Dependence of combustion dynamics in a gasoline engine upon the in-cylinder flow field, determined by high-speed PIV

We apply time-resolved high-speed particle image velocimetry (PIV) in an optically accessible gasoline engine to determine the effect of the in-cylinder flow field upon combustion dynamics. Our PIV setup involves solid particles as tracer, which enables also measurements at firing top dead center and during the combustion process itself. We analyze the flow field for the entire intake and compression phase, as well as the decay of a prominent large-scale tumble structure in the flow field. The data indicate significant cycle-to-cycle flow field variations, characterized by detection of kinetic energy and tumble center. Measurements in fired engine operation demonstrate the influence of the flow field on combustion dynamics. At stoichiometric operation, we find that variations in the kinetic energy of the flow field are a major cause of cycle-to-cycle variations. From simultaneous imaging of the combustion flame and PIV at lean operation, we find that the velocity distribution in the flow field induces a macroscopic motion of the flame kernel—which significantly effects the combustion process.