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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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Experimental and Numerical Analysis of a Pre-Chamber Turbulent Jet Ignition Combustion System

Istituto Motori CNR-Francesco Catapano, Paolo Sementa
Politecnico di Bari-Elia Distaso, Riccardo Amirante, Egidio Cassone, Pietro De Palma, Paolo Tamburrano
  • Technical Paper
  • 2019-24-0018
Published 2019-09-09 by SAE International in United States
Recent needs of reducing pollutant emissions of internal combustion engines have pushed the development of non-conventional ignition systems. One of the most promising techniques appears to be the so-called pre-chamber turbulent jet ignition combustion system in which a jet of hot combusting gases is employed to initiate the combustion in the main chamber. In the present study, the combustion process related to this ignition system has been experimentally investigated in an optically accessible single cylinder spark-ignition engine. The pre-chamber was composed of a gas injector and a spark-plug, embedded in a small annular chamber connected to the cylinder through a four-hole pipette. A small amount of methane is injected within the pre-chamber for initiating the combustion. The flame reaches the combustion chamber through four narrow orifices and rapidly consumes a homogeneous mixture of port injected methane and air. Wide open throttle condition at an engine speed of 2000 rpm was considered. The combustion process evolution and engine’s performance were analyzed in terms of 2D-digital imaging measurements as well as pressure and heat release rate traces.…
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Experimental Investigation of a Fueled Prechamber Combustion in an Optical Small Displacement SI Methane Engine

Istituto Motori CNR-Paolo Sementa, Francesco Catapano, SILVANA Di Iorio, Bianca Maria Vaglieco
Published 2019-09-09 by SAE International in United States
The constant aim of the automotive industry is the further improvement of engine efficiency and the simultaneous reduction of the exhaust emissions. In order to optimize the internal combustion engines it is necessary to further improve the basic knowledge of the thermo-fluid dynamic phenomena occurring during the combustion process. In this context, the application of optical diagnostic techniques permits a deep insight into the fundamental processes such as flow development, fuel injection, and combustion process. In this paper the analysis of the combustion process of gaseous fuel ignited by the plasma jets coming from a prechamber was performed. The investigation was carried out in an optically accessible small Direct Injection Spark-Ignition (DI SI) engine fueled with Methane. The ignition was obtained with a properly designed fueled prechamber prototype. It was equipped with a gas Direct Injector, used to inject the fuel into the prechamber, and a spark plug used to ignite the mixture. The combustion of the prechamber mixture generates four plasma jets that quickly ignite the mixture into the combustion chamber. The development of…
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Experimental Characterization of Methane Direct Injection from an Outward-Opening Poppet-Valve Injector

Istituto Motori CNR-Maurizio Lazzaro, Francesco Catapano, Paolo Sementa
Published 2019-09-09 by SAE International in United States
The in-cylinder direct injection of natural gas can be a further step towards cleaner and more efficient internal combustion engines (ICE). However, the injector design and its characterization, both experimentally and by numerical simulation, is challenging because of the complex fluid dynamics related to gas compressibility and the small length scale. In this work, the under-expanded flow of methane from an outward-opening poppet-valve injector has been experimentally characterized by high-speed schlieren imaging. The investigation has been performed at ambient temperature and pressure and different nozzle pressure ratios (NPR) ranging from 10 to 18. The gaseous jet has been characterized in terms of its macroscale parameters. A scaling-law analysis of the results has been performed. The gas-dynamic structure at the nozzle exit has been also investigated.
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Quasi-Dimensional Simulation of Downsizing and Inverter Application for Efficient Part Load Operation of Spark Ignition Engine Driven Micro-Cogeneration Systems

Istituto Motori CNR-Adrian Irimescu, Francesco Catapano, Silvana Di Iorio, Simona Merola, Paolo Sementa, Bianca Maria Vaglieco
Published 2018-10-30 by SAE International in United States
Within the context of distributed power generation, small size systems driven by spark ignition engines represent a valid and user-friendly choice, that ensures good fuel flexibility. One issue is that such applications are run at part load for extensive periods, thus lowering fuel economy. Employing an inverter (fitted between the generator and load) allows engine operation within a wide range of crankshaft rotational velocity, therefore improving efficiency. For the purpose of evaluating the benefits of this technology within a co-generation framework, two configurations were modeled by using the GT-Power simulation software. After model calibration based on measurements on a small size engine for two-wheel applications, the downsized version was compared to a larger power unit operated at constant engine speed for a scenario that featured up to 10 kW rated power. Indeed, the downsizing concept was found to ensure an electrical efficiency improvement of around 10% at 50% load, over 30% at 20% load, and reduced fuel consumption by over 50% at lower load. The co-generation potential was also evaluated, and it resulted practically the…
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Influence of Combustion Efficiency on the Operation of Spark Ignition Engines Fueled with Methane and Hydrogen Investigated in a Quasi-Dimensional Simulation Framework

