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1

Spray Combustion Investigation through Optical Techniques in a Prototype Compression Ignition Engine fuelled with n-Butanol-Diesel Blends

Marchitto L., Merola S. S., Tornatore C., Valentino G.

Prace Naukowe Instytutu Nafty i Gazu

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2015

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nr 204

199--215

EN

The increasing energy demand from emerging countries and the simultaneous fossil oil shortage promote the use of alternative fuels. Even if gasoline and diesel continue to dominate automotive market, the use of non-conventional fuels such as biodiesel or alcohols is growing. Exhaust emissions and performance of compression ignition engines fuelled with diesel-alcohol fuel blends have been widely investigated. On the other hand, a deeper understanding of in-cylinder combustion is necessary as the different chemical physical properties of alcohols, such as oxygen content, volatility and cetane number affect the ignition, combustion mechanism and the pollutants formation. This work reports results of cycle resolved visualization and UV-visible optical imaging, carried out in an optically accessible compression ignition engine. Two different blends of diesel and n-butanol were tested: 20% and 40% of n-butanol by volume. The effect of n-butanol concentration on flame lift-off length and soot formation was investigated. Exhaust Gas Recirculation (O2 at intake 17%) was used for further reducing the local temperature peak. The combined effect of EGR and high oxygen content of n-butanol/diesel blends induced a simultaneous reduction of both NOx and soot emission. The correlation of optical measurements with thermodynamic and exhaust emission analysis allowed to emphasize the role of n-butanol oxygen content in the soot oxidation process.

2

Optical investigations of alternative fuel combustion in common rail compression ignition engine

Merola S. S., Tornatore C., Valentino G., Marchitto L.

Journal of KONES

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2012

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Vol. 19, No. 3

279-288

EN

The increasing global energy demand and the decreasing fossil-energy resources are enhancing the interest in the combustion characteristics of alternative fuels for diesel engines. Alternative-fuel combustion has been studied in detail in light-duty diesel engines, even if the comparison of test results from different chemical nature fuels obtained by integrated optical methodologies is lacking. Thus, it is the primary objective of the present study to characterize the combustion of selected alternative fuels in an optical common rail compression ignition engine by high-speed luminescence imaging and natural emission spectroscopy. The effects of the fuels on in-cylinder spray combustion and soot formation were investigated through UV-visible digital imaging and natural emission spectroscopy. Experiments were performed in a single cylinder high swirl compression ignition engine. The test engine was optically accessible and equipped with a common rail multi-jets injection system. Several injection pressures and timings at two EGR rates were tested. Digital imaging allowed characterizing the evaporating spray and the combustion process. UV-visible emission spectroscopy was used to follow the evolution of the combustion process chemical markers. Chemiluminescence signal due to OH was identified. The soot spectral feature in the visible wavelength range was correlated to soot engine out emissions. Conventional and optical data related to diesel fuel blended with gasoline and butanol were compared.

3

In - cylinder OH and CO2* detection in SI engine through UV natural emission spectroscopy

Merola S. S., Tornatore C., Marchitto L., Valentino G.

Journal of KONES

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2012

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Vol. 19, No. 4

429-437

EN

Processes of the combustion of liquid fuels and solid are more complex than combustion of fuel gases. With reference to liquid fuels occur additionally processes of vaporization of the fuel, and with reference to solid fuels - decomposition of the solid phase with processes of melting and vaporization, pyrolysis, or gasification. This simultaneous and also different influence of different parameters is sometimes a reason of incorrect interpretation of experimental results. The study of the theoretical model of the combustion process concerning of liquid and solid fuels and which then the model takes into account also the gas- phase, because combustion processes take place in this phase, and occurs the interaction of the phase gas- and liquid or the solid one. The theoretical model is presented basing on experimental initial researches realized in a model with reference to liquid fuels and solid ones. Researches realized in the constant volume chamber with measurements of the pressure during the process of the combustion with the use of quick photography and with measurement of the distribution of the velocity in the spray of the fuel and droplet measurements by means the laser Doppler equipment LDV and PDPA. There were obtained a good agreement of findings experimental researches with the theoretical model. Generally, on the combustion velocity of liquid fuels and solid one significant influence has a kind (laminar, temporary and turbulent) and the thickness of the thermal boundary layer.

4

Effect of butanol blend on in-cylinder combustion process. Part 1: Spark ignition engine

Tornatore C., Marchitto L., Mazzei A., Valentino G.

