Particle-image velocimetry measurement errors when imaging through a transparent engine cylinder

Abstract

When making particle-image velocimetry measurements through the quartz cylinder of a reciprocating engine, the particle images are aberrated. This work quantifies the practical field-of-view and the errors in the velocity measurements caused by those aberrations. Electro-optical image shifting was used to create a repeatable particle-image displacement distribution for 60 images. Ensemble averaging of these images is used to quantify the rms errors due to the shot-to-shot variation in (1) the particle-image fields, (2) the camera noise, (3) the variance in the correlation-peak detection and (4) the particle-image aberrations. These results demonstrate that the field-of-view is restricted to the centre 66 mm of the 86 mm inside-diameter cylinder due to decreased accuracy, decreased image-to-image precision and decreased displacement-peak detectability of the image-displacement correlation. The correlation-peak detectability was degraded by both particle-image aberrations and decreased transmission of the scattered light.