Dimensional homogeneity-based motion and tracking analysis of tracer particles in an actual combustion flow

The tracking performance of tracer particles is crucial for the accuracy and reliability of particle image velocimetry (PIV) measurements. However, the motion and tracking behavior of particles in actual combustion flows remain poorly understood, leading to a lack of theoretical basis for selecting the optimal tracer particles. In this study, the tracking performance of tracer particles in methane combustion flow is analyzed based on dimensional homogeneity, with particular focus on the effects of fluid velocity, acceleration, particle diameter, and particle density. The results show that the tracking performance is poorest near the premixed flame front. Particles moving along the streamlines passing through the waist of the premixed flame have weaker tracking capability compared to those following other streamlines. The tracking coefficient exhibits a symmetric negative correlation with the ratio of fluid acceleration to velocity. Specifically, when fluid accelerates, the particle velocity lags behind the fluid velocity, but when fluid decelerates, the particle velocity exceeds the fluid velocity. In steady flows with constant acceleration, an increase in fluid velocity improves tracking performance. When both fluid velocity and acceleration increase, however, the tracking performance deteriorates. Moreover, the tracking coefficient decreases exponentially with increasing particle diameter and linearly with increasing particle density. The critical diameter, which defines threshold for acceptable tracking performance, are 62.5, 49.6, 45.0, and 38.3 mu m for SiO2, Al2O3, TiO2, and ZrO2 particles. Both critical diameter and density, decrease with increasing fluid acceleration, suggesting that smaller, low-density particles are more suitable for accurate PIV measurements, particularly in high-acceleration flows.