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This paper shows a numerical comparison between DBI and focused shadowgraph imaging techniques applied in the characterization of macroscopic parameters and optical thickness of a multi-hole GDI spray. Simulated experiments were designed around a synthetic spray, whose jets have been modelled through the Musculus and Kattke model. The DBI configuration was in line with the experimental constraints for beam steering suppression reported in the literature. A simple ray-tracing programme based on geometrical optics and radiometric laws was developed, and the attenuation of light through the spray was evaluated according to Lambert-Beer law. The results show that diffuse backlighting can appreciably bias the measurement of the optical thickness and the macroscopic spray parameters, net of any beam steering effects. Significant discrepancies between techniques occur when the spray develops out of the focal plane and away from the optical axis, especially when the spray develops asymmetrically to the focal plane.

The DI (Direct Injection) in SI (Spark Ignition) engines is rapidly developing and seems very attractive offering the possibility of multi-mode operation, homogeneous and stratified charge, with valuable benefits respect to conventional PFI (Port Fuel Injection). One of the major drawbacks of the GDI-fueled engine is the impingement of liquid fuel on the combustion chamber walls that generally produces an increasing of HC emissions and detrimental effects on the combustion process, like soot formation in the wall guided engines due to the diffusive combustion of fuel film deposits on the piston head. This paper investigates the structure of gasoline spray-wall interaction generated by a single-hole injector for GDI engines in an optically-accessible quiescent vessel. The axially-disposed hole diameter is 0.200 mm with a L/d ratio of 1.0 while the injection pressure and the wall temperature varied in the range of 10.0–20.0 MPa and ambient to 300 °C, respectively. Injection duration of 1.0 ms was investigated and the nozzle tip-wall distance was 22.5 mm. Optical investigations were carried out at atmospheric backpressure by an in-line schlieren optical setup using a LED source while the cycle-resolved images of the evolving impact were captured by a C-Mos high-speed camera with a time resolution of 80 μs and a window size of 640 × 464 pixels. The optic-geometrical setup realized a spatial resolution of 0.039 mm/pixel. The images were treated by a digital processing software for background subtraction and both liquid and vapor contour extractions. The spatial and temporal evolution of the liquid and vapor phases as a function of the wall temperature is described for the different operative conditions.

This article introduces an innovative method for the segmentation of Mie-scattering and schlieren images of GDI sprays. The contours of the liquid phase are obtained by segmenting the scattering images of the spray by means of optimal filtering of the image, relying on variational methods, and an original thresholding procedure based on an iterative application of Otsu's method. The segmentation of schlieren images, to get the contours of the spray vapour phase, is obtained by exploiting the surface curvature of the image to strongly enhance the intensity texture due to the vapour density gradients. This approach allows one to unambiguously discern the whole vapour phase of the spray from the background. Additional information about the spray liquid phase can be obtained by thresholding filtered schlieren images. The potential of this method has been substantiated in the segmentation of schlieren and scattering images of a GDI spray of isooctane. The fuel, heated to 363 K, was injected into nitrogen at a density of 1.12 and 3.5 kg m-3 with temperatures of 333 K and 573 K.

In internal combustion engines, the direct injection at high pressures produces a strong impact of the fuel on the combustion chamber wall, especially in small-bore sizes used for passenger cars. This effect is relevant for the combustion process resulting in an increase of the pollutant emissions and in a reduction of the engine performances. This paper aims to report the effects of the injection pressure and wall temperature on the macroscopic behavior and atomization of the impinging sprays on the wall. The gasoline spray-wall interaction was characterized inside an optically accessible quiescent chamber using a novel make ready Z-shaped schlieren-Mie scattering set-up using a high-speed C-Mos camera as imaging system. The arrangement was capable to acquire alternatively the schlieren and Mie-scattering images in a quasisimultaneous fashion using the same line-of-sight. This methodology allowed complementing the Mie scattering images, adapting to the liquid phase, with the schlieren ones for the determination both of the liquid and vaporing phase during the single cycle. A single-hole axially disposed injector was used, 0.200 mm in diameter L/d=1.0, while the injection pressure and the wall temperature ranged between 5.0 - 20.0 MPa and ambient to 573 K, respectively. Optical investigations were carried out at atmospheric backpressure and ambient gas temperature. The images of the impact, resolved in the cycle, were processed by a customized algorithm able to catch the contours of the liquid phase and the vapor/atomized zone. Spatial and temporal evolutions were measured for both the phases in terms of width penetration and thickness growth.

Soot aggregates have been produced in a series of experiments based on the pyrolysis of ethylene in a shock tube facility, for pressure and temperature varying, respectively, in the range ∼ 10–15 bar and ∼ 1800–2000 K. In situ light scattering/extinction coupled measurements have been performed and the process has been followed with high spatial and temporal resolution (μm/μs). On the basis of the Kumar and Tien approach for randomly oriented aggregates [Kumar and Tien (1989) Combust. Sci. Technol. 66, 199–216], we investigated the sensitivity of the angular scattering pattern and of the dissymmetry ratio for straight chain and random cluster morphologies to the refractive indices, the number and diameters of primary spheres (spherules) in the agglomerate and the solid volume fraction of the cluster. The time variation of the scattered light intensity measured at different scattering angles θ (30°, 90°, 150°) is shown to enable deduction of the prevailing morphology of the (self-organizing) aggregate. At the end of the examined agglomeration process, the resulting soot aggregates appear to be structured on average as chains of 5–10 spherules with spherule diameter of ≈ 25–30 nm.

