Gerardo Valentino

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.

Analysis of in-cylinder flow processes by LDA

The in-cylinder turbulent flow field of a small modern d.i. diesel engine motored over a wide speed range (from 1,000 to 3,000 rpm) has been studied with LDA. The engine has been modified with an optical access on the head, to allow measurements along horizontal planes. The experiments provide operational conditions similar to those of a real engine. Cycle-resolved LDA measurements were made in a reentrant combustion chamber. Data have been analyzed using the ensemble-averaging, low-pass filtering and spectral analysis techniques. Measurements during the intake and compression strokes highlight the jetlike character of the intake flow that generates large-scale rotating flow. This is characterized by high turbulence and unstable swirling flow, which becomes more stable during the compression stroke. The mean motion, as well as the rms turbulent velocity scale almost linearly with engine speed. The spectral analysis shows the turbulent flow field during the compression to be nonisotropic and nonstationary at all engine speeds.

Optical Diagnostics of Temporal and Spatial Evolution of a Reacting Diesel Fuel Jet

Laser Doppler anemometry, spectral extinction-absorption, and flame chemiluminescence measurements were carried out to characterize the fluid flow and to analyze the temporal and spatial distribution of liquid, vapor and some pollutant species in an optically accessed high swirl combustion chamber Extinction-absorption measurements from UV to visible have shown that the spray, strongly distorted, is mixed downstream by the high swirling flow and the vapor region expands rapidly from the tip of the jet toward the chamber walls. The entrainment of hot air into the jet accelerates the vaporization process and the strong swirling flow transports the vapor around the chamber The OH emission, indicating the spatial location of autoignition, occurs at the same crank angle as that of the minimum of the heat release rate, and in the vapor region far from the tip of the liquid jet. The first appearance of soot occurs later across a wide portion of the leading part of the jet located between the tip of the jet and t...

Effects of gasoline–diesel and n-butanol–diesel blends on performance and emissions of an automotive direct-injection diesel engine

In the present paper, results of an experimental investigation carried out in a modern diesel engine running at different operating conditions and fuelled with blends of gasoline–diesel and n-butanol–diesel, are reported. The exploration strategy was focused on the management of injection pressure and timing to achieve a condition in which the whole amount of fuel was delivered before ignition. The aim of the paper is to evaluate the effects of fuel blends, which have low cetane number (CN) and are more resistant to auto-ignition than diesel fuel, on performance and engine-out emissions. Blends were mixed by the baseline diesel (D00) with 40% of commercial unleaded gasoline (G40) and 40% of n-butanol (B40). Fuel consumption and engine-out gaseous and smoke emissions from fuel blends were measured and compared to the neat diesel fuel. The investigation was performed on a turbocharged, water-cooled, direct-injection diesel engine, equipped with a common-rail injection system. The engine equipment included an exhaust gas recirculation system controlled by an external driver, a piezo-quartz pressure transducer to detect the in-cylinder pressure signal and a current probe to acquire the energizing current to the injectors. Engine tests were carried out at two engine operating conditions: 2000 r/min at 0.5 MPa and 2500 r/min at 0.8 MPa brake mean effective pressure, exploring the effect of start of injection, O2 concentration at intake and injection pressure on combustion behaviour and engine-out emissions. Taking advantages of the higher resistance of G40 and B40 to auto-ignition, it was possible to extend the range in which a partial premixed combustion was achieved. The management of injection pressure, O2 concentration at intake and injection timing allowed partial premixed combustion to be obtained by extending the ignition delay, both for diesel fuel and blends. The longer ignition delay and the better mixing before combustion made more advanced injection timings, which reduced smoke and nitrogen oxide emissions, possible. The joint effect of higher resistance to auto-ignition and higher volatility of n-butanol and gasoline improved the emissions of the blends compared to the neat diesel fuel, with a low penalty on fuel consumption.

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.

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.

Water Spray Flow Characteristics Under Synthetic Jet Driven By a Piezoelectric Actuator

Particle Image Velocimetry (PIV) and Phase Doppler Anemometry (PDA) have been applied to investigate the droplets size and velocity distribution of a water spray, under the control of a piezo-element driven synthetic jet (SJ). Tests were carried out under atmospheric conditions within a chamber test rig equipped with optical accesses at two injection pressures, namely 5 and 10 MPa, exploring the variation of the main spray parameters caused by the synthetic jet perturbations. The SJ orifice has been placed at 45° with respect to the water spray axis; the nozzle body has been moved on its own axis and three different nozzle quotes were tested. PIV measurements have been averaged on 300 trials whereas about 105 samples have been acquired for the PDA tests. For each operative condition, the influence region of the SJ device on the spray has been computed through a T-Test algorithm. The synthetic jet locally interacts with the spray, energizing the region downstream the impact. The effect of the actuator decreases at higher injection pressures and moving the impact region upwards. Droplets coalescence can be detected along the synthetic jet axis, while no significant variations are observed along a direction orthogonal to it.

Experimental and numerical investigation of diesel spray behaviour in high pressure common-rail systems

The behaviour of a diesel spray, generated by a common-rail injection system, has been investigated. The experimental investigation was carried out by testing a high pressure injection system, for heavy duty direct injection marine diesel engines, to calibrate a reliable model for the simulation of liquid jet atomisation and droplet break-up of the fuel spray. The experimental facility comprised instantaneous measurements of the fuel injection rate and the characterisation of the spatial and temporal evolution of the diesel spray, injected in a high pressure, non-evaporative quiescent vessel. The fuel tip penetration was estimated by digital processing of spray images captured at different instants after the start of injection. The spray was modelled using KIVA-3v algorithm, with a Kelvin-Helmholtz, Rayleigh-Taylor spray break-up model on a 45° sector grid. The mathematical model was verified with experimental results and a reasonable agreement was obtained.

Droplet Size and Velocity Distributions of a Transient Hollow-Cone Spray for GDI Engines

An experimental investigation of a gasoline direct injection (GDI) spray, emerging from an electronically controlled swirl-type injector, was carried out at an injection pressure and duration of 7.0 MPa and 3.0 ms, respectively, in an optically accessible vessel, at atmospheric pressure and ambient temperature. The temporal and spatial spray evolution was investigated in terms of global spray structure, interaction with the external gas, time-resolved droplet size and velocity distribution. The measurements were carried out with an AVL Engine Video System with a CCD camera, a frame grabber and a strobe flash triggered by the injection apparatus. Digital image processing software for the study of the global parameters of the spray was used. A particle Doppler analyzer (PDA) system was used to estimate the local droplet size and velocity as function of the radial coordinate and distance from the nozzle. A laser light extinction technique was applied to investigate the region close to the nozzle up to 5 mm. The spray emerging from the nozzle, at an early time, showed a hollow-cone type of structure because of the swirl motion of the fuel in the orifice that produces a rotational momentum at the nozzle exit. The spray starts with a central pre-injection phase followed, later, by the main body characterized by a large cone angle. The interaction of the fuel with the gas in the spray chamber was evidenced; curls on the external boundary and re-filling of the central part of the cone, during the second part of the injection, were observed. Measurements at different locations within the spray showed high values of the droplet velocity close to the nozzle exit at an early time. These high values were found downstream in the final stage of injection. Radial velocities were present along the entire injection process with an outer direction in the first stage, while an inner direction was observed in the second part. The droplet size distribution showed increasing values along the injector axis and towards the periphery of the spray.