Reaction rate during flame-flame interactions in highly turbulent premixed jet flames measured using high-speed and simultaneous T-PIV and OH/CH2O-PLIF

The high turbulence intensity present in advanced aerospace propulsion systems generate a highly convoluted flamelet topology, which can lead to the formation of flamelets that propagate towards one another. Regions of... [ view full abstract ]

The high turbulence intensity present in advanced aerospace propulsion systems generate a highly convoluted flamelet topology, which can lead to the formation of flamelets that propagate towards one another. Regions of converging flame surfaces can be manifested either in the form of negatively curved flame surfaces (concave towards the reactants), thin ‘fingers’ of reactants that stretch well into the products, or pocket of reactants that convect through the products. Negatively curved flame surfaces can be induced by turbulence or flame instabilities, which will grow into long fingers due to a positive pressure gradient across the flame surface. These fingers can then separate from the reactants as a result of flamelet closure, resulting in pockets of reactants in the products region. Regardless of the mechanism, these highly convoluted flame surfaces can result in flame-flame interactions, leading to the destruction of the flame surface via merging. Moreover, in these regions of flame-flame interactions, there is a substantial increase in the local displacement of the flame, thus impacting the overall reaction rate. This study used simultaneous and high-speed (10 kHz) tomographic particle image velocimetry (T-PIV), hydroxyl planar laser induced fluorescence (OH-PLIF), and formaldehyde (CH2O)-PLIF to examine the effect of flame-flame interactions on reaction rate in a highly turbulence premixed methane/air jet flame. The conditions tested extend from the classically defined thinned flamelet region up into the distributed reaction region, at Karlovitz and turbulent Reynolds numbers upwards of 700 and 33,000 respectively.