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Experimental and Numerical Assessment of Active Pre-chamber Ignition in Heavy Duty Natural Gas Stationary Engine

Istituto Motori CNR-Carlo Beatrice
Istituto Motori CNR - Univ. "Parthenope"-Gessica Onofrio
  • Technical Paper
  • 2020-01-0819
To be published on 2020-04-14 by SAE International in United States
Gas engines (fuelled with CNG, LNG or Biogas) for generation of power and heat are, to this date, taking up larger shares of the market with respect to diesel engines. In order to meet the limit imposed by the TA-Luft regulations on heavy duty engines, lean combustion represents a viable solution for achieving lower emissions as well as efficiency levels comparable with diesel engines. Leaner mixtures however affect the combustion stability as the flame propagation velocity and consequently heat release rate are slowed down. As a strategy to deliver higher ignition energy, an active pre-chamber may be used. This work focuses on assessing the performance of two pre-chambers with different nozzle orifice diameters, in a stationary heavy-duty engine for power generation, operating at different loads, equivalence ratios and spark timings. The engine was originally a 6-cylinder compression ignition engine which is here employed as a single cylinder engine and then suitably modified to host the pre-chamber (with its natural gas injection system and spark plug) with a new bowl piston to decrease compression ratio. A…
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Under-expanded Gaseous Jets Characterization for Application in Direct Injection Engines: Experimental and Numerical Approach

Istituto Motori CNR-Luigi Allocca, Alessandro Montanaro, Giovanni Meccariello
Università degli Studi de L'Aquila-Francesco Duronio, Stefano Ranieri, Angelo De Vita
  • Technical Paper
  • 2020-01-0325
To be published on 2020-04-14 by SAE International in United States
In the last years, increasing concerns about environmental pollution and fossil sources depletion led transport sector’s research and development towards the study of new technologies capable to reduce vehicle’s emissions and fuel consumption. Direct-injection systems (DI) for internal combustion engines propose as an effective way to achieve these goals. This technology has already been adopted in gasoline engines (GDI) and, lately, a great interest is growing for its use in natural gas fuelling engines, so increasing efficiency with respect to port-fuel injection engines. Alone or in combination with other fuels, compressed natural gas (CNG) represents an attractive way to reduce exhaust emission (high H/C ratio), can be produced in renewable ways, and is more widespread and cheaper than gasoline or diesel fuels. Gas direct-injection process involves the occurrence of under-expanded jets in the combustion chamber. An accurate characterization of such phenomena is crucial for a consequent application in DI-CNG engines. In this paper an experimental and numerical analysis of methane under-expanded jets (as surrogate of CNG) has been carried out. The fuel has been injected…
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Experimental and 1D Numerical investigations on the exhaust emissions of a small Spark Ignition engine considering the cylinder-by-cylinder variability

Istituto Motori CNR-Luca Marchitto, Luigi Teodosio, Cinzia Tornatore, Gerardo Valentino
Univ of Naples-Fabio Bozza
  • Technical Paper
  • 2020-01-0578
To be published on 2020-04-14 by SAE International in United States
The stringent legislations on pollutant and CO2 emissions require relevant efforts to improve both the combustion efficiency and the exhaust emissions of internal combustion engines. In the case of spark ignition (SI) engines, various techniques have been tested and implemented in the last generation SI engine architectures. On the other hand, a reduced emphasis has been posed on the analysis of individual cylinder behavior, since a systematic sub-optimal operation may occur, due to cylinder-by-cylinder non-uniformities. The main purpose of this work is to accurately forecast the combustion and the exhaust emissions of a twin-cylinder turbocharged SI engine, taking into account the overall performance and individual cylinder-by-cylinder operation, with particular attention to volumetric efficiency, injected fuel quantity, and residuals content. To this aim, a dedicated experimental activity is performed on the engine under investigation. Preliminary measurements have shown relevant differences in combustion evolution in the two cylinders, mainly ascribed to variations in the injected fuel quantities, which in turn depend on the fuel rail geometry . As a consequence, cylinder out emissions are also quite different…
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Development of a Sectional Soot Model-Based Methodology for the Prediction of Soot Engine-Out Emissions in GDI Units

