Experimental Tests on a Pre-Heated Combustion Chamber for Ultra Micro Gas Turbine Device: Air/Fuel Ratio Evaluation

Current portable power generators are mainly based on internal combustion engine since they present higher values of efficiency comparing to other engines;the main reason why internal combustion engine is not convenient for micro power generation (5 - 30 kW) is because of their heaviness. Micro and ultra micro gas turbine devices, based on a micro compressor and a micro turbine installed on the same shaft, are more suitable for this scope for several reasons. Micro turbine systems have many advantages over reciprocating engine generators, such as higher power density (with respect to size and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. Micro turbines also have the advantage of having the majority of their waste heat contained in their relatively high temperature exhaust. Micro turbines offer several potential advantages compared to other technologies for small-scale power generation, including: a small number of moving parts, compact size, lightweight, greater efficiency, lower emissions, lower electricity costs, and opportunities to utilize waste fuels. The object of this study is the experimental tests on a stand-alone gas turbine device with a pre-heated combustion chamber (CC), to validate the fuel consumption reduction, compared to an actual and commercial device, used on air models.

Micro gas turbine:Developments,applications,and key technologies on components

Owing to their precedent characteristics,micro gas turbines(MGTs)have been favored as popular power machinery in plenty of energy systems such as distributed energy systems,range extenders,solar power generations,fuel cell systems and individual power supplies.Their specific features essentially include but are not limited to strong fuel adaptability,low emissions,flexible structure,and easy maintenance.Over the past 20 years,various types of MGTs have been developed.Classical and forward-looking technologies have been employed in the design and production of MGTs and their components.Among them,fully radial flow structures,gas lubricated bearings and efficient recuperators are typical approaches to enhance the overall performance and compactness,however,the exploitation of ceramic based materials and intelligent algorithms in component design can also assist in improving the performance.The applications of MGTs have been expanded to many fields,and the research on related components has also made new progress.Due to the time frame,there is no systematic summary of the latest relevant research,so it is essential to have a comprehensive understanding of the applications of MGTs and their pertinent components.This paper aims to present a comprehensive review on MGTs,covering the development status,applications,factors of performance and representative explorations of their components.Some investigations regarding the characteristics of commercial MGTs are also conducted.Applications in distributed energy,range extenders,solar generations,and fuel cell systems are distinctly introduced.Recent research work on compressors,turbines,combustors,recuperators,and rotor systems are reviewed and analyzed.The technologies and methods associated with materials,manufacturing,and cycles beneficial to the future development of MGTs are also explained and discussed in some detail.

Fluid-Dynamics Analysis and Structural Optimization of a 300 kW MicroGas Turbine Recuperator

Computational Fluid Dynamics(CFD)is used here to reduce pressure loss and improve heat exchange efficiency in the recuperator associated with a gas turbine.First,numerical simulations of the high-temperature and lowtemperature channels are performed and,the calculated results are compared with experimental data(to verify the reliability of the numerical method).Second,the flow field structure of the low-temperature side channel is critically analyzed,leading to the conclusion that the flow velocity distribution in the low-temperature side channel is uneven,and its resistance is significantly higher than that in the high-temperature side.Therefore,five alternate structural schemes are proposed for the optimization of the low-temperature side.In particular,to reduce the flow velocity in the upper channel,the rib length of each channel at the inlet of the low-temperature side region is adjusted.The performances of the 5 schemes are compared,leading to the identification of the configuration able to guarantee a uniform flow rate and minimize the pressure drop.Finally,the heat transfer performance of the optimized recuperator structure is evaluated,and it is shown that the effectiveness of the recuperator is increased by 1.5%.

