ABSTRACT The flame stabilisation process in turbulent non-premixed flames is not fully understood... more ABSTRACT The flame stabilisation process in turbulent non-premixed flames is not fully understood and several models have been developed to describe the turbulence–chemistry interaction. This work compares the performance of the multiple Representative Interactive Flamelet (mRIF) model, the Volume Reactor Fraction Model (VRFM), and the Well-Stirred reactor (WS) model in describing such flames. The predicted ignition delay and flame lift-off length of n-heptane sprays are compared to experimental results published within the Engine Combustion Network (ECN). All of the models predict the trend of ignition delay reasonably well. At a low gas pressure (42 bar) the ignition delay is overpredicted compared to the experimental data, but the difference between the models is not significant. However, the predicted lift-off lengths differ. At high pressure (87 bar) the difference between the models is small. All models slightly underpredict the lift-off length compared to the experimental data. At low gas pressure (42 bar) the mRIF model gives the best results. The VRFM and WS models predict excessively short lift-off lengths, but the VRFM model gives better results than the WS model. The flame structures of the models are also compared. The WS model and the VRFM model yield a well defined flame stabilisation point whereas the mRIF model does not. The flame of the mRIF model is more diffuse and the model is not able to predict flame propagation. All models were able to predict the experimental trends in lift-off and ignition delay, but certain differences between them are demonstrated.
ABSTRACT Prediction of in-cylinder flows and fuel-air mixing are two fundamental pre-requisites f... more ABSTRACT Prediction of in-cylinder flows and fuel-air mixing are two fundamental pre-requisites for a successful simulation of direct-injection engines. Over the years, many efforts were carried out in order to improve available turbulence and spray models. However, enhancements in physical modeling can be drastically affected by mesh structure and quality which can negatively influence the predicted structure of organized charge motions, turbulence generation and interaction between in-cylinder flows and injected sprays. This is even more relevant for modern direct injection engines where multiple injections and control of charge motions are employed in a large portion of the operating map. Currently, two different approaches for mesh generation exist: manual and automatic. The first makes generally possible to generate high-quality meshes but, at the same time, it is very time consuming and not completely free from user errors. Automatic mesh generation is very fast, but does not easily allow to align grid with flow and spray in regions of interest, for instance where fuel is delivered or where air enters the cylinder. Within this context, the authors have developed a novel approach for automatic mesh generation, where both mesh quality and flow alignment are taken into account. Such methodology has been incorporated into the Lib-ICE code, which is based on the OpenFOAM technology. On the basis of combustion chamber details and/or user specified parameters (piston bowl points, injector direction, squish height, valve lift diagram,...), body fitted, high quality grids are automatically generated to perform full-cycle or compression/combustion simulations. To assess the proposed approach, two direct-injection engines were simulated. The first is Diesel fueled and only compression and combustion phases are simulated, showing the advantages of a spray-oriented grid, compared to a conventional Cartesian one, in terms of prediction of fuel-air mixing and combustion process. The second chosen configuration is a gasoline, direct-injection engine. In this case full-cycle simulations were performed and computed flow field data were compared with optical experimental ones.
ABSTRACT Large eddy simulation is performed to investigate air entrainment and mixing in diesel s... more ABSTRACT Large eddy simulation is performed to investigate air entrainment and mixing in diesel sprays with and without combustion. The Spray A case of the Engine Combustion Network (ECN) is considered in the study, in which liquid n-Dodecane is injected at 1500 bar through a nozzle of 90 μm into a constant volume vessel with an ambient density of 22.8 kg/m3 and an ambient temperature of 900 K. Primary and secondary breakup processes of the liquid fuel are taken into account. The gas and liquid phases are modeled using Eulerian/Lagrangian coupling approach. Detailed chemical kinetics for n-Dodecane is employed to simulate the ignition process and the lifted flames. A chemistry coordinate mapping approach is used for speeding up the calculations. The effect of low temperature ignition (cool flame) on the evaporation process and on the liquid penetration length is analyzed. The effect of combustion heat release from the lifted flames on the vapor spreading in the radial direction and on the vapor transport in the streamwise direction (vapor penetration) is investigated.
ASME 2009 Internal Combustion Engine Division Spring Technical Conference, 2009
Nowadays, Computational Fluid Dynamic (CFD) codes are widely used in different industrial fields.... more Nowadays, Computational Fluid Dynamic (CFD) codes are widely used in different industrial fields. Although hardware and numerical model improvements, the mesh generation remains one of the key points for a successful CFD simulation. Mesh quality is influenced by the adopted mesh generator tool and, after all, by the designer's experience and it becomes very important when moving meshes are required. In fact, mesh skewness, aspect ratio, and non-orthogonality have to be controlled during the deforming process since their wrong ...
