• Proceedings of the KSR Conference
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• 2009.05b
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• pp.615-619
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• 2009

There are many increasing demands for efficient high power density of auxiliary power unit(APU) for high speed traction application. Many techniques have been proposed to measure the voltage flicker on the traditional pulse width modulation(PWM) inverter. This paper proposes a novel functionality of the static inverter on the APU to mitigate the voltage flicker and regulate the output voltage. A new control algorithm for the inverter based on the Hilbert transform(HT) is presented. The HT is employed as an effective technique for tracking the voltage flicker levels in APU systems. Simulation results are provided to verify the tracking capabilities of the HT and to evaluate the performance of the proposed DG interface for multi-function operation.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1162-1169
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• 2009

Two kinds of welding methods were carried out for 22APU stainless steel, one is a Laser welding and the other is the TIG welding. In this case, difference of corrosion characteristics of welded zone with two welding methods mentioned above was investigated with electrochemical methods such as measurement of corrosion potential, polarization curves and cyclic voltammogram etc.. Vickers hardness of all welded zone (WM:Weld Metal, HAZ:Heat Affected Zone, BM:Base Metal)in the case of Laser welding showed a relatively higher value than those of TIG welding. Futhermore their corrosion current density in all welding zone were also observed with a lower value compared to TIG welding. In particular corrosion current density of BM regardless of welding method indicated the lowest value than those of other welding zone. Intergranular corrosion was not observed at the corroded surface of all welding zone in the case of Laser welding, however it was observed at WM and HAZ with TIG welding, which is suggested that chromiun depletion due to forming of chromium carbide appears to WM and HAZ which is in the range of sensitization temperature. Therefore their zone can easily be corroded with more active anode. Consequently we can see that corrosion resistance of all welding zone of 22APU stainless steel can apparently be improved by using of Laser welding.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.11-11
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• 2000

가스터빈엔진의 연소기는 개발 방법상 가장 시험에 의존적인 구성품 중의 하나로 성공적인 개발을 위해서는 설계자의 경험 및 수많은 시험 평가가 필수적으로 수반된다. 본 논문에서도 삼성테크윈(주)과 한국항공우주연구소에서 공동 개발중인 APU 용 연소기에 대하여 이러한 설계 및 시험 개발 연구 과정 및 결과를 중심으로 기술하였다.(중략)

• Journal of Ocean Engineering and Technology
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• v.26 no.4
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• pp.64-69
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• 2012

Laser welding was carried out on austenitic 304 (STS 304) and 22 APU stainless steels. In this case, the differences between the corrosion characteristics of the welding zones of the two stainless steels were investigated using electrochemical methods. The Vickers hardness values of the weld metal (WM) zones in both cases, the STS 304 and 22 APU stainless steels, showed relatively higher values than those of other welding zones. The corrosion current densities of the heat affected zone (HAZ) of the 22 APU and the base metal (BM) zone of the STS 304 exhibited the highest values compared to the other welding zones. It is generally accepted that when STS 304 stainless steel is welded using a general welding method, intergranular corrosion is often observed at the grain boundary because of its chromium depletion area. However, when laser welding was performed on both the STS 304 and 22 APU stainless steels, no intergranular corrosion was observed at any of the welding zones. Consequently, it is considered that the intergranular corrosion of stainless steel can be controlled with the application of laser welding.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.840-845
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• 2001

Development of a small gas-turbine combustor for 100kW class APU(Auxiliary Power Unit) has been performed. This combustor is a reverse-annular type and has a tangential swirler in the liner head to improve the fuel/air mixing and flame stability. Three main and three pilot fuel injectors of the simplex pressure-swirl type are used. The performance target at the design condition includes a turbine inlet temperature of 1170K, a combustion efficiency of 99%, a pattern factor of 30%, and an engine durability of 3000 hours. Under developing the combustor, we conducted performance test of our first prototype(TS1) with some variants. As a result of the test, the performance targets of the combustor are satisfied except that the pattern factor is about 4% higher than target value. So, we redesigned the second prototype(TS2) and conduct performance test with the critical focus on pattern factor and exit mean temperature. We adopted TS2 four variant to check the improvement of pattern factor. As the result, the pattern factors of several variants were satisfied with the performance target. Finally, We chose the TS2A variant as a final combustor for our APU model.

• Journal of Mechanical Science and Technology
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• v.17 no.1
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• pp.57-63
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• 2003

An eigenvalue design sensitivity formulation of a general nonsymmetric-matrix rotor-bearing system is devised. using the DDM (direct differential method). Then, investigations on the design sensitivities of critical speeds are carried out for an APU turbogenerator with a spline shaft connection. Results show that the dependence of the rate of change of the critical speed on the stiffness changes of bearing models of spline shaft connection points is negligible, and thereby their modeling uncertainty does not present any problem. And the passing critical speeds up to the 4th critical speed are not sensitive to the design stiffness coefficients of four main bearings. Further, the dependence of the rate of change of the critical speed on the shaft-element length changes shows quantitatively that the spline shaft has some limited influence on the 4th critical speed but no influence on the 1st to 3rd critical speeds. With no adverse effect from the spline shaft, the APU system achieves a critical speed separation margin of more than 40% at a rated speed of 60,000 rpm.

• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.394-398
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• 2019

In this paper, the joining characteristics of GDC-LSM ceramics with Crofer 22 APU metal alloys was investigated at different brazing temperatures and holding times by reactive air brazing. Brazing was performed using Ag-10 wt% CuO filler, at three different temperatures (1000, 1050, and 1100℃ for 30 minutes) as well as for three different holding times (10, 30, and 60 minutes at 1050℃). The interfacial microstructures were examined by scanning electron microscopy and the joining strengths were assessed by measuring shear strengths at room temperature. The results show that with increasing brazing temperature and holding time, joint microstructure changed obviously and shear strength was decreased. Shear strength varied from a maximum of 100±6 MPa to a minimum of 18±5 MPa, depending on the brazing conditions. These changes were attributed to an increase in the thickness of the oxide layer at the filler/metal alloy interface.

• Transactions of The Korea Fluid Power Systems Society
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• v.6 no.2
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• pp.1-6
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• 2009

The APU(Auxiliary Power Unit) needs a set of complex pipeline for the fuel supply system where some of the main valves controlling the flow rate consist of the servo valve worked with a torque motor. The input electric current produces an induced magnetic field almost perpendicular to the background magnetic filed generated by fixed permanent magnets. The induced torque deforms the tubular bushing, and directly rotates an armature, which can open and close the valve. In this study, we start from a basic analytic model using a simple electro-magneto-statics, and expand our model to the three-dimensional one computationally applying a commercial code named COMSOL. The result is compared with each other, and reasonable numerical data are obtained for the dynamic behavior and multi-physics system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.825-828
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• 2010

APU for aircraft is operated under severe condition as high altitude and low temperature, and demand high reliability in flight. This study is to be verified of the ignition and the combustion stability of APU under the harsh conditions. The basic data obtained in combustion rig test were directly applied to the altitude test with a engine. That start logic was obtained in ground development test. The results of altitude test show that air swirl injector has good operation and ignition performance at 20kft, hot/cold($-40^{\circ}C$) day.

• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.3
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• pp.281-287
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• 2016

The purpose of this study is to analyze the vibration characteristics and develop a mounting which can improve the strength safety factor to replace the high failure rate APU(auxiliary power unit) imported metal mounts with rubber mount that can be domestically produced. For this study, we analyzed in 3 kinds of rubber mounts hardness for the natural frequency to avoid the average excited frequency of the APU. In addition, allowed vibration acceleration of rubber mount confirmed to 90.8 g by adding a strength safety factor. To assure the validity of the design, we measure the vibration acceleration equipped with a metal mount and rubber mount 2 species(Hs 50 and 60). As a result, the proposed design method in this study is reasonable because the rubber mounts is excellent strength safety factor and vibration transmissibility than metal mounts.