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Optical investigation of mixture formation in a small bore DISI engine by laser induced exciplex fluorescence (LIEF)

Technische Univ. Braunschweig-Alexander Pauls, Peter Eilts
  • Technical Paper
  • 2019-24-0133
To be published on 2019-08-15 by SAE International in United States
Legislative and customer demands in terms of fuel consumption and emissions are an enormous challenge for the development of modern combustion engines. Downsizing in combination with turbocharging and direct injection is one way to increase efficiency and therefore meet the requirements. This results in a reduction of the displacement and thus the bore diameter. The application of direct injection with small cylinder dimensions increases the probability of the interaction of liquid fuel with the cylinder walls, which may result in disadvantages concerning especially particulate emissions. This leads to the question which bore diameter is feasible without drawbacks concerning emissions as a result of wall wetting. The emerging trends towards long-stroke engine design and hybridization make the use of small bore diameters in future gasoline engines a realistic scenario. In the previous project “GDI Boundary Bore” the feasibility of an SI engine with direct injection and small bore diameter was shown by the analyses of two different cylinder head concepts (3V and 4V). For the acquirement of deeper understanding of the mixture formation in such engines…
 

Development and validation of SI combustion models for natural-gas heavy-duty engines

Politecnico di Milano-Lorenzo Sforza, Tommaso Lucchini, Giovanni Gianetti, Gianluca D'Errico
  • Technical Paper
  • 2019-24-0096
To be published on 2019-08-15 by SAE International in United States
Flexible, reliable and consistent combustion models are necessary for the improvement of the next generation spark-ignition engines. Different approaches have been proposed and widely applied in the past. However, the complexity of the process involving ignition, laminar flame propagation and transition to turbulent combustion need further investigations. Purpose of this paper is to compare two different approaches describing turbulent flame propagation. The first approach is the one-equation flame wrinkling model by Weller, while the second is the Coherent Flamelet Model (CFM). Ignition is described by a simplified deposition model while the correlation from Herweg and Maly is used for the transition from the laminar to turbulent flame propagation. Validation of the proposed models was performed with experimental data of a natural-gas, heavy duty engine running at different operating conditions. To deeply analyze main differences between Weller and CFM models, a detailed comparison of computed and experimental data was performed in terms of cylinder pressure, heat release rate, wall heat transfer, distribution of progress variable and flame surface density.
 

A Review of Spark-Assisted Compression Ignition (SACI) Research in the Context of Realizing a Production SACI Strategy

Clemson Univ-Robert Prucka
Clemson Univ.-Dennis Robertson
  • Technical Paper
  • 2019-24-0027
To be published on 2019-08-15 by SAE International in United States
Low temperature combustion (LTC) strategies have been a keen interest in the automotive industry for over four decades since they offer improved fuel efficiency compared to conventional spark-ignition (SI) engines. LTC strategies use high dilution to keep combustion temperatures below about 2000 K to reduce heat transfer losses while avoiding locally rich in-cylinder regions that produce high soot. High dilution also enables an efficiency improvement from reduced pumping work and improved thermodynamic properties, though it requires high ignition energy. Combustion can be achieved by triggering autoignition from compression energy. High compression ratios are typically required to produce this level of ignition energy, which further improves fuel efficiency. The timing of the autoignition event is influenced by fuel properties and mixture composition, and is exponentially sensitive to temperature. Control of autoignition timing is difficult without a direct actuator, and has been a significant obstacle for realizing LTC in production. Spark-assisted compression ignition (SACI) addresses this challenge by using a spark plug to initiate chemical reactions that trigger autoignition. The combustion chamber is slightly stratified to promote…
 

Performance and Emissions of an Ammonia-Fueled SI Engine with Hydrogen Enrichment

