The objective of this research was to investigate the influence of the in-cylinder surfaces on the net emission of particulate matter in the exhaust of a single-cylinder diesel engine. In order to obtain this information, time resolved sampling was performed to characterize the particulate matter emitted in the engine exhaust. A rotating probe sampled the free exhaust plume once every engine cycle. The rotation of the probe was synchronized with the engine cycle in such a way that the samples could be taken at any predetermined crank angle degree window. The sampling probe was designed for isokinetic sampling in order to obtain reliable results. To accomplish this, the unsteady flow through the probe was modeled based on the measured instantaneous velocities and temperatures of the exhaust. Two methods were used to characterize the exhaust particulate matter in real time: a filter for mass concentration measurements, and an electrical aerosol analyzer (EAA) for size distribution and volume concentration measurements. The results showed about 45% higher mass concentrations as well as larger diameter particles emitted during blowdown than late in the displacement phase of the exhaust stroke. This suggests that high in-cylinder shear rates and velocities which are associated with the blowdown process cause the deposited soot to be reentrained from the surfaces of the combustion chamber, where reentrainment is favored by conditions of high surface shear.
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