Contribution à l’étude de la propension de différents types de carburants à former des suies via l’emploi d’indicateurs de pouvoir suitant

Abstract

An increasing attention has been devoted to biofuels during the last few years, especially in the transportation domain, due to their ability to reduce pollutant emissions including soot particles. In order to assess and compare the propensity of a wide range of engine-fuels to produce soot, several sooting indexes have been developed which includes the TSI, the OESI, the YSI and the FESI. Even though many molecules have been studied in the literature, the number of compounds characterized with each indicator taken separately remains quite limited. It has therefore been proposed within the present work to synthetize all the data available from past studies to build, through a ormalization process of the abovementioned indicators, an original and extensive database integrating 391 molecules, including alkanes, alkenes, alkynes, aromatics and numerous oxygenated molecules such as alcohols, ketones, aldehydes and esters. Additional OESI measurements performed with furans have moreover been carried as such molecules have only been seldom studied in the literature. By analyzing the so-gathered data by means of a group additivity approach, it has been possible to decompose each considered molecule into a set of fragments having specific sooting contributions. Overall, 67 structural groups have been identified and characterized to allow a fine analysis of the impact of the fuel structure and chemical composition on the sooting propensity. In addition, the present work also allowed proposing a set of predictive contribution factors that are essential to estimate the ability of a wide range of fuel to generate soot particles only based on their chemical composition. In the end, the trends highlighted within this study lead to conclude that the sooting propensity of the main considered compounds increases in the following order: ester < aldehydes < ketones < alcohols < aromatics. Although this theoretical work provided valuable insights as far as the understanding of the soot formation mechanisms is concerned, it has also illustrated the limited ability of some indexes to account for the synergistic effects that are likely to occur when adding an oxygenated biofuel into a complex engine fuel. This particularly justifies why using the FESI as an index remains a consistent option as such an indicator relies on the measurement of the peak soot volume fraction estimated within in a standardized flame burning a mixture composed of a realistic engine-fuel (diesel, gasoline or their surrogates) with the molecule whose sooting propensity has to be estimated. In order to pursue the experimental developments allowing the FESI to be determined, it has been proposed herein to use an Auto-Compensating-LII (AC-LII) approach that relies on the continuous measurement of the soot temperature by two-color pyrometry. Since the calibration of the detection set up is a crucial step in the implementation of AC-LII application, a particular attention has thus been devoted to the choice of the calibration system. This latter consists in an integrating sphere the technical characteristics of which have been defined likewise those of other components of the experimental setup including photomultipliers and optical elements. In the end, a welldefined experimental test bench has been designed to contribute tackling, through upcoming FESI measurements that will be achieved within the framework of a Ph.D thesis, the issues highlighted during the analysis of the literature data using the structural group additivity method.

Date	24 May 2019
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Romain Lemaire (Supervisor)