SILVANA Di Iorio
Istituto Motori CNR-Adrian Irimescu
  • Technical Paper
  • 2020-01-0239
To be published on 2020-04-14 by SAE International in United States
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 application to gasoline direct injection engine 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 dedicated 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, particular attention…
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Infrared/Visible Optical Diagnostics of RCCI Combustion with Dieseline in a Compression Ignition Engine

Istituto Motori CNR-Luigi Sequino, Ezio Mancaruso
Universitat Politecnica de Valencia-Javier Monsalve-Serrano, Antonio Garcia
  • Technical Paper
  • 2020-01-0557
To be published on 2020-04-14 by SAE International in United States
Compression ignition engines are widely used for transport and energy generation thanks to their high efficiency and low fuel consumption. Conversely, they are source of pollutant emissions at the exhaust that are strictly regulated. To face this issue, alternative strategies as low temperature combustion (LTC) concepts are born, recently. The reactivity controlled compression ignition (RCCI) uses two fuels (direct- and port fuel- injected) with different reactivity to control the reactivity of the charge by adjusting the proportion of both fuels. Beside this, the characteristics of the direct-injected fuel play a main role on the combustion process. Use of gasoline for direct injection is attractive to retard the start of combustion and to improve the air-fuel mixing process. In this work, RCCI combustion mode is performed in an optical compression ignition engine. Gasoline is injected in the intake manifold while a high reactivity fuel is directly injected in the cylinder. To investigate the effect of the direct-injected fuel properties on combustion, the engine is fed alternately with pure diesel and with a blend in volume of…
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Effects of Ultra-High Injection Pressures up to 100 MPa on Gasoline Spray Morphology

Istituto Motori CNR-Alessandro Montanaro, Luigi Allocca, Giovanni Meccariello
  • Technical Paper
  • 2020-01-0320
To be published on 2020-04-14 by SAE International in United States
Very high pressures for injecting gasoline in i.c. engines are recently explored to improve the air/fuel mixing process in order to control UBHC and particulate matter emissions such as for investigating new combustion concepts. The challenge remains the improvement of the spray parameters in terms of atomization, smaller droplets and their spread in the combustion chamber in order to enhance the combustion efficiency. In this framework, the raise of the injection pressure plays a key role in GDI engines for the trade-off of CO2 vs other pollutant emissions. This study aims contributing to the knowledge of the physical phenomena and mechanisms occurring when fuel is injected at ultra-high pressures for mapping and controlling the mixture formation for the combustion processes. Liquid and vapor phases of the fuel, injected by a GDI multi-hole device, were investigated to highlight the pressure role (up to 100 MPa) on the spray morphology under different ambient conditions. Commercial gasoline was injected in a constant volume vessel by a prototypal 5-hole, L/D: 2.6, solenoid activated GDI injector. Nitrogen gas was pressurized…
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Sub-23 nm particle emissions: nature and measure

Istituto Motori - CNR-SILVANA Di Iorio
Istituto Motori CNR-Paolo Sementa, Francesco Catapano, Bianca Maria Vaglieco
  • Technical Paper
  • 2020-01-0396
To be published on 2020-04-14 by SAE International in United States
Air quality is one of the greatest challenges of today because of the many sources of pollutant emissions. In the urban area the internal combustion engines play a dominant role on pollution despite the innovative technologies. Great efforts have been paid to reduce NOx and PM as their serious toxicological impact on human health and the environment. Nowadays, the regulation regards only the particles larger than 23 nm, but the attention is shifting towards the sub-23 nm particles because of their large presence at the exhaust of the modern engines and their negative impact on human health. The main challenge of the regulation of these particles is the definition of a proper procedure for their measure. The nature of the sub-23 nm particles is not well understood and their measure is strongly affected by the sampling conditions. The aim of this paper is to provide information on the nature of the sub-23 nm particles in order to define the most suitable procedure for their measure. The analysis was performed on a 4-cylinder GDI engine fueled…
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High-Speed Imaging of a Vaporizing GDI Spray: A Comparison Between Schlieren, Shadowgraph, DBI and Scattering

