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Diesel low temperature combustion (LTC) is an operational strategy that effectively limits soot and oxides of nitrogen (NOx) emissions in-cylinder. Unfortunately, LTC results in increased hydrocarbon emissions as compared to conventional diesel combustion (CDC). Previous work has shown that exhaust conditions resulting from LTC inhibit oxidation of HC within a diesel oxidation catalyst (DOC). Further, these elevated HC emissions result in engine-out particulate matter (PM) that primarily consists of semi-volatile organic material. The current work shows that a DOC incompletely oxidizes this PM forming material. These results investigated the effectiveness of both a DOC and a diesel particulate filter (DPF) in reducing particle emissions for LTC. In this work, engine-out, DOC-out, and DPF-out exhaust were sampled using a micro-dilution system. Particle distributions were determined with a scanning mobility particle sizer (SMPS) and engine exhaust particle sizer (EEPS).

Diesel low temperature combustion (LTC) is an operational strategy that is effective at reducing soot and oxides of Nitrogen (NOx) emissions at low engine loads in-cylinder. A downside to LTC in diesel engines is increased hydrocarbon (HC) emissions. This study shows that semi-volatile species from LTC form the bulk of particulate matter (PM) upon dilution in the atmosphere. The nature of gas-to-particle conversion from high HC operating modes like LTC has not been well characterized. In this work, we explore engine-out PM and HC emissions from LTC and conventional diffusion combustion (CC) operation for two different engine load and speed modes using a modern light-duty diesel engine. An experimental method to investigate PM volatility was implemented. Raw exhaust was diluted under two dilution conditions. A tandem differential mobility analyzer (TDMA) was used to identify differences in volatility between particle sizes.

Diesel particulate filter (DPF) technology has proven performance and reliability. However, the addition of a DPF adds significant cost and packaging constraints leading some manufacturers to design engines that reduce particulate matter in-cylinder. Such engines utilize high fuel injection pressure, moderate exhaust gas recirculation and modified injection timing to mitigate soot formation. This study examines such an engine designed to meet US EPA Interim Tier 4 standards for off-highway applications without a DPF. The engine was operated at four steady state modes and aerosol measurements were made using a two-stage, ejector dilution system with a scanning mobility particle sizer (SMPS) equipped with a catalytic stripper (CS) to differentiate semi-volatile versus solid components in the exhaust. Gaseous emissions were measured using an FTIR analyzer and particulate matter mass emissions were estimated using SMPS data and an assumed particle density function.