Feasibility Study of an Oil-Free Turbocharger Supported on Gas Foil Bearings via On-Road Tests of a 2-Liter Class Diesel Vehicle

2012 ◽  
Author(s):  
Kyuho Sim ◽  
Suk Bum Kwon ◽  
Tae Ho Kim ◽  
Yong-Bok Lee
Keyword(s):  
Feasibility Study ◽  
Vehicle Suspension ◽  
External Shocks ◽  
Variable Geometry Turbocharger ◽  
Foil Bearings ◽  
Synchronous Motion ◽  
Vehicle Engine ◽  
Compressor Impeller ◽  
Non Destructive ◽  
Diesel Vehicle

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, while being 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 sub-synchronous 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 roads. Sub-synchronous rotor motions initiate with a frequency of ∼100 Hz at the TC speed of ∼37 krpm. The TC rotor motion also shows multiple EG-induced harmonics, as expected. Upon external shocks given by passing the vehicle on road-bumps, the sub-synchronous motions are excited only when the rotor rotates above the initiation speed of sub-synchronous motion. The excitation is non-destructive 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.

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

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Yong-Bok Lee ◽  
Suk Bum Kwon ◽  
Tae Ho Kim ◽  
Kyuho Sim
Keyword(s):  
Feasibility Study ◽  
External Shocks ◽  
Variable Geometry Turbocharger ◽  
The Road ◽  
Foil Bearings ◽  
Synchronous Motion ◽  
Vehicle Engine ◽  
Compressor Impeller ◽  
On The Road ◽  
Diesel Vehicle

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.

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

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Yong-Bok Lee ◽  
Dong-Jin Park ◽  
Tae Ho Kim ◽  
Kyuho Sim
Keyword(s):  
Power Loss ◽  
Time Delays ◽  
Operating Conditions ◽  
Total Power ◽  
Stable Operation ◽  
Compressor Wheel ◽  
Foil Bearings ◽  
Vehicle Engine ◽  
Turbine Inlet ◽  
Diesel Vehicle

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.

Rotordynamic Performance of a Rotor Supported on Bump Type Foil Gas Bearings: Experiments and Predictions

2006 ◽  
Vol 129 (3) ◽  
pp. 850-857 ◽  
Author(s):  
Luis San Andrés ◽  
Dario Rubio ◽  
Tae Ho Kim
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Load Capacity ◽  
Test System ◽  
Foil Bearings ◽  
Rotor Imbalance ◽  
Synchronous Motion ◽  
Damping Characteristics ◽  
Rotor Surface ◽  
Stiffness And Damping

Gas foil bearings (GFBs) satisfy the requirements for oil-free turbomachinery, i.e., simple construction and ensuring low drag friction and reliable high speed operation. However, GFBs have a limited load capacity and minimal damping, as well as frequency and amplitude dependent stiffness and damping characteristics. This paper provides experimental results of the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10mm. Coast down rotor responses from 25krpm to rest are recorded for various imbalance conditions and increasing air feed pressures. The peak amplitudes of rotor synchronous motion at the system critical speed are not proportional to the imbalance introduced. Furthermore, for the largest imbalance, the test system shows subsynchronous motions from 20.5krpm to 15krpm with a whirl frequency at ∼50% of shaft speed. Rotor imbalance exacerbates the severity of subsynchronous motions, thus denoting a forced nonlinearity in the GFBs. The rotor dynamic analysis with calculated GFB force coefficients predicts a critical speed at 8.5krpm, as in the experiments; and importantly enough, unstable operation in the same speed range as the test results for the largest imbalance. Predicted imbalance responses do not agree with the rotor measurements while crossing the critical speed, except for the lowest imbalance case. Gas pressurization through the bearings’ side ameliorates rotor subsynchronous motions and reduces the peak amplitudes at the critical speed. Posttest inspection reveal wear spots on the top foils and rotor surface.

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