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The effect of exhaust gas recirculation on particulate matter emissions from a compression-ignition, natural gas fuelled engine Brakel, Thomas Willem

Abstract

A mini-dilution tunnel was designed and built to measure particulate matter (PM) emissions from a single-cylinder research engine (SCRE) based on the Cummins ISX 400 series. The SCRE relies on the high-pressure direct injection of natural gas, pilot ignited with diesel fuel for combustion. Two methods were used for PM measurements: pre-weighed filters and a tapered element oscillating microbalance (TEOM). A repeatability study was conducted to determine the experimental error associated with PM measurements and to compare results from pre-weighed filters with those taken using a TEOM. The PM emission rate uncertainty was determined to be at maximum 29%, with 10-12% due to measurement uncertainty and the remainder due to poor engine repeatability. PM emission rates from the TEOM showed excellent correlation with measurements using pre-weighed filters by applying a correction factor of 1.43. The second part of this work was to examine the effect of replacement exhaust gas recirculation (EGR) on particulate emissions. EGR is primarily used in engines to reduce the formation of oxides of nitrogen (NOx). The drawback of using high EGR flow rates is a deterioration in combustion and an increase in the amount of unburned species (HC, CO, PM) that are formed. The results show the PM penalty is negligible for EGR rates up to 15% and that increasing the exhaust pressure significantly affects PM and CO emissions. It was also found that increasing the amount of diesel pilot at 800 RPM 75% load with 17% EGR significantly increases PM and CO emissions.

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