V.5. PIV Measurements during combustion in a reciprocating internal combustion engine

摘要

Two-dimensional particle image velocimetry (PIV) measurements were made in the burned and unburned gas of a firing, reciprocating internal-combustion engine. Cross correlation was used to analyze the double-exposure photographs using a 1.25 mm interrogation sport on a 0.5 mm grid. Electrooptical image shifting was used to resolve the directional ambiguity. The particle properties and the seeding density are the two key features enabling simultaneous measurements in the burned-and unburned-gas regions. The flame coordinates were identified as the interface between the low and high seding density regions on the PIV photographs. Those coordinates were used to identify the burned and unburned regions of the velocity distribution. High-pass spatial filtering is used to visualize coherent structures of spatial scales L, where 1.25 mm < L < 10 mm. Vorticity and strain-rate distribution are computed from the instantaneous velocity. PDFs of these distributions were computed, conditionally smapled on the burned gas, unburned gas and proximity to the flame front. For this paper, analysis of only one realization is presented in detail in order to maintain a manageable number of illustrations yet demonstrate flow properties observed in fifteen recorded realizations.