of flow field as compared to steady flow operation. It has also been indicated that the flow behaves very differently between pressure increment and decrement instances. During the pressure decrement instance, flow blockage in terms of low pressure region occupies most of the turbine passage as the flow exit the turbine

Non-adiabatic pressure loss boundary condition for modelling turbocharger turbine pulsating flow

This paper presents a simplified methodology of pulse flow turbine modelling, as an alternative over the meanline integrated methodology outlined in previous work, in order to make its application to engine cycle simulation codes much more straight forward. This is enabled through the development of a bespoke non-adiabatic pressure loss boundary to represent the turbine rotor. In this paper, turbocharger turbine pulse flow performance predictions are presented along with a comparison of computation duration against the previously established integrated meanline method. Plots of prediction deviation indicate that the mass flow rate and actual power predictions from both methods are highly comparable and are reasonably close to experimental data. However, the new boundary condition required significantly lower computational time and rotor geometrical inputs. In addition, the pressure wave propagation in this simplified unsteady turbine model at different pulse frequencies has also been found to be in agreement with data from the literature, thereby supporting the confidence in its ability to simulate the wave action encountered in turbine pulse flow operation

Downsizing Capability Evaluation of Active Control Turbocharger (ACT)

This study aims to evaluate the downsizing capability of active control turbocharger (ACT) by means of computer simulation approach. One dimensional simulation package was used to model a commercial 13L diesel engine equipped with variable geometry turbocharger (VGT) and a 10L diesel engine equipped ACT. The 10L ACT engine delivered up to 34.42% of higher brake power than 13L VGT engine at 1000RPM and below, but for the higher engine speed, 13L VGT engine delivered higher brake power (up to 14.5%) than 10L ACT engine

Unsteady performance of a mixed-flow turbine with nozzled twin-entry volute confronted by pulsating incoming flow

Turbine with twin-entry volute has advantage of utilising energy from pulsatile exhaust gas and improving low-speed torque of an internal combustion engine. This paper investigates unsteady performance of a mixed flow turbine with nozzled twin-entry volute confronted by pulsatile incoming flow. The turbine performance at pulsating conditions with different Strouhal numbers (St) is studied via experimentally validated numerical method. Results show that the unsteadiness of turbine performance is enhanced as Strouhal number increases. In particular, the cycle-average efficiency at St = 0.522 is about 3.4% higher than that of quasi-steady condition (St = 0). Instantaneous loss breakdown of the turbine shows that the entropy generation rate of turbine components reduces evidently at pulsating conditions as Strouhal number increases, especially for the nozzle. Specifically, the cycle-averaged reduction of the loss in the nozzle is 37.3% at St = 0.522 compared with that of St = 0. The flow analysis shows that secondary flow which contributes to the majority of loss in the nozzle, including flow separation, horseshoe vortex, and reversed flow near the leading edge, are notably alleviated as Strouhal number increases. The alleviation of the flow structures are resulted from two reasons: one is that the flow distortion at the nozzle inlet is evidently depressed by the pulsating conditions, the other is that the inertia of the low momentum flow in the nozzle damps flow evolution at pulsating incoming flow. Consequently, the loss is reduced and the turbine performance is benefited by the pulsating inflows

Ultra Boost for Economy: Extending the Limits of Extreme Engine Downsizing

The paper discusses the concept, design and final results from the ‘Ultra Boost for Economy’ collaborative project, which was part-funded by the Technology Strategy Board, the UK's innovation agency. The project comprised industry- and academia-wide expertise to demonstrate that it is possible to reduce engine capacity by 60% and still achieve the torque curve of a modern, large-capacity naturally-aspirated engine, while encompassing the attributes necessary to employ such a concept in premium vehicles. In addition to achieving the torque curve of the Jaguar Land Rover naturally-aspirated 5.0 litre V8 engine (which included generating 25 bar BMEP at 1000 rpm), the main project target was to show that such a downsized engine could, in itself, provide a major proportion of a route towards a 35% reduction in vehicle tailpipe CO2 on the New European Drive Cycle, together with some vehicle-based modifications and the assumption of stop-start technology being used instead of hybridization. In order to do this vehicle modelling was employed to set part-load operating points representative of a target vehicle and to provide weighting factors for those points. The engine was sized by using the fuel consumption improvement targets and a series of specification steps designed to ensure that the required full-load performance and driveability could be achieved. The engine was designed in parallel with 1-D modelling which helped to combine the various technology packages of the project, including the specification of an advanced charging system and the provision of the necessary variability in the valvetrain system. An advanced intake port was designed in order to ensure the necessary flow rate and the charge motion to provide fuel mixing and help suppress knock, and was subjected to a full transient CFD analysis. A new engine management system was provided which necessarily had to be capable of controlling many functions, including a supercharger engagement clutch and full bypass system, direct injection system, port-fuel injection system, separately-switchable cam profiles for the intake and exhaust valves and wide-range fast-acting camshaft phasing devices. Testing of the engine was split into two phases. The first usied a test bed Combustion Air Handling Unit to enable development of the combustion system without the complication of a new charging system being fitted to the engine. To set boundary conditions during this part of the programme, heavy reliance was placed on the 1-D simulation. The second phase tested the full engine. The ramifications of realizing the engine design from a V8 basis in terms of residual friction versus the fuel consumption results achieved are also discussed. The final improvement in vehicle fuel economy is demonstrated using a proprietary fuel consumption code, and is presented for the New European Drive Cycle, the FTP-75 cycle and a 120 km/h (75 mph) cruise condition

