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CFD Analysis and Knock Prediction into Crevices of Piston to Liner Fireland of an High Performance ICE

Ferrari Gestione Sportiva-Angelo Rosetti, Corrado Iotti, Andrea Bedogni
University of Modena e Reggio Emilia-Giuseppe Cantore, Stefano Fontanesi, Fabio Berni
Published 2019-09-09 by SAE International in United States
The paper aims at defining a methodology for the prediction and understanding of knock tendency in internal combustion engine piston crevices by means of CFD simulations. The motivation for the analysis comes from a real design requirement which appeared during the development of a new high performance SI unit: it is in fact widely known that, in high performance engines (especially the turbocharged ones), the high values of pressure and temperature inside the combustion chamber during the engine cycle may cause knocking phenomena. “Standard” knock can be easily recognized by direct observation of the in-cylinder measured pressure trace; it is then possible to undertake proper actions and implement design and control improvements to prevent it with relatively standard 3D-CFD analyses. Some unusual types of detonation may occur somewhere else in the combustion chamber: knocking inside piston/liner crevices belongs to the latter category and damages on the piston top land (very similar to pitting) are one of the evidence of knock onset in this region. The very localized regions of damage onset, the cycle to cycle…
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Design of a Hybrid Power Unit for Formula SAE Application: Packaging Optimization and Thermomechanical Design of the Electric Motor Case

University of Modena and Reggio Emilia-Valerio Mangeruga, Matteo Giacopini, Saverio Giulio Barbieri, Fabio Berni, Enrico Mattarelli, Carlo Rinaldini
Published 2019-09-09 by SAE International in United States
This paper presents the development of a parallel hybrid power unit for Formula SAE application. In particular, the system is made up of a brand new, single-cylinder 480 cc internal combustion engine developed on the basis of the Ducati “959 Superquadro” V90 2-cylinders engine. The thermal engine is assisted by a custom electric motor (30 kW), powered by a Li-Ion battery pack. The performance of the ICE has been optimized through CFD-1D simulation (a review of this activity is reported in a parallel paper). The main design goal is to get the maximum amount of mechanical energy from the fuel, considering the car typical usage: racing on a windy track. The Ducati “959 Superquadro” engine is chosen because of its high power-to-weight ratio, as well as for its V90 2-cylinder layout. In fact, the vertical engine head is removed and it is subsequently replaced by the electric motor directly engaged to the crankshaft using the original valvetrain transmission chain, thus achieving a very compact package. The mechanical behaviour of the original chain is investigated for…
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A Comparison between Different Moving Grid Techniques for the Analysis of the TCC Engine under Motored Conditions

R&D CFD S.r.l.-Giuseppe Cicalese
Siemens PLM-Antonella Perrone
Published 2019-04-02 by SAE International in United States
The accurate representation of Internal Combustion Engine (ICE) flows via CFD is an extremely complex task: it strongly depends on a combination of highly impacting factors, such as grid resolution (both local and global), choice of the turbulence model, numeric schemes and mesh motion technique. A well-founded choice must be made in order to avoid excessive computational cost and numerical difficulties arising from the combination of fine computational grids, high-order numeric schemes and geometrical complexity typical of ICEs. The paper focuses on the comparison between different mesh motion technologies, namely layer addition and removal, morphing/remapping and overset grids. Different grid strategies for a chosen mesh motion technology are also discussed. The performance of each mesh technology and grid strategy is evaluated in terms of accuracy and computational efficiency (stability, scalability, robustness). In particular, a detailed comparison is presented against detailed PIV flow measurements of the well-known "TCC Engine III" (Transparent Combustion Chamber Engine III) available at the University of Michigan. Since many research groups are simultaneously working on the TCC engine using different CFD codes…
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Understanding the Origin of Cycle-to-Cycle Variation Using Large-Eddy Simulation: Similarities and Differences between a Homogeneous Low-Revving Speed Research Engine and a Production DI Turbocharged Engine

