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This work shows the results of an experimental campaign carried out in two spark ignition engines, a small optical research engine and its commercial counterpart, using a turbulent ignition system (pre-chamber) specifically designed for small engines. Advanced optical techniques and conventional methods were used to study the combustion process under various operating conditions. The pre-chamber operated actively in the research engine and passively in the commercial engine. Results showed that the pre-chamber configuration resulted in an increase in indicated mean effective pressure (IMEP) and a decrease in the coefficient of variation (CoV) of IMEP. These improvements compensated for challenges such as slow methane combustion rate, poor lean burn capability, and air displacement. In addition, the pre-chamber configuration exhibited lower fuel consumption and specific exhaust emissions compared to the standard ignition system. The novelty of this work lies in the successful implementation of the turbulent ignition system as a retrofit solution for SI engines, showing improved combustion efficiency and lower emissions. The study goes beyond previous efforts by demonstrating the benefits of the pre-chamber configuration in small engines without requiring extensive modifications. The results provide valuable insights into the automotive industry’s pursuit of engine optimization and highlight the significance of innovative approaches for spark ignition engines in contributing to sustainable mobility.

In the last few years, car manufacturers are moving toward electrified powertrains, like Battery Electric Vehicles (BEV) and Hybrid Electric Vehicles (HEV), to reduce the levels of CO2 in the atmosphere. A promising alternative to BEVs to reduce CO2 emissions, while maintaining an existing and well-developed technology, could be the use of hydrogen for internal combustion engines (ICEs). Particularly, the zero-carbon content of hydrogen allows for guaranteeing very clean combustion and near-zero carbon footprint. Within this context, the present study aims to deeply investigate the effects of pure hydrogen fueling of Spark Ignition (SI) engines, especially on specific fuel consumption and NOx emissions. Particularly, the benefits of pure hydrogen fueling were assessed in a production small Direct Injection (DI) SI engine. The engine is intended to operate in steady state conditions as an Auxiliary Power Unit (APU) for a series hybrid powertrain. The effects of pure hydrogen fueling were investigated at two engine speeds, namely 2000 and 3000 rpm. All tests were carried out at unthrottled conditions and lean mixture. A 1-D engine model was developed within a commercial software. Combustion, heat transfer, and NOx emissions embedded sub-models were tuned based on the experimental data, to accurately reproduce the engine behavior in a wide range of operating conditions. Both experimental and simulation results demonstrated that hydrogen fueling, together with lean mixture operation, allow for significantly improving engine thermal efficiency. The results of 1-D model simulations supported the energy management strategies of the hybrid powertrain in selecting the most suitable ICE operating condition. Particularly, the best engine operating conditions in terms of fuel consumption are achieved at 2500 rpm, with λ = 2.0, while the lowest NOx emissions are reached when λ is increased up to 2.4.

Particle emissions from engines have long been topic of research studies because of their detrimental impact on human health and environment. Light duty vehicles represent the main contributor of particles in the congested urban areas and in the next future thought there will be a drastic reduction of fossil fuels, an increasing of the electric vehicles and an improvement of battery technology, a good control of exhaust particle emissions must be yet guaranteed using accurate and effective measurements for their characterization. This paper is an excursus of commercial and innovative techniques used for the evaluation of the particle emissions due to the engine exhaust. The effect of the main parameters on the soot formation and particle emissions were analyzed and described such as the influence of the injection strategies, the fuel type including commercial and not commercial fuels, and the lubricant oil. The particulate matter was characterized at the exhaust by means of the measure of number and size. Moreover, non-conventional diagnostics based on the optical detection of the natural flame chemiluminescence was applied to follow the combustion evolution and to evaluate the in-cylinder soot concentration. The correlation between the formation mechanisms of soot in the combustion chamber and the particle emissions at exhaust allows a comprehensive analysis. Particular attention was payed to the particles smaller than 23 nm that will be object of the next European emission regulation. The difficulties correlated to their measurement caused by the large fraction of volatiles in the 10 - 23 nm range that can nucleate or condense on existing particles was highlighted. In this regard a methodological approach consisting in the sampling and conditioning of the particles at two different temperature settings was defined within the project Sureal-23 to evaluate the volatile organic fraction of these particles. The knowledge developed within the exhaust particle emissions allowed to develop an experimental layout and a methodology for the sampling and measurement of non-exhaust particles.