Journal of KONES

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2011

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Vol. 18, No. 2

427-438

EN

The addition of alcohol to conventional hydrocarbon fuels for a spark-ignition engine can increase the fuel octane rating and the power for a given engine displacement and compression ratio. In this work, the influence of butanol addition to gasoline in a port fuel-injection, spark ignition engine was investigated. The experiments were realized in a single cylinder ported fuel injection SI engine with an external boosting device. The optical accessible engine was equipped with the head of commercial SI turbocharged engine with the same geometrical specifications (bore, stroke, compression ratio) as the research engine. The effect on the spark ignition combustion process of 40% n-butanol blended in volume with gasoline was investigated by cycle resolved visualization. The engine worked at low speed, medium boosting and wide open throttle. Changes in spark timing and fuel injection phasing were considered in order to investigate normal and abnormal combustion. Comparisons between the parameters related to the flame luminosity and to the pressure signals were performed. The duration of injection for butanol blend was increased to obtain stoichiometric mixture. In open valve injection condition, the fuel deposits on intake manifold and piston surfaces decreased, allowing a reduction in fuel consumption. Butanol blend granted the performance levels of gasoline and in open valve injection allowed to minimize the abnormal combustion effects and the formation of ultrafine carbonaceous particles.

5

Effect of butanol blend on in-cylinder combustion process. Part 2: Compression ignition engine

Tornatore C., Marchitto L., Mazzei A., Valentino G., Corcione F. E., Merola S. S.

Journal of KONES

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2011

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Vol. 18, No. 3

473-483

EN

To meet the future stringent emission standards, innovative diesel engine technology, exhaust gas after-treatment, and clean alternative fuels are required. Oxygenated fuels showed tendency to decrease internal combustion engine emissions. In the same time, advanced fuel injection modes can promote further reduction in pollutants at the exhaust without penalty for the combustion efficiency. One of the more interesting solutions is provided by the premixed low temperature combustion (LTC) mechanism jointly to lower-cetane, higher-volatility fuels. In this paper, to understand the role played by these factors on soot formation, cycle resolved visualization, UV-visible optical imaging were applied in an optically accessed high swirl multi-jets compression ignition engine. Combustion tests were carried out using two fuels: commercial diesel and a blend of diesel with n-butanol. The fuels were tested at 70MPa injection pressure and different timings. At late injection timing coupled to high EGR rate (50%), the blends increased the ignition delay allowing operating in partially premixed LTC (PPLTC) regime in which the fuel is completely injected before the start of combustion. Strong reduction in engine out emissions of smoke and NOx were obtained with a little penalty on engine efficiency. This limitation was overcome operating at earlier injection timing in which a mixing controlled combustion (MCC) LTC regime was realized. In this regime, a good compromise between low engine out emissions and efficiency was achieved.

6

Optical diagnostics of the cyclic variation in the kernel development and abnormal combustion: SI boosted engine

Gallardo-Ruiz J. M., Ballais R., Merola S. S., Sementa P., Tornatore C.

Journal of KONES

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2010

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Vol. 17, No. 2

103-111

EN

The combustion stability of a spark ignition engine significantly influences its performances. The cyclic variation is generally evaluated by the fluctuation of in-cylinder peak pressure which changes in both magnitude and position measured from TDC. In this work the cyclic variation of combustion process were analysed as function of crank angles. The different SI engine process phases were investigated. The pressure related data were correlated with cycle resolved visualization measurements. The cycle resolved digital imaging was applied to follow the kernel inception and growth and to study the flame front propagation until the exhaust phase. A custom numerical post-detection procedure was applied to correlate the optical data from the integral luminous signal measured in the combustion chamber with the pressure related parameters .The flame kernel and the abnormal combustion due to the fuel deposits burning resulted particular relevant for the cycle-to-cycle variations. Optical measurements outlined better than pressure related analysis the role of the early andfinal stages of the combustion process. The experiments were performed in a 400 cm3 single cylinder, port fuel injection, four-stroke spark ignition engine. The engine was optical accessible with the same geometrical parameters as a 1600 cm3 passenger car engine. The head and the injection system of a commercial engine mounted on a passenger car were used. Standard EURO IV gasoline was used

7

Optical diagnostics of the cycle-to-cycle variation in the kernel development and abnormal combustion: SI small engine

Ballais, Gallardo-Ruiz J. M., Merola S. S., Sementa P., Tornatore C.

