Small Gas Turbine Research Articles

A Novel Three-Phase Single-Stage Distributed Power Inverter

In this paper, a novel three-phase, DC/AC converter suitable for distributed power applications is proposed. The system consists of three DC/DC boost converters with a common point and operating as a three-phase inverter with intrinsic step-up capability. The converter obtained can invert, amplify and, where possible, regenerate bidirectional power sources such as fuel-cells, small gas turbines, and photovoltaic arrays. There are two main advantages to the system: the use of only six insulated gate bipolar transistors and small passive elements, and the fact that it does not need reverse voltage blocking capability. Simulation and experimental results show the effectiveness of the proposed system during both steady-state and dynamic operations.

DESIGN AND DEVELOPMENT OF A 70 N THRUST CLASS TURBOJET ENGINE

Small turbojet engines are being used for propulsion of radio-controlled model airplanes. The design and development of the model 505 small jet engine are reviewed. Small size gas turbines present special design and construction difficulties, some of which are addressed; design choices leading to the final configuration are discussed. Aero-thermodynamic aspects are covered along with experimental data when available. The unit is comprised of a radial compressor, an annular combustion chamber, and an axial turbine plus accessories; details on these components and on production aspects are presented.

DESIGN AND DEVELOPMENT OF A 70 N THRUST CLASS TURBOJET ENGINE

Small turbojet engines are being used for propulsion of radio-controlled
model airplanes. The design and development of the model 505 small jet
engine are reviewed. Small size gas turbines present special design and
construction difficulties, some of which are addressed; design choices
leading to the final configuration are discussed. Aero-thermodynamic
aspects are covered along with experimental data when available. The unit
is comprised of a radial compressor, an annular combustion chamber, and
an axial turbine plus accessories; details on these components and on
production aspects are presented.

Uncertainty Analysis and Improvement of an Altitude TestFacility for Small Jet Engines

The verification and improvement of the measurement uncertainty have beenperformed in the altitude test facility for small gas turbine engines, which was built atthe Korea Aerospace Research Institute (KARI) in October 1999. This test is performedwith a single spool turbojet engine at several flight conditions. This paper discussesthe evaluation and validation process for the measurement uncertainty improvements usedin the altitude test facility. The evaluation process, defined as tests before the facilitymodification, shows that the major contnbutors to the measurement uncertainty are theflow meter discharge coefficient, the inlet static and total pressures, the cell pressureand the fuel flow rate. The measurement uncertainty is focused on the primary parametersof the engine performance such as airflow rate, thrust and specific fuel consumption (SFC).The validation process, defined as tests after the facility modification, shows that themeasurement uncertainty, in seal level condition, is tmproved to the acceptable level throughthe facility modification. In altitude test conditions, the measurement uncertainties arenot improved as much as the uncertainty in sea level condition.

An experimental investigation into the use of molten carbonate fuel cells to capture CO 2 from gas turbine exhaust gases

As part of its climate change mitigation initiative, BP is evaluating technologies for the separation and capture of CO 2 from combustion sources, for subsequent geologic storage. Ansaldo Fuel Cells S.p.A. is developing molten carbonate fuel cell (MCFC) technology targeted at industrial applications from 50 kW to 10 MW. This paper describes the conceptual design of a hybrid MCFC system to generate power and simultaneously capture CO 2 from small (<10 MW) gas turbine exhaust streams. Initial modeling studies indicated that a 1.6 MW MCFC could reduce the CO 2 emissions from a 4.6 MW gas turbine by 50% on a per kWh basis. Experimental studies are in progress to understand the system behaviour, operating envelope and impact of contaminants. Initial data from these investigations are presented, which confirm that the fuel cell can operate at sub-optimal CO 2 levels with limited loss in power and efficiency.

KGT-74소형 가스터빈 블레이드의 진동 신뢰성 평가

To ensure a safe operation of the prototype KGT-74 kW small gas turbine, vibrational reliabilities of the compressor 1st, 2nd, and 3rd stages and turbine blades have been estimated and reviewed. FE analyses have been carried out to obtain the natural vibration characteristics of the blades, and impact modal testings have been performed on every each one of the blades to measure their 1st natural frequencies. Then, the Campbell diagram analyses have been carried out to judge the safety of the blades from resonant failures up to 6k harmonics. Results show that the compressor 1st stage blade is exposed to a potential resonant failure with 3k harmonic around a rated speed of 30,000 rpm but that the other compressor 2nd and 3rd stages and turbine blades are safe from resonant failures. Finally, 27,900 rpm is selected as the safe operation limit for the KGT-74 ㎾ gas turbine relative to the blade vibrations.

