The present work pursues a twofold objective. On the one hand, the effect of fuel properties on soot formation has been analysed, under different engine operating conditions. On the other hand, sensitivity and performance of the three optical techniques has been evaluated, identifying their main advantages and drawbacks in the framework of the current study. LEM has been considered as the reference technique, as the measurement principle can be implemented without important limitations associated to the other two. Results highlight that larger molecules produce more soot than the smaller ones, with both reactivity and soot formation changing with the proportion of the heavier fraction. Despite describing similar trends, LEM and 2C do not provide the same KL values, with the pyrometry reaching some sort of saturation when increasing flame soot. A detailed analysis confirms that 2-Colar measurements are strongly biased by soot and temperature distribution inside the flame. Nevertheless, it could still be a good option for low sooting conditions. On the other hand, an attempt to calibrate LII signal by means of LEM measurements has been reported. This approach should make it possible to obtain additional information on the soot spatial distribution. However, inconsistencies have been identified which stem from the inherent limitations of LII technique in highly sooting conditions. (c) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Authors wold like to acknowledge that part of this work has been funded by the Spanish Ministry of Science and Technology through project TRA2011-26359 and grant BES-2012-059721. Some other parts of this works were financially supported by "COMET K2 - Competence Centres for Excellent Technologies Programme" (project B03T02). In addition, the authors acknowledge that some equipment used in this work has been partially supported by FEDER project funds (FEDER-ICTS-2012-06)", framed in the operational program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain.Pastor Soriano, JV.; García Oliver, JM.; García Martínez, A.; Micó Reche, C.; Möller, S. (2016). Application of optical diagnostics to the quantification of soot in n-alkane flames under diesel conditions. Combustion and Flame. 164:212-223. https://doi.org/10.1016/j.combustflame.2015.11.018S21222316