SAE International Journal of Engines

University of Modena and Reggio Emilia, Italy-Alessandro d'Adamo, Sebastiano Breda, Fabio Berni, Stefano Fontanesi
  • Journal Article
  • 03-12-01-0007
Published 2018-12-14 by SAE International in United States
A numerical study using large-eddy simulations (LES) to reproduce and understand sources of cycle-to-cycle variation (CCV) in spark-initiated internal combustion engines (ICEs) is presented. Two relevantly different spark-ignition (SI) units, that is, a homogeneous-charge slow-speed single-cylinder research unit (the transparent combustion chamber (TCC)-III, Engine 1) and a stratified-charge high-revving speed gasoline direct injection (GDI) (Engine 2) one, are analyzed in fired operations. Multiple-cycle simulations are carried out for both engines and LES results well reproduce the experimentally measured combustion CCV. A correlation study is carried out, emphasizing the decisive influence of the early flame period variability (1% of mass fraction burnt (MFB1)) on the entire combustion event in both ICEs. The focus is moved onto the early flame characteristics, and the crucial task to determine the dominant causes of its variability (if any) is undertaken. A two-level analysis is carried out: the influence of global parameters is assessed at first; second, local details in the ignition region are analyzed. A comparison of conditions at combustion onset is carried out and case-specific leading factors for combustion…
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Experimental and Numerical Analysis of Spray Evolution, Hydraulics and Atomization for a 60 MPa Injection Pressure GDI System

Universita degli Studi di Perugia-Lucio Postrioti, Andrea Cavicchi, Gabriele Brizi
Universita di Modena e Reggio Emilia-Fabio Berni, Stefano Fontanesi
Published 2018-04-03 by SAE International in United States
In recent years, the GDI (Gasoline Direct Injection) technology has significantly spread over the automotive market under the continuous push toward the adoption of combustion systems featuring high thermodynamic conversion efficiency and moderate pollutant emissions. Following this path, the injection pressure level has been progressively increased from the initial 5-15 MPa level nowadays approaching 35 MPa. The main reason behind the progressive injection pressure increase in GDI engines is the improved spray atomization, ensuring a better combustion process control and lower soot emissions. On the other hand, increasing injection pressure implies more power absorbed by the pumping system and hence a penalty in terms of overall efficiency. Therefore, the right trade-off has to be found between soot formation tendency reduction thanks to improved atomization and the energetic cost of a high pressure fuel injection system.In this paper, a 5-hole, side-mounted prototype GDI injector was tested in a wide range of injection pressure conditions - from 5 up to 60 MPa - in terms of injection rate and spray development. The injection rate was detected by means of a…
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Refinement of a 0D Turbulence Model to Predict Tumble and Turbulent Intensity in SI Engines. Part I: 3D Analyses

FCA EMEA-Luigi Maresca
Universita di Modena e Reggio Emilia-Fabio Berni, Alessandro D'Adamo
Published 2018-04-03 by SAE International in United States
Recently, a growing interest in the development of more accurate phenomenological turbulence models is observed, since this is a key pre-requisite to properly describe the burn rate in quasi-dimensional combustion models. The latter are increasingly utilized to predict engine performance in very different operating conditions, also including unconventional valve control strategies, such as EIVC or LIVC. Therefore, a reliable phenomenological turbulence model should be able to physically relate the actuated valve strategy to turbulence level during the engine cycle, with particular care in the angular phase when the combustion takes place. Similarly, the capability to sense the effects of engine architecture and intake geometry would improve the turbulence model reliability.3D-CFD codes are recognized to be able to accurately forecast the evolution of the in-cylinder turbulence field, taking into account both geometrical features (compression ratio, bore-to-stroke ratio, intake runner orientation, valve, piston and head shapes, etc.) and operating conditions (engine speed, boost level, valve strategy). Instead, more common 0D turbulence models usually synthesize geometrical effects in a number of tuning constants and “try” to be sensitive…
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Chemistry-Based Laminar Flame Speed Correlations for a Wide Range of Engine Conditions for Iso-Octane, n-Heptane, Toluene and Gasoline Surrogate Fuels

Siemens PLM Software-Jens Prager
Universita di Modena e Reggio Emilia-Alessandro D'Adamo, Marco Del Pecchia, Sebastiano Breda, Fabio Berni, Stefano Fontanesi
Published 2017-10-08 by SAE International in United States
CFD simulations of reacting flows are fundamental investigation tools used to predict combustion behaviour and pollutants formation in modern internal combustion engines. Focusing on spark-ignited units, most of the flamelet-based combustion models adopted in current simulations use the fuel/air/residual laminar flame propagation speed as a background to predict the turbulent flame speed. This, in turn, is a fundamental requirement to model the effective burn rate.A consolidated approach in engine combustion simulations relies on the adoption of empirical correlations for laminar flame speed, which are derived from fitting of combustion experiments. However, these last are conducted at pressure and temperature ranges largely different from those encountered in engines: for this reason, correlation extrapolation at engine conditions is inevitably accepted. As a consequence, relevant differences between proposed correlations emerge even for the same fuel and conditions. The lack of predictive chemistry-grounded correlations leads to a wide modelling uncertainty, often requiring an extensive model tuning when validating combustion simulations against engine experiments.In this paper a fitting form based on fifth order logarithmic polynomials is applied to reconstruct correlations…
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A Comprehensive CFD-CHT Methodology for the Characterization of a Diesel Engine: from the Heat Transfer Prediction to the Thermal Field Evaluation