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field

Design methodology for radial turbo expanders in mobile organic Rankine cycle applications

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

Development of Active Flow Control in a Turbocharger Turbine for Emission Reduction

The increase in particle emissions restrictions in recent years coupled with improvements in such key automotive engine performance areas as low-end torque, increased boost and the elimination of turbolag now required, has led to conventional Variable Geometry Turbochargers (VGTs) to become quite popular in matching turbine inlet geometry to the characteristics of the exhaust gas stream throughout the engine operating range. However, over all these years of turbocharger development the fundamental issue of the less than ideal combination of a reciprocating engine providing energy to drive a rotodynamic machine such as a turbocharger turbine has not been addressed satisfactorily. This paper, therefore, introduces a new concept in turbocharger development, namely, that of active turbocharger flow control. It demonstrates the application of an active flow control device (nozzle) at the inlet to the turbine rotor to help harness the energy contained as a result of the pulsating characteristics of the incoming flow. In the Active Control Turbocharger (ACT), therefore, the nozzle (in this case a sliding vane) is able to alter the inlet area at the throat of the turbine inlet casing (volute) in phase and at the same frequency as that of the incoming exhaust stream pulses. Actuated by a high speed electrodynamic shaker the nozzle can adapt according to the engine exhaust gas pulse pressure variation, thus taking advantage of the lower energy levels existent before and after each pulse pressure peak, which the current systems do not take advantage of. Thus, ACT makes better use of the exhaust gas energy of the engine than a conventional VGT. The experimental work concentrates on the potential gain in turbine expansion ratio and eventual power output as well as the corresponding efficiency trace and nozzle area schedule. Exploration of the full turbine range was made possible by the use of a new eddy-current dynamometer, also, presented here. Early simulation work has, already, provided encouraging results with a theoretical potential gain in terms of cycle expansion ratio and actual power output of approximately 9% and 29%, respectively at typical engine operating points (40Hz or equivalent to 1600 engine rpm). Direct comparisons between VGT and ACT operation are also provided, at selected, typical, laboratory-simulated engine operating conditions, showing the benefits arising from the use of this innovative technology

Radial turbine rotor response to pulsating inlet flows

The performances of automotive turbocharger turbines have long been realized to be quite different under pulsating flow conditions compared to that under the equivalent steady and quasi-steady conditions on which the conventional design concept is based. However, the mechanisms of this phenomenon are still intensively investigated nowadays. This paper presents an investigation of the response of a stand-alone rotor to inlet pulsating flow conditions by using validated unsteady Reynolds Averaged Navier-Stokes solver (URANS). The effects of the frequency, the amplitude and the temporal gradient of pulse waves on the instantaneous and cycle integrated performances of a radial turbine rotor in isolation were studied, decoupled from the upstream turbine volute. Numerical method was used to help gaining the physical understandings of these effects. A validation of the numerical method against the experiments on a full configuration of the turbine has been performed prior to the numerical tool being used in the investigation. The rotor is then taken out to be studied in isolation. The results show that the turbine rotor alone can be treated as a quasi-steady device only in terms of cycle integrated performance; however, instantaneously, the rotor behaves unsteadily which increasingly deviates from the quasisteady performance as the local Strouhal number of the pulsating wave is increased. This deviation is dominated by the effect of quasi-steady time-lag; at higher local Strouhal number, the transient effects also become significant. Based on this study, an interpretation and a model of estimating the quasisteady time lag have been proposed; a criterion for unsteadiness based on the temporal local Strouhal number concept is developed, which reduces to the Λcriterion proposed in the published literature when cycle averaged; this in turn emphasizes the importance of the pressure wave gradient in time. Copyright © 2013 by ASME