Operation of a Mesoscopic Gas Turbine Simulator at Speeds in Excess of 700,000rpm on Foil Bearings

A small mesoscopic gas turbine engine (MGTE) simulator was tested at speeds over 700,000rpm. The MGTE was operated with specially designed miniature compliant foil journal and thrust air bearings. The operation of the simulator rotor and foil bearing system is a precursor to development of turbine powered micro-aerial vehicles and mesoscopic power generators. The foil bearings use a new fabrication technology in which each bearing is split. This feature permits the use of these bearings in highly advanced engines where single piece ceramic rotors may be required. The simulator weighed 56g (including the 9g rotor) and included two non-aerodynamic wheels to simulate the compressor and turbine wheels. Each compliant foil journal bearing had a diameter of 6mm and was located equidistant from each end of the rotor. Experimental work included operation of the simulator at speeds above 700,000rpm and at several different orientations including having the spin axis vertical. Results of the rotor bearing system dynamics are presented along with experimentally measured natural frequencies at many operating speeds. Good correlation between measurement and analysis is observed indicating the scalability of the analysis tools and hardware used. The rotor was very stable and well controlled throughout all testing conducted. Based on this successful testing it is expected that the goal of operating the rotor at speeds exceeding 1 million rpm will be achieved.

Small gas turbine technology

Small Gas Turbine Technology: Small gas turbine, in the power range up to 500 kW, requires a recuperated thermodynamic cycle to achieve an electrical efficiency of about 30%. This efficiency is the optimum, which is possible for a cycle pressure ratio of about 4–1. The cycle airflow is function of the power requirement. To increase the efficiency, in view to reduce the CO 2 emission, it is mandatory to develop a more efficient thermodynamic cycle. Different thermodynamic cycles were examined and the final choice was made for an Intercooled, Recuperated cycle. The advantage of this cycle, for the same final electrical efficiency of about 35%, is the smaller cycle airflow, which is the most dimensional parameter for the important components as the heat exchanger recuperator and the combustion chamber. In parallel with the thermodynamic cycle it is necessary to develop the High Speed Alternator technology, integrated on the same shaft that the gas turbine rotating components, to achieve the constant efficiency at part loads, from 50% up to 100%, by the capacity to adjust the engine speed at the required load. To satisfy the stringent requirement in pollutant emissions of NO x and CO, the catalytic combustion system is the most efficient and this advance technology has to be proven. The major constraints for the small gas turbine technology development are the production cost and the maintenance cost of the unit. In the power range of 0–500 kW the gas turbine technology is in competition with small reciprocating engines, which are produced in large quantity for automotive industry, at a very low production cost.

Cyclone gasifier and cyclone combustor for the use of biomass derived gas in the operation of a small gas turbine in cogeneration plants

An inverted cyclone gasifier and secondary cyclone combustor have been developed for use in a biomass fired small-scale cogeneration plant. The gasifier was designed with a vortex collector pocket (VCP) and a central collector pocket (CCP) to maximise particle and ash separation from the flow, and remove alkali and other heavy metal traces that agglomerate with the ash particles. The gasifier design was robust and suitable for firing with varying input conditions. The gasifier exhaust gas is suitable for directly firing into the secondary cyclone combustor without any complex hot gas clean up systems. The cyclone combustor produces a strong swirling flow with good mixing and burnout patterns, creating stable combustion conditions. The use of an additional VCP situated before the combustor exit removes the need for additional cyclone separators. An exhaust mounted tangential off-take on the combustor reduces pressure drop across the system and gives near uniform exhaust velocity profiles. The gasifier achieved 98–99% burnout with good separation/retention rates and 50% alkali, Na and K removal. A good quality low calorific value (LCV) gas was produced that could be effectively utilised in the cyclone combustor. The cyclone combustor produces a stable flow, with good mixing and burnout rates, and uniform exit conditions and could be operated in a lean mode to minimize NO x . The additional use of a VCP removed particles above 5 μm, as specified by turbine inlet conditions. The gas was suitable for directly firing into the gas turbine. Low pressure drop was found across the system.

小型高速マイクロガスタービン用ラジアルフォイル軸受特性の計算法(FR1 マイクロエネルギー変換)

Generators with small gas turbines that generate less than 100kW are drawing attention as a power source of cogeneration systems. Dynamic pressure type air foil bearings are expected to serve as shaft bearings. The design that these bearing are simply designed, easy to produce and maintenance free without requiring lubrication, holds the key to miniaturization of micro-gas turbines. However, the details of such design guidelines have not been clarified though this technology is used in APC for aircraft units. In this study, in order to obtain design guidelines of foil bearing, in making the foil to be the discretion beam, the modeling of the foil was carried out. Taking the frictional forces of attachment part of the foil and the protrusion, etc. into consideration, static characteristic and dynamic characteristic were analyzed to examine performance and stability of the radial foil bearing.