An Integrated Approach for Optimal Design of Micro Gas Turbine Combustors

The present work presents an approach for the optimized design of small gas turbine combustors, that integrates a0-D code, CFD analyses and an advanced game theory multi-objective optimization algorithm. The output of the0-D code is a baseline design of the combustor, given the required fuel characteristics, the basic geometry (tubularor annular) and the combustion concept (i.e. lean premixed primary zone or diffusive processes). For the optimizationof the baseline design a simplified parametric CAD/mesher model is then defined and submitted to a CFDcode. Free parameters of the optimization process are position and size of the liner hole arrays, their total area andthe shape of the exit duct, while different objectives are the minimization of NOx emissions, pressure losses andcombustor exit Pattern Factor. A 3D simulation of the optimized geometry completes the design procedure. As afirst demonstrative example, the integrated design process was applied to a tubular combustion chamber with alean premixed primary zone for a recuperative methane-fuelled small gas turbine of the 100 kW class.

Development of Compressor for Ultra Micro Gas Turbine

The major problems for the development of an ultra micro gas turbine system were discussed briefly from the stand point of the internal flow and the performance characteristics. Following to these, the development of ultra micro centrifugal compression systems for the ultra micro gas turbine is explained with the design and the manufacturing processes. The measured results of ultra micro centrifugal compressors are shown.

A data-driven approach for predicting long-term degradation of a fleet of micro gas turbines

Predictive health monitoring of micro gas turbines can significantly increase the availability and reduce the operating and maintenance costs.Methods for predictive health monitoring are typically developed for large-scale gas turbines and have often focused on single systems.In an effort to enable fleet-level health monitoring of micro gas turbines,this work presents a novel data-driven approach for predicting system degradation over time.The approach utilises operational data from real installations and is not dependent on data from a reference system.The problem was solved in two steps by:1)estimating the degradation from time-dependent variables and 2)forecasting into the future using only running hours.Linear regression technique is employed both for the estimation and forecasting of degradation.The method was evaluated on five different systems and it is shown that the result is consistent(r>0.8)with an existing method that computes corrected values based on data from a reference system,and the forecasting had a similar performance as the estimation model using only running hours as an input.

Micro Gas Turbine Range Extender Performance Analysis Using Varying Intake Temperature

A micro gas turbine(MGT)can potentially be an alternative power source to the conventional internal combustion engine as a range extender in hybrid electric vehicles.The integration of the MGT into a hybrid vehicle needs a new approach for technical validation requirements compared to the testing of an internal combustion engine.Several attributes of the MGT are predicted to cause concerns for vehicle sub-system requirements such as high ambient temperature and start-stop behaviour.This paper describes the results from specially developed experimental techniques for testing the MGT in a typical automo-tive environment.A black box MGT was used in this study for performance investigation during hot and cold starts.The MGT was instrumented and fitted with automotive standard components to replicate typical vehicle operational conditions.The intake air temperature was varied between 10 and 24°C.A significant reduction in the power output of the MGT was observed as the intake temperature was increased.The proposed case scenario caused a reduction in nitrogen oxide emis-sions in the range of 0.02−0.04 g/km because of the lower combustion temperature at high intake temperature.However,hydrocarbon and carbon monoxide emissions have not shown a noticeable reduction during the power output degradation.The experimental results have highlighted the potential issues of using the MGT at higher intake temperatures and suggest design change to take the effect of higher engine bay temperature into account.

Research on Modeling and Control of a 100 kW Micro Bio-Gas Turbine

In order to know about the influences of disturbance on the operating performance, the present work developed the overall dynamic simulation model of the micro gas turbine and investigated the control system under the disturbances of environmental temperature and unit load. The response processes of main parameters have been obtained. It found that the compressor pressure ratio and the fuel flow rate increase in the case of natural gas being replaced by pine gas. When the system reaches a new steady state, the main parameters change to different values. The output power decreases with the declining of the air mass flow when the ambient temperature rises, the biomass gas mass flow rate increases under the regulation of the control system to maintain the output power and rotating speed in which the thermal efficiency reduces by 1.40%. The thermal efficiency enhances with the increase of output load. The control system can quickly and effectively act to maintain the key parameters at desired value.

