Felice E. Corcione

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.

Fluid-dynamic analysis of the intake system for a HDDI Diesel engine by STAR-CD code and LDA technique

The paper illustrates an experimental and numerical investigation of the flow generated by an intake port model for a heavy duty direct injection (HDDI) Diesel engine. Tests were carried out on a steady state air flow test rig to evaluate the global fluid-dynamic efficiency of the intake system, made by a swirled and a directed port, in terms of mass flow rate, flow coefficients and swirl number. In addition, because the global coefficients are not able to give flow details, the Laser Doppler Anemometry (LDA) technique was applied to obtain the local distribution of the air velocity within a test cylinder. The steady state air flow rig, made by a blower and the intake port model mounted on a plexiglas cylinder with optical accesses, was assembled to supply the, actual intake flow rate of the engine, setting the pressure drop across the intake ports at ΔP=300 and 500 mm of H 2 O. The flow coefficients and the swirl number were computed measuring the flow rate by a turbine flow meter and a paddle wheel to evaluate the air vortex speed into the cylinder test. The LDA technique was used to obtain the tangential and axial components of the flow velocity on two planes and along three diameters within the test cylinder. The computation was carried out by the fluid-dynamic code STAR-CD that solves the ensemble averaged conservation equations for mass, momentum and energy in steady state conditions with the turbulence model k-e. The grid, reproducing the geometry of the intake port and the real fluid system, was made using CAD data and the boundary conditions were the same as the experimental ones. Results of the computed mass flow rate, flow coefficients, and velocity profiles were compared to the experimental ones. The substantial agreement between experiments and computations suggests that an acceptable level of confidence may be assigned to calculations to design the intake port geometry of heavy duty Diesel engines.

Spectral extinction measurements of spray combustion in a divided-chamber diesel engine system

Sepctral flame extinction measurements from UV to visible with high temporal and spatial resolution were performed in an optically accessible divided-chamber diesel system. This system was developed ad hoc by modifying a real engine to realize a soot-forming premixed spray combustion at high pressure, high temperature, and high swirl. The large optical accesses of the divided chamber allowed us to follow the progress of fuel injection, vaporization, autoignition, and combustion by direc high-speed photography (8000 frames/s). Light extinetion measurements were carried out in 153 different spatial locations for 250 consecutive combustion cycles from the start of injection to the end of combustion. The photographic sequences have shown that spray is strongly distorted and mixed downstream of the high-swirling flow, resulting in a well premixed region in which the combustion starts. Then, the combustion proceeds rapidly, involving the entire chamber volume. Consequently, the flame luminosity increases, denoting fast soot formation-oxidation processes in the region close to the tangential duet in which the mising is higher. The analysis of the extinction spectra in the UV and visible range has allowed us to follow spatially and temporally the soot formation process and to identify the nature of the particulate matter and the agglomeration degree of soot particles, as well as the time history of the soot volume fraction.

Determination of Size of Fuel Droplets and Soot Particles in a Diesel Engine by Broadband Extinction and Scattering Spectroscopy

The Diesel process was studied and characterized by ultraviolet-visible extinction and scattering spectroscopy. Measurements were performed on an optically accessible Diesel engine, realized by modifying a single-cylinder, air-cooled, 4-stroke Diesel engine, by means of an external combustion chamber with three optical accesses. Two of them were along the longitudinal direction, for the extinction measurements, and the third along the orthogonal direction, for the scattering measurements. The optical measurements were performed with a temporal resolution of 0.05 ms and with a spatial resolution of 0.1×1 mm2. The simultaneous use of broadband extinction and scattering coefficients in the above-mentioned spectral range permitted the real time evaluation of size, concentration of droplets and soot particles and their optical properties. Aromatic hydrocarbons and carbonaceous matter exhibit strong absorption bands in the 200–350 nm spectral range. At fixed time or crank angle, the optical properties change with the wavelength, hence each measurement furnishes independent information on fuel droplets and soot particle size inside the combustion chamber. The experimental results were compared with a model simulation based on Mie theory for the fuel droplets and on Rayleighs theory for soot particles.

Two dimensional analysis of diesel combustion by spectral flame emissivity measurements

Spectral flame emissivity and absorption measurements with high temporal and spatial resolution were performed in an optically accessible high-swirl divided-chamber Diesel system. Simultaneous determination of soot temperature, soot volume fraction and the OH radical concentration were made from the start to the end of the combustion in 153 locations equally distributed in the chamber. The engine was run at 2,000 rpm and at fixed air-fuel ratio realizing 200 consecutive combustion cycles. To visualize the spatial and temporal spray and flame evolution, direct high-speed photographic sequences were taken at 8,000 frames/s. The photographic sequences showed that the spray is strongly distorted and mixed by very high swirl resulting in a well premixed region where the combustion starts. The OH radicals were detected in the fuel reaction zone. Moreover OH concentration and soot volume fraction are well correlated with soot temperature.

Evaluation of temporal and spatial distribution of nanometric particles in a diesel engine by broadband optical techniques

Abstract In the last few years, there has been an increasing concern about the emissions of ultrafine particles in the atmosphere. A detailed study of the formation and oxidation of these particles in the environment of the diesel engine cylinder presents many experimental difficulties due to the high temperatures, pressures and extremely reactive intermediate species. To allow investigation of the different phases of the diesel combustion process, high temporal and spatial resolution optical techniques were applied in the optically accessible chamber of a diesel engine at fixed engine speed and air-fuel ratio. Simultaneous extinction, scattering and flame chemiluminescence measurements from the ultraviolet to the visible region were carried out in order to study the diesel combustion process from the soot inception to the formation of soot particles, through the growth of their precursors. These species were characterized as carbonaceous nanometric structures and their sizes were evaluated by the Mie theory.

Multidimensional modelling of diesel combustion by a detailed kinetic scheme and comparison with in-cylinder optical measurements

The present work aims at a comprehensive study of diesel combustion based on detailed kinetic modelling and experimental investigations performed on an optically accessible engine. A diesel fuel surrogate model of combustion is included in a three-dimensional CFD code properly designed for application to internal combustion engines. The fuel spray is treated by discrete droplet models tuned on the ground of measurements of penetration lengths effected in a vessel at controlled conditions. The detailed chemistry of the turbulent reacting flow is computed by means of the partially stirred reactor approximation, which leads to an appreciable computational economy. Test-bench experimental data allow the code validation and the assessment of its predictability as operating conditions are modified. Optical measurements clarify major physical and chemical aspects related to fuel autoignition and combustion evolution. The proposed approach is believed to be valuable in optimising performances of diesel engines equipped with Common Rail (CR) injection systems.