Experimental Evaluation of Active Flow Control Mixed-Flow Turbine for Automotive Turbocharger Application

[+] Author and Article Information
Apostolos Pesiridis

 Imperial College London, Department of Mechanical Engineering, United Kingdom

Ricardo F. Martinez-Botas1

 Imperial College London, Department of Mechanical Engineering, United Kingdom


Address all correspondence to this author.

J. Turbomach 129(1), 44-52 (Feb 01, 2005) (9 pages) doi:10.1115/1.2372778 History: Received October 01, 2004; Revised February 01, 2005

In the current paper we introduce an innovative new concept in turbochargers—that of using active control at the turbine inlet with the aim of harnessing the highly dynamic exhaust gas pulse energy emanating at high frequency from an internal combustion engine, in order to increase the engine power output and reduce its exhaust emissions. Driven by the need to comply to increasingly strict emissions regulations as well as continually striving for better overall performance, the active control turbocharger is intended to provide a significant improvement over the current state of the art in turbocharging: the Variable Geometry Turbocharger (VGT). The technology consists of a system and method of operation, which regulate the inlet area to a turbocharger inlet, according to each period of engine exhaust gas pulse pressure fluctuation, thereby actively adapting to the characteristics of the high frequency, highly dynamic flow, thus taking advantage of the highly dynamic energy levels existent through each pulse, which the current systems do not take advantage of. In the Active (Flow) Control Turbocharger (ACT) the nozzle is able to adjust the inlet area at the throat of the turbine inlet casing through optimum amplitudes, at variable out-of-phase conditions and at the same frequency as that of the incoming exhaust stream pulses. Thus, the ACT makes better use of the exhaust gas energy of the engine than a conventional VGT. The technology addresses, therefore, for the first time the fundamental problem of the poor generic engine-turbocharger match, since all current state of the art systems in turbocharging are still passive receivers of this highly dynamic flow without being able to provide optimum turbine inlet geometry through each exhaust gas pulse period. The numerical simulation and experimental work presented in this paper concentrates on the potential gain in turbine expansion ratio and eventual power output as well as the corresponding effects on efficiency as a result of operating the turbocharger in its active control mode compared to its operation as a standard VGT.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 12

Pressure recovery achieved by an ACT compared to a VGT at 50% equivalent speed at 20Hz (simulated exhaust gas frequency)

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Figure 1

The active control concept for turbochargers. Exhaust process cycle (240° CA) for one cylinder, where the nozzle gap (1) is in the minimum gap position at the start of the exhaust process, and progressively opens up to the fully open position (2) at peak pressure and then retracts back to the minimum vane gap position (3) at the end of the exhaust process

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Figure 2

(a) Turbocharger test rig schematic and (b) laboratory schematic of major high-speed data acquisition hardware and software as well as the setup for ACT control

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Figure 3

ACT sectional view with Mixed Flow Turbine. The thin section nozzle can be seen protruding axially at the inlet to the turbine. The supporting guides and part of the actuator yoke are, also, shown

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Figure 4

(a) Active control turbocharger exploded view and (b) assembled turbocharger

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Figure 5

Active control turbocharger with electrodynamic shaker and dynamometer

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Figure 6

(a) to (f) Steady state turbine maps for 50%, 60%, and 70% equivalent speeds

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Figure 7

Overall steady state VGT map for 70% equivalent speed. At each normalized throat open area (0.538, 0.385, 0.231, 0.173) constant speed parameter curves can be seen (26.8, 32.2, and 37.5)

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Figure 8

(a) Turbine expansion ratio, (b) actual power, and (c) efficiency plots with changing turbine inlet areas at 70% equivalent speed for different loads

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Figure 9

A comparison of VGT and ACT simulation results. (a) Benefit in actual power, (b) pressure recovered, and (c) efficiency drop during one pulse

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Figure 10

Available nozzle amplitude performance over the test frequency range

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Figure 11

Nozzle (LVDT position signal) lag in relation to the FWG control input waveform (35ms lag in this case) during a 50ms pulse period (20Hz)



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