Presentation of the libraries and solvers developed at Politecnico di Milano, Lib-ICE, under the ... more Presentation of the libraries and solvers developed at Politecnico di Milano, Lib-ICE, under the OpenFOAM(R) techonolgy for engine simulations (Oct. 2014).
ABSTRACT This paper presents an approach for modelling combustion in homogeneous charge compressi... more ABSTRACT This paper presents an approach for modelling combustion in homogeneous charge compression ignition (HCCI) conditions based on the first order conditional moment closure (CMC) method. The model is implemented into the open source C++ computational fluid dynamic (CFD) code known as OpenFOAM. Direct numerical simulations (DNSs) are used to evaluate the performance of the CFD-CMC solver. In the two-dimensional (2D) DNS cases, ignition of a lean n-heptane/air mixture with thermal inhomogeneities is simulated for nine cases, with two different mean temperatures and several different levels of thermal stratification. Results from the CFD-CMC solver are in excellent agreement with the DNS for cases which exhibit a spontaneous sequential ignition mode of combustion whereas for the cases in which a mixed mode of deflagration and spontaneous ignition exists, the CMC underpredicts the ignition delay. Further investigation using the DNS data demonstrates that this discrepancy is primarily attributed to the first order closure assumption. Conditional fluctuations are found to be more significant in the case with deflagrations. Further analysis of the DNS shows that scalar dissipation fluctuations are the cause of conditional fluctuations.
The main emphasis of this study is to examine the effects of biodiesel thermo-physical properties... more The main emphasis of this study is to examine the effects of biodiesel thermo-physical properties on the fuel spray development using CFD modelling. A complete set of 12 thermo-physical properties is estimated for PME, SME and CME. The methods employed for this as reported here are generic as the methods are dependent on the chemical compositions and temperature. Sensitivity analysis is performed by integrating the estimated fuel properties into CFD modelling. Variations in spray development such as mass of fuel evaporated and liquid and vapour axial penetration length of biodiesel fuels are found to be different from fossil diesel due to the difference in thermo-physical properties. A total of five biodiesel properties are identified to have profound impacts on fuel spray development, which are liquid density, liquid viscosity, liquid surface tension, vapour pressure and vapour diffusivity. Nevertheless, only liquid surface tension and vapour pressure are the most sensitive fuel properties to the fuel spray development. The work has provided better representation of biodiesel properties, which improve the in-cylinder CFD simulation of reacting spray jet for the fuel.
Résumé/Abstract The paper describes the development of a reduced kinetic scheme for the evaluatio... more Résumé/Abstract The paper describes the development of a reduced kinetic scheme for the evaluation of the main chemical species (particularly NO and CO) in premixed turbulent flame and its application to a quasi-dimensional combustion model for spark ignition engines. The proposed mechanism is based on the kinetic solution of three transport equations for NO, CO and H, coupled with the partial equilibrium of the so-called water-shuffle equations to derive the OH, O and H 2 concentrations. The remaining species are ...
Effects of exhaust-gas recirculation (EGR) on the structure and emissions of n-heptane diesel com... more Effects of exhaust-gas recirculation (EGR) on the structure and emissions of n-heptane diesel combustion are numerically investigated. Two cases with different volumetric oxygen concentrations of 21% and 10% are considered. It is shown that the structure of reaction zone at the onset ignition is independent of the oxygen concentration in the ambient gases, namely and consistent with the experiments, the equivalence ratio in the premixed-burn region is around 2 for both cases presented here. A cool-flame is formed at almost the ...
Page 1. Automatic Mesh Motion with Topological Changes for Engine Simulation T. Lucchini, G. D'Er... more Page 1. Automatic Mesh Motion with Topological Changes for Engine Simulation T. Lucchini, G. D'Errico Department of Energetics, Politecnico di Milano, Italy H. Jasak WIKKI Ltd, London, England Z. Tuković FSB, University of Zagreb, Croatia SAE Paper 2007-01-0170 Page 2. TOPICS • INTRODUCTION • MESH MOTION FOR IC ENGINES ➢ Topological changes ➢ Automatic mesh motion • ENGINE MESH SETUP • VALIDATION Page 3.
