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Experimental investigations of butanol-gasoline blends effects on the combustion process in a SI engine

Fuel blend of alcohol and 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 spark-ignition (SI) engine with an external boosting device. The optically accessible engine was equipped with the head of a commercial SI turbocharged engine with the same geometrical specifications (bore, stroke and compression ratio) as the research engine. The effect on the spark ignition combustion process of 20% and 40% of n-butanol blended in volume with pure gasoline was investigated through cycle-resolved visualization. The engine worked at low speed, medium boosting and wide-open throttle. Fuel injections both in closed-valve and open-valve conditions were considered. Comparisons between the parameters related to the flame luminosity and the pressure signals were performed. Butanol blends allowed working in more advanced spark timing without knocking occurrence. The duration of injection for butanol blends was increased to obtain a stoichiometric mixture. In open-valve injection condition, the fuel deposits on intake manifold and piston surfaces decreased, allowing a reduction in fuel consumption. BU40 granted the performance levels of gasoline and, in open-valve injection, allowed to minimize the abnormal combustion effects including the emission of ultrafine carbonaceous particles at the exhaust. In-cylinder investigations were correlated to engine out emissions.

Knocking diagnostics in the combustion chamber of boosted port fuel injection spark ignition optical engine

High spatial resolution optical techniques have been used to get information about the timing and the location of knocking and about the chemical species involved in this phenomenon. The experiments were realised in the combustion chamber of a boosted single-cylinder spark ignition port-fuel injection optical engine fuelled with commercial gasoline. Engine conditions with different levels of knock were considered from the borderline case onto standard knocking and heavy knocking. Cycle-resolved digital imaging was used to follow the combustion and the flame propagation in normal combustion and knocking conditions. Moreover, the effects of an abnormal combustion due to the firing of fuel deposition near the intake valves and on the piston surface were investigated. The knocking influence on the flame front propagation and combustion speed was investigated following the time evolution of the mean flame radius in the different engine conditions. The appearance of the auto-ignition centres in the end gas during the knock was evaluated in terms of timing, location and frequency of occurrence. Finally, UV-visible natural emission spectroscopy was applied to detect radical species that marked the knock. HCO and OH were identified as markers of the knocking onset and OH of its intensity.

Effect of the Fuel-Injection Strategy on Flame-Front Evolution in an Optical Wall-Guided DISI Engine with Gasoline and Butanol Fueling

AbstractThis work investigates the effect of n-butanol on combustion processes in a direct injection spark ignition (DISI) engine through the analysis of flame front propagation. Specific attention is given to the sensitivity of n-butanol when changing injection mode in terms of timing and number of injections. Tests were carried out on an optically accessible single-cylinder DISI engine fueled with n-butanol and gasoline, alternatively. The engine is equipped with the head of a commercial turbocharged engine with similar geometrical specifications (bore, stroke, compression ratio). The head has four valves and a centrally located spark device. A conventional elongated hollow piston is used and an optical crown, accommodating a fused-silica window, is screwed onto it. The injector is side mounted and features six holes oriented so that the spray is directed toward the piston crown. During the experimental activity, injection pressure was maintained at 100 bar for all conditions; homogeneous charge conditi...

Optical Investigation of Postinjection Strategy Effect at the Exhaust Line of a Light-Duty Diesel Engine Supplied with Diesel/Butanol and Biodiesel Blends

Ultraviolet (UV)-visible-near infrared (IR) multiwavelength extinction spectroscopy was applied in the exhaust line of an automotive common rail diesel engine to investigate the postinjection strategy impact on the fuel vapor. Four fuels were tested: a baseline diesel and three blends of diesel with 20% by volume of rapeseed methyl ester (RME), 20% of n-butanol and 20% of RME along with 20% of n-butanol. Experiments were performed at the engine speed of 2,750 rpm and 1.2 MPa of brake mean effective pressure. Preliminary engine tests were carried out to explore the postinjection activation aptitude to produce hydrocarbons at the exhaust, needed for the diesel oxidation catalyst (DOC) and the regeneration of the diesel particulate filter (DPF). Results of hydrocarbon and smoke emissions at the exhaust, with and without postactivation, are presented for the different blends. The optical diagnostic allowed to evaluate, during the postinjection activation, the evolution of the fuel vapor in the engine exhaust line. The spectroscopic investigation was focused on evaluation of the postinjection aptitude and fuel composition to produce hydrocarbon-rich exhaust gaseous. The main results showed that the butanol blended with diesel and/or biodiesel induced a higher concentration of fuel vapor within the exhaust manifold and consequently a lower tendency to lubrication oil dilution.

