Assessment of portable emission measurement systems (PEMS) for heavy-duty diesel engines with respect to particulate matter

The performance of three Portable Emission Measurement Systems (PEMS) for Particulate Matter (PM) was assessed in our laboratory against reference instrumentation in engine dynamometer testing of five Heavy Duty Engines (HDEs) of different aftertreatment technologies. The candidate systems were designed around the minimum requirements of allowing a gravimetric determination of the total emitted PM mass and incorporating a real time particle sensor. All PEMS-PM systems were found to reproduce within ±30% the gravimetric PM results determined with reference measurement systems under non-regenerative operating conditions, at emission levels lying at and above the Euro VI limit of 10 mg/kWh. The use of prolonged sampling times envisaged in In Service Conformity (ISC) testing (>120 min) was found to be beneficial, as it reduced the limit of detection of the PEMS-PM instrumentation to 1–3 mg/kWh (120 min) from 3 to 9 mg/kWh (30 min). The real time aerosol instrumentation exhibited a much higher sensitivity, being capable of quantifying emission levels below the EURO VI particle number limit of 6×1011 #/kWh. Some modifications were required though in two particle sensors that were based on diffusion charging, in order to avoid a disproportional increase in their responses in the presence of homogeneously nucleated particles. Passive regeneration of the particulate filter resulted in excessive emission of volatile PM but also large discrepancies between the PEMS-PM and reference systems. The accurate quantification of absolute emission levels of non-volatile PM from the real time sensors can assist in the identification of such excessive volatile PM fractions, to avoid properly working DPF systems to fail an ISC test.