Within the context of environmental impact reduction for small size spark ignition (SI) engines, especially green-house gas emissions, this study looked at laminar flame speed as an optimization parameter for hydrogen-methane fueled micro-generators. To this aim, SI engine operation was modeled in a 0D/1D simulation framework, so as to identify the best choice of methane-hydrogen ratios in different conditions. Starting from experimental data recorded on a small size engine, an optimization method was implemented for achieving the proposed goal. One of the main conclusions is that high concentrations of hydrogen and resulting fast burn rates are beneficial at high engine speed settings, while the opposite is true at low engine speed. Hydrogen addition was also considered as an additional control margin during lean operation, given that stable combustion can be achieved even with very low equivalence ratios. This aspect was closely correlated to limits imposed by non-road emission standards.

In the last few years, concern about the environmental impact of vehicles has increased, considering the growth of the dangerous effects on health of noxious exhaust emissions. For this reason, car manufacturers are moving towards more efficient combustion systems for Spark Ignition (SI) engines, aiming to comply with the increasingly stringent regulation imposed by EU and other legislators. Engine operation with very lean air/fuel ratios has demonstrated to be a viable solution to this problem. Stable ultra-lean combustion can be obtained with a Pre-Chamber (PC) ignition system, installed in place of the conventional spark plug. The efficiency of this configuration in terms of performance and emissions is due to its combustion process, that starts in the PC and propagates in the main chamber in the form of multiple hot turbulent jets. In this work, the benefits of the PC were assessed in a production small SI engine, fueled with gasoline, and equipped with a proper designed pre-chamber. The engine is intended to operate in steady state conditions as a range extender for a series hybrid powertrain. The effects of the PC on combustion process, engine performance and fuel consumption were experimentally analyzed at the engine test bed. Three different engine speeds were investigated, namely 2000, 3000 and 4000 rpm. All tests were carried out at full load, both in stoichiometric and lean conditions. A 1D model of the engine under study was developed by a commercial software. Combustion, heat transfer and emissions embedded sub-models were tuned based on experimental data, in order to accurately reproduce the engine behavior. Both numerical and experimental results demonstrated that lean engine operation allows to significantly improve thermal efficiency. The results of 1D model simulations are useful to support the energy management strategies of the hybrid powertrain in selecting the most suitable ICE operating condition, considering the trade-off between low fuel consumption and high power supplied to the battery charger.

Growing interest of the European Union to introduce new emission regulations seeking to lower the particle cut-off size down to the current limit set at 23 nm, has made crucial to achieve an extensive comprehension on their nature. In this regard, it is necessary to deepen their knowledge under different engine technologies, operating conditions, fuel properties and after-treatment devices and how their measure is affected by the sampling and dilution procedure. This paper provides a study on the sub-23 nm particles emitted from a small direct/port fuel injection, spark ignition engine fueled with gasoline, ethanol and a 30% v/v ethanol/gasoline blend, at different operating conditions. Particles were measured both upstream and downstream of a three-way catalyst. The conditions of the sampling were changed in order to investigate the volatile organic fraction. For this purpose, the exhaust gas sample was diluted through a Particulate Measurement Programme compliant system. The temperature of the first dilution stage and of evaporation chamber were changed to discriminate the volatile compounds by enhancing the condensation and the nucleation processes. An engine Exhaust Particle Sizer was used for the sizing and the counting of the particles in the range 5.6–560 nm. The results show a strong dependence of the sub-23 nm particle emissions from the engine operating condition and the fuel type. A moderate impact of the three-way catalyst was instead observed. Moreover, a significant effect of the dilution parameters in the sampling system was noted pointing out the importance to define an appropriate protocol for the measurement of the sub-23 nm particles.

he use of lean or ultra-lean ratios is an efficient and proven strategy to reduce fuel consumption and pollutant emissions. However, the lower fuel concentration in the cylinder hinders the mixture ignition, requiring greater energy to start the combustion. The prechamber is an efficient method to provide high energy favoring the ignition process. It presents the potential to reduce the emission levels and the fuel consumption, operating with lean burn mixtures and expressive combustion stability. In this paper the analysis of the combustion process of SI engines equipped with an innovative architecture and operating in different injection modes was described. In particular, the effect of the prechamber ignition on the engine stability and the efficiency was investigated in stoichiometric and leanburn operation conditions. The activity was carried out in two parts. In the first part the investigation was performed in a research small direct injection spark ignition (DISI) engine, running at 2000 rpm WOT, and fueled with Methane. The combustion process was studied using optical diagnostics. Methane was injected both in the prechamber and in the main chamber through the port fuel injection (PFI) mode. 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 gaseous fuel in the main chamber was ignited by the plasma jets coming from the prechamber. The combustion of the prechamber mixture generates four plasma jets that quickly ignite the mixture into the combustion chamber, and the flame speed is much faster than the traditional ignition. The optical data were correlated with the engine performance and indicated measurements that showed an increase of the Indicated Mean Effective Pressure (IMEP) and the reduction of the Coefficient of Variation (CoV). In the second part, the optimization of the gasoline combustion by means of a passive prechamber was performed. The investigation was carried out in a commercial small SI engine at 2000 rpm, fueled with gasoline in PFI mode and equipped with the same prechamber used in the first part of the activity. But in this case the prechamber works in passive mode.