Universite D'Orleans-Pierre BREQUIGNY, Christine Rousselle
Université D'Orleans-Charles Lhuillier
  • Technical Paper
  • 2019-24-0137
To be published on 2019-08-15 by SAE International in United States
While the optimization of the internal combustion engine (ICE) remains a very important topic, alternative fuels are also expected to play a significant role in the reduction of CO2 emissions. High energy densities and handling ease are their main advantages amongst other energy carriers. Ammonia (NH3) additionally contains no carbon and has a worldwide existing transport and storage infrastructure. It could be produced directly from renewable electricity, water and air, and is thus currently considered as a smart energy carrier and combustion fuel. However, ammonia presents a low combustion intensity and the risk of elevated N-based emissions, thus rendering in-depth investigation of its suitability as an ICE fuel necessary. In the present study, a recent single-cylinder GDI SI engine is fueled with gaseous ammonia/hydrogen/air mixtures at various hydrogen fractions, equivalence ratios and intake pressures. Hydrogen is used as combustion promoter and might be generated in-situ through NH3 catalytic dissociation. In-cylinder pressure and exhaust concentrations of selected species are recorded and analyzed. Results show that ammonia is a very suitable fuel for SI engine operation, since…
 

A Study on Combustion Characteristics of a High Compression Ratio SI Engine with High Pressure Gasoline Injection

Mazda Motor Corp-Takashi Youso, Tatsuya Fujikawa, Masahisa Yamakawa
Waseda Univ-Takashi Kaminaga, Kyohei Yamaguchi, Sok Ratnak, Jin Kusaka
  • Technical Paper
  • 2019-24-0106
To be published on 2019-08-15 by SAE International in United States
In order to improve the thermal efficiency of spark ignition (SI) engines, an improved technology to avoid irregular combustion under high load conditions of high compression ratio SI engines is required. In this study, the authors focused on high-pressure gasoline direct injection in a high compression ratio SI engine, which its rapid air-fuel mixture formation, turbulence, and flame speed, are enhanced by high-speed fuel spray jet. Effects of fuel injection pressure, fuel mass ratio between direct injection and port fuel injection, and spark ignition timing on combustion characteristics were experimentally investigated. It was found that the heat release rate was drastically increased simultaneously by raising the fuel injection pressure. The increase of direct injected fuel mass ratio can also favorably improve the combustion speed. However, longer delay time between end-of-injection and spark timing worsens the combustion rate due to turbulence dissipation. A three-dimensional computational fluid dynamics simulation was also conducted to analyze and discuss the experimental results. The numerical results show that the high-pressure gasoline direct injection enhanced small-scale turbulent intensity and fuel evaporation, respectively.…
 

Experimental Investigation and Modeling of Ignition and Early Flame Propagation Stages in Operating Conditions Representative of Modern High Efficiency Spark Ignition Engines

IFP Energies nouvelles-Alessio Dulbecco, Gregory Font
Université D'Orléans-Fabrice Foucher, Pierre BREQUIGNY
  • Technical Paper
  • 2019-24-0073
To be published on 2019-08-15 by SAE International in United States
The present social context imposes effective reductions of transport greenhouse gases and pollutant emissions. To answer to this demand, car manufacturers adopted technologies such as downsizing, turbocharging, intense in-cylinder aerodynamics and diluted combustion process. In this context, to master mixture ignition is crucial to ensure an efficient heat release. To get to a clearer knowledge about the physics holding early stages of premixed mixture combustion, the PRISME institute in the framework of the French government research project ANR MACDOC generated a consistent experimental database to study ignition and spherical flame propagation processes in a constant volume vessel in laminar and turbulent environment. This allowed to have a detailed description of the flame dynamics of an air / iso-octane mixture depending on thermochemical properties of the mixture and nature of the diluent (O2, H2O, CO2 and synthetic stoichiometric EGR), as well as on turbulent intensity and ignition energy. A system simulation model based on the Coherent Flame Model approach was used was then setup at IFPEN accounting for ignition, influence of the flame stretch, through the…
 

Development of 1D/0D cycle simulation model for highly lean burn SI engine operation

Chiba Univ.-Tatsuya Kuboyama
  • Technical Paper
  • 2019-24-0004
To be published on 2019-08-15 by SAE International in United States
In the development processes for an engine control scheme and a novel engine configuration, 1D or 0D engine cycle simulation is effective and has been widely utilized, in these years. In SI engines, engine operations with the highly lean air-fuel mixture or highly diluted with EGR gas have been known as one of the most effective strategies to save fuel consumption. Following these situations, it is strongly demanded to develop a predictive combustion model capable of accurately predicting the effects of air-fuel ratio and EGR ratio on combustion characteristics, and thus on engine performance. In this paper, to predict highly lean or EGR diluted combustion with enough accuracy in 1D/0D engine simulation, a spark ignition model capable of predicting spark discharge circuit and a spark discharge channel behavior in the cylinder, and a flamelet concept model were applied into a single cylinder engine performance prediction model. In this paper, to predict highly lean or EGR diluted combustion with enough accuracy in 1D/0D engine simulation, a spark ignition model capable of predicting spark discharge circuit and…
 

