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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.

A major challenge for internal combustion engines (ICEs), and diesel engines, in particular, is the reduction of exhaust emissions, essentially nitrogen oxides (NOx) and particulate matter (PM). In this regard, the potential of LPG-diesel blends was evaluated in this work. The LPG and diesel blends were externally prepared by exploiting their perfect miscibility at high pressures. Two diesel-LPG mixtures with 20% and 35% by mass LPG concentrations were tested. In terms of spatial and temporal evolution, the spray characterization was performed for the two blends and pure diesel fuel through high-speed imaging technique. The combustion behavior, engine performance and exhaust emissions of LPG-diesel blends were evaluated through a test campaign carried out on a single-cylinder diesel engine. Diesel/LPG sprays penetrate less than pure diesel. This behavior results from a lower momentum, surface tension and viscosity, of the blend jets in comparison to diesel which guarantee greater atomization. The addition of LPG to diesel tends to proportionally increase the spray cone angle, due to the stronger turbulent flow interaction caused by, the lower density and low flash-boiling point. Because of improved atomization and mixing during the injection phase, the blends have shown great potential in reducing PM emissions, without affecting engine performance (CO2 emissions). The addition of LPG resulted in a significant smoke reduction (about 95%) with similar NOx emissions and acceptable THC and CO emissions. Furthermore, the low cetane number (CN) and high low-heating value (LHV) ensuring leaner air-fuel mixture, and improvements in terms of efficiency, particularly for a blend with a higher concentration of LPG.

The paper describes the results of a co-operative research project aimed at the energetic exploitation of the biodiesel derived glycerol. The research objective is the definition and validation of a synthesis process for conversion of glycerol in an oxygenated fuel additive (glycerol alkyl–ether) suitable for blending with diesel and biodiesel. The employed facilities, methodologies and first results from engine tests are described, including a preliminary Life Cycle Assessment (LCA). Etherification of glycerol with tert-butyl alcohol and isobutylene allowed to identify the suitable experimental conditions required to obtain a mixture predominantly composed of higher glycerol ethers (GEM). Novel catalysts, based on perfluorosulphonic ionomers as active species and spherical silica as support, were found to be stable and easy reusable allowing to obtain mixtures containing very low amount of monoethers and oligomers considered as undesired products. Engine tests with blends of GEM in diesel fuels revealed good combustion and emission performances when compared both to neat diesel fuel and a blend diesel/biodiesel. LCA analysis indicates that the GEM/diesel blend generates an environmental impact which is lower than the one of neat diesel.

[EN] The present work includes findings from proof-of-principle feasibility studies on iron nanopowder combustion under idealized, enginelike, and real engine conditions. The study was conducted under the scope of recent interest in metallic nanoparticles as alternative fuels for internal combustion engines. More specifically, Fe nanoparticles with different morphologies and average primary particle sizes ranging from 25 to 85 nm were studied with respect to their oxidation characteristics via thermogravimetric analysis as well as in customized shock tube, constant-volume vessel, and compression-ignition (CI) engine configurations. Combusted powder samples were in all cases examined via in situ and ex situ techniques for the identification of combustion products and their morphologies. The findings facilitated the determination of the main phenomena involved during oxidation. The results verified that combustion of Fe nanoparticles in a slightly modified CI engine is feasible, albeit with various technological challenges related to ignition and scavenging that inhibit combustion quality., The authors thank the European Commission for partial funding of this work through the Project “COMETNANO” (FP7-NMP4-SL-2009-229063).

[EN] The prominent aim of this investigation was the examination of the in-principle easibility of aluminum combustion under internal combustion engine (ICE)-like conditions. This study was performed in the framework of recent consideration of metallic nanoparticles as alternative fuels for ICE engines. Aluminum nanoparticles of different morphologies and sizes were studied with respect to their fundamental oxidation characteristics via thermogravimetric analysis under various nitrogen−oxygen environments and by spark-ignition of Al nanopowder strips under controlled airflow at ambient pressure. The ICE-like tests included measurements performed in two different arrangements; namely, a shock-tube setup and a constantvolume combustion vessel. A set of engine tests was also performed in a single-cylinder compression-ignition engine with a customized, single-shot aerosol injection system. Burned powder samples were, in all cases, examined via in situ and ex situ techniques for the identification of products and their morphologies. The results largely verified that combustion of aluminum particles in an engine environment is indeed feasible. Nonetheless, prominent differences, in terms of the products formed and their morphologies/structures, were identified among the various oxidation/combustion techniques employed., We thank the European Commission for partially funding of this work through the Project "COMETNANO" (FP7-NMP4-SL-2009-229063).

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.