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Analysis of Polar Organic Compounds Condensed on Engine Particulate Matter Formed during Advanced Compression Ignition Combustion
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
Advanced compression ignition (ACI) combustion has been the subject of many recent studies due to the high thermal efficiencies that can be achieved in internal combustion engines. ACI can also be used in multi-mode combustion engines, which combine spark ignition (SI) operation at high loads with ACI operation at low loads. ACI can limit the emissions of both soot carbon and oxides of nitrogen (NOx) from engines due to lower peak temperatures of combustion, but hydrocarbons (HC) and carbon monoxide (CO) tend to increase. While all ACI combustion strategies are lean, fuel-air stratification levels span a range from completely homogeneous mixtures to highly stratified mixtures. The presence of fuel aromatic compounds and the lean, low temperature combustion environment provide the opportunity for the formation of carboxylic acids and nitro-aromatic compounds. These polar species tend to be non-volatile and condense on exhaust particles. To better understand these polar species, a capillary electrophoresis /electrospray ionization mass spectrometry (CE-ESI MS) method has been developed to identify nitrophenols and carboxylic acids on exhaust PM extracted from sample filters. Results from a study on ACI PM showed that homogeneous combustion modes tend to favor carboxylic acid formation while more stratified modes tended to favor nitro-aromatic compounds, including several nitrophenols. Since the PM mass from ACI combustion is largely organic, a better understanding and identification of all PM organic carbon species is essential in developing pathways that may help in lowering the overall PM from these modes.