Pollutant emission of vehicle cars is nowadays a fundamental aspect to take into account. In the last decays, the company have been forced to study new solutions, such as alternative fuel and learn burn mixture strategy, to reduce the vehicle's pollutants below the limits imposed by emission regulations. Pre-chamber ignition system presents potential reductions in emission levels and fuel consumption, operating with lean burn mixtures and alternative fuels. As alternative fuels, methane is considered one of the most interesting. It has wider flammable limits and better anti-knock properties than gasoline. Moreover, it is characterized by lower CO2 emissions. The aim of this work is to study the evolution of the plasma jets in a different in-cylinder conditions. The activity was carried out in a research optical small spark ignition engine equipped alternatively with standard ignition system and per-chamber. The engine runs at 2000 rpm at wide open throttle in standard ignition condition and slightly turbocharged in pre-chamber condition in order to overcome the decrease of compression ratio. In this activity methane and gasoline were used. Methane was always injected in the pre-chamber and ignited by spark plug; meanwhile gasoline was injected in the main chamber by port fuel injection mode. The combustion of the pre-chamber methane mixture generates four plasma jets that quickly ignite the mixture made with gasoline/air into the combustion chamber. In this condition the flame speed was much faster than the traditional ignition (gasoline injected in intake manifold without prechamber). Using optical data, significant information about the flame propagation in terms of the speeds and radius were obtained. The optical data were correlated with the engine performance and indicated measurements that showed an increase indicated mean effective pressure and coefficient of variation reduction when the pre-chamber was used. Furthermore the effect of pre-chamber ignition on the engine stability and efficiency in stoichiometric and lean-burn operation conditions was investigated.

Nowadays, the regulation regards only the particles larger than 23 nm. 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 leading to not reliable measure. The aim of this paper is to provide information on the emissions of sub-23 nm particles from GDI vehicles/engines. At the same time, the presence of volatiles, which mainly contribute to the formation of sub-23 nm particles, was evaluated and the effect of sampling conditions was investigated. The analysis was performed on a 1.8L GDI powered vehicle, widely used both in North America and Europe, and a 4-cylinder GDI engine, whose features are similar to those of the vehicle. For both the facilities, vehicle and engine, the Worldwide harmonized Light vehicles Test Cycle (WLTC) was performed. Particle emissions were characterized in terms of number and size by using both commercial systems and prototype systems developed within the European Project SUREAL23. For the vehicle analysis a MEXA 2000 SPCS, for particles larger than 23 nm, and the Induced Current Aerosol Detector (ICAD), developed with in the SUREAL23 European Project, for particles larger than 11 nm, were used. A commercial Engine Exhaust Particle Sizer (EEPS), working in the size range 5.6-560 nm, was used for the sizing and counting of the particles emitted from the GDI engine. For the characterization of the sampling conditions on the measurements were performed on the GDI engine. In this case the sampling was performed by a Particle Measurement Programme (PMP) compliant system, which permits to change the main sampling parameters, i.e. the temperature of the dilution air and of the evaporation chamber, to enhance the nucleation and/or condensation of volatiles. At the decrease of the sampling temperatures, a large concentration of sub-23 nm particles were measured suggesting the presence of large volatile material especially in the first phase of the Cold-start WLTC.

The effective compression ratio of spark ignition engines is influenced by several factors, and can feature a relatively wide range even for production power units. This is given mainly by the tolerances used for different components, but also due to the actual operating parameters that can result in different thermal regimes and therefore in dimensional variations. Given their design, optical engines are characterized by high crevice volumes and increased blow-by losses. Within this context, this work was aimed at developing a procedure for estimating the effective compression ratio and charge losses, based on the analysis of in-cylinder pressure traces. Compared to existing methods that require heat release rate modeling for ensuring good accuracy, the proposed route follows a different approach, that uses sub-models only for simulating heat transfer and blow-by losses. In this way, acceptable error levels were ensured, with minimum computational demand. The new procedure was applied on two different engine configurations, as well as operation with different fuels. Estimation of combustion efficiency was found to be an important issue for correct blow-by losses determination, while compression ratio evaluation depended mostly on the thermal regime of the piston.