Journal of KONES

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2010

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Vol. 17, No. 2

17-25

EN

The combustion stability and more in details the cyclic variability significantly influences the performance and the pollutant emissions of a spark ignition engine. In this work, an experimental research activity was carried out to investigate the influence of the different combustion phases on the cycle-to-cycle variation. In particular the flame kernel development and the fuel deposits burning were investigated by in-cylinder pressure measurements and optical investigations. Engine cycle resolved visualization was applied to characterize the spatial evolution of the flame front from the spark ignition until the exhaust phase. A numerical custom post-detection procedure was used to correlate the optical data with the pressure related parameters during the combustion process. The simultaneous use of optical diagnostics and pressure related analysis demonstrated the fundamental role of the first stage and late phase of the combustion on the spark ignition engine process. Flame kernel and diffusion controlled flame due to fuel deposits burning dominated the cyclic variability of in-cylinder combustion. The experiments were realized in a 250 cm3 single cylinder, port fuel injection, four-stroke spark ignition engine. The engine was optically accessible and it was equipped with the head, injection system and exhaust device of a commercial engine mounted on small motorcycles and scooters. Standard EURO IVgasoline was used.

8

Optical diagnostics in a spark ignition engine for two-wheel vehicles

Merola S. S., Sementa P., Tornatore C.

Journal of KONES

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2010

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Vol. 17, No. 4

323-336

EN

Different optical techniques were applied to describe the thermal and chemical processes that occur in a SI small engine from the ported fuel injection and in-cylinder mixture formation to the combustion process and the exhaust emission. In PFI SI engines, the atomized fuel is sprayed towards the intake valves, where it may evaporate, puddle or rebound. Furthermore, a portion of the fuel may flow directly into the cylinder or impinge upon the port walls. These phenomena occur in varying degrees and depend upon the engine design, injector location and engine operation. Potentially the fuel can enter the cylinder in a poorly atomized state, leading to an increased unburned hydrocarbon emissions. This is particularly true during cold operation, when evaporation is low. In the small-motorcycle and scooter engines the fuel injection occurs in smaller intake manifold than light-duty vehicle engines, increasing the criticism of the fuel-wall interaction. The experimental investigations were performed in a single cylinder engine constituted by an elongated optically accessible piston and equipped with the head and injection system of a reference 4-stroke engine for small vehicles. High spatial resolution imaging was used to characterize the fuel injection phase. The cycle resolved visualization was performed to follow the flame propagation from the intake spark ignition to the exhaust phase. Natural emission spectroscopy measurements were applied in the ultraviolet-visible wavelength range to identify the chemical species that are markers of the combustion process and to follow the formation of pollutants.

9

In-cylinder formation and exhaust emission of particulates from a 4-stroke engine of a 2-wheel vehicle

Merola S. S., Sementa P., Tornatore C.

Nafta-Gaz

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2009

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R. 65, nr 11

849--856

EN

The efficiency of small engines in two-wheel vehicles can be further improved especially at low speeds and high loads. In these conditions fuel consumption and pollutant emission should be reduced maintaining the performance levels. This optimization can be realized only by the improvement in the basic knowledge of the thermo-fluid dynamic phenomena occurring during the combustion process. It is known that during the fuel injection phase in PFI SI engines, thin films of liquid fuel can form on the valves surface and on the cylinder walls. Successively the fuel films interact with the intake manifold and the combustion chamber gas flow. Du-ring the normal combustion process, it is possible to achieve gas temperature and mixture strength conditions that lead to fuel film ignition. This phenomenon can create diffusion-controlled flames. These flames persist well after the normal combustion event and induce the formation and then the exhaust emission of soot and unburned hydrocarbons. In this paper, experimental activities were carried out in the combustion chamber of a single-cylinder optical engine in order to investigate the in-cylinder formation and exhaust emission of particulates from a 4-stroke engine of a 2-wheel vehicle. The engine was equipped with the four-valve head of a commercial scooter engine and it was fuelled with European commercial gasoline. Cycle-resolved digital imaging and high spatial resolution visualization with two-color pirometry tool were used to follow in detail the flame front propagation and related phenomena. In particular the inception of diffusion-controlled flames near the valves and on the cylinder walls was studied. These flames induced the in-cylinder formation of unburned hydrocarbons and soot particles and the following exhaust emissions. The optical data were correlated with conventional combustion pressure measurements and particulate exhaust emission. The effect of three-way catalyst was investigated too.