While HCCI engines have many advantages such as better efficiency and lower emissions, the contro... more While HCCI engines have many advantages such as better efficiency and lower emissions, the control of these engines is still complex. In this context, cycle-to-cycle control using oxidizing species such as ozone (O3) presents a good potential.
Only 1 ppm of O3 has already a significant impact on the ignition. Predicting this effect as well as the low temperature combustion and ignition generally requires a detailed mechanism.
Using CFD simulations with the Tabulation of Dynamic Adaptive Chemistry (TDAC) method and a mechanism including more than 1000 chemical species, we have predicted the effect of ozone seeding on the combustion of iso-octane in a HCCI engine.
This paper presents the validation of the CFD simulations with a large range of ozone concentration and initial temperature.
It shows that the TDAC method is able to reproduce accurately such complex chemical phenomena accounting for heat transfer and chemical reactions in a real geometry.
... pp.24-42, 1997. Granata S., Faravelli T., Ranzi E., A wide range kinetic modeling study of t... more ... pp.24-42, 1997. Granata S., Faravelli T., Ranzi E., A wide range kinetic modeling study of the pyrolysis and combustion of naphthenes, Combustion and Flame, 132, Issue: 3, February, 2003, pp. 533-544, 2003. Ranzi, E. A ...
Abstract The high complexity of the interplaying physical and chemical phenomena occurring in Die... more Abstract The high complexity of the interplaying physical and chemical phenomena occurring in Diesel combustion has brought an increasing interest versus experimental and computational fundamental studies. A relevant contribution to the availability of suitable and accessible experimental data is represented by the Engine Combustion Network database, which are of great interest for model development and validation because of the well-defined boundary conditions and the wide range of conditions employed [1].
ABSTRACT The flame stabilisation process in turbulent non-premixed flames is not fully understood... more ABSTRACT The flame stabilisation process in turbulent non-premixed flames is not fully understood and several models have been developed to describe the turbulence–chemistry interaction. This work compares the performance of the multiple Representative Interactive Flamelet (mRIF) model, the Volume Reactor Fraction Model (VRFM), and the Well-Stirred reactor (WS) model in describing such flames. The predicted ignition delay and flame lift-off length of n-heptane sprays are compared to experimental results published within the Engine Combustion Network (ECN). All of the models predict the trend of ignition delay reasonably well. At a low gas pressure (42 bar) the ignition delay is overpredicted compared to the experimental data, but the difference between the models is not significant. However, the predicted lift-off lengths differ. At high pressure (87 bar) the difference between the models is small. All models slightly underpredict the lift-off length compared to the experimental data. At low gas pressure (42 bar) the mRIF model gives the best results. The VRFM and WS models predict excessively short lift-off lengths, but the VRFM model gives better results than the WS model. The flame structures of the models are also compared. The WS model and the VRFM model yield a well defined flame stabilisation point whereas the mRIF model does not. The flame of the mRIF model is more diffuse and the model is not able to predict flame propagation. All models were able to predict the experimental trends in lift-off and ignition delay, but certain differences between them are demonstrated.
ABSTRACT Prediction of in-cylinder flows and fuel-air mixing are two fundamental pre-requisites f... more ABSTRACT Prediction of in-cylinder flows and fuel-air mixing are two fundamental pre-requisites for a successful simulation of direct-injection engines. Over the years, many efforts were carried out in order to improve available turbulence and spray models. However, enhancements in physical modeling can be drastically affected by mesh structure and quality which can negatively influence the predicted structure of organized charge motions, turbulence generation and interaction between in-cylinder flows and injected sprays. This is even more relevant for modern direct injection engines where multiple injections and control of charge motions are employed in a large portion of the operating map. Currently, two different approaches for mesh generation exist: manual and automatic. The first makes generally possible to generate high-quality meshes but, at the same time, it is very time consuming and not completely free from user errors. Automatic mesh generation is very fast, but does not easily allow to align grid with flow and spray in regions of interest, for instance where fuel is delivered or where air enters the cylinder. Within this context, the authors have developed a novel approach for automatic mesh generation, where both mesh quality and flow alignment are taken into account. Such methodology has been incorporated into the Lib-ICE code, which is based on the OpenFOAM technology. On the basis of combustion chamber details and/or user specified parameters (piston bowl points, injector direction, squish height, valve lift diagram,...), body fitted, high quality grids are automatically generated to perform full-cycle or compression/combustion simulations. To assess the proposed approach, two direct-injection engines were simulated. The first is Diesel fueled and only compression and combustion phases are simulated, showing the advantages of a spray-oriented grid, compared to a conventional Cartesian one, in terms of prediction of fuel-air mixing and combustion process. The second chosen configuration is a gasoline, direct-injection engine. In this case full-cycle simulations were performed and computed flow field data were compared with optical experimental ones.
ABSTRACT Large eddy simulation is performed to investigate air entrainment and mixing in diesel s... more ABSTRACT Large eddy simulation is performed to investigate air entrainment and mixing in diesel sprays with and without combustion. The Spray A case of the Engine Combustion Network (ECN) is considered in the study, in which liquid n-Dodecane is injected at 1500 bar through a nozzle of 90 μm into a constant volume vessel with an ambient density of 22.8 kg/m3 and an ambient temperature of 900 K. Primary and secondary breakup processes of the liquid fuel are taken into account. The gas and liquid phases are modeled using Eulerian/Lagrangian coupling approach. Detailed chemical kinetics for n-Dodecane is employed to simulate the ignition process and the lifted flames. A chemistry coordinate mapping approach is used for speeding up the calculations. The effect of low temperature ignition (cool flame) on the evaporation process and on the liquid penetration length is analyzed. The effect of combustion heat release from the lifted flames on the vapor spreading in the radial direction and on the vapor transport in the streamwise direction (vapor penetration) is investigated.
ASME 2009 Internal Combustion Engine Division Spring Technical Conference, 2009
Nowadays, Computational Fluid Dynamic (CFD) codes are widely used in different industrial fields.... more Nowadays, Computational Fluid Dynamic (CFD) codes are widely used in different industrial fields. Although hardware and numerical model improvements, the mesh generation remains one of the key points for a successful CFD simulation. Mesh quality is influenced by the adopted mesh generator tool and, after all, by the designer's experience and it becomes very important when moving meshes are required. In fact, mesh skewness, aspect ratio, and non-orthogonality have to be controlled during the deforming process since their wrong ...
Presentation of the libraries and solvers developed at Politecnico di Milano, Lib-ICE, under the ... more Presentation of the libraries and solvers developed at Politecnico di Milano, Lib-ICE, under the OpenFOAM(R) techonolgy for engine simulations (Oct. 2014).
ABSTRACT This paper presents an approach for modelling combustion in homogeneous charge compressi... more ABSTRACT This paper presents an approach for modelling combustion in homogeneous charge compression ignition (HCCI) conditions based on the first order conditional moment closure (CMC) method. The model is implemented into the open source C++ computational fluid dynamic (CFD) code known as OpenFOAM. Direct numerical simulations (DNSs) are used to evaluate the performance of the CFD-CMC solver. In the two-dimensional (2D) DNS cases, ignition of a lean n-heptane/air mixture with thermal inhomogeneities is simulated for nine cases, with two different mean temperatures and several different levels of thermal stratification. Results from the CFD-CMC solver are in excellent agreement with the DNS for cases which exhibit a spontaneous sequential ignition mode of combustion whereas for the cases in which a mixed mode of deflagration and spontaneous ignition exists, the CMC underpredicts the ignition delay. Further investigation using the DNS data demonstrates that this discrepancy is primarily attributed to the first order closure assumption. Conditional fluctuations are found to be more significant in the case with deflagrations. Further analysis of the DNS shows that scalar dissipation fluctuations are the cause of conditional fluctuations.
The main emphasis of this study is to examine the effects of biodiesel thermo-physical properties... more The main emphasis of this study is to examine the effects of biodiesel thermo-physical properties on the fuel spray development using CFD modelling. A complete set of 12 thermo-physical properties is estimated for PME, SME and CME. The methods employed for this as reported here are generic as the methods are dependent on the chemical compositions and temperature. Sensitivity analysis is performed by integrating the estimated fuel properties into CFD modelling. Variations in spray development such as mass of fuel evaporated and liquid and vapour axial penetration length of biodiesel fuels are found to be different from fossil diesel due to the difference in thermo-physical properties. A total of five biodiesel properties are identified to have profound impacts on fuel spray development, which are liquid density, liquid viscosity, liquid surface tension, vapour pressure and vapour diffusivity. Nevertheless, only liquid surface tension and vapour pressure are the most sensitive fuel properties to the fuel spray development. The work has provided better representation of biodiesel properties, which improve the in-cylinder CFD simulation of reacting spray jet for the fuel.
Résumé/Abstract The paper describes the development of a reduced kinetic scheme for the evaluatio... more Résumé/Abstract The paper describes the development of a reduced kinetic scheme for the evaluation of the main chemical species (particularly NO and CO) in premixed turbulent flame and its application to a quasi-dimensional combustion model for spark ignition engines. The proposed mechanism is based on the kinetic solution of three transport equations for NO, CO and H, coupled with the partial equilibrium of the so-called water-shuffle equations to derive the OH, O and H 2 concentrations. The remaining species are ...
Effects of exhaust-gas recirculation (EGR) on the structure and emissions of n-heptane diesel com... more Effects of exhaust-gas recirculation (EGR) on the structure and emissions of n-heptane diesel combustion are numerically investigated. Two cases with different volumetric oxygen concentrations of 21% and 10% are considered. It is shown that the structure of reaction zone at the onset ignition is independent of the oxygen concentration in the ambient gases, namely and consistent with the experiments, the equivalence ratio in the premixed-burn region is around 2 for both cases presented here. A cool-flame is formed at almost the ...
Page 1. Automatic Mesh Motion with Topological Changes for Engine Simulation T. Lucchini, G. D'Er... more Page 1. Automatic Mesh Motion with Topological Changes for Engine Simulation T. Lucchini, G. D'Errico Department of Energetics, Politecnico di Milano, Italy H. Jasak WIKKI Ltd, London, England Z. Tuković FSB, University of Zagreb, Croatia SAE Paper 2007-01-0170 Page 2. TOPICS • INTRODUCTION • MESH MOTION FOR IC ENGINES ➢ Topological changes ➢ Automatic mesh motion • ENGINE MESH SETUP • VALIDATION Page 3.
While HCCI engines have many advantages such as better efficiency and lower emissions, the contro... more While HCCI engines have many advantages such as better efficiency and lower emissions, the control of these engines is still complex. In this context, cycle-to-cycle control using oxidizing species such as ozone (O3) presents a good potential.
Only 1 ppm of O3 has already a significant impact on the ignition. Predicting this effect as well as the low temperature combustion and ignition generally requires a detailed mechanism.
Using CFD simulations with the Tabulation of Dynamic Adaptive Chemistry (TDAC) method and a mechanism including more than 1000 chemical species, we have predicted the effect of ozone seeding on the combustion of iso-octane in a HCCI engine.
This paper presents the validation of the CFD simulations with a large range of ozone concentration and initial temperature.
It shows that the TDAC method is able to reproduce accurately such complex chemical phenomena accounting for heat transfer and chemical reactions in a real geometry.
... pp.24-42, 1997. Granata S., Faravelli T., Ranzi E., A wide range kinetic modeling study of t... more ... pp.24-42, 1997. Granata S., Faravelli T., Ranzi E., A wide range kinetic modeling study of the pyrolysis and combustion of naphthenes, Combustion and Flame, 132, Issue: 3, February, 2003, pp. 533-544, 2003. Ranzi, E. A ...
Abstract The high complexity of the interplaying physical and chemical phenomena occurring in Die... more Abstract The high complexity of the interplaying physical and chemical phenomena occurring in Diesel combustion has brought an increasing interest versus experimental and computational fundamental studies. A relevant contribution to the availability of suitable and accessible experimental data is represented by the Engine Combustion Network database, which are of great interest for model development and validation because of the well-defined boundary conditions and the wide range of conditions employed [1].
Uploads
Papers by T. Lucchini
Only 1 ppm of O3 has already a significant impact on the ignition. Predicting this effect as well as the low temperature combustion and ignition generally requires a detailed mechanism.
Using CFD simulations with the Tabulation of Dynamic Adaptive Chemistry (TDAC) method and a mechanism including more than 1000 chemical species, we have predicted the effect of ozone seeding on the combustion of iso-octane in a HCCI engine.
This paper presents the validation of the CFD simulations with a large range of ozone concentration and initial temperature.
It shows that the TDAC method is able to reproduce accurately such complex chemical phenomena accounting for heat transfer and chemical reactions in a real geometry.
Only 1 ppm of O3 has already a significant impact on the ignition. Predicting this effect as well as the low temperature combustion and ignition generally requires a detailed mechanism.
Using CFD simulations with the Tabulation of Dynamic Adaptive Chemistry (TDAC) method and a mechanism including more than 1000 chemical species, we have predicted the effect of ozone seeding on the combustion of iso-octane in a HCCI engine.
This paper presents the validation of the CFD simulations with a large range of ozone concentration and initial temperature.
It shows that the TDAC method is able to reproduce accurately such complex chemical phenomena accounting for heat transfer and chemical reactions in a real geometry.