The permanent aim of the automotive industry is the further improvement of the engine efficiency and the simultaneous pollutant emissions reduction. In order to optimize the small 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. The aim of this study was the optimization of the compressed natural gas direct injection by means of the analysis of the injection phase and combustion process. This analysis allowed the improvement of the engine efficiency in lean-burn operation condition too. The investigation was carried out in an optically accessible small direct injection spark ignition single-cylinder engine. Two different injectors were tested. The first one was the injector designed according to the results of model simulation, and the second one was a modified prototype obtained using the findings of the optical analysis carried out in the combustion chamber. The characteristic parameters of the gaseous fuel jet were evaluated through an image processing procedure. The fuel rail was modified in order to allow the injection of seeding particles into the gaseous fuel. The gas jet was analyzed using a white light source coupled with a high spatial and temporal resolution fast camera. The combustion process development was investigated for same engine operative condition performing a cycle-resolved visualization of the flame. Moreover, this methodology permitted the evaluation of motion field and turbulence during the injection process directly into the combustion chamber. The results of investigation evidenced that the modification of the injector, designed according to the optical analysis made in the optically accessible engine, allowed an optimization of compressed natural gas direct injection resulting in improved combustion and emissions reduction

In the last years, even more attention was paid to the alternative fuels that allow both reducing the fossil fuel consumption and the pollutant emissions. Gaseous fuels like methane and hydrogen are the most interesting in terms of engine application. This paper reports a comparison between methane and different methane/hydrogen mixtures in a single-cylinder Port Fuel/Direct Injection spark ignition (PFI/DI SI) engine operating under steady state conditions. It is representative of the gasoline engine for automotive application. Engine performance and exhaust emissions were evaluated. Moreover, 2D-digital cycle resolved imaging was performed with high spatial and temporal resolution in the combustion chamber. In particular, it allows characterizing the combustion by means of the flame propagation in terms of mean radius and velocity. Moreover, the interaction of turbulence with the local flame was evaluated. For both the engine configurations, it was observed that the addition of hydrogen results in a more efficient combustion, even though the engine configuration plays an important role. In PFI mode, the lower density of hydrogen causes a lower energy input. In DI mode, instead, the larger hydrogen diffusivity counteracts the charge stratification especially for larger hydrogen content. © 2016 Elsevier Ltd. All

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. 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 have been proposed.

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

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 the combustion process was investigated for different engine operative conditions performing a cycle resolved visualization of the flame in the combustion chamber. This approach allowed the acquisition of significant information on the flame propagation. Using the prechamber, the flame speed is many times faster with respect to the traditional ignition. All the optical data were correlated with the engine performance and the exhaust emissions

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 strongly inf luenced by the prechamber

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 sparkignition 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. In order to provide a more detailed analysis of the phenomena, 3D numerical simulations were also performed, and the results were compared with the experimental ones. The proposed combustion system ensured a stable and faster combustion, as highlighted by the imaging of the flame evolution. Furthermore, higher peaks of pressure and heat release rate demonstrated a faster and more efficient combustion

The implementation of environmentally friendly internal combustion engines (ICEs) has become an urgent need in recent years due to the strict current legislation. The high pollutant emissions such as particulate matter (PM) exhausted from ICE has driven many researchers to explore the possible advantages of alternative fuels. Ethanol is one of the most suitable alternative fuel for spark-ignition (SI) engines due to its higher heat of evaporation, octane number and larger oxygen content that allow to obtain positive effects on engine performance and particle formation and emissions. The main goal of the experimental research is the study of the effect of the different methods of ethanol fueling on particulate matter by means of the correlation between the in-cylinder soot formation and the exhaust particle emissions. The experimental investigation was carried out in a 4-stroke small displacement optical spark ignition engine operated at 2000 and 4000 rpm under full load conditions. The engine was fueled with gasoline and ethanol pure, blended (E30) and dual fueled (EDF). For both E30 and EDF configurations, 30 vol% of ethanol in gasoline was supplied. An optical technique based on 2D-digital imaging was used. Two-color pyrometry theory was applied to assess the in-cylinder soot formation. Particle emissions were measured at the exhaust by means of a smoke meter. The particle size distribution function (PSDF) was measured in the range from 5.6 to 560 nm with an Engine Exhaust Particle Sizer (EEPS). The research has shown that the effect of ethanol on soot formation and particle emission depends not only on ethanol fuel properties, but also on engine configuration and engine operating conditions.

