Comparison of the Diffusive Flame Structure for Dodecane and OME _X Fuels for Conditions of Spray A of the ECN

Abstract

A comparison of the flame structure for two different fuels, dodecane and oxymethylene dimethyl ether (OMEX), has been performed under condition of Spray A of the Engine Combustion Network (ECN). The experiments were carried out in a constant pressure vessel with wide optical access, at high pressure and temperature and controlled oxygen concentration. The flame structure analysis has been performed by measuring the formaldehyde and OH radical distributions using planar Laser-Induced Fluorescence (PLIF) techniques. To complement the analysis, this information was combined with that obtained with highspeed imaging of OH * chemiluminescence radiation in the UV. Formaldehyde molecules are excited with the 355-nm radiation from the third harmonic of a Nd:YAG laser, whilst OH is excited with a wavelength of 281.00-nm from a dye laser. In both cases, the beam was transformed into a laser sheet in order to excite an axial flame plane and the fluorescence radiation was collected with an intensified camera (ICCD) and proper filtering. Consequently, two-dimensional maps in the axial flame plane were obtained at different instants after the start of injection (ASOI). Signal from both formaldehyde and OH chemical species can be compared, in order to analyze spatial distribution and interaction. When dodecane and OMEX are compared, several differences arise. The second one presents larger lift-off length but remarkably shorter flame length. Additionally, it has been possible to appreciate for this fuel a lower amount of soot formation during combustion.

LES Study on Spray Combustion With Renewable Fuels Under ECN Spray-A Conditions

“…The current work aims to compare an oxygenated e-fuel with a reference fuel n-dodecane at the nominal conditions of the Spray A of the Engine Combustion Network (ECN) [15]. Following previously reported experiments [10,11], a representative OMEx fuel was chosen, which is made up of blends of different single-component fuels with a generic molecular formula of CH 3 O-(CH 2 O)n-CH 3 (where n varies between 3 and 5) and a composition of 57.9, 28.87 and 10.08% for OME3, OME4 and OME5, respectively. However, regarding the simulations, as the chemical mechanism does not contain OME5, its corresponding composition has been added to that of OME4 due to the similarity in the chemistry of the molecules [13].…”

“…This section shows a validation of the predictions of the modelling tools in terms of characteristic spray and combustion metrics. The simulations are compared with a recent experimen- tal database of renewable fuels generated in the high-pressure high-temperature vessel from CMT-Motores Térmicos [10,11]. The experimental database contains spray diagnostics based on high-speed Schlieren, Diffuse Back-Illuminated (DBI), OH* chemiluminescence and Natural Luminosity (NL) imaging [10], as well as planar Laser-Induced Fluorescence (PLIF) of OH radical and formaldehyde (CH 2 O) [11].…”

“…Published works indicate that the research on these fuels is diverse, with publications mainly being associated with production, engine performance, environmental impact and political and economic implications. Starting from enginerelated investigations [5][6][7][8], which indicate that these fuels can be a good alternative to fossil fuels, experimental studies have moved towards more fundamental works [9][10][11], as fundamental knowledge on the flame structure is needed. Currently, many efforts are focused on improving chemical mechanisms [12,13] and computational fluid dynamics models [9,14] to deliver more accurate predictions on the combustion behaviour of these fuels.…”

“…The large amount of results provided a clear picture of the underlying phenomena, with special attention to the analysis of the combustion structure at the lift-off length (LOL) and flame stabilization mechanisms as well as soot formation [19,23,24]. However, there is a need to expand the research and gain insights on the physical and chemical interactions in high-pressure spray flames with new fuels such as OMEx, following recent research [9][10][11]14]. This study is focused on gaining further insights into the flame structure of high pressure spray flames of OMEx at the nominal condition of the ECN Spray A.…”

“…The analysis evidences the differences in flame structure between OMEx and dodecane from the perspective of the laminar flame structure and turbulent spray development. Finally, the numerical results are compared with the experiments carried out at the CMT Motores Termicos facility [10,11].…”