Combustion
Research focus
The Peer review has evaluated this group as Good
Combustion is likely the most popular and oldest technology. It is of fundamental importance in aerospace, terrestrial and naval propulsion systems, in electrical power generation, and in everyday life also. Nowadays the environmental issues and the goal of increasing efficiency and improving product quality of gas turbines, engines and industrial burners highlight the need for further advances in both the understanding of combustion systems and in the predictive capability of numerical models. Moreover the increasingly tight regulations on pollutant emissions and efficiency, and the emergent fields of micropropulsion and portable power systems put forward the need for the development of high performance micro and small scale combustion systems able also to operate with alternative fuels (hydrogen, syngas, biofuels etc.). Combustion is a multidisciplinary science and requires different investigation approaches. Among them fluid dynamic analysis of a combustion process is one of the most important, and when performed in conjunction with conventional gas analysis and spectroscopic investigations it provides valuable information on stability and efficiency of the phenomenon. In this frame, the research activities of the Combustion Laboratory are focused on the experimental investigation of the thermo-fluid dynamic phenomena relevant to the combustion process by means of the latest diagnostic techniques. Besides fundamental studies on the optimization of the mixing process between the reactants in turbulent non-premixed gaseous flames and on the spray-gas or spray-wall interaction in model combustion engines, the current research activities are aimed at: the improvement of combustion efficiency, reduction of pollutant emission and soot formation, development of new solutions for specific applications and use of different fuels (natural gas, hydrocarbon/hydrogen mixtures, syngas). Finally, the experimentally activity has the objective to provide also reliable and detailed experimental data necessary for the validation of advanced CFD models. The most significant research topics covered in the last four years are the following: Basic studies on mixture formation with gaseous or spray fuel injection. - Performance optimization of a single-ended self-recuperative radiant tube burner with pollutant emissions reduction. - Development of non-premixed swirl burners with high efficiency and very low pollutant emissions (NOx, soot and nanoparticles). - Analysis of hydrogen enriched non-premixed natural gas flames. The interest is focused on the experimental investigation of stability, combustion efficiency, pollutant emissions, soot formation in confined swirl stabilized flames burning either hydrogen/natural gas (hydrogen fractions up to 100%) or syngas fuel mixtures. - Development of a combustor with a size of less then 1 cm3 in volume (meso-scale) to be used in micropower generators or micro-propulsion systems. The meso-scale combustor has an input thermal power of about 100 W and can operate with either hydrogen or hydrocarbon fuels (methane, propane, butane), Stability range, chemical and thermal efficiencies are the main investigated parameters. - Characterization of liquid fuel sprays for industrial and automotive applications, in terms of penetration, velocity and size distributions, jet morphology, gas entrainment and mixture formation. 12 Research activities are supported by national (University&Research Ministry) and international (U.E. Commission) research projects, and by private contracts from leading Italian companies. Several experimental methodologies, mainly based on optical techniques, have been developed by the Combustion Laboratory, and widely applied to steady and unsteady phenomena to measure: - Velocity (two components) in gaseous, two-phase (sprays), non-reacting and reacting flows (flames), by Laser Doppler Velocimetry and Digital Particle Image Velocimetry. - Concentration and size distribution of solid/liquid particulate/droplets, by Phase Doppler Velocimetry. - Soot volume fraction in reacting flows (flames), through laser induced incandescence and fluorescence, and visible light extinction. - Temperature and species concentration, by laser based Rayleigh and Raman scattering. - 2-D visualizations of particle dispersion, mixing processes, reactive phenomena, etc. - Flame front detection, by spontaneous visible light emission from radicals. - Tomographic analysis of axisymmetric co-axial systems. Other research activities are focused on aeronautical propulsion and particularly on the thermodynamic study and characterization of gas turbine engines (turbojet, turboprop and turbofan engines) with the introduction of innovative solutions, as heat regeneration, staged and intercooled compression process. The main advantages coming from the introduction of these practices consist in optimizing the thermal cycle of the different propulsion systems and consequently to improve the performances and to reduce fuel consumption and emissions. For this purpose thermodynamic codes have been developed to simulate the behavior of these aeronautical engines in different operating conditions (parametric and off-design analysis). A second research topic is the study of the constant volume combustion turbine engine. It allows to increase gas pressure during combustion without the need of a compressor, or with a low pressure compressor. A prototype of this engine has been built, and, after a preliminary numerical study, experimental tests are planned.
Dipartimento di afferenza
Docenti afferenti
Full Professors
Aldo Coghe
Umberto Ghezzi
Assistant Professors
Roberto Andriani
Fabio Cozzi
Giulio Solero