Aldo Coghe | Politecnico di Milano (original) (raw)
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Papers by Aldo Coghe
Proceedings of the Seventh International Conference on Liquid Atomization and Spray Systems
The entrainment rate in the initial region of axisymmetric turbulent swirling air jets has been m... more The entrainment rate in the initial region of axisymmetric turbulent swirling air jets has been measured by Particle Image Velocimetry (PIV) for a number of swirl strengths from S = 0 up to S = 1.5 and two Reynolds numbers. From the complete PIV maps of the jet and its surroundings, entrainment has been evaluated by using two methods: a) integration of the radial profiles of time-mean axial velocity of the jet; b) direct measurements of the radial velocity component of ambient air entrained into the jet. The entrainment rate increases with increasing axial distance from the nozzle in a non linear way and shows a rapid enhancement with the swirl number, particularly after inception of vortex breakdown and when the processing vortex core (PVC) is observed. The results allow to better understand the entrainment process in swirling jets and related effects on mixture formation and flame structure in industrial burners. Introduction Entrainment is an essential feature of shear flows and ...
The effects of hydrogen addition on the flame stability of non-premixed, swirled flame of a natur... more The effects of hydrogen addition on the flame stability of non-premixed, swirled flame of a natural gas burner were experimentally investigated. The burner configuration consists of a central jet, composed by mixed natural gas and hydrogen, surrounded by a swirled airflow. The swirl generator consists of four tangential air inlets that mix tangential air with axial air upstream of the burner. Different percentage (by volume) of hydrogen has been added to the natural gas flow while the total volumetric fuel flow was kept constant. The experimental results show an increasing in flame stability and a decreasing in flame height as the hydrogen percentage in the fuel increases. At the same time a central yellow flame of increasing brightness appears. INTRODUCTION The increasingly stringent ambient regulations direct the research towards the developments of burner with reduced fuel consumption and low pollutant emissions. In this perspective, the currently favored approach is the use of l...
Thermo- and Fluid-dynamic Processes in Diesel Engines, 2002
4th International Symposium on Air Breathing Engines, 1979
The present work describes the experimental investigation on NOx emissions of partially premixed ... more The present work describes the experimental investigation on NOx emissions of partially premixed flames characterised by air staging through radial injection of premixed jets into a co-flow swirling air. NOx emissions were found to increase with increasing partial premixing and reach a maximum value at Φp ≈ 5, followed by a dramatic decrease as Φp approaches values ≈ 3. In the most favourable conditions, single digit NOx levels were reached without penalizing combustion performances or increasing CO emissions. The effects of staging on the amount of NO2 found at the exhaust were also examined and the results corroborate the idea that NO2 is formed in the turbulent mixing region, favoured by the increasing cooling rate of the combustion gas by entrainment of cold unburned gas. PIV measurements of the isothermal flow field are used to confirm the analysis and to better understand how the emissions are related to the turbulent mixing of the premixed first stage with the secondary swirl...
Droplet Impact Phenomena & Spray Investigations, DIPSI Workshop 2012, 2012
The present paper reports the 3-D CFD modelling of an industrial swirl radiant burner (12.8 – 18 ... more The present paper reports the 3-D CFD modelling of an industrial swirl radiant burner (12.8 – 18 kW) performed by means of a commercial code (FLUENT). The first step was the validation of the code through a detailed comparison with experimental velocity data acquired under isothermal flow regimes for different operating conditions. On this basis the reactive characterization was carried out and the thermal and fluid dynamic flow patterns were compared with the experimental measurements. The k – ε RSM (Reynolds Stress Model) model was used for Navier – Stokes equation closure and the air – methane reaction was modelled with the 2 step reaction approach with Finite Rate – Eddy Dissipation model. For the radiative characterization it was chosen the DO (Discrete Ordinates) model. Moreover, the simulation of a modified burner geometry with internal EGR was performed and confirmed the experimentally observed reduction of pollutant emissions. INTRODUCTION Industrial radiant burners have be...