The investigation of phenomena involved in gasoline direct injection 4-stroke, 4-cylinder, optically-accessible engine were carried out at part load and speed condition with different ethanol-gasoline blends. The influence of injection pressure on ethanol addition, at percentages of 10%, 50% and 85%, was investigated by conventional and optical diagnostics. Combustion characteristics, such as mass fraction burned, heat release rate and combustion duration were calculated based on in-cylinder pressure curve data, Emissions of UHC, NO X , CO, CO 2 , and PM were measured. The injection and combustion phase by high spatial and temporal optical measurements were characterized. The spray penetration, and the flame structure and propagation speed were obtained by optical data. The addition of ethanol in gasoline allowed an improvement of engine performance in terms of IMEP and COVIMEP and emissions. In particular, for E50 the better performance was obtained thanks to an earlier vaporization during the injection and a spray almost compact with a higher penetration especially at 100 bar, that avoided the formation of liquid fuel deposits on the piston and subsequently pollutants in the exhaust. Meanwhile, for E85 the spray was characterized by a slower vaporization that created a less homogeneous charge and reduction of the flame front propagation in the late propagation phase. This allows a faster and more efficient combustion with respect to fuels characterized by high gasoline fraction. Finally, E85 and E50 showed higher values of the integral flame luminosity in the first phase of combustion due to the higher flame speed with respect to gasoline one. Moreover, the chemiluminescence imaging confirmed a lower number of diffusive flames with respect gasoline and E10 in the late combustion phase, when the flame burns the fuel film on the piston crown. These results validated the lower emission of UHC and smoke of E50 and E85 with respect to gasoline and E10.

This article reports on the application of independent component analysis (ICA) to line-of-sight, cycle-resolved images of luminosity during combustion, acquired in an optically accessible engine. The experiments are conducted on a port fuel injection spark ignition (PFI SI) engine. The analysis identifies the independent components related to the underlying phenomena of the combustion process. The components, along with their corresponding time dependent coefficients, are used to characterize the morphological evolution of the luminous combustion during a single cycle and over a number of cycles. When ICA is applied to a single cycle, independent structures are identified, clearly separated in time, and related to the spatial distribution in the high-luminosity zone. The corresponding coefficients correlate well with the integral flame luminosity, and characterize the time evolution of the combustion morphological pattern in the chamber. The analysis over several cycles shows that independent com...

Various solutions are being proposed and adopted by manufactures and researchers to improve the en- ergetic and environmental performance of internal combustion engines within the transportation sector. For automotive spark ignition engines, gasoline direct injection is one of the presently preferred technolo- gies, in conjunction with turbocharging and downsizing. One of the limiting phenomena of this kind of engines, however, still remains the occurrence of knocking, namely the self-ignition of the so-called end- gas zones of the mixture, not yet reached by the flame front. This phenomenon causes strong in-cylinder pressure oscillations, high stress levels and even damage to engine components. Present work focuses on a numerical and experimental study of a turbocharged GDI engine and is aimed at assessing CFD-O (computational fluid dynamics optimization) procedures to be used in the phase of design as a decision making tool for the development of control strategies for a smooth and efficient operation. A preliminary experimental analysis is performed in order to characterize the con- sidered engine and to investigate the phenomenon of knocking that occurs under some circumstances as the spark advance is increased. The collected data are employed to elaborate a predictive criterion for the appearance of this kind of abnormal combustion, as well as to validate both a 1D and a 3D model for the simulation of the engine working cycle. Various numerical optimization procedures are then realized to increase the engine power output and simultaneously avoid conditions leading to undesired self-ignitions. These are either based on the use of a non-evolutionary algorithm or employ a genetic algorithm in the case multiple contrasting objectives are set. The response surface methodology is also explored as a way to reduce the computational effort.

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 Turbulent Jet Ignition (TJI) system, in which a jet of high-energy reactive gases is generated by means of a pilot combustion in a pre-chamber and used to initiate the main combustion event in the cylinder. Considering the complex nature of some phenomena typical of TJI systems, 3D CFD studies are essential to provide a detailed analysis for an efficient design. In this study, numerical simulations of an active pre-chamber TJI system applied to a lean operating methane engine were performed to provide a thorough analysis of the combustion process that characterizes such a technology. The numerical model was validated against experimental measurements carried out on an optically accessible single cylinder spark-ignition engine equipped with the pre-chamber prototype. The numerical simulations provided an insight view of both physical and chemical phenomena occurring inside the pre-chamber otherwise difficult to achieve by experiments alone. The evolution of some species of interest was analyzed in order to study the main charge ignition process, as well as the overall combustion progress. The results show that the main charge ignition is made possible by the large amount of energy and active radicals released from the pre-chamber and this ensures an overall stable and faster combustion in lean conditions. The performance improvements of the TJI system with respect to a traditional spark-ignition engine were evaluated in terms of efficiency and pollutant emission levels.