Particle and nanoparticle characterization at the exhaust of internal combustion engines

Abstract The aim of this work is the characterization of the emissions of exhaust particles in terms of number size distribution and chemical—physical properties. Laser-induced incandescence and broadband ultraviolet—visible extinction and scattering spectroscopy were used at the exhaust of a common-rail diesel engine and of a port fuel injection (PFI) spark ignition (SI) engine. The optical results were compared with size distributions obtained with an electrical low-pressure impactor and a scanning mobility particle sizer. Moreover, the fundamental engine parameters and the particulate mass and gas concentrations were measured using conventional instrumentation. With respect to the diesel engine, the effect of the exhaust after-treatment was investigated. The exhaust gas recirculation influenced the particle size distribution in terms of number concentration owing to the formation of accumulation mode particles. The catalysed diesel particulate filter strongly reduced the particle number concentration in the loading phase. Effects on the chemical nature of the particles were observed during the filter regeneration phase. With respect to the PFI SI engine, high number concentrations of nanoparticles (D<50nm) were measured for all the engine operating conditions. The chemical nature of the nanoparticles was investigated.

Effect of injection timing on combustion and soot formation in a direct injection spark ignition engine fueled with butanol

Ever tighter restrictions on pollutant emissions, energy security and a continuous drive for improving fuel economy have extended the range of application for direct injection in spark ignition engines and promoted the use of alternative fuels. Direct injection features higher soot formation compared to external mixture preparation, and therefore, intensive research is performed for understanding the processes related to this pollutant category. This study looked into the effect of injection timing in a wall-guided direct injection spark ignition engine when gasoline was completely replaced with n-butanol. Thermodynamic measurements were coupled with optical investigations that provided improved insight into local distribution of diffusive flames during late combustion stages. These data were correlated with exhaust gas measurements of CO, HC and NOx, as well as opacity. The optimum setting for injection timing was found to be a compromise between intake airflow velocity and piston positioning that influenced wall impingement. Late injection resulted in reduced soot but higher HC emissions, as well as lower performance compared to the optimum point. Early fuel delivery had roughly the same effect on indicated mean effective pressure and stability, with the downside of increased opacity. These observations were detailed with data obtained through cycle-resolved imaging that showed different integral luminosities with respect to injection phasing and confirmed that fuel impingement on the piston crown is the main factor of influence for soot formation. Ultraviolet–visible spectroscopy in the late combustion phase was also applied in repetitive mode in order to provide better insight into cyclic variability of the emission intensity in the range specific for carbonaceous structures.

Optical investigations of the early combustion phase in spark ignition boosted engines

An improved understanding of the thermo-fluid dynamic phenomena that occur during the combustion process in boosted spark ignition engines is necessary for future developments in these engines. In particular, increased understanding of flame kernel evolution is fundamental since the initial growth of the flame contributes significantly to cycle-to-cycle variation in engine performance and emissions. In this work, flame inception and early stages of the combustion process were investigated in an optically accessible single-cylinder ported fuel injection engine. This engine was equipped with the cylinder head of new generation spark ignition turbocharged engine with the same characteristics as the research engine. Cycle-resolved visualization was applied to follow the flame propagation from the spark ignition to the flame kernel growth. A retrieval procedure for the optical data was realized to obtain information about the flame radius evolution. Natural emission spectroscopy in the ultraviolet–visible wavelength range allowed the detection of the chemical markers of the combustion process such as CH, OH, and HCO radicals, and formaldehyde molecules. In-cylinder optical investigations were correlated with engine parameter measurements obtained by conventional methods.

Analysis of flame kinematics and cycle variation in a Port Fuel Injection Spark Ignition Engine

ABSTRACT This paper reports on the analysis of flame kinematics and cycle variation in port fuel injection (PFI) spark ignition (SI) engine. The engine was equipped with a four-valve head and with an external boost device. Different operating conditions were considered. Cycle-resolved digital imaging was used to investigate flame motion and the effects of an abnormal combustion due to the firing of fuel deposition near the intake valves and on the piston surface. Various algorithms are applied to the acquired images. Coefficients of Proper Orthogonal Decomposition (POD) were computed and used for a statistical analysis of cycle variability. The advantage is that the analysis can be run on a small number of scalar coefficients rather than on the full data set of pixel valued luminosity. POD modes are then discriminated by means of normality tests, to separate the mean from the coherent and the incoherent parts of the fluctuation of the luminosity field, in a non truncated representation of the data.

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

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 gasphase, because combustion processes take place in this phase, and occurs the interaction of the phase gasand 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.

UV-Visible Emission Spectroscopy of the Combustion Process in a Common Rail Cl Engine Fulled with N-Butanol - Diesel Blends

This paper is focused on the study of the effects of the injection strategy and fuel blends on spray combustion and soot formation in compression ignition engines. UV-visible natural emission spectroscopy was applied in the combustion chamber of a single cylinder high swirl compression ignition engine equipped with a common rail multi-jet injection system. The engine was fuelled with low-sulphur neat diesel and blended with 20 and 40% by volume of n-butanol. For all the fuels, the evolution of radical species, such like OH and soot was followed during the spray combustion processes examining different pilot-main dwell timings. Optical data were correlated to engine parameters and exhaust emissions.