Proceedings of the Seventh International Conference on Liquid Atomization and Spray Systems
The entrainment rate in the initial region of axisymmetric turbulent swirling air jets has been m... more The entrainment rate in the initial region of axisymmetric turbulent swirling air jets has been measured by Particle Image Velocimetry (PIV) for a number of swirl strengths from S = 0 up to S = 1.5 and two Reynolds numbers. From the complete PIV maps of the jet and its surroundings, entrainment has been evaluated by using two methods: a) integration of the radial profiles of time-mean axial velocity of the jet; b) direct measurements of the radial velocity component of ambient air entrained into the jet. The entrainment rate increases with increasing axial distance from the nozzle in a non linear way and shows a rapid enhancement with the swirl number, particularly after inception of vortex breakdown and when the processing vortex core (PVC) is observed. The results allow to better understand the entrainment process in swirling jets and related effects on mixture formation and flame structure in industrial burners. Introduction Entrainment is an essential feature of shear flows and ...
The effects of hydrogen addition on the flame stability of non-premixed, swirled flame of a natur... more The effects of hydrogen addition on the flame stability of non-premixed, swirled flame of a natural gas burner were experimentally investigated. The burner configuration consists of a central jet, composed by mixed natural gas and hydrogen, surrounded by a swirled airflow. The swirl generator consists of four tangential air inlets that mix tangential air with axial air upstream of the burner. Different percentage (by volume) of hydrogen has been added to the natural gas flow while the total volumetric fuel flow was kept constant. The experimental results show an increasing in flame stability and a decreasing in flame height as the hydrogen percentage in the fuel increases. At the same time a central yellow flame of increasing brightness appears. INTRODUCTION The increasingly stringent ambient regulations direct the research towards the developments of burner with reduced fuel consumption and low pollutant emissions. In this perspective, the currently favored approach is the use of l...
Thermo- and Fluid-dynamic Processes in Diesel Engines, 2002
4th International Symposium on Air Breathing Engines, 1979
The present work describes the experimental investigation on NOx emissions of partially premixed ... more The present work describes the experimental investigation on NOx emissions of partially premixed flames characterised by air staging through radial injection of premixed jets into a co-flow swirling air. NOx emissions were found to increase with increasing partial premixing and reach a maximum value at Φp ≈ 5, followed by a dramatic decrease as Φp approaches values ≈ 3. In the most favourable conditions, single digit NOx levels were reached without penalizing combustion performances or increasing CO emissions. The effects of staging on the amount of NO2 found at the exhaust were also examined and the results corroborate the idea that NO2 is formed in the turbulent mixing region, favoured by the increasing cooling rate of the combustion gas by entrainment of cold unburned gas. PIV measurements of the isothermal flow field are used to confirm the analysis and to better understand how the emissions are related to the turbulent mixing of the premixed first stage with the secondary swirl...
Droplet Impact Phenomena & Spray Investigations, DIPSI Workshop 2012, 2012
The present paper reports the 3-D CFD modelling of an industrial swirl radiant burner (12.8 – 18 ... more The present paper reports the 3-D CFD modelling of an industrial swirl radiant burner (12.8 – 18 kW) performed by means of a commercial code (FLUENT). The first step was the validation of the code through a detailed comparison with experimental velocity data acquired under isothermal flow regimes for different operating conditions. On this basis the reactive characterization was carried out and the thermal and fluid dynamic flow patterns were compared with the experimental measurements. The k – ε RSM (Reynolds Stress Model) model was used for Navier – Stokes equation closure and the air – methane reaction was modelled with the 2 step reaction approach with Finite Rate – Eddy Dissipation model. For the radiative characterization it was chosen the DO (Discrete Ordinates) model. Moreover, the simulation of a modified burner geometry with internal EGR was performed and confirmed the experimentally observed reduction of pollutant emissions. INTRODUCTION Industrial radiant burners have be...