Istituto Motori CNR-Adrian Irimescu, Francesco Catapano, Silvana Di Iorio, Paolo Sementa
Published 2018-05-30 by SAE International in United States
Within the context of widening application of numerical simulations for shortening engine development times, the present work covers the issue of quasi-dimensional simulation of spark ignition engines. Multi-fuel operation was the main goal of the study, with the analysis of methane and its blends with hydrogen; gasoline was also considered as a reference case. Data recorded on two engines with practically the same geometry, was used for calibrating the model. The first power unit was of commercial derivation for small applications, while the second one featured optical accessibility through the piston crown. The relative difference between the two engines allowed the top-land region crevice to be identified as the major contributor to overall combustion evolution, especially during its late stages. Using an in-cylinder pressure based method, compression ratio and blow-by losses were determined, and differences between fuel types were recognized in the sense of oxygen utilization rates. Then, the effects of the latter parameter were investigated with regard to model calibration. It was found that the entrainment coefficient was practically insensitive to combustion efficiency, while…
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On the Entrainment Velocity and Characteristic Length Scales Used for Quasi-Dimensional Turbulent Combustion Modeling in Spark Ignition Engines

Istituto Motori CNR-Adrian Irimescu, Silvana Di Iorio, Simona Merola, Paolo Sementa, Bianca Maria Vaglieco
Published 2017-09-04 by SAE International in United States
Quasi-dimensional modeling is used on a wide scale in engine development, given its potential for saving time and resources compared to experimental investigations. Often it is preferred to more complex CFD codes that are much more computationally intensive. Accuracy is one major issue of quasi-dimensional simulations and for this reason sub-models are continuously developed for improving predictive capabilities. This study considers the use of equivalent fluid velocity and characteristic length scales for simulating the processes of fresh charge entrainment and oxidation behind the flame front. Rather than dividing combustion into three different phases (i.e. laminar kernel, turbulent flame propagation and oxidation near the walls), the concept of turbulent heat and mass transfer is imposed throughout the entire process. Within this framework, the calibration of the two coefficients for fresh charge entrainment and oxidation behind the flame front was investigated, based on in-cylinder pressure and flame imaging recorded in a spark ignition (SI) engine fueled with gasoline, ethanol, methane and hydrogen. After the procedure of identifying the pairs of coefficients that ensured good accuracy during flame…
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Experimental Investigations on the Sources of Particulate Emission within a Natural Gas Spark-Ignition Engine

Istituto Motori CNR-Silvana Di Iorio, Paolo Sementa, Bianca Maria Vaglieco
Politecnico di Bari-Riccardo Amirante, Elia Distaso, Davide Pettinicchio, Paolo Tamburrano
Published 2017-09-04 by SAE International in United States
The aim of the present work is to provide further guidance into better understanding the production mechanisms of soot emissions in Spark-Ignition SI engines fueled with compressed natural gas. In particular, extensive experimental investigations were designed with the aim to isolate the contribution of the fuel from that of lubricant oil to particle emissions. This because the common thought is that particulate emerging from the engine derives mainly from fuel, otherwise the contribute of lubricant oil cannot be neglected or underestimated, especially when the fuel itself produces low levels of soot emissions, such as in the case of premixed natural gas.The fuel-derived contribution was studied by analyzing the influence that natural gas composition has on soot emitted from a single cylinder Spark-Ignition (SI) engine. To achieve this purpose, methane/propane mixtures were realized and injected into the intake manifold of a Single-Cylinder SI engine. The results were compared with pure methane and propane, as well as with natural gas.The lubricant-derived contribution was investigated by injecting lubricant oil either into the intake manifold or directly within the…
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Characterization of Knock Tendency and Onset in a GDI Engine by Means of Conventional Measurements and a Non-Conventional Flame Dynamics Optical Analysis

SAE International Journal of Engines

Istituto Motori CNR-Francesco Catapano, Paolo Sementa, Bianca Maria Vaglieco
  • Journal Article
  • 2017-24-0099
Published 2017-09-04 by SAE International in United States
Gasoline direct injection (GDI) allows knock tendency reduction in spark-ignition engines mainly due to the cooling effect of the in-cylinder fuel evaporation. However, the charge formation and thus the injection timing and strategies deeply affect the flame propagation and consequently the knock occurrence probability and intensity. In particular, split injection allows a reduction of knock intensity by inducing different AFR gradient and turbulent energy distribution.Present work investigates the tendency to knock of a GDI engine at 1500 rpm full load under different injection strategies, single and double injections, obtained delivering the same amount of gasoline in two equal parts, the first during intake, the second during compression stroke. In these conditions, conventional and non-conventional measurements are performed on a 4-stroke, 4-cylinder, turbocharged GDI engine endowed of optical accesses to the combustion chamber. Imaging in the UV-visible range is carried out by means of a high spatial and temporal resolution camera through a wide transparent window in the piston head allowing the view of the whole combustion chamber almost until the cylinder walls, to include the…
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