PL

Sprawność małych silników pojazdów dwukołowych można poprawić, szczególnie przy dużych obciążeniach i niskich prędkościach. W tych warunkach dla utrzymania odpowiedniego poziomu pracy emisja zanieczyszczeń i zużycie paliwa powinny zostać obniżone. Taką optymalizację można było przeprowadzić tylko na podstawie wiedzy o dynamice zjawisk przepływu ciepła zachodzących podczas procesu spalania. Wiadomo jest, że w fazie wtrysku paliwa do silnika typu PFI (port-fuel-injected) z zapłonem iskrowym (SI), na powierzchni zaworów i ścianach cylindra mogą tworzyć się cienkie warstewki ciekłego paliwa. Z kolei warstewki paliwa oddziałują z przepływem gazów w kolektorze i komorze spalania. W trakcie normalnego procesu spalania możliwe jest osiągnięcie temperatury gazu i mieszanki umożliwiającej zapłon filmu paliwa. To zjawisko może prowadzić do wytwarzania płomieni sterowanych dyfuzyjnie. Takie, utrzymujące się dłuższy czas po normalnym spaleniu mieszanki, płomienie mogą być w dalszym ciągu przyczyną tworzenia i emisji sadzy oraz niespalonych węglowodorów. W pracy opisano badania doświadczalne nad tworzeniem i emisją cząsteczek stałych (PM), prowadzone metodą optyczną w komorze silnika jednocylindrowego, czterosuwowego, przeznaczonego dla pojazdów dwukołowych. Silnik został wyposażony w głowicę czterozaworową z handlowego skutera i był zasilany handlową benzyną europejską. Do dokładnej, cyfrowej analizy obrazu wykorzystano narzędzia trójwymiarowej pirometrii dwubarwnej o wysokiej rozdzielczości, przede wszystkim dla szczegółowego zbadania propagacji frontu płomienia i zachodzących przy tym zjawisk. Głównie badano powstawanie płomieni sterowanych dyfuzyjnie w pobliżu zaworów i na ściankach cylindra. Te płomienie powodują tworzenie się w cylindrze cząsteczek sadzy i pozostawanie niespalonych węglowodorów, obserwowanych następnie w wydechu. Uzyskane dane z pomiarów optycznych skorelowano z konwencjonalnymi pomiarami ciśnienia i emisji cząstek. Badano również efektywność katalizatora trójdrożnego.

10

Nanoparticles characterisation at the spark ignition engine exhaust

Merola S. S., Tornatore C., Vaglieco B. M.

Journal of KONES

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2008

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Vol. 15, No. 3

347-355

EN

The particles at the exhaust of two Port Fuel Injection Spark Ignition (PFI-SI) engines were characterised in terms of number size distribution and chemical properties. Optical techniques based on the Laser Induced Incandescence (LII) and on the Broadband Ultraviolet - Visible Extinction and Scattering Spectroscopy (BUVESS) were applied. The optical results were compared with those obtained by Electrical Low Pressure Impactor (ELPI). The aim of the work was the characterisation of the nanoparticles emitted by Port Fuel Injection Spark Ignition (PFI - SI) engines in terms of number size distribution and chemical-physical properties. Two PFI - SI engines were used for the experiments: a four-cylinder engine and a research optically accessible single cylinder engine. The experiments were performed at the exhaust of a multi-cylinder SI engine equipped with a three way catalyst (TWC) and in the combustion chamber and at the exhaust of a single-cylinder optical engine. High number concentrations of nanoparticles (D less than 50 nm) were detected. The presence of carbonaceous particles at the exhausts was due to the ignition of the fuel film deposits on the intake valves and on the cylinder walls. This was demonstrated by the optical measurements performed in the combustion chamber of the research engine. Different engine operating conditions were considered.

11

Effect of the fuel injection splitting on the combustion process in a PFI boosted spark-ignition engine

Merola S. S., Sementa P., Tornatore C., Vaglieco B. M.

Journal of KONES

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2008

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Vol. 15, No. 4

331-339

EN

Future stringent legislation on emissions in combination with the market request of an increase in engine efficiency and optimization poses a great challenge to the engine and components manufacturers. The technologies developed in the last years for Spark Ignition (SI) engines such as turbocharging and variable valve actuation are not able to totally satisfy the future normative. More progress still has to be made in terms of in-cylinder combustion process and efficiency. The aim of this paper is the optimisation of a boosted SI engine in terms of performances, fuel consumption and pollutants emissions with low costs. The experimental activity was carried out on a port fuel injection SI optical engine, equipped with a commercial four-valve head. Innovative injection strategies were tested: in particular, single and double injections were performed when the intake valves were open. Optical techniques based on 2D-digital imaging were used to follow the fuel injection in the intake manifold and simultaneously the flame propagation in the combustion chamber. Conventional measurements of engine parameters and exhaust emissions completed the experimental investigations. The tests demonstrated that the double injection strategies were characterized by higher combustion process efficiency than single injection on. The injection splitting resulted a suitable solution for the reduction in pollutants concentration in the combustion chamber and at the exhaust with a good compromise between performance and fuel consumption.

