Nuova ricerca

VALENTINA PESSINA

Home |


Pubblicazioni

2023 - An integrated 0D/1D/3D numerical framework to predict performance, emissions, knock and heat transfer in ICEs fueled with NH3–H2 mixtures: The conversion of a marine Diesel engine as case study [Articolo su rivista]
Berni, F.; Pessina, V.; Teodosio, L.; D'Adamo, A.; Borghi, M.; Fontanesi, S.
abstract

In the maritime transportation, e-fuels represent a valid alternative to fossil energy sour- ces, in order to accomplish the European Union goals in terms of climate neutrality. Among the e-fuels, the ammonia-hydrogen mixtures can play a leading role, as the combination of the two allows to exploit the advantages of each one, simultaneously compensating their gaps. The main goal of the present publication is the proposal of a robust numerical frame- work based on 0D, 1D and 3D tools for CFD analyses of internal combustion engines fueled with ammonia-hydrogen mixtures. The 1D engine model provides boundary conditions for the multi-dimensional in- vestigations and estimates the overall engine performance. 3D in-cylinder detailed ana- lyses are proficiently used to predict combustion efficiency (via the well-established G-equation model supported by laminar flame speed correlations for both ammonia and hydrogen) and emissions (with a detailed chemistry based approach). Heat transfer and knock tendency are evaluated as well, by in-house developed models. As for the 0D/1D chemical kinetics calculations, firstly they support 3D analyses (for example via the gen- eration of ignition delay time tables). Moreover, they allow insights on aspects such as NOx formation, to individuate mixture qualities able to strongly reduce the emissions.

2023 - Modeling of gaseous emissions and soot in 3D-CFD in-cylinder simulations of spark-ignition engines: A methodology to correlate numerical results and experimental data [Articolo su rivista]
Berni, F.; Mortellaro, F.; Pessina, V.; Paltrinieri, S.; Pulvirenti, F.; Rossi, V.; Borghi, M.; Fontanesi, S.
abstract

2022 - Laminar flame speed correlations of ammonia/hydrogen mixtures at high pressure and temperature for combustion modeling applications [Articolo su rivista]
Pessina, V.; Berni, F.; Fontanesi, S.; Stagni, A.; Mehl, M.
abstract

Ammonia/hydrogen mixtures are among the most promising solutions to decarbonize the transportation and energy sector. The implementation of these alternative energy carriers in practical systems requires developing suitable numerical tools, able to estimate their burning velocities as a function of both thermodynamic conditions and mixture quality. In this study, laminar flame speed correlations for ammonia/hydrogen/air mixtures are provided for high pressures (40 bar–130 bar) and elevated temperatures (720 K–1200 K), and equivalence ratios ranging from 0.4 to 1.5. Based on an extensive dataset of chemical kinetics simulations for ammonia/hydrogen blends (0-20-40-60-80-90-100 mol% of hydrogen), dedicated correlations are derived using a regression fitting. Besides these blend-specific correlations, a generalized (i.e., hydrogen-content adaptive) formulation, with hydrogen content used as additional parameter, is proposed and compared to the dedicated correlations.

2022 - Quantitative investigation on the impact of injection timing on soot formation in a GDI engine with a customized sectional method [Articolo su rivista]
Fontanesi, S.; Del Pecchia, M.; Pessina, V.; Sparacino, S.; Di Iorio, S.
abstract

Soot engine-out emissions are no longer a prerogative of Diesel engines. Emission regulations related to Gasoline units aim to curb the soot emissions along with other pollutants. In this scenario, Computational Fluid Dynamics (CFD) is a very promising research and development tool to explore the influence of engine design and operational parameters, as well as of the fuel chemical nature, on the particulate matter formation. Among the soot models, the Sectional Method is an advanced resource to provide information on Particle Number, Particulate Mass and Particle Size Distribution. In this study, the Sectional Method is applied in conjunction with a customized soot library, where the source terms governing the soot sections transport equations are stored. The library is computed via chemical kinetics simulation of a 0D constant pressure reactor, which provides fuel-related coefficients for each individual source term over the entire range of conditions experienced by the 3D-CFD model. 3D-CFD simulations are then carried out for three different injection timings without case-by-case tuning. Numerical results are then compared to the experimental dataset by using a consistent methodology. A satisfactory agreement between 3D-CFD results and experimental measurements is reached for soot mass and particle numbers, while the particle size distribution function is only partially reproduced. Soot-related quantities are thoroughly analyzed for each of the examined injection strategies to understand the mechanisms leading to soot formation and emissions.

2021 - Potentials of the Oversizing and H2-Supported Lean Combustion of a VVA SI Gasoline Engine towards Efficiency Improvement [Relazione in Atti di Convegno]
Bozza, F.; Berni, F.; Cicci, F.; D'Adamo, A.; De Bellis, V.; Fontanesi, S.; Malfi, E.; Pessina, V.; Teodosio, L.
abstract

In recent years, internal combustion engine (ICE) downsizing coupled with turbocharging was considered the most effective path to improve engine efficiency at low load, without penalizing rated power/torque performance at full load. On the other side, issues related to knocking combustion and excessive exhaust gas temperatures obliged adopting countermeasures that highly affect the efficiency, such as fuel enrichment and delayed combustion. Powertrain electrification allows operating the ICE mostly at medium/high loads, shifting design needs and constraints towards targeting high efficiency under those operating conditions. Conversely, engine efficiency at low loads becomes a less important issue. In this track, the aim of this work is the investigation of the potential of the oversizing of a small Variable Valve ActuationSpark Ignition gasoline engine towards efficiency increase and tailpipe emission reduction. To enhance the potential improvements of such an approach, a lean combustion concept is adopted, where the flame speed propagation is supported by doping gasoline with the addition of a percentage of hydrogen (10% by mass). The analysis is carried out by a 1D simulation tool, widely validated for the base engine supplied with pure gasoline and under stoichiometric/rich combustion. The combustion and knock models are here extended to handle the flame speed and auto-ignition characteristics of gasoline/H2 blends. The comparison between the base gasoline engine and the oversized gasoline/H2 variant highlights significant efficiency advantages at full load operations, which are due to the possibility to remove fuel enrichment and combustion delays. Exceptfor unburned hydrocarbons, pollutants and CO2 emissionsare reducedthanks to the synergic effects of H2addition and ultra-lean mixtures. A certain penalization of efficiency arises at very low loads, where engine oversizingdegrades the combustion process.

2020 - Application of the Sectional Method to Investigate Particle Number and Soot Mass in Ethanol and Gasoline Fueled Premixed Spark Ignition Engines [Relazione in Atti di Convegno]
Pessina, V.; Del Pecchia, M.; Breda, S.; Dalseno, L.; Borghi, M.
abstract

Emission modelling is still a timely topic in the engine research community. Soot emission reduction has gained its spotlight among the pollutants-related issues mainly due to the renewed interest in Gasoline Direct Injection. The conjunction of experimental measurements and numerical investigations provides an effective tool to cope with the constant evolution of the emission regulations. Thus, numerical models must be validated over a wide range of engine operating points and fuels. To this aim, the Sectional Method was applied to investigate Particulate Matter and Particle Number produced during combustion in a premixed spark ignition engine using 3D-CFD. Soot-related quantities were investigated for different values of equivalence ratio (from 1.0 up to 1.5) as well as for different fuels. Three different fuel types were examined: a commercial nonoxygenated American gasoline (TIER-2), a commercial Chinese gasoline (CHINA-6) with ethanol 10 %vol and pure Ethanol (E100). A detailed chemistry-based tabulated approach was exploited to compute a dedicated soot library, for each of the analyzed fuels, by means of 0D chemical kinetic simulations using a constant pressure reactor approach. Numerical results were compared to a database of experimental measurements collected from literature. The sooting tendency threshold dependency on equivalence ratio was also investigated and the results showed that the ethanol is the less sooting among the examined fuels, while the non-oxygenated gasoline exhibited the highest soot mass and Particle Number. This paper provides a CFD-based benchmark for soot mass and Particle Number for three fuel types with largely different chemical nature.

2020 - Comparison between Experimental and Simulated Knock Statistics Using an Advanced Fuel Surrogate Model [Relazione in Atti di Convegno]
Cicci, F.; Pessina, V.; Iacovano, C.; Sparacino, S.; Barbato, A.
abstract

The statistical tendency of a GDI spark-ignition engine to undergo knocking combustion as a consequence of spark timing variation is numerically investigated. In particular, attention is focused on the importance to match combustion-relevant and knock-relevant fuel properties to ensure consistency with the experimental evidence. An inhouse surrogate formulation methodology is used to emulate real gasoline properties, comparing fuel models of increasing complexity. Knock is investigated using a proprietary statistical knock model (GruMo Knock Model, GK-PDF). The model can infer a log-normal distribution of knock intensity within a RANS formalism, by means of transport equations for variances and turbulence-derived probability density functions (PDFs) for physical quantities. The calculated distributions are compared to measured statistical distributions. The proposed numerical/experimental comparison constitutes an advancement in synthetic chemistry integration into 3D-CFD combustion simulations.

2020 - Development of a Sectional Soot Model Based Methodology for the Prediction of Soot Engine-Out Emissions in GDI Units [Relazione in Atti di Convegno]
Del Pecchia, M.; Sparacino, S.; Pessina, V.; Fontanesi, S.; Breda, S.; Irimescu, A.; Di Iorio, S.
abstract

With the aim of identifying technical solutions to lower the particulate matter emissions, the engine research community made a consistent effort to investigate the root causes leading to soot formation. Nowadays, the computational power increase allows the use of advanced soot emissions models in 3D-CFD turbulent reacting flows simulations. However, the adaptation of soot models originally developed for Diesel applications to gasoline direct injection engines is still an ongoing process. A limited number of studies in literature attempted to model soot produced by gasoline direct injection engines, obtaining a qualitative agreement with the experiments. To the authors' best knowledge, none of the previous studies provided a methodology to quantitatively match particulate matter, particulate number and particle size distribution function measured at the exhaust without a case-by-case soot model tuning. In the present study, a Sectional Method-based methodology to quantitatively predict gasoline direct injection soot formation is presented and validated against engine-out emissions measured on a single-cylinder optically accessible gasoline direct injection research engine. While adapting the model to the gasoline direct injection soot framework, attention is devoted to modelling the dependence of the processes involved in soot formation on soot precursors chemistry. A well-validated chemical kinetics mechanism is chosen to accurately predict soot precursors formation pathways retaining an accurate description of the main oxidation pathways for oxygenated fuel surrogates. To account for the prominent premixed combustion mode characterizing modern GDI units, a constant pressure reactor library is generated containing the rates for the chemistry-based processes involved in soot formation and evolution at engine-like conditions. The proposed methodology is successfully applied to a 3D computational fluid dynamics model of the engine to predict soot engine-out emissions at the exhaust.

2020 - Gasoline-ethanol blend formulation to mimic laminar flame speed and auto-ignition quality in automotive engines [Articolo su rivista]
Del Pecchia, M.; Pessina, V.; Berni, F.; D'Adamo, A.; Fontanesi, S.
abstract

Several environment agencies worldwide have identified biofuels as a viable solution to meet the stringent targets imposed by future regulations in terms of on-road transport emissions. In the last decades, petroleum-based gasoline has been increasingly blended with oxygenated fuels, mostly ethanol. Blending ethanol with gasoline has two major effects: an increase of the octane number, thus promoting new scenarios for engine efficiency optimization, and a potential reduction of soot emissions. 3D-CFD simulations represent a powerful tool to optimize the use of ethanol-gasoline blends in internal combustion engines. Since most of the combustion models implemented in 3D-CFD codes are based on the “flamelet assumption”, they require laminar flame speed as an input. Therefore, a thorough understanding of the gasoline-ethanol blend chemical behavior at engine-relevant conditions is crucial. While several laminar flame speed correlations are available in literature for both gasoline and pure ethanol at ambient conditions, none is available, to the extent of authors’ knowledge, to describe laminar flame speed of gasoline-ethanol blends (for different ethanol volume contents) at engine relevant conditions. For this reason, in the present work, laminar flame speed correlations based on 1D detailed chemical kinetics calculations are derived targeting typical full-load engine-like conditions, for different ethanol-gasoline blends. A methodology providing a surrogate able to match crucial properties of a fuel is presented at first and validated against available experimental data. Then, laminar flame speed correlations obtained from 1D chemical kinetics simulations are proposed for each fuel blend surrogate.

2019 - Development of gasoline-ethanol blends laminar flame speed correlations at full-load Si engine conditions via 1D simulations [Relazione in Atti di Convegno]
Pecchia, M. D.; Pessina, V.; Iacovano, C.; Cantore, G.
abstract

Nowadays, most of the engineering development in the field of Spark-Ignited (SI) Internal Combustion Engines (ICEs) is supported by 3D-CFD simulations relying on flamelet combustion models. Such kind of models require laminar flame speed as an input to be specified by the user. While several laminar flame speed correlations are available in literature, for gasoline and pure ethanol at ambient conditions, there is a lack of correlations describing laminar flame speed of gasoline-ethanol blends, for different ethanol volume content, at conditions deemed to be representative of engine-like conditions. Toluene Reference Fuel surrogates with addition of ethanol (ETRF), suitable for representing gasoline-ethanol blends up to 85% vol. ethanol content are formulated. Thanks to these surrogates, 1D premixed laminar flame speed calculations are performed at selected engine-relevant conditions for a E5, E20 and E85 fuels. As a final outcome, three different laminar flame speed correlations based on the chemistry-based calculations are derived for E5, E20 and E85 gasoline-ethanol fuel blends focusing on typical full-load engine conditions. Such kind of correlations can be easily implemented in any 3D-CFD code to provide a chemistry-grounded estimation of laminar flame speed during combustion calculations. Such correlations are of practical use, since they might help in developing the next generation of bio-fuels powered internal combustion engines.

2019 - Numerical Simulation of Syngas Blends Combustion in a Research Single-Cylinder Engine [Relazione in Atti di Convegno]
Pessina, V.; D'Adamo, A.; Iacovano, C.; Fontanesi, S.; Martinez, S.; Lacava, P
abstract

Despite syngas is a promising alternative fuel for internal combustion engines (ICEs), its extensive adoption has not been adequately investigated so far. The dedicated literature offers several fundamental studies dealing with H2/CO blends burning at high pressure and room temperature, as well as preheated mixture at low pressure. However, these thermodynamic states are far from the operational conditions typical of ICEs. Therefore, it is essential to investigate the syngas combustion process at engine-like conditions to shed light on this fuel performance, in order to fully benefit from syngas characteristics in ICE application. One of the key properties to characterize a combustion process is laminar flame speed, which is also used by the most widespread turbulent combustion models. In the first part, a database of premixed laminar burning rates at engine-like conditions for different syngas (H2/CO) blends is created based on one-dimensional unstretched flame simulations using two validated chemical mechanisms. Then the resulting laminar flame speed values are fitted using a validated in-house method based on logarithmic correlations. In the second part of the paper, these are implemented in the G-equation combustion model and three-dimensional simulations of a four stroke Spark Ignition (SI) optical access engine fueled by syngas are carried out. The combustion characteristics of two H2/CO blends (50/50 and 75/25 volume fraction, respectively) are investigated and the simulation results are compared to the available experimental data for the same fuels. This joint numerical/experimental study allows to investigate and optimize the syngas combustion for ICEs and it provides general guidelines to further understand the feasibility of this alternative fuel in terms of ICE utilizations.