Efficacy of in-cylinder control of particulate emissions to meet current and future regulatory standards

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. Though the tested engine is predicted to largely meet current US particle mass standards it has significantly higher particle number emissions compared to the Euro 6 solid particle number emissions standard. Our work suggests that engine out solid particle mass would have to be reduced to extremely low levels, much lower than current standards, in order to meet the number standard without DPF aftertreatment.