Research Papers: Gas Turbines: Vehicular and Small Turbomachines

Feasibility Study of an Oil-Free Turbocharger Supported on Gas Foil Bearings Via On-Road Tests of a Two-Liter Class Diesel Vehicle

[+] Author and Article Information
Yong-Bok Lee

Principal Research Scientist Center for Urban Energy System,
Korea Institute of Science and Technology,
39-1 Hawolgok-dong, Songbuk-gu,
Seoul, Korea, 136-791

Suk Bum Kwon

Research Assistant

Tae Ho Kim

Assistant Professor
School of Mechanical Systems Engineering,
Kookmin University,
Jeongneung 3-dong, Seongbuk-gu,
Seoul, Korea 136-702

Kyuho Sim

Department of Mechanical System Design Engineering,
Seoul National University of Science and Technology,
232 Gongneung-ro, Nowon-gu 139-743,
Seoul, Korea, 139-743

1Conducted work as a senior research scientist at Korea Institute of Science and Technology.

2Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received September 24, 2012; final manuscript received September 24 2012; published online April 23, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(5), 052701 (Apr 23, 2013) (10 pages) Paper No: GTP-12-1375; doi: 10.1115/1.4007883 History: Received September 24, 2012; Revised September 24, 2012

This paper presents the feasibility study of an oil-free turbocharger (TC) supported on gas foil bearings (GFBs) via on-road tests of a 2-liter class diesel vehicle. The oil-free TC is constructed using a hollow rotor with a radial turbine at one end and a compressor impeller at the other end, a center housing with journal and thrust GFBs, and turbine and compressor casings. The oil-free TC reuses parts of a commercial variable geometry turbocharger, except for the rotor-bearing system. In a test rig driven by a diesel vehicle engine (EG), the rotordynamic performance of the oil-free TC is evaluated up to the rotor speed of 130 krpm, which is measured at the compressor end. The journal GFBs are modified to enhance the rotordynamic performance by inserting three metal shims between the bump-strip layers and bearing housing. The rotordynamic performance is also measured during on-road tests by replacing the original TC of the test diesel vehicle with the constructed oil-free TC. The journal GFBs have a relatively large bearing clearance and no metal shims to generate subsynchronous motions at low TC and EG speeds. During normal vehicle driving, the TC rotor motions show steady rotordynamic operations. The oil-free TC rotates at 25 krpm ∼ 50 krpm while the vehicle runs at 20 km/h ∼ 30 km/h on the road. Subsynchronous rotor motions initiate with a frequency of ∼100 Hz at the TC speed of ∼37 krpm. As expected, the TC rotor motion also shows multiple EG-induced harmonics. Upon external shocks, produced by driving the vehicle on road-bumps, the subsynchronous motions are only excited when the rotor rotates above the initiation speed of subsynchronous motion. The excitation is nondestructive because the vehicle suspension absorbs most of the external shock. Incidentally, the external shocks appear to have no influence on the synchronous motion and engine-induced harmonics of the TC rotor.

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Fig. 1

Schematic of bump-type test GFBs, journal and thrust. Three 30 μm metal shims were used for preload: (a) journal GFB and (b) thrust GFB.

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Fig. 2

Picture of test oil-free TC: (a) oil-free TC rotor, (b) journal and thrust GFBs, and (c) oil-free TC assembly with impeller casing removed

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Fig. 3

GFB displacement versus static load recorded during consecutive loading–unloading tests. Estimated nominal radial clearance C = 100 μm: (a) static load performance measurement test rig and (b) GFB displacement versus static load.

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Fig. 4

Finite-element model of oil-free TC rotor on journal GFBs

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Fig. 5

Predicted synchronous dynamic force coefficients for original and shimmed GFBs of long GFBs at the turbine side: (a) stiffness coefficients and (b) damping coefficients

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Fig. 6

Predicted natural frequency versus rotor speed for original and shimmed GFBs. CON and CYL indicates conical and cylindrical rigid modes.

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Fig. 7

Test rig for oil-free TC driven by diesel vehicle engine (2.0 liter, four cylinders, combustion-ignited, intercooled, and turbocharged): (a) oil-free TC driven by a diesel vehicle engine and (b) magnified view for sensors

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Fig. 8

Measurements of engine crank shaft speed and vibration frequency of engine-induced harmonics in TC rotor motion. EG indicates engine.

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Fig. 9

Measured lateral motions of TC rotor in the vertical direction at compressor end with four-pad thrust GFBs: (a) circular journal GFBs with C = 50 μm and (b) shimmed journal GFBs with C = 50 μm

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Fig. 10

Picture of failed TC rotor and GFBs from the experiment in Fig. 9(b)

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Fig. 11

Measured TC rotor motions in vertical and axial directions at compressor end with shimmed journal GFBs (C = 50 μm) and five-pad thrust GFBs: (a) waterfall of lateral motion (vertical direction), (b) waterfall of axial motion, (c) axial position, and (d) picture of five-pad thrust GFBs

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Fig. 12

Calculated total bearing loads for four and five pad thrust GFBs against inclined angle from 20 deg to 50 deg. Total bearing load is summation of each pad bearing load. Minimum film thickness on flat plane is 5 μm.

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Fig. 13

Picture of test oil-free TC installed into test diesel vehicle, viewed from vehicle bottom. EG is behind TC.

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Fig. 14

Overall waterfall response of measured lateral motions of test TC rotor in the vertical direction at compressor end from on-road vehicle tests. “Amp” and “EG” denote amplitude and engine.

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Fig. 15

Picture of oil-free TC rotor and GFBs after on-road vehicle test

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Fig. 16

Measured TC rotor lateral motions and TC housing acceleration of test oil-free TC in the vertical direction at compressor end from on-road tests, magnified from 120 sec to 176 sec: (a) waterfall response of TC rotor lateral motion, (b) contour plot of TC rotor lateral motion, and (c) contour plot of TC housing acceleration

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Fig. 17

Predicted synchronous dynamic force coefficients for the circular and shimmed GFBs of the short GFBs at compressor: (a) stiffness coefficients and (b) damping coefficients

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Fig. 18

Pressure distribution on one pad of (a) four pad with inclined angle of 45 deg and (b) five pad with inclined angle of 35 deg



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