Performance and emissions of an advanced multi-cylinder SI engine operating in ultra-lean conditions

Renault SA-Cédric LIBERT
Univ of Naples-Fabio Bozza, Luigi Teodosio, Vincenzo De Bellis
  • Technical Paper
  • 2019-24-0075
To be published on 2019-08-15 by SAE International in United States
Along the design process of a new engine, the calibration phase at the test bench usually involves a relevant percentage of the overall time-to-market. Each control variable, in fact, needs to be properly selected to optimize the performance and emissions, complying with thermal and mechanical stresses limits of the engine. This issue is still more critical for advanced engine architectures, which include additional control variables, such as valve phasing, turbocharger control, EGR level, etc. The aim of this work is the development of a numerically performed calibration procedure, applied to a prototype multi-cylinder Spark Ignition (SI) engine, designed to operate at very lean mixtures. To this aim, an active Pre-Chamber ignition system is considered. The required air flow rate is indeed provided by a Low-Pressure (LP) variable geometry turbocharger group, coupled to a high-pressure e-compressor. A Variable Valve Timing (VVT) device is also selected to reduce pumping losses at low load and for knock control at high-load. For the above engine, seven control variables have to be fixed in each operating condition, namely the Air/Fuel…
 

CFD Investigation of the Effects of Gas’ Methane Number on the Performance of a Heavy-Duty Natural-Gas Spark-Ignition Engine

Universita degli Studi di Perugia-Luca Ambrogi, Michele Battistoni, Lorenzo Gasbarro
West Virginia Univ-Jinlong Liu
  • Technical Paper
  • 2019-24-0008
To be published on 2019-08-15 by SAE International in United States
Natural gas (NG) is an alternative fuel for spark-ignition engines. In addition to its cleaner combustion, recent breakthroughs in drilling technologies increased its availability and lowered its cost. NG consists of mostly methane, but it also contains heavier hydrocarbons and inert diluents, the levels of which vary substantially with geographical source, time of year, and treatments applied during production or transportation. To investigate the effects of NG composition on engine performance and emissions, a 3D CFD model of a heavy-duty diesel engine retrofitted to spark ignition operations simulated engine operation under lean-combustion, low-speed, and medium load conditions. To eliminate the effect of different gas energy density, three NG blends of similar lower heating value but different H/C ratio have been investigated at fixed spark timing. The results indicated that a lower H/C ratio increased flame propagation and thus increased in-cylinder pressure and indicated mean effective pressure. In addition, the lower H/C ratio increased thermal efficiency despite the higher heat transfer, most probably due to the more advanced combustion phasing. Also, a higher H/C ratio reduced…
 

MULTI-LEVEL MODELING OF REAL SYNGAS COMBUSTION IN A SPARK IGNITION ENGINE AND EXPERIMENTAL VALIDATION

C.M.D. S.p.A.-Domenico Cirillo
CNR Istituto Motori-Michela Costa, Gabriele Di Blasio, Daniele Piazzullo
  • Technical Paper
  • 2019-24-0012
To be published on 2019-08-15 by SAE International in United States
Syngas produced from biomass gasification is being increasingly considered as a promising alternative to traditional fuels in Spark-Ignition (SI) Internal Combustion Engines (ICEs). This gaseous fuel, composed by a mixture of CO, CH4, H2, CO2, N2 (and other minor hydrocarbon compounds), is however characterized by an extreme variability of its composition and a low energy density. In order to assure good energy performance and stability of operation as the syngas composition slightly changes, numerical modeling can give an important contribution as a tool to investigate the main parameters affecting the combustion process development and the formation of main pollutants. The present work introduces a multi-level set of numerical approaches to a SI ICE fueled with syngas deriving from biomass gasification. Combustion characteristics are investigated at different levels of increasing detail, aiming at giving a complete outlook over the influence of this non-conventional fuel on the engine performances and on its environmental impact. At first, a specific characterization of the dependency of the syngas laminar flame speed upon its composition is achieved through an iterative approach…