Low temperature combustion (LTC) is an advanced mode of combustion that has attained much attention due to ever increasing emission standards. LTC simultaneously reduces soot and nitric oxide (NO) emissions by having combustion take place at, for example bulk gas temperatures below 1200K (as observed in this study) so that soot and NO formation is substantially reduced. Soot is typically considered a building block for particulate matter (PM); both PM and NO are heavily regulated emissions by government agencies due to their potential effects on human and environmental health. Although LTC is believed to substantially reduce soot, it is not clear what is the end effect on PM. Because PM is composed of other agents, such as condensed liquid and solid hydrocarbons, there could potentially be non-negligible emission of PM from LTC combustion. This study will compare the gravimetric-based PM data from 3 different modes of combustion in a direct injection diesel engine; specifically: conventional combustion, combustion with high exhaust gas recirculation (EGR) at conventional injection timing, and combustion with high EGR and late injection timing (all other control parameters are the same, including fuel flow rate and engine speed). The objective of this study is to quantify PM emissions of LTC and assess potential differences relative to the soot concentration (the latter as assessed by a smokemeter). PM is gravimetrically measured using a mini-dilution tunnel. Further, chemical analysis of the collected PM is analyzed by an independent laboratory to develop an understanding of the constituent species composing conventional and LTC PM. PM results show that there are differences among the three modes of combustion. The PM differs in appearance as well as composition, and due to the change in appearance FSN may not correlate with PM when running LTC modes of combustion.

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