Particulate matter emission comparison from conventional and premixed low temperature combustion with diesel, biodiesel and biodiesel-ethanol fuels

As worldwide energy and environmental pressures increase, interest in biofuels such as biodiesel and ethanol, and low emission diesel combustion modes such as premixed low temperature combustion (LTC), continues to grow. This study takes a detailed look at particulate matter (PM) from a single cylinder common rail diesel engine operated under conventional and premixed LTC combustion modes with diesel, biodiesel and biodiesel-ethanol fuels. Soot, particle number and particle size distribution are investigated. Experiments show that for conventional combustion, accumulation mode particulates are reduced by biodiesel and reduced further by biodiesel-E20 (20% ethanol by volume). The reduction is attributed to higher fuel oxygen content, lower stoichiometric air-fuel ratio and reduced aromatic content reducing carbonaceous soot. Nucleation mode particles from conventional combustion with diesel, biodiesel and biodiesel-E20 fuels show similar size distributions. For premixed LTC, biodiesel shifts the accumulation mode size distribution curve upwards (i.e., more particles) and towards smaller size particles relative to diesel. In LTC, biodiesel produces more semi-volatile organic carbon and lower soot. The shift in size distribution for biodiesel may be caused by more semi-volatile organic carbon in the exhaust causing an increase in the growth of particles nucleated from volatile species, and less soot leading to a reduction in the number of large carbonaceous agglomerates. Biodiesel-E20 decreases accumulation mode particles of all sizes by reducing soot and the amount of biodiesel-derived semi-volatile organic carbon available for growing particles. Biodiesel increases LTC nucleation mode particles relative to diesel. Biodiesel-E20 increases the amount of small nucleation particles (<20 nm) and decreases the amount of large nucleation particles (20-50 nm) relative to diesel. The increases in nucleation particles for biodiesel and small nucleation particles (<20 nm) for biodiesel-E20 are believed to be caused by less soot and more exhaust semi-volatile organic carbon causing increased nucleation. Biodiesel-B20 produces the lowest soot and total particle number concentration, both at conventional and premixed LTC, demonstrating its potential as an alternative fuel for diesel engines. (C) 2013 Elsevier Ltd. All rights reserved.