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Aerosols produced by combustion processes have a relevant impact on the chemistry and physics of the atmosphere and on human health. Soot particles are one of the main constituents of the elemental carbon present in the atmosphere, but the role of combustion processes in the formation of organic carbon, which is more abundant than the elemental one in the atmosphere, is less well characterized. Nanoparticles of Organic Carbon (NOC) have been detected in laminar flames employing a variety of experimental diagnostics and some of their chemical and physical properties have been characterized. NOC are not easily detected at the exhausts of practical combustion devices like vehicles equipped with spark ignition or diesel engines because the current available instrumentations do not allow detection of nanoparticles smaller than 3 nm. Also, the number concentration of nanoparticles smaller than 10 nm is strongly variable with temperatures and flow rates of the exhaust products.

The DEXA Cluster consisted of three closely interlinked projects. In 2003 the DEXA Cluster concluded by demonstrating the successful development of critical technologies for Diesel exhaust particulate after-treatment, without adverse effects on NOx emissions and maintaining the fuel economy advantages of the Diesel engine well beyond the EURO IV (2000) emission standards horizon. In the present paper the most important results of the DEXA Cluster projects in the demonstration of advanced particulate control technologies, the development of a simulation toolkit for the design of diesel exhaust after-treatment systems and the development of novel particulate characterization methodologies, are presented. The motivation for the DEXA Cluster research was to increase the market competitiveness of diesel engine powertrains for passenger cars worldwide, and to accelerate the adoption of particulate control technology.

An experimental and theoretical work on the low temperature oxidation of n-heptane in a jet stirred reactor has been carried out at different inlet temperatures. The presence of the typical low temperature pathologies of hydrocarbons (slow combustion, periodic and dumped cool flames) have been observed experimentally and correctly reproduced by the model. The selectivities of the intermediate and final products are also measured and compared with the theoretical evaluations. The agreement is satisfactory for all the investigated species in the whole temperature range (550–800 K). The introduction of 40% (volume) in the fuel has allowed to investigate the antiknock effect of toluene on the autoignition of n-heptane. At the same inlet temperature the n-heptane conversion shows the same general behaviour, but it is about 10% lower when toluene is fed in the mixture.

The microstructures of atmospheric pressure, counter-flow, sooting, flat, laminar ethylene diffusion flames have been studied numerically. Aromatics growth beyond 2-, 3-ring PAH is analyzed through a radical-molecule reaction mechanism which, in combination with a previously developed PAH model, is able to predict the concentration profiles of aromatic structures formed in flames. Modelling results are in good agreement with experimental data and are used to interpret the soot volume fraction and PAH fluorescence measured in flames.

A modified version of KIVA II code was used to perform three-dimensional calculations of combustion in a DI diesel engine. Both an ignition delay submodel and a different formulation of the fuel reaction rate were implemented and tested. The experiments were carried out on a single cylinder D.I. diesel of 0.75 I displacement equipped with sensors to detect injection characteristics and indicated pressure. A fast acting sampling valve was also installed in the combustion chamber to allow the measurement of main pollutants during the combustion cycle, by an ensemble average technique. Computational and experimental results are compared and the discrepancies are discussed. Today the demand for light duty engines that produce less emission and consume less fuel is increasing. Thus, if limits on CO2 emissions are established, the direct injection diesel engine for light duty applications will become an attractive option.

The formation and oxidation of soot, light and heavy hydrocarbons, CO, CO2 and NOx in a D.I. diesel engine have been studied by means of direct fast sampling and chemical analysis of the combustion products collected during the combustion cycle. Particular attention has been paid to the histories of each fuel hydrocarbon class analyzing the chemical transformations that the paraffins, and monoaromatic and polyaromatic compounds, contained in a diesel fuel oil, undergo during the combustion cycle. This approach is able to give information on the origin of soot and heavy hydrocarbon emission from a diesel engine. The concentration of the heavy hydrocarbons decreases during the early stages of the combustion cycle and their profile corresponds roughly to the fuel disappearance rate because of the chemical similarity with the fuel compounds.