Spatial and temporal resolution of the particle image velocimetry technique in flame speed measurements

Limitations of the spatial and temporal resolution of the particle image velocimetry (PIV) technique in velocity field measurements in a laminar flame have been investigated. The limitations are due to the need to introduce a suspension of tracer particles into the flow. For a methane-air mixture with a stoichiometry coefficient of 0.9, it is determined that at a mass fraction of TiO$_2$ solid particles over 0.08%, the change in the flame propagation velocity by the particles exceeds 5%. The maximum spatial resolution of PIV for which the influence of the particles is insignificant corresponds to a concentration of 0.03%; in this case, the minimum resolvable scale is limited by a value 200 times larger than the size of tracer particles. Based on analytical estimates and a comparison of measured and numerically calculated particle velocities in the flame, it is concluded that particles smaller than 2 mm adequately track the flow velocity. Under these conditions, the error of the velocity measurement is mainly determined by the limited spatial resolution of PIV. The results of the work can be used to evaluate PIV measurement errors in other experimental studies of flames.