Universita di Modena e Reggio Emilia-Giuseppe Cicalese, Fabio Berni, Stefano Fontanesi, Alessandro D'Adamo, Enrico Andreoli
Published 2017-10-08 by SAE International in United States
High power-density Diesel engines are characterized by remarkable thermo-mechanical loads. Therefore, compared to spark ignition engines, designers are forced to increase component strength in order to avoid failures. 3D-CFD simulations represent a powerful tool for the evaluation of the engine thermal field and may be used by designers, along with FE analyses, to ensure thermo-mechanical reliability.The present work aims at providing an integrated in-cylinder/CHT methodology for the estimation of a Diesel engine thermal field. On one hand, in-cylinder simulations are fundamental to evaluate not only the integral amount of heat transfer to the combustion chamber walls, but also its point-wise distribution. To this specific aim, an improved heat transfer model based on a modified thermal wall function is adopted to estimate correctly wall heat fluxes due to combustion. On the other hand, a detailed Conjugate Heat Transfer model including both the solid components and the coolant circuit of the engine is needed, accounting for all the thermo-mechanical effects acting simultaneously during actual operations. Such comprehensive CHT methodology is here presented, with particular emphasis on a…
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Investigation of Sub-Grid Model Effect on the Accuracy of In-Cylinder LES of the TCC Engine under Motored Conditions

Seoul National Univ-Insuk Ko, Kyoungdoug Min
Universita degli Studi di Modena-Federico Rulli, Alessandro D'Adamo, Fabio Berni, Stefano Fontanesi
Published 2017-09-04 by SAE International in United States
The increasing interest in the application of Large Eddy Simulation (LES) to Internal Combustion Engines (hereafter ICEs) flows is motivated by its capability to capture spatial and temporal evolution of turbulent flow structures. Furthermore, LES is universally recognized as capable of simulating highly unsteady and random phenomena driving cycle-to-cycle variability (CCV) and cycle-resolved events such as knock and misfire. Several quality criteria were proposed in the recent past to estimate LES uncertainty: however, definitive conclusions on LES quality criteria for ICEs are still far to be found.This paper describes the application of LES quality criteria to the TCC-III single-cylinder optical engine from University of Michigan and GM Global R&D; the analyses are carried out under motored condition. In particular, attention is focused on sub-grid scale (SGS) model effects, which are evaluated using single grid estimators to compare three different sub-filter models: static Smagorinsky, dynamic Smagorinsky and dynamic structure model.Information on LES quality criteria are cross-linked to the analysis of in-cylinder gas-dynamics and flow structures. These are in turn analyzed by comparing experimental results (Particle Image…
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Critical Aspects on the Use of Thermal Wall Functions in CFD In-Cylinder Simulations of Spark-Ignition Engines

SAE International Journal of Commercial Vehicles

Universita degli Studi di Modena-Stefano Fontanesi
Universita' di Modena e Reggio Emilia-Fabio Berni, Giuseppe Cicalese, Alessandro D'Adamo
  • Journal Article
  • 2017-01-0569
Published 2017-03-28 by SAE International in United States
CFD and FE tools are intensively adopted by engine manufacturers in order to prevent thermo-mechanical failures reducing time- and cost-to market. The capability to predict correctly the physical factors leading to damages is hence essential for their application in the industrial practice. This is even more important for last generation SI engines, where the more and more stringent need to lower fuel consumption and pollutant emissions is pushing designers to reduce engine displacement in favor of higher specific power, usually obtained by means of turbocharging. This brings to a new generation of SI engines characterized by higher and higher adiabatic efficiency and thermo-mechanical loads.A recent research highlighted the different behavior of the thermal boundary layer of such engines operated at high revving speeds and high loads if compared to the same engines operated at low loads and revving speeds or even engines with a lower specific power. This means that CFD heat transfer models proposed and validated in the past decades on these last may not be predictive when applied to high specific power engines.…
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