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 same from full to 50% load, while at low load the larger engine featured heat recovery potential up to two times larger compared to the smaller unit.

In questo WP sono stati progettati e realizzati gli strumenti hardware e software necessari alla verifica della funzionalità e al controllo di sistemi per recupero energetico da accoppiare ad un motore a combustione interna marino, In particolare è stato realizzato e messo a punto un sistema di controllo in grado di gestire il funzionamento di un sistema ORC e motore Stirling accoppiati alternativamente o congiuntamente al motore a combustione interna ed uno di accumulo al fine di aumentare l'efficienza di recupero di calore dai gas di scarico, in funzione della domanda di energia/calore da parte dell'utenza..

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 the characteristic length was closely linked to its modification. An important decrease was observed in the characteristic length when oxidation completeness was lower. Hydrogen addition to methane was found to improve combustion efficiency, most likely linked to its higher reactivity. These results emphasize the importance of incorporating fuel effects in quasi-dimensional simulation and given insight into how specific properties could be integrated for correct interpretation of results.

Nell'ambito di tale WP sono state individuate le unità Stirling con riferimento alla taglia, alla tecnologia, alle prestazioni e ai costi attraverso un'analisi di mercato e dello stato dell'arte. Particolare attenzione è stata rivolta all'efficienza di conversione ed alle potenzialità dei sistemi considerati in relazione ai loro possibili assetti nelle configurazioni richieste, anche in rapporto alle impegnative condizioni ambientali marine. Con riferimento poi all'obiettivo dell'integrazione Stirling-sistema nave, ed in particolare alle criticità dello scambio termico, è stata condotta una campagna sperimentale in sala prove con un motore Stirling in scala associato agli scarichi di un motore a combustione interna. E' stato inoltre studiata la configurazione ottimale per lo scambiatore, con modelli dettagliati ed ottimizzatori, fino allo sviluppo di unità di codice autonomamente funzionante che sono state efficacemente utilizzate in fase progettuale.

Data decomposition techniques have become a standard approach for the analysis of 2D imaging data originating from optically accessible internal combustion engines. In particular, the method of Proper Orthogonal Decomposition (POD) has proven to be a valuable tool for the evaluation of cycle-to-cycle variability based on luminous combustion imaging and particle image velocimetry (PIV) measurements. POD basically permits to characterize the dominant structures of the process under consideration. Recently, an alternative procedure based on Independent Component Analysis (ICA) has been introduced in the engine field. Unlike POD, the method of ICA identifies the patterns corresponding to physical processes that are statistically independent. In this work, a Group-ICA approach is applied to 2D cycle-resolved images of the luminosity emitted by the combustion process. The analysis is meant to characterize cyclic variability of a port fuel injection spark ignition (PFI SI) engine. For example, any flame front ignited independently by a hot spot is expected to behave independently from the other observed flames. In the Group-ICA approach, image sequences collected synchronically over a number of cycles are grouped together and then analyzed to identify common independent components. These should correspond to the independent phenomena underlying the combustion process at the group level. By this way, a projection is implicitly defined that permits the reconstruction of each member of the group (cycle) through the independent components and their coefficients. The successive analysis of the associated time courses (coefficients), specific for each cycle, permits to capture and discuss differences among cycles.

The influence of carboxylic acids on water nucleation in the gas phase has been explored in the supersonic expansion of water vapour mixed with acetic acid (AcA) at various concentrations. The sodium-doping method has been used to detect clusters produced in supersonic expansions by using UV photoionisation. The mass spectra obtained at lower acid concentrations show well-detected Na+-AcA(H2O)n and Na+-AcA2(H2O)n clusters up to 200 Da and, in the best cooling expansions, emerging Na+-AcAm(H2O)n signals at higher masses and unresolved signals that extend beyond m/e values >1000 Da. These signals, which increase with increasing acid content in water vapour, are an indication that the cluster growth taking place arises from mixed water-acid clusters. Theoretical calculations show that small acid-water clusters are stable and their formation is even thermodynamically favoured with respect to pure water clusters, especially at lower temperatures. These findings suggest that acetic acid may play a significant role as a pre-nucleation embryo in the formation of aerosols in wet environments.