Istituto Motori CNR-Maurizio Lazzaro
  • Technical Paper
  • 2020-01-0326
To be published on 2020-04-14 by SAE International in United States
The evolution of the liquid and vapor phases of an iso-octane GDI spray was investigated in a constant volume vessel, under inert environment, using high-speed imaging techniques. The tests were performed in nitrogen, at temperatures and density varying between the operating conditions representative of late injection, flash boiling conditions and early injection in a GDI engine. Large scale parameters of the spray were obtained by processing Schlieren, shadowgraph, DBI and scattering images. The segmentation of spray images, for both the liquid and vapor phase, was carried out through an in-house image processing method. The method essentially involves three basic steps: an optimal filtering of the spray images by means of their regularization through variational methods; an original thresholding procedure based on the iterative application of the Otsu's method; the magnification of the Schlieren/Shadowgraph intensity pattern by means of the principal curvatures of the spray image surface. The boundaries of the vapor phase were obtained from the Schlieren and shadowgraph images of the spray. The processing method allows to accurately distinguish the contours of the vapor…
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Effects of Prechamber on Efficiency Improvement and Emissions Reduction of a SI Engine Fuelled with Gasoline

Istituto Motori CNR-Paolo Sementa, Francesco Catapano, Silvana Di Iorio, Bianca Maria Vaglieco
Published 2019-10-07 by SAE International in United States
The permanent aim of the automotive industry is the further improvement of the engine efficiency and the simultaneous pollutant emissions reduction.The aim of the study was the optimization of the gasoline combustion by means of a passive prechamber. This analysis allowed the improvement of the engine efficiency in lean-burn operation condition too. The investigation was carried out in a commercial small Spark Ignition (SI) engine fueled with gasoline and equipped with a proper designed passive prechamber.It was analyzed the effects of the prechamber on engine performance, Indicated Mean Effective Pressure, Heat Release Rate and Fuel Consumption were used. Gaseous emissions were measured as well. Particulate Mass, Number and Size Distributions were analyzed. Emissions samples were taken from the exhaust flow, just downstream of the valves. Four different engine speeds were investigated, namely 2000, 3000, 4000 and 5000 rpm. Stoichiometric and lean conditions at full load were considered in all tests. The results were compared with those obtained with the engine equipped with the standard spark plug. The results indicated that both performance and emissions were…
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Knock Onset Detection Methods Evaluation by In-Cylinder Direct Observation

Istituto Motori CNR-Francesco Catapano, Paolo Sementa, Bianca Maria Vaglieco
Published 2019-10-07 by SAE International in United States
Improvement of performance and emission of future internal combustion engine for passenger cars is mandatory during the transition period toward their substitution with electric propulsion systems. In middle time, direct injection spark ignition (DISI) engines could offer a good compromise between fuel economy and exhaust emissions. However, abnormal combustion and particularly knock and super-knock are some of the most important obstacles to the improvement of SI engines efficiency. Although knock has been studied for many years and its basic characteristics are clear, phenomena involved in its occurrence are very complex and are still worth of investigation. In particular, the definition of an absolute knock intensity and the precise determination of the knock onset are arduous and many indexes and methodologies has been proposed.In this work, most used methods for knock onset detection from in- cylinder pressure signal have been considered. Moreover, knock intensity has been evaluated by means of two common indexes. High speed imaging has been carried out in the combustion chamber of a high performance DISI engine provided with an optical window in…
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