Measurements of the transient velocity field in a strongly curved diffusing bend with periodic inflow unsteadiness

This study examined the effects of periodic inflow unsteadiness on the flow development through fishtail-shaped diffusers utilized on small gas turbine engines. The periodic unsteadiness is due to the distortion of the flow in the peripheral direction at the exit of the centrifugal compressor impeller, caused by the jet-wake type of flow discharging from each impeller passage. Measurements of the transient velocity field were performed throughout the diffuser using a miniature 4-wire probe, at frequencies of inflow unsteadiness corresponding to design and off-design operating conditions in gas turbine installations. At the low end of the tested inflow unsteadiness frequencies, significant effects of inflow unsteadiness were observed on the time-averaged flow distortion throughout the diffuser. At these frequencies, the time variation of flow distortion was found to remain at comparable magnitudes throughout the diffuser.

Transient and Harmonic Overvoltages Related to Transformer and Transmission Line Interaction During Black Start Energization

Restoration of the power grid following a blackout is a subject of major concern for all power utilities. Such a black start typically begins by starting small gas turbine or hydro generators and using them to backfeed the high-voltage grid, energizing one piece of the system at a time. However, the energization of high-voltage transmission lines and large transformers is a challenge, since this can result in a combination of transient and sustained harmonic resonant overvoltages which may cause damage to equipment and/or lead to surge arrester failure. This paper addresses the transient and harmonic overvoltages occurring during black start procedures, discusses the development of Electromagnetic Transient Program (EMTP) models, and presents simulation results. The results of EMTP simulation using more complex models compare more favorably to the event records than the results using simpler models. Based on comparisons with measurements, modeling requirements and some guidelines necessary for obtaining accurate results are provided.

Modelling of NOx and Co Emissions of a Small Gas Turbine Unit Based on Operational Data and Neural Networks

Compact models of NOx and CO emissions of a small gas turbine power plant are discussed, to be used in a plant simulator; the models are based either on semiempirical correlations or neural networks. Experimental data collected during five months of operation are used to calibrate and validate the models. The results obtained with the different models are shown: semi-empirical correlations fail to accurately describe the observed emissions, while neural-network based models perform well, provided their structure is carefully selected.

Advances in solar thermal electricity technology

Various advanced solar thermal electricity technologies are reviewed with an emphasis on new technology and new market approaches. In single-axis tracking technology, the conventional parabolic trough collector is the mainstream established technology and is under continued development but is soon to face competition from two linear Fresnel reflector (LFR) technologies, the CLFR and Solarmundo. A Solarmundo prototype has been built in Belgium, and a CLFR prototype is awaiting presale of electricity as a commercial plant before it can be constructed in Queensland. In two-axis tracking technologies, dish/Stirling technologies are faced with high Stirling engine costs and emphasism may shift to solarised gas micro-turbines, which are adapted from the small stationary gas turbine market and will be available shortly at a price in the US$1 ppW range. ANU dish technology, in which steam is collected across the field and run through large steam turbines, has not been commercialised. Emphasis in solar thermal electricity applications in two-axis tracking systems seems to be shifting to tower technology. Two central receiver towers are planned for Spain, and one for Israel. Our own multi-tower solar array (MTSA) technology has gained Australian Research Council funding for an initial single tower prototype in Australia of approximately 150 kW(e) and will use combined microturbine and PV receivers. Non-tracking systems are described of two diverse types, Chimney and evacuated tubes. Solar chimney technology is being proposed for Australia based upon German technology. Air is heated underneath a large glass structure of about 5 km in diameter, and passes up a large chimney through a wind turbine near the base as it rises. A company Enviromission Ltd. has been listed in Australia to commercialise the concept. Evacuated tubes are growing rapidly for domestic hot water heating in Europe and organic rankine cycle engines such as the Freepower 6 kW are being considered for operation with thermal energy developed by evacuated tube and trough systems. These may replace some PV in medium sized applications as they offer potential for inexpensive pressurised water storage for 24 h operation, and backup by fuels instead of generators. In the medium term there is a clear trend to creation of smaller sized systems which can operate on a retail electricity cost offset basis near urban and industrial installations. In the longer term large low cost plants will be necessary for large scale electricity and fuels production. Retrofit central generation solar plants offer a cost effective transition market which allows increased production rates and gradual cost reduction for large solar thermal plant. In the paper the author describes current funding systems in Europe, Australia, and the USA, and makes suggestions for more effective programmes of support.