This paper aims to correlate the in-cylinder soot formation and the exhaust particle emissions for different methods of gasoline/ethanol fueling in spark ignition engine. In particular, the engine was fueled with gasoline and ethanol separately and not, in this latter case both blended (E30) and dual fueled (EDF). For E30 the bend was direct injected and for EDF, the ethanol was injected in the combustion chamber and the gasoline into the intake duct. For both the injection configurations, the same percentage of ethanol in gasoline was supplied: 30%v/v. The measurements were carried out at 2000 and 4000 rpm, under full load, and stoichiometric condition, in small single cylinder optical engine. 2D-digital imaging was performed to follow the combustion process with a high spatial and temporal resolution through a full-bore optical piston. The two-color pyrometry was applied for the analysis of the in cylinder soot formation in the combustion chamber. Particle mass concentration was evaluated at the exhaust by means of a smoke meter. The particle size distribution function was measured in the range from 5.6 to 560 nm by an Engine Exhaust Particle Sizer (EEPS). It was observed that the use of ethanol allows the reduction of soot formation and particles emission in DI configuration. However, for E30 the in-cylinder soot formation and emissions are larger than EDF. This result is mainly due to the different contribution of gasoline. Optical analysis shows that in E30 the direct injected gasoline causes wide diffusive flames where soot formation is promoted; whereas for EDF the better evaporation and mixing of gasoline, typical of PFI configuration, results in few, small, and localized diffusive flames producing smaller particle emissions.

This work presents experimental tests where lubricant oil was added to the engine in order to highlight its contribution to particle emissions from both gasoline and compressed natural gas spark-ignition engines. Three different ways of feeding the extra lubricant oil and two fuel-injection modes--port fuel injection and direct injection--were investigated to mimic the different ways by which lubricant may reach the combustion chamber. In particular, in the tests using compressed natural gas, the oil was injected either into the intake manifold or directly into the combustion chamber, whereas in both the port-fuel-injection and direct-injection tests using gasoline, the oil was premixed with the fuel. The experiments were performed on a single-cylinder, optically accessible spark-ignition engine, running at 2000 r/min under stoichiometric and full-load conditions, and requiring no lubrication. Particle size distribution functions were measured in the range from 5.6 to 560nm by means of an engine exhaust particle sizer. Particle samples were taken directly from the exhaust flow, just downstream of the valves. Opacity was measured by an AVL 439 opacimeter, and gaseous emissions were measured by means of an exhaust gas analyzer in order to globally monitor the combustion process. Detailed analysis of the recorded total particulate number and particle size distributions allowed to determine the size ranges and relative amounts associated with the lubricant-oil-derived particles. Oil addition produced a significant increase in the particles emitted in the lowest range size, independent of the way lubricant was added. Only when lubricant was injected directly into the combustion chamber (either blended with the fuel or by itself), an increase in the number of particles with sizes larger than 50 nm was recorded

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 end-gas zones. Optical data are correlated to in-cylinder pressure-based indicated analyses and ion current data, on a cycle resolved basis. Normal flame front propagation before knock onset, end-gas auto-ignition and the effect of in-cylinder pressure waves of knock on the residual flame are deeply investigated. This synergic analysis is used to explore the effect of modulating injection on the charge formation optimization and the deriving improvement of combustion and reduction of knock tendency. Split injection reduces engine cycle-by-cycle variability with respect to the single injection case, all the others relevant parameters remaining unchanged. It is also able to increase the resistance to knock also changing relevantly the location of the knock onset. A new methodology based on high temporal resolution optical diagnostics for the determination of the knock intensity and onset has been proposed. This procedure is focused on the cycle resolved analysis of the centroid of luminosity dynamics under the knock pressure waves. It allows the precise determination of knock onset timing and spatial location within the combustion chamber. Furthermore, the amplitude of the luminous centroid oscillation has been found in good agreement with the knock index obtained by in-cylinder pressure and the ion current based analyses. This work and the proposed methodology can contribute to give a further insight to knock mechanism under real engine conditions.

In vehicles fueled with compressed natural gas, a variation in the fuel composition can have non-negligible effects on their performance, as well as on their emissions. The present work aimed to provide more insight on this crucial aspect by performing experiments on a single-cylinder port-fuel injected spark-ignition engine. In particular, methane/propane mixtures were realized to isolate the effects of a variation of the main constituents in natural gas on engine performance and associated pollutant emissions. The propane volume fraction was varied from 10 to 40%. Using an experimental procedure designed and validated to obtain precise real-time mixture fractions to inject directly into the intake manifold. Indicative Mean Effective Pressure, Heat Release Rate and Mass Burned Fraction were used to evaluate the effects on engine performance. Gaseous emissions were measured as well. Particulate Mass, Number and Size Distributions were analyzed with the aim to identify possible correlations existing between fuel composition and soot emissions. Emissions samples were taken from the exhaust flow, just downstream of the valves. Opacity was measured downstream the Three-Way Catalyst. Three different engine speeds were investigated, namely 2000, 3000 and 4000 rpm. Stoichiometric and full load conditions were considered in all tests. The results were compared with pure methane and propane, as well as with natural gas. The results indicated that both performance and emissions were strongly influenced by the variation of the propane content. Increasing the propane fraction favored more complete combustion and increased NO x emissions, due to the higher temperatures. In all tests, natural gas showed the highest PN values. At high speeds, adding propane increased the number of particles between 5 and 30 nm, highlighting the relevance of the ultrafine particles. Smaller differences were recorded at low speeds.

