Early flame propagation in a spark-ignition engine measured with quasi 4D-diagnostics

This paper presents the first results toward experimentally resolving the local three-dimensional (3D) flame propagation and turbulence-chemistry interaction in a spark-ignition engine using temporally resolved multi-planar laser diagnostics. The experimental method utilizes simultaneous dual-plane laser induced fluorescence (LIF) of OH and stereoscopic PIV (SPIV) to locally resolve 3D flame displacement speed during the early flame development when less than 5% of the mass has been consumