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Evaluation of Water and EGR Effects on Combustion Characteristics of GDI Engines Using a Chemical Kinetics Approach

NAIS-Claudio Forte
University of Bologna-Giulio Cazzoli, Gian Marco Bianchi, Stefania Falfari, Matteo Ricci
  • Technical Paper
  • 2019-24-0019
Published 2019-09-09 by SAE International in United States
The modern spark ignition engines, due to the introduced strategies for limiting the consumption without reducing the power, are sensitive to both the detonation and the increase of the inlet turbine temperature. In order to reduce the risk of detonation, the use of dilution with the products of combustion (EGR) is an established practice that has recently improved with the use of water vapor obtained via direct or indirect injection.The application and optimization of these strategies cannot ignore the knowledge of physical quantities characterizing the combustion such as the laminar flame speed and the ignition delay, both are intrinsic property of the fuel and are function of the mixture composition (mixture fraction and dilution) and of its thermodynamic conditions.The experimental measurements of the laminar flame speed and the ignition delay available in literature, rarely report the effects of dilution by EGR or water vapor. To overcome the limitations of the experimentation is possible to predict the value of the ignition delay using numerical models based on chemical kinetics theory. The increased performance of computing systems…
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Numerical Aspects Affecting Heat Transfer in ICE Applications and Definition of a Temperature Wall Function Accounting for the Boundary Layer Compressibility

SAE International Journal of Engines

DIN-University of Bologna, Italy-Leonardo Pulga, Gian Marco Bianchi, Stefania Falfari
Nais s.r.l., Italy-Claudio Forte
  • Journal Article
  • 03-12-05-0034
Published 2019-08-22 by SAE International in United States
The heat transfer phenomena in Internal Combustion Engines (ICEs) are one of the main research topics that need to be addressed to enhance the performance in terms of power, efficiency, emissions and reliability. The present study is focused on the evaluation of the in-cylinder heat fluxes through the use of Computational Fluid Dynamic (CFD) simulations, with a wall function approach. In particular, the aim of this work is to present a new fully non-isothermal wall function obtained from the one-dimensional (1-D) energy balance equation for turbulent flows in the boundary layers, specifying all the steps and assumptions which have carried to the final fully compressible formulation. The new proposed wall function has been validated against experimental data of the General Motors (GM) Pancake Engine, representative of low Brake Mean Effective Pressure (bmep) operating point, comparing the results with other existing wall functions. With the objective of a mesh independency analysis, the wall functions considered have been tested with three different grids, varying the height of the first layer. Globally, it has been found that the…
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Water Injection Applicability to Gasoline Engines: Thermodynamic Analysis

NAIS srl-Claudio Forte
University of Bologna-Stefania Falfari, Gian Marco Bianchi, Giulio Cazzoli, Matteo Ricci
Published 2019-04-02 by SAE International in United States
The vehicle WLTP and RDE homologation test cycles are pushing the engine technology toward the implementation of different solutions aimed to the exhaust gases emission reduction. The tightening of the policy on the Auxiliary Emission Strategy (A.E.S.), including those for the engine component protection, faces the Spark Ignited (S.I.) engines with the need to replace the fuel enrichment as a means to cool down both unburnt mixture and exhaust gases to accomplish with the inlet temperature turbine (TiT) limit. Among the whole technology solutions conceived to make SI engine operating at lambda 1.0 on the whole operation map, the water injection is one of the valuable candidates. Despite the fact that the water injection has been exploited in the past, the renewed interest in it requires a deep investigation in order to outcome its potential as well as its limits. Many experimental campaigns have been performed while only few researches have deeply investigated the effect of the water injection on the air-fuel mixture under engine operating conditions. Since the experiments perform like a black box…
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Geometric and Fluid-Dynamic Characterization of Actual Open Cell Foam Samples by a Novel Imaging Analysis Based Algorithm

SAE International Journal of Engines

Politecnico di Milano-Augusto Della Torre, Gianluca Montenegro, Angelo Onorati
University of Bologna-Stefania Falfari, Gian Marco Bianchi, Giacomo Micci
  • Journal Article
  • 2017-01-9288
Published 2017-10-05 by SAE International in United States
Metallic open-cell foams have proven to be valuable for many engineering applications. Their success is mainly related to mechanical strength, low density, high specific surface, good thermal exchange, low flow resistance and sound absorption properties.The present work aims to investigate three principal aspects of real foams: the geometrical characterization, the flow regime characterization, the effects of the pore size and the porosity on the pressure drop. The first aspect is very important, since the geometrical properties depend on other parameters, such as porosity, cell/pore size and specific surface. A statistical evaluation of the cell size of a foam sample is necessary to define both its geometrical characteristics and the flow pattern at a given input velocity. To this purpose, a procedure which statistically computes the number of cells and pores with a given size has been implemented in order to obtain the diameter distribution. In particular, a morphological characterization of an actual foam sample was performed by applying an image processing method. The analyzed foam was a cubic open-cell foam made by Silicon Carbide (SiC).…
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A Chemical-Kinetic Approach to the Definition of the Laminar Flame Speed for the Simulation of the Combustion of Spark-Ignition Engines

NAIS-Claudio Forte
University of Bologna-Giulio Cazzoli, Gian Marco Bianchi, Stefania Falfari
Published 2017-09-04 by SAE International in United States
The laminar burning speed is an important intrinsic property of an air-fuel mixture determining key combustion characteristics such as turbulent flame propagation. It is a function of the mixture composition (mixture fraction and residual gas mass fraction) and of the thermodynamic conditions.Experimental measurements of Laminar Flame Speeds (LFS) are common in literature, but initial pressure and temperature are limited to low values due to the test conditions: typical pressure values for LFS detection are lower than 25 bar, and temperature rarely exceeds 550 K.Actual trends in spark ignition engines are to increase specific power output by downsizing and supercharging, thus the flame front involves even more higher pressure and temperature since the beginning of combustion. The most widespread models used to extrapolate the experimental data to the engine like conditions are derived from that of Metghalchi and Keck, but they often fail to correctly predict LFS values outside the experimental space.Thanks to the development of accurate chemical kinetic models together with the increase of computer performance, it is possible to numerically predict the laminar flame…
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Parametric Analysis of the Effect of the Fluid Properties and the Mesh Setup by Using the Schnerr-Sauer Cavitation Model

NAIS ENGINEERING-Claudio Forte PhD
Univ of Toronto-Sergio Negro
Published 2017-09-04 by SAE International in United States
The primary target of the internal combustion engines design is to lower the fuel consumption and to enhance the combustion process quality, in order to reduce the raw emission levels without performances penalty.In this scenario the direct injection system plays a key role for both diesel and gasoline engines. The spray dynamic behaviour is crucial in defining the global and the local air index of the mixture, which in turns affects the combustion process development. At the same time it is widely recognized that the spray formation is influenced by numerous parameters, among which also the cavitation process inside every single hole of the injector nozzle. The proper prediction of the cavitation development inside the injector nozzle holes is crucial in predicting the liquid jet emerging from them. In this mechanism the CFD simulation is of great importance because of the too small dimension of the nozzle holes, which are mostly non suitable for an accurate experimental investigation and, when they are, these analyses need to be limited to a few cases for cost reasons.…
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Design of Catalytic Devices by Means of Genetic Algorithm: Comparison Between Open-Cell Foam and Honeycomb Type Substrates

SAE International Journal of Engines

Politecnico di Milano-Gianluca Montenegro, Augusto Della Torre, Angelo Onorati
University of Bologna-Stefania Falfari, Giacomo Micci, Gian Marco Bianchi, Federico Brusiani
  • Journal Article
  • 2016-01-0965
Published 2016-04-05 by SAE International in United States
Metallic foams or sponges are materials with a cell structure suitable for many industrial applications, such as reformers, heat catalytic converters, etc. The success of these materials is due to the combination of various characteristics such as mechanical strength, low density, high specific surface, good thermal exchange properties, low flow resistance and sound absorption. Different materials and manufacturing processes produce different type of structure and properties for various applications. In this work a genetic algorithm has been developed and applied to support the design of catalytic devices. In particular, two substrates were considered, namely the traditional honeycomb and an alternative open-cell foam type. CFD simulations of pressure losses and literature based correlations for the heat and mass transfer were used to support the genetic algorithm in finding the best compromise between flow resistance and pollutant abatement. The CFD analysis was conducted by means of numerical simulations carried out on a geometry sample obtained by the micro-tomography technique to investigate the flow regime type and to extract pressure drop information. The result of this analysis was…
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Assessment of Advanced SGS Models for LES Analysis of ICE Wall-Bounded Flows - Part I: Basic Test Case

SAE International Journal of Engines

University of Bologna-Cristian Catellani, Gian Marco Bianchi, Stefania Falfari, Giulio Cazzoli, Claudio Forte
  • Journal Article
  • 2016-01-9041
Published 2016-03-14 by SAE International in United States
Large Eddy Simulation (LES) represents nowadays one of the most promising techniques for the evaluation of the dynamics and evolution of turbulent structures characterizing internal combustion engines (ICE). In the present paper, subdivided into two parts, the capabilities of the open-source CFD code OpenFOAM® v2.3.0 are assessed in order to evaluate its suitability for engine cold flow LES analyses. Firstly, the code dissipative attitude is evaluated through an inviscid vortex convection test to ensure that the levels of numerical dissipation are compatible with LES needs. Quality and completeness estimators for LES simulations are then proposed. In particular the Pope M parameter is used as a LES completeness indicator while the LSR parameter provides useful insights far calibrating the grid density. Other parameters such as the two-grid LESIQk index are also discussed. Then advanced SGS models such as the dynamic WALE and the Sigma models are compared with models traditionally used for LES simulations of ICE wall-bounded flows, i.e. the dynamic Smagorinsky and the WALE models. The proposed SGS models have been implemented in the open-source…
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Analysis of the Mixture Formation at Partial Load Operating Condition: The Effect of the Throttle Valve Rotational Direction

University of Bologna-Stefania Falfari, Claudio Forte, Gian Bianchi, Giulio Cazzoli, Cristian Catellani
University of Perugia-Lucio Postrioti, Fabrizio Ottobre
Published 2015-09-06 by SAE International in United States
In the next incoming future the necessity of reducing the raw emissions leads to the challenge of an increment of the thermal engine efficiency. In particular it is necessary to increase the engine efficiency not only at full load but also at partial load conditions. In the open literature very few technical papers are available on the partial load conditions analysis. In the present paper the analysis of the effect of the throttle valve rotational direction on the mixture formation is analyzed. The engine was a PFI 4-valves motorcycle engine. The throttle valve opening angle was 17.2°, which lays between the very partial load and the partial load condition. The CFD code adopted for the analysis was the FIRE AVL code v. 2013.2. The exhaust, intake and compression phases till TDC were simulated: inlet/outlet boundary conditions from 1D simulations were imposed. The injection system operation was experimentally investigated in terms of spray shape and drop sizing and velocity for a proper tuning of the numerical model. The injection process was modelled and the final results…
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The Effect of the Throttle Valve Rotational Direction on the Tumble Motion at Different Partial Load Conditions

University of Bologna-Stefania Falfari, Gian Marco Bianchi, Giulio Cazzoli, Federico Brusiani, Claudio Forte, Cristian Catellani
Published 2015-04-14 by SAE International in United States
In PFI and GDI engines the tumble motion is the most important charge motion for enhancing the in-cylinder turbulence level at ignition time close to the spark plug position. In the open literature different studies were reported on the tumble motion, experimental and not. In the present paper the research activity on the tumble generation at partial load and very partial load conditions was presented. The added value of the analysis was the study of the effect of the throttle valve rotational direction on the tumble motion and the final level of turbulence at the ignition time close to the spark plug location. The focus was to determine if the throttle rotational direction was crucial for the tumble ratio and the turbulence level.The analyzed engine was a PFI 4-valves motorcycle engine. The engine geometry was formed by the intake duct and the cylinder. The CFD code was FIRE AVL code 2013.1. The intake and the compression phases till TDC were simulated: inlet boundary conditions from 1D simulations were imposed. The modelled fluid was only air…
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