One general conclusion that emerged from studies of spark ignition (SI) engines fuelled with hydrogen, was that stoichiometric operation is associated with high heat losses compared to other gaseous fuels such as methane. A confirmation of higher heat transfer rates was obtained through heat flux measurements, that were found to be much higher for hydrogen compared to methane stoichiometric fuelling. Given that quasi-dimensional models offer an acceptable compromise between accuracy and computational requirements, this study employed three zone simulation in order to study the effects of fuel composition and engine speed on heat transfer rates in a premixed charge SI engine. After an initial validation based on in-cylinder pressure measurements performed on a research engine, a comprehensive numerical study was undertaken in order to evaluate the effects of crank angle rotational velocity and fuel composition. Engine speed was swept in a wide range, that covers the specific case of automotive and stationary energy production applications; combined use of methane and hydrogen (dual fuelling) was considered, ranging from one pure fuel to the other. Stoichiometric operation was simulated for all cases, given that this is the closest situation to real-world applications, for which closed-loop air-fuel ratio control is employed. The results of predicted heat flux suggest that hydrogen addition in its blend with methane increases laminar flame speed (and therefore shortens combustion development), but also results in higher heat losses due to augmented convective heat transfer. Both effects were found to be less evident as engine speed was increased. These findings can be used for adapting engine control strategies when using methane-hydrogen blends in premixed charge SI engines, in order to optimize efficiency and reduce environmental impact.

In the context of stringent exhaust gas emission regulations and requirements of increased efficiency, spark ignition (SI) engine research is looking at ever more detailed approaches, that cover a large number of processes. Ignition is one of the determining factors for repeatable combustion and its study is associated with extensive difficulties due to the turbulent nature of fluid motion. In order to provide data on the energy transfer and thermal conditions of the flame kernel in its initial stages, vibrational and rotational temperatures were evaluated using UV emission spectra detected in a SI engine. Stoichiometric operation with methane and hydrogen methane blends was employed, so as to identify any influence of the fuel's molecular structure on these processes. The consolidated methodology for temperature estimation using the ratio between the emission bands of CN and OH, was implemented considering the effects of collisional broadening. Vibrational temperatures evaluation showed and evolution from 8000 K to 4000 K during the arc and glow phase specific for SI. The evolution of CN emission intensity confirmed its formation only in the initial stages of ignition, for which kernel temperature is high enough. Simulations of chemical equilibrium showed that the evaluation of temperatures based on spectroscopic measurements is in line with the decreasing trend correlated with the electrical current evolution, measured in the secondary circuit. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The effects of different injection strategies on the mixture formation and combustion processes in a gasoline direct injection (GDI) engine are investigated. A synergic experimental and numerical analysis is realized on an optically accessible multi-cylinder engine under single and double injections, these last delivering the same amount of gasoline in two equal parts, the first during intake, the second during compression. In-cylinder pressure cycles and high temporal and spatial resolution combustion images are collected to highlight the possible occurrence of abnormal phenomena. AVL FIRE simulations are realized to characterize into detail the turbulent reacting flow and to evaluate the influence of mixture formation on flame propagation and the possible formation of zones in the end-gas region with conditions leading to self-ignition. Pollutants formation is also analysed. The flame propagation characteristics are indeed found different for the various injection strategies: for single injection, a faster spread occurs in the opposite side with respect to the injector position and towards the exhaust valves, while under split injection the flame front preferentially moves towards the intake valves. Computational fluid dynamics results give the relevant support to understand these peculiarities as related to in-cylinder equivalence ratio distribution and turbulent kinetic energy. In-chamber knock visualization is related to the numerical results of a simple self-ignition chemical model active in the end-gas zone, not yet reached by the main flame front. Split injection is shown to lead to advantages in terms of reduction of cyclic variability and tendency to knock, hence in increasing energy efficiency and in determining an overall reduction of undesired products of incomplete combustion.