12

Effect of the fuel injection pressure on the combustion process in a PFI boosted spark-ignition engine

Merola S. S., Sementa P., Tornatore C., Vaglieco B. M.

Journal of KONES

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2008

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Vol. 15, No. 4

341-349

EN

In this paper, low-cost solutions were proposed to reduce the fuel consumption in a boosted port fuel injection spark ignition (PFI SI) engine, taking into account the engine performances and the pollutants emission. To this purpose, the optical characterization of the fuel injection and of the combustion process was carried out in a PFI SI engine. The experiments were performed on a partially transparent single-cylinder SI engine, equipped with a four-valve head and an external boost device. The intake manifold was optically accessible through three holes that allowed the introduction of an endoscope and of optical fibres. The standard injection condition planned by the engine manufacturer was investigated; it consisted in the fuel injection at 3.5 bar when the intake valves were closed. Moreover, the fuel injection with open intake valves was tested; 3.5 and 6.5 bar fuel pressures were studied for open and closed valves conditions. Optical techniques based on 2D-digital imaging were used to follow the fuel injection spray in the intake manifold and the flame propagation in the combustion chamber. The results of in-cylinder optical investigations were correlated with the engine performances and with the exhaust emissions.

13

Effect of EGR on nanoprticles at Common-rail diesel engines exhaust

Merola S. S., Tornatore C., Vaglieco B. M.

Silniki Spalinowe

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2007

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R. 46, nr SC3

206-217

EN

In the last years, diesel emission control strategies based on engine design and after-treatment devices, have been very successful in the reduction of the total particulate mass and gaseous emissions. Nevertheless they have been significantly less effective in reducing the total number of particles. Thus, when EURO 5 will be introduced, it will be difficult to meet the emission standards with the present technologies. Nowadays diesel engines are equipped with the Exhaust Gas Recirculation (EGR) system that allows the reduction of thermal-Nitrogen Oxides but it could also influence particles emissions. For this reason, the aim of the present work is to evaluate the effect of EGR on the balance between the primary particles and the aggregates at the exhaust of diesel engines. The idea is to find out a relation between EGR percentage and the size of the emitted particles for every speed and load. Two different methodologies for detection, sizing and counting nanoparticles were used. Electrical Low Pressure Impactor (ELPI) measured the particle size distributions in the range 7 nm-10 μm, without distinction between primary particles and aggregates. Laser Induced Incandescence (LII) allowed to determine soot primary particles diameter. ELPI measurements pointed out the increasing of number concentration and size of particles with the EGR. The size distributions showed a maximum in the range of 54-91nm with negligible number of particles larger than 300 nm. For alt the conditions, an increase of number concentration of particles bigger than 54 nm and a reduction of smaller ones was measured. This was due to the agglomeration effect caused by the reintroduction of particles contained in the exhaust gases into the cylinder during the EGR. LII measurements showed that at fixed engine speed and for alt EGR values, the diameters of primary particles increased with engine load. Moreover smaller primary particles were formed at higher speed. With respect to EGR variation, for every condition the primary particles diameters increased due to the partial oxidation of soot recirculated in the combustion chamber ad the successive superficial growth. Taking into account the proposed results, for each engine operating condition, the best EGR value could be chosen taking into account the size distribution of the produced particles and not only the NOx-soot trade-off.

14

Effect of fuel film deposition on combustion process in PFI SI engine

Merola S. S., Sementa P., Tornatore C., Vaglieco B. M.

Journal of KONES

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2007

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Vol. 14, No. 3

395-402

EN

The present paper discusses the experimental investigations on the flame induced by fuel film deposition ignition in a single cylinder, ported fuel injection, four-stroke, over-boosted spark-ignition engine with a four-valve production head. The engine was optically accessible and equipped with a transparent quartz window in the bottom of the combustion chamber. 2D-digital imaging and UV-visible natural emission spectroscopy were used to follow the flame propagation in the combustion chamber. Two colour pyrometers were applied to evaluate flame temperature and soot concentration. Particulate matter and soot primary particles diameters were measured and correlated with the soot amount produced in the combustion chamber. The effect of the intake air pressure and injection phasing was investigated. Optical setup for spectroscopic measurements and visible digital imaging, visible flame emission detected in the chamber for the selected operating conditions, visible emission spectra measured at 60 CAD ASOS in the chamber, soot concentration measured at the selected operating conditions, integral soot concentration measured at the selected operating conditions, particulate mass concentration measured by the Opacimeter and particles number concentration measured by LII at the engine exhaust are presented in the paper.