Soot and chemiluminescence in diesel combustion of bio-derived, oxygenated and reference fuels

High-speed imaging, spectroscopy and thermodynamical characterization are applied to an optically accessible, heavy-duty diesel engine in order to compare sooting and chemilunlinescence behaviour of bio-derived, oxygenated fuels and various reference fuels. The fuels concerned include the bio-derived fuels Jatropha oil (pure), Jatropha-methylester (JME) and rapeseed-methylester (RME), all containing approximate to 10%(mass) oxygen, and fossil oxygenated fuels tripropyleneglycolmonomethylether (TPGME) and cyclohexa none, both mixed with synthetic fuel to have similar total oxygen content. Commercial diesel, model fuel IDEA, a Fischer-Tropsch synthetic fuel (FT) and a blend containing cyclohexane serve its reference fuels. The start of hot combustion is derived from OH* and CH* cheminescence as observed through a spectrograph. Both species occur at about the same time, CH* signal being weaker. Soot incandescence is observed two-dimensionally at 0.3 degrees crank angle resolution (200 images/cycle). Ignition delays derived from soot incandescence and chemiluminescence are compared to those determined from heat release. The heat release rate and exhaust NO concentrations are used as indicators of average and peak temperatures, respectively, which are combined with soot incandescence signal to get a relative measure for a fuel's sooting propensity. Both the fuel molecular structure and its oxygen content are found to be important for soot abatement. (c) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.