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Mico Reche, C. (2016). Application of optical diagnostics to the quantification of soot in n-alkane flames under diesel conditions. Combustion and Flame. 164:212-223. doi:10.1016/j.combustflame.2015.11.018. Nevertheless, it could still be a good option for low sooting conditions. On the other hand, an 36 attempt to calibrate LII signal by means of LEM measurements has been reported. This approach 37 should make it possible to obtain additional information on the soot spatial distribution. 38 However, inconsistencies have been identified which stem from the inherent limitations of LII 39 technique in highly sooting conditions. 40 Application of optical diagnostics to the quantification of soot in

The stringent emission regulations have motivated the development of cleaner fuels as diesel surrogates. However, their different physical-chemical properties make the study of their behavior in compression ignition engines essential. In this sense, optical techniques are a very effective tool for determining the spray evolution and combustion characteristics occurring in the combustion chamber. In this work, quantitative parameters describing the evolution of diesel-like sprays such as liquid length, spray penetration, ignition delay, lift-off length and flame penetration as well as the soot formation were tested in a constant high pressure and high temperature installation using schlieren, OH∗ chemiluminescence and diffused back-illumination extinction imaging techniques. Boundary conditions such as rail pressure, chamber density and temperature were defined using guidelines from the Engine Combustion Network (ECN). Two paraffinic fuels (dodecane and a renewable hydrotreated vegetable oil (HVO)) and two oxygenated fuels (methylal identified as OME1 and a blend of oxymethylene ethers, identified as OMEx) were tested and compared to a conventional diesel fuel used as reference. Results showed that paraffinic fuels and OMEx sprays have similar behavior in terms of global combustion metrics. In the case of OME1, a shorter liquid length, but longer ignition delay time and flame lift-off length were observed. However, in terms of soot formation, a big difference between paraffinic and oxygenated fuels could be appreciated. While paraffinic fuels did not show any significant decrease of soot formation when compared to diesel fuel, soot formed by OME1 and OMEx was below the detection threshold in all tested conditions.

ElsevierPastor Soriano, JV.; García Oliver, JM.; García Martínez, A.; Mico Reche, C.; Durret, R. (2013). A spectroscopy study of gasoline partially premixed compression ignition spark assisted combustion. Applied Energy. 104:568-575. doi:10.1016Energy. 104:568-575. doi:10. /j.apenergy.2012. and increases efficiency. However these combustion concepts have some drawbacks, related to 24 combustion phasing control, which must be overcome. In this way, the use of a spark plug has shown 25 to be a good solution to improve phasing control in combination with lean low temperature 26 combustion. Its performance is well reported on bibliography, however phenomena involving the 27 combustion process are not completely described. The aim of the present work is to develop a detailed 28 description of the spark assisted compression ignition mode by means of application of UV-Visible 29 spectrometry, in order to improve insight on the combustion process. 30 Page 1/24 A Spectroscopy Study of Gasoline Partially PremixedTests have been performed in an optical engine by means of broadband radiation imaging and 31 emission spectrometry. The engine hardware is typical of a compression ignition passenger car 32 application. Gasoline was used as the fuel due to its low reactivity. Combining broadband luminosity 33 images with pressure-derived heat-release rate and UV-Visible Spectra, it was possible to identify 34 different stages of the combustion reaction. After the spark discharge, a first flame kernel appears and 35 starts growing as a premixed flame front, characterized by a low and constant heat-release rate in 36 combination with the presence of remarkable OH radical radiation. Heat release increases 37 temperature and pressure inside the combustion chamber, which causes the auto-ignition of the rest 38 of the unburned mixture. This second stage is characterized by a more pronounced rate of heat release 39 and a faster propagation of the reactions through the combustion chamber. Moreover, the measured 40 UV-Visible spectra show some differences in comparison with the other stages. The relative intensities 41 in of spectra from different combustion radicals have also been related to the different combustion 42 phases. NOMENCLATURE 54 CI Compression Ignition 55 ICE Internal combustion engine 56 EGR Exhaust gas recirculation 57 PPCPartially premixed combustion 58 SACI Spark assisted compression ignition 59 ROHR Rate of heat release 60 CAD Crankangle degree 61 ACVApparent combustion velocity 62 63

Visualization of single-hole nozzles into quiescent ambient has been used extensively in the literature to characterize spray mixing and combustion. However in-cylinder flow may have some meaningful impact on the spray evolution. In the present work, visualization of direct diesel injection spray under both non-reacting and reacting operating conditions was conducted in an optically accessible two-stroke engine equipped with a singlehole injector. Two different high-speed imaging techniques, Schlieren and UV-Light Absorption, were applied here to quantify vapor penetration for non-reacting spray. Meanwhile, Mie-scattering was used to measure the liquid length. As for reacting conditions, Schlieren and OH* chemiluminescence were simultaneously applied to obtain the spray tip penetration and flame lift-off length under the same TDC density and temperature. Additionally, PIV was used to characterize in-cylinder flow motion. Results were compared with those from the Engine Combustion Network database obtained under quiescent ambient conditions in a high pressure high temperature vessel. Because of the air flow induced by piston movement, in-cylinder conditions in the two-stroke engine during the spray injection are highly unsteady, which has a significant impact on the spray development and interference on the spray visualization. From the comparison with quiescent data from the Engine Combustion Network, air flow induced by piston movement was found to slow down tip penetration. Moreover, both ignition delay and lift-off length under unsteady flow conditions show less sensitivity with ambient temperature than that of quasi-steady conditions.