The use of oxygenated and renewable fuels is nowadays a widespread means to reduce regulated pollutant emissions produced by internal combustion engines, as well as to reduce the greenhouse impact of transportation. Besides PM, NOx and HC emissions, also the size distribution of particles emitted at the engine exhaust represent a meaningful information, considering its adverse effects on the environment and human health. In this work, the results of a comprehensive investigation on the combustion characteristics and the exhaust emissions of a GDI high performance engine, fuelled with pure Bio-ethanol and European gasoline, are shown. The engine is a 4-cylinder, 4 stroke, 1750 cm3 displacement, and turbocharged. The engine was operated at different speed/load conditions and two fuel injection strategies were investigated: homogeneous charge mode and stratified charge mode. The particle size distribution at the engine exhaust was measured in the range 5-1000 nm using a differential mobility spectrometer. Simultaneously, the air-fuel mixing and the combustion process inside the cylinder were followed by means of high-speed imaging in the UV-visible. To this aim, the last cylinder was optically accessible through a sapphire window (5mm wide) in the engine head. The particles size distributions measured at the engine exhaust for both gasoline and bio-ethanol show similar trends, suggesting a common route for the particles formation. For bio-ethanol the accumulation mode is shifted towards smaller sizes, which could be ascribed to the chemical and physical properties of the fuel, as observed by optical investigation of the fuel injection and combustion process. On the other hand, an increase of particles number concentration for stratified charge operating mode was observed for both fuels, due to the poorer air fuel mixing and the diffusive combustion of the fuel films deposited on the piston and cylinder wall.

The effect of fuel injection strategy and charge dilution on NOx and soot emissions has been investigated with a modern DI diesel engine. Particulate mass has been measured by a standard smoke meter and soot particles have been characterized by means of time-resolved Laser Induced Incandescence (LII) at the exhaust of the engine. Two steady- state test points have been selected, representative of low and medium load conditions. The influence of the different engine management strategies has been assessed, highlighting the potential of unconventional operating modes to meet forthcoming emission limits.

The characterization of the particulate aggregates is a topic widely covered within the main field of aerosol and colloid science. A satisfactory description of agglomerates requires the knowledge of at least six parameters, namely the number density of clusters, the mean number of the primary particles per cluster, the mean diameter of such primary particles, the characteristic length of the aggregate depending on the shape of the aggregate, the refractive and absorption index of the primary particles. To this aim it is common in the literature to hypothesize about the dominant morphology and to think about the aggregate as constituted by identical primary particles and optical properties. As a matter of fact the scattering and extinction techniques are of common use in the literature in conjunction with the results of Mie theory in spite of the fact that such agglomerates are neither spherically shaped nor homogeneous. Alternatively the study of the agglomeration morphology can be afforded by means of Berry and Percival theory and static light scattering applied to fractals. An equivalent Mie sphere can be introduced which best simulates the data. The effective diameter of the agglomerate can be defined behind different criteria which yields often to quite different results. The objective of the present paper is to characterize the carbonaceous agglomerates produced by ethylene pyrolysis into a shock tube environment via both classical light scattering/extinction measurements and a theoretical analysis for randomly oriented aggregates. The agglomeration process is investigated in a ms time scaling. The high temporal and spatial resolution involved are expected to furnish useful information about the fundamental kinetics of the surfiace growth and coagulation process of the soot particles.

A light-scattering anaysis based on Lorenz-Mie theory shows that the size and refractive index of transparent droplets can be determined by measuring the polarized components of the scattered light at two angles in the forward direction. The horizontally polarized cross section C(HH)(33°) depends exclusively on the droplet diameter, whereas the ratio C(HH)(33°)/C(HH)(60°) is a sensitive function of the refractive index and hence of the temperature. On this basis, a new optical system for measuring the temperature, size, and velocity of transparent droplets has been developed. This system can make possible the determination of droplet temperature within a few degrees centigrade. In addition, a critical review of the rainbow method to determine droplet temperature is also presented. These techniques have been applied to vaporizing tetradecane droplets (D(0) = 72 µm), which are heated up in a tube furnace with a temperature range of 20°-200 °C.

The present work relates to the investigation of the basic oxidation characteristics of iron and aluminium nanoparticles as well as the feasibility of their combustion under both Internal Combustion Engine (ICE)-like and real engine conditions. Based on a series of proof-of-concept experiments, combustion was found to be feasible taking place in a controllable way and bearing similarities to the respective case of conventional fuels. These studies were complimented by relevant in-situ and ex-situ/post-analysis, in order to elaborate the fundamental phenomena occurring during combustion as well as the extent and ‘quality’ of the process. The oxidation mechanisms of the two metallic fuels appear different and -as expected- the energy release during combustion of aluminium is significantly higher than that released in the case of iron. The peak gas temperatures recorded during combustion of iron under engine-like and real engine conditions indicate that the NOx formation threshold is not reached. Combustion of aluminium yields substantially higher peak combustion temperatures and thus it is likely that is accompanied by NOx emissions. In addition, the experimental results provided indication that the approach of Exhaust Gas Recirculation (EGR) could be an efficient means of controlling the combustion process.