Reliability Assessment of Microgrid Using Sequential Monte Carlo Simulation

Sequential Monte Carlo simulation method is introduced to the reliability assessment of microgrid,and a Weibull distribution wind speed model is built to simulate the hourly wind speed of a specific site.Wind turbine generator model combined with a two-state reliability model is applied to Monte Carlo simulation method,and results show that the wind turbine reliability model works well with sequential Monte Carlo simulation.A two-state reliability model of micro gas turbine and a load model from IEEE reliability test system （IEEE RTS） are also introduced to the reliability evaluation of microgrid.Case studies show that Monte Carlo simulation method is flexible and efficient dealing with microgrid consisting of renewable resources with fluctuation characteristics.

Effects of Pilot Fuel Ratio on Combustion Process:Flow Field Structure and Pollutant Emissions

As the only controllable means of a micro gas turbine(MGT)combustor during unit operation,pilot fuel ratio(PFR)is the key to achieving stable combustion and low pollutant emission.This paper discusses the influence of PFR on the inner flow field structure and pollutant emissions.The steady-state three-dimensional RANS method with a 40-step reduced methane-air kinetics mechanism is used to study the reaction flow field and species field with PFR of 9.0%,12.7%,15.2%and 17.6%.Results show that,with the decrease in PFR,the axial velocity and temperature near the central axis of the combustion chamber show a tendency to decrease.A similar separation phenomenon occurred in the core pyrolysis reaction zone(measured by HCO)and oxidation zone(measured by OH),which is more conducive to promoting the oxidation of CO.The quantitative effect of the pilot flame on nitrogen oxides(NO_(x))was separated by using inert gas instead of nitrogen in combustion air.It was found that the NOx produced by the pilot flame under the operation condition with a PFR of 9.0%was 3.2×10^(−6),accounting for 17.4%of the total NOx emission,which was twice that of PFR.

Numerical Study on Thermoelectric Power Generator in Combustor

Micro gas turbine is a typical distributed energy resource system. The temperature of the burning gas in the combustor reaches 1000 K or even more, which makes a huge temperature difference in the combustor an interesting topic for heat recovery. In this work, thermoelectric devices are used for heat recovery in the combustor of the micro gas turbine. A flow-thermal-electric multiple-physical numerical model is used for the combustor and thermoelectric device power generation system. The effect of the winglet vortex generators installed at the outer wall of the flame tube on the system performance is examined. The numerical results show that the best matching load is about 1.4 times the internal resistance which provides the maximum power output for the thermoelectric generator. Active cascade control of heat transfer enhancement elements on flame tube considering wall safety and conversion efficiency of thermoelectric generator under high temperature and large temperature drop is proposed. The numerical results show that the conversion efficiency of thermoelectric generator can be increased by more than 80%, and the average wall temperature can be reduced by 35 K by using non-uniform arrangement of the winglet vortex generators.

Effect of the Structure Parameters of a Low Swirler on Premixed Characteristics

Combustion with lean premixed and low swirl is an effective way of flame organization.It can improve the flame stability and reduce NOX emission.In this kind of combustion,one of the most important issues is fuel/air premixed characteristics.How the structure parameters influence that issue is figured out through numerical simulation.The structure parameters concerned in the study are as follows.They are shape of blades,number of blades,location and shape of gas jet.The influences of them are analysed with comprehensive consideration of many aspects.With the same light shading rate and stagger angle,the axial swirler with curved blades has worse premixed uniformity and lower pressure loss than the one with straight blades.With the same structure of each blade,the decrease of the quantity of blades does influence the pressure loss,while the quantity of gas jets changes correspondingly.But it has little effect on premixed uniformity in a certain range.However,more blades make contribution to better premixed performance.When the total flow area is the same,the axial and circumferential positions of the fuel jets also greatly influence the premixing process.When the fuel jets are upstream the blades and locate at middle of the vanes,the premixing performance is the best.Meanwhile,the jet direction of the fuel jets is a very important influencing factor of the premixing process.When the fuel jet direction is oblique downward at an angle of 30°to the horizontal,the premixing effect is better than the horizontal outflow,which is better than the oblique upward structure.