In recent years, the interest in the research on energy production systems fed by biofuels has increased. Gaseous fuels obtained through biomass conversion processes such as gasification, pyrolysis and pyrogasification are generally defined as synthesis gas (syngas). The use of synthesis gas in small-size energy systems, such as those used for distributed micro-cogeneration, has not yet reached a level of technological maturity that could allow a large market diffusion. For this reason, further analyses (both experimental and numerical) have to be carried out to allow these technologies to achieve performance and reliability typical of established technologies based on traditional fuels. In this paper, a numerical analysis of a combustor of a 100-kW micro gas turbine fed by natural gas and biomass-derived synthesis gas is presented. The work has been developed in the framework of a collaboration between the Engineering Department of the University of Ferrara, the Istituto Motori - CNR (Napoli), and Turbec S.p A. of Corporeno di Cento (FE). The main features of the micro gas turbine Turbec T100, located at the Istituto Motori - CNR, are firstly described. A decompression and distribution system allows the feeding of the micro gas turbine with gaseous fuels characterized by different compositions. Moreover, a system of remote monitoring and control together with a data transfer system has been developed in order to set the operative parameters of the machine. The results of the tests performed under different operating conditions are then presented. Subsequently, the paper presents the numerical analysis of a model of the micro gas turbine combustor. The combustor model is validated against manufacturer performance data and experimental data with respect to steady state performance, i.e., average outlet temperature and emission levels. A sensitivity analysis on the model capability to simulate different operating conditions is then performed. The combustor model is used to simulate the combustion of a syngas, composed of different ratios of hydrogen, carbon monoxide, methane, carbon dioxide and water. The results in terms of flame displacement, temperature and emission distribution and values are analyzed and compared to the natural gas simulations. Finally, some simple modifications to the combustion chamber are proposed and simulated both with natural gas and syngas feeding
The aim of this paper is to perform an accurate analysis of the evaporation of single component and binary mixture fuels sprays in a hot weakly turbulent pipe flow by means of experimental measurement and numerical simulation. This gives a deeper insight into the relationship between fuel composition and spray evaporation. The turbulence intensity in the test section is equal to 10%, and the integral length scale is three orders of magnitude larger than the droplet size while the turbulence microscale (Kolmogorov scales) is of same order as the droplet diameter. The spray produced by means of a calibrated droplet generator was injected in a gas flow electrically preheated. N-nonane, isopropanol, and their mixtures were used in the tests. The generalized scattering imaging technique was applied to simultaneously determine size, velocity, and spatial location of the droplets carried by the turbulent flow in the quartz tube. The spray evaporation was computed using a Lagrangian particle solver coupled to a gas-phase solver. Computations of spray mean diameter and droplet size distributions at different locations along the pipe compare very favorably with the measurement results. This combined research tool enabled further investigation concerning the influencing parameters upon the evaporation process such as the turbulence, droplet internal mixing, and liquid-phase thermophysical properties.
The combustion efficiency and the gaseous emission of a 100 kWe MGT, designed for working with natural gas but fuelled with blends containing up to 10% of hydrogen is investigated. A critical comparison between experimental data and results of the CFD analysis of the combustor is discussed. The k-epsilon RANS turbulence model and the Finite Rate – Eddy Dissipation combustion model were used in the numerical computations. The chemical kinetic mechanisms embedded were the 2-step Westbrook and Dryer for methane oxidation, 1-step Westbrook and Dryer for hydrogen oxidation and the Zeldovich mechanism for NO formation. The experimental data and numerical computations are in agreement within the experimental accuracy for NO emissions. Regarding CO, there is a significant deviation between experimental and computational data due to the scarce predictive capability of the simple two steps kinetic mechanism was adopted. From a practical point of view, the possibility of using fuels with a similar Wobbe index was confirmed. In particular the addiction of 10 % of hydrogen to pure methane doesn’t affect the behavior of the micro gas turbine either in terms of NO or CO emissions.
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