Research Papers: Gas Turbines: Structures and Dynamics

Development and Performance Measurement of Oil-Free Turbocharger Supported on Gas Foil Bearings

[+] Author and Article Information
Yong-Bok Lee

 Korea Institute of Science and Technology, Energy Mechanics Center, Seoul, Republic of Korealyb@kist.re.kr

Dong-Jin Park

 Korea Institute of Science and Technology, Energy Mechanics Center, Seoul, Republic of Koreadjpark@kist.re.kr

Tae Ho Kim

 Korea Institute of Science and Technology, Energy Mechanics Center, Seoul, Republic of Koreathk@kist.re.kr

Kyuho Sim

 Korea Institute of Science and Technology, Energy Mechanics Center, Seoul, Republic of Koreakhsim@kist.re.kr

J. Eng. Gas Turbines Power 134(3), 032506 (Jan 04, 2012) (11 pages) doi:10.1115/1.4004719 History: Received March 31, 2011; Revised July 18, 2011; Published January 04, 2012; Online January 04, 2012

This paper present the development of an oil-free turbocharger (TC) supported on gas foil bearings (GFBs) and its performance evaluation in a test rig driven by a diesel vehicle engine (EG). The rotor-bearing system was designed via a rotordynamic analysis with dynamic force coefficients derived from the analysis of the GFBs. The developed oil-free TC was designed using a hollow rotor with a radial turbine at one end and a compressor wheel at the other end, a center housing with journal and thrust GFBs, and turbine and compressor casings. Preliminary tests driven by pressurized shop air at room temperature demonstrated relatively stable operation up to a TC speed of 90,000 rpm, accompanied by a dominant synchronous motion of ∼20 μm and small subsynchronous motions of less than 2 μm at the higher end of the speed range. Under realistic operating conditions with a diesel vehicle engine at a maximum TC speed of 136,000 rpm and a maximum EG speed of 3140 rpm, EG and TC speeds and gas flow properties were measured. The measured time responses of the TC speed and the turbine inlet pressure demonstrated time delays of ∼3.9 and ∼1.3 s from that of the EG speed during consecutive stepwise EG speed changes, implying the GFB friction and rotor inertia led to time delays of ∼2.6 s. The measured pressures and temperatures showed trends following second-order polynomials against EG speed. Regarding TC efficiency, 4.3 kW of mechanical power was supplied by the turbine and 3.3 kW was consumed by the compressor at the top speed of 136,000 rpm, and the power loss reached 22% of the turbine power. Furthermore, the estimated GFB power losses from the GFB analysis were approximately 25% of the total power loss at higher speeds, indicating the remainder of the power loss resulted from heat transfer from the exhaust gas to the surrounding solid structures. Incidentally, as the TC speed was increased from 45,000 to 136,000 rpm, the estimated turbine inlet power increased from 19 to 79 kW, the compressor exit power increased from 7 to 26 kW, and the TC output mass flow rate from the compressor increased from 21 to 74 g/s. The average TC compressor exit power was estimated at ∼34% of the turbine inlet power over this range.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Configurations of TC rotors for (a) gas foil bearings (GFBs) and (b) floating ring bearings (FRBs)

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Figure 2

Schematic diagram of journal and thrust GFBs

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Figure 3

Predicted synchronous dynamic force coefficients for the long and short GFBs at the turbine and compressor sides, respectively. Solid lines indicate the long GFB, and dashed lines indicate the short GFB.

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Figure 4

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

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Figure 5

Predicted natural frequency versus rotor speed. ωn indicates critical speed. cpm indicates cycles per minute.

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Figure 6

Manufactured TC rotor and GFBs

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Figure 7

Drawing of oil-free TC assembly. Inset is the manufactured TC with impeller casings removed.

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Figure 8

Test rig for oil-free TC for preliminary tests at room temperature

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Figure 9

Measured lateral motions of TC rotor at compressor end: (a) orbital response at 90,000 rpm and (b) waterfall response to 90,000 rpm in the vertical direction

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Figure 10

Pressure ratio versus flow rate at the compressor measured at rotor speeds of 48,000, 60,000, 78,000, and 90,000 rpm

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Figure 11

Test rig for oil-free TC driven by a diesel vehicle engine

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Figure 12

Measured time responses of TC speed and pressures and temperatures at the compressor exit and turbine inlet to steep and stepwise changes of EG speed. EG and TC indicate engine and turbocharger, respectively.

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Figure 13

Measured TC speed and TC performance at increasing EG speed from 1420 to 3140 rpm: (a) pressure, (b) temperature, and (c) volume flow rate

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Figure 14

Mechanical power supplied by the turbine and consumed by the compressor and power losses versus TC speed from 45,000 to 136,000 rpm, along with estimated GFB power losses

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Figure 15

TC power and compressor mass flow versus TC speed from 45,000 to 136,000 rpm




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