Maria Cristina Cameretti

Adapting the Micro-Gas Turbine Operation to Variable Thermal and Electrical Requirements

This paper examines the possibilities for a micro-gas turbine operation under a wide range of thermal and mechanical load requirements. The authors focus the attention on a partially recuperated thermal cycle based on a by-pass option towards the heat recovery boiler, in order to adapt the gas turbine operation to increasing needs of thermal output. In addition, a variable speed operation is considered as a more reliable method for decreasing the mechanical output without producing an excess in efficiency decay. The actual possibilities of the above-named regulation tools are examined by an integrated procedure which involves, besides an accurate thermodynamic preliminary analysis, the component matching study and the CFD based simulation of the combustion chamber.

Combustion Simulation of an Exhaust Gas Recirculation Operated Micro-gas Turbine

Following their recent experiences in the search of methods for reducing the nitric oxide emissions from a micro-gas turbine, the authors discuss in this paper the results of the combustion simulation under different conditions induced by the activation of an exhaust recirculation system. The theoretical approach starts with a matching analysis of the exhaust gas recirculation equipped microturbine, and then proceeds with the computational fluid dynamics analysis of the combustor. Different combustion models are compared in order to validate the method for NO x reduction by the point of view of a correct development of the chemically reacting process.

Comparing Different Solutions for the Micro-Gas Turbine Combustor

This paper compares different types of combustion chambers for a micro-gas turbine which operates with both different fuels and variations in the inlet air conditions. The combustor types examined cover a wide variety of conditions for the primary combustion, whose fuel/air equivalence ratio ranges from typical lean-premixed levels up to dramatically rich values. The latter is attained in a combustion chamber of the RQL type, while the lean mixture burns in a tubular swirled combustor also equipped with a pilot igniter. The comparison is completed by including an annular combustor with a primary diffusive burner. The CFD based analysis highlights the main differences among the three types of combustors, in terms of temperature and pollutant distributions, and by focusing the attention on the self-ignition occurrence.Copyright

Cycle Optimization and Combustion Analysis in a Low-NOx Micro-Gas Turbine

The authors discuss in this paper the potential of a method for NO x suppression from power plants based on microgas turbines. The method is based on the mild combustion concept but needs to be adapted to the actual operating parameters of the microturbine, thus resulting in an effective employment of the flue gas recirculation for diluting the oxygen in the inlet air. The results are first presented on a thermodynamic basis, and some cases are then analyzed with a computational fluid dynamics simulation. Both approaches suggest good perspectives for the nitric oxide control but also highlight some disadvantages in terms of increase in carbon species.

Combustion Simulation of an EGR Operated Micro-Gas Turbine

Following their recent experiences in the search of methods for reducing the nitric oxide emissions from a micro-gas turbine, the authors discuss in this paper the results of the combustion simulation under different conditions induced by the activation of an exhaust recirculation system. The theoretical approach starts with a matching analysis of the EGR equipped micro-turbine, and then proceeds with the CFD analysis of the combustor. Different combustion models are compared in order to validate the method for NOx reduction by the point of view of a correct development of the chemically reacting process.Copyright

Flow and Atomization Models for C.R. Diesel Engine CFD Simulation

In the present work, the authors investigate the spray evolution and, in particular, the atomization process in a diesel engine bowl by using the KIVA3-V computational code with different break-up models. After a preliminary test of the break-up models sensitivity to the grid size and topology, the same atomization models are employed for the two-phase flow calculation in the combustion chamber of a common rail, turbocharged diesel engine conceived for future HCCI applications. The computations are extended to the combustion process in order to proceed with an overall validation with experimental engine test data characterized by variable EGR rates. The liquid spray-air interaction is studied within a flow field generated by the previous gas exchange process, the external ducts being included in the computational domain. This allows a more realistic evaluation of the fuel-air mixing under the actual conditions occurring at different engine regimes.Copyright

NOx Suppression From a Micro-Gas Turbine Approaching the Mild-Combustion Regime

The authors present in this paper a refined methodology, already introduced in a recent paper, aiming to find the best compromises between the need of reducing the NOx emission from a micro-gas turbine and the preservation of satisfactory efficiency and energy saving levels. The method founds on an integrated approach consisting of an advanced cycle analysis, which includes the component matching study, and the CFD based validation of the most interesting cases. The latter refer to the activation of the exhaust recirculation to the compressor inlet, in order to generate conditions close to those characterized by a mild combustion.Copyright

Employing Micro-Turbine Components in Integrated Solar – MGT - ORC Power Plants

The authors propose in this paper the integration of a combined power plant, with a micro gas turbine (MGT) and an ORC system, and a solar field that allows a temperature increase of the air at the MGT recuperator inlet. Consequently, an increase is also obtained for the exhausts and this leads to an enhanced heat recovery in the ORC boiler and a greater availability of thermal energy.The purpose of the authors’ work is to analyze the effectiveness of the above proposal under several aspects, therefore, under a preliminary thermodynamic study of the plant set-up in CHP mode, the attention is paid to the choice of the organic fluid expander with a low-cost objective. Classical similarity criteria are helpful for a first estimate of the adaptability of a radial flow turbine from the down-sized turbocharger technology to an organic working fluid. A CFD validation of such choice is then carried out and this phase also determines the characteristic curves of the radial flow turbine.Basing on the availability of the characteristic maps of all the rotating components, a reliable off-design analysis of the solar-assisted CHP plant is performed under several load levels and environmental conditions, the latter strongly influencing the solar irradiance on the parabolic trough collectors.Finally, since the examples refer to both natural gas and biogas fuelling, a CFD analysis of the reacting flow through the MGT combustor checks the combustion effectiveness under challenging variations of the boundary conditions.Copyright

Combustion Analysis in a Micro-Gas Turbine Supplied With Bio-Fuels

The authors examine in this paper the response of a micro gas turbine (MGT) combustor when supplied with gaseous fuels from biomass treatment or solid waste pyrolysis. Actually, a sort of off-design operation is induced by the employment of low calorific value fuels both in the combustor and in the whole micro turbine system. The objective is to optimize the combustor behaviour under the point of view of combustion efficiency and pollutant control.To this aim, several solutions are experienced for a combustor fuelled with low LHV gaseous fuels derived from biomasses or solid waste treatment. An external EGR option is also considered as activated. The combustion development is analyzed by a combined approach based on the partially stirred reactor hypothesis and on the flamelet concept within a CFD simulation workbench.Copyright

Comparison of External and Internal EGR Concepts for Low Emission Micro Gas Turbines

The external recirculation of exhaust gases represents an effective tool for approaching an almost flameless regime and controlling the nitric oxide formation, like demonstrated by a number of authors’ papers. Such a system penalizes, on the other hand, the micro-gas turbine performance due to the high EGR rates that are needed for the pollutant reduction. Basing on this consideration, the author consider, in this paper, the possibility of exploiting the internal combustion fluid-dynamics for achieving the same level of pollutant abatement. The comparison of the combustion regimes that are induced by either the external or internal EGR adoption are carried out on a CFD basis. The results refer to different load conditions of the micro-gas turbine, with both gaseous and liquid fuel supply.Copyright