Abstract
Low temperature compression ignition combustion, in its many forms, can result in nearly “smokeless” combustion, as indicated by a smokemeter or other form of soot measurement that relies on absorbance due to elemental carbon content. Highly pre-mixed, low temperature combustion modes do not form particulate matter in the traditional pathways seen with conventional diesel combustion. Previous research into reactivity compression ignition (RCCI) PM has shown, despite a near zero smoke number, significant mass can be collected on filter media used for PM certification measurement. In addition, PM size distributions reveal that some particles survive the heated double dilution conditions similar to that of the European particulate measurement protocol. The majority of the mass on the sample filters was found to be due to hydrocarbon adsorption to the filter. For all fuels, the particle organic carbon fraction was one as measured by thermal-optical analysis. The particle size measurements and the transmission electron microscopy results show the presence of soot particles, however, the elemental carbon fraction was, in many cases, within the uncertainty of the thermal-optical measurement. PM collected during RCCI operation was also collected with a novel sampling technique and analyzed by thermal desorption/pyrolysis gas chromatography mass spectroscopy . PM speciation results indicated the high boiling range of diesel hydrocarbons was likely responsible for the PM mass captured on the filter media. To investigate potential fuel chemistry effects, either ethanol or biodiesel were incorporated to assess whether oxygenated fuels may enhance particle emissions reduction. The gasoline/ULSD particle number-size distribution showed a 100-fold reduction in peak concentration relative to that for conventional diesel combustion. The gasoline/ULSD particle number-size distribution was not altered significantly at low load by the incorporation of biofuels. For higher loads, use of E85/ULSD resulted in an increase of sub-30 nm particles, a size range associated with condensable hydrocarbons species.