B304 Development of Components for Chemically Recuperated Gas Turbine with Natural Gas Steam-Reforming

Small and medium size gas turbines are widely used for distributed power and combined heat and power. However, most have power generation efficiency of less than 35% because of the simple cycle. A chemically recuperated gas turbine (CRGT) has an advanced cycle, which recovers exhaust heat by endothermic reaction converting fuel into hydrogen-rich gas. Several papers report that the results of feasibility studies indicate CRGT would be effective for improving power generation efficiency of the simple cycle GT. Also, the CRGT using methanol steam reforming has been demonstrated, but the components and system operation have not been assessed technically in the case of natural gas. In order to realize the CRGT with natural gas steam reforming, we applied the CR system to a commercial 4MW simple cycle GT and examined the static mass and heat balance by process simulator. We designed a reformer consisting of tube bundles by numerical analysis, which considered mass and heat transfer and chemical reaction in the catalyst bed and clarified the master plan figure of the heat recovery system. Also, the reformer was structurally analyzed using FEM and the stresses due to internal pressure, gravity and temperature distribution were calculated and the stresses in the cross section under severe condition were evaluated with ASME code. This paper presents the results and discussions of these studies.

2209 小型マイクロガスタービン用ラジアル・スラストフォイル軸受の試作

Recently, much attention is paid to foil bearings for micro gas turbine use because these bearings are indispensable elements for realizing maintenance free small size gas turbines. We designed and manufactured a small size radial and thrust foil bearing for the shaft the size of which is 20mm in diameter. In this test apparaturs, the shaft is equipped with radial turbine blades and is driven by compressed air. As a result, we succeeded to operate it at the speed of 60000rpm and measured vibration characteristics.

Development and Evaluation of a High-Resolution Turbine Pyrometer System

Optical pyrometers provide many advantages over intrusive measuring techniques in determining the spatial and time varying temperature distribution of fast rotating components in gas turbines. This paper describes the development and evaluation of a versatile high-resolution pyrometer system and its application to radial turbine rotor temperature mapping as has been done in a R&amp;D project at the Technical University Berlin under funding from Siemens Power Generation (KWU). The development goal was a pyrometer system with a temporal resolution of 1 μs, a minimum field of view of 1 mm, and a measurement range from 600 to 1500°C. A prototype of the pyrometer system has been built and tested at the small gas turbine test facility of the Technical University Berlin. The system yielded excellent results with respect to measurement uncertainty, resolution, and reliability. Finally, measurement results obtained with the new system on a radial turbine rotor and on a heavy duty industrial gas turbine are compared with measurements conducted with a commercially available turbine pyrometer system.

Financing Distributed Generation

This paper introduces the engineer who is undertaking distributed generation projects to a wide range of financing options. Distributed generation systems (such as internal combustion engines, small gas turbines, fuel cells and photovoltaics) all require an initial investment, which is recovered over time through revenues or savings. An understanding of the cost of capital and financing structures helps the engineer develop realistic expectations and not be offended by the common requirements of financing organizations. This paper discusses several mechanisms for financing distributed generation projects: appropriations; debt (commercial bank loan); mortgage; home equity loan; limited partnership; vendor financing; general obligation bond; revenue bond; lease; Energy Savings Performance Contract; utility programs; chauffage (end-use purchase); and grants. The paper also discusses financial strategies for businesses focusing on distributed generation: venture capital; informal investors (''business angels''); bank and debt financing; and the stock market.

Financing Distributed Generation

ABSTRACT This article introduces the engineer who is undertaking distributed generation projects to a wide range of financing options. Distributed generation systems (such as internal combustion engines, small gas turbines, fuel cells and photovoltaics) all require an initial investment, which is recovered over time through revenues or savings. An understanding of the cost of capital and financing structures helps the engineer develop realistic expectations and not be offended by the common requirements of financing organizations. This article discusses several mechanisms for financing distributed generation projects: appropriations; debt (commercial bank loan); mortgage; home equity loan; limited partnership; vendor financing; general obligation bond; revenue bond; lease; Energy Savings Performance Contract; utility programs; chauffage (end-use purchase); and grants. The article also discusses financial strategies for businesses focusing on distributed generation: venture capital; informal investors (“bu...

Performance of a Foil-Magnetic Hybrid Bearing

Abstract To meet the advanced bearing needs of modern turbomachinery, a hybrid foil-magnetic hybrid bearing system was designed, fabricated, and tested in a test rig designed to simulate the rotor dynamics of a small gas turbine engine (31 kN to 53 kN thrust class). This oil-free bearing system combines the excellent low and zero-speed capabilities of the magnetic bearing with the high-load capacity and high-speed performance of the compliant foil bearing. An experimental program is described which documents the capabilities of the bearing system for sharing load during operation at up to 30,000 rpm and the foil bearing component’s ability to function as a backup in case of magnetic bearing failure. At an operating speed of 22,000 rpm, loads exceeding 5300 N were carried by the system. This load sharing could be manipulated by an especially designed electronic control algorithm. In all tests, rotor excursions were small and stable. During deliberately staged magnetic bearing malfunctions, the foil bearing proved capable of supporting the rotor during continued operation at full load and speed, as well as allowing a safe rotor coastdown. The hybrid system tripled the load capacity of the magnetic bearing alone and can offer a significant reduction in total bearing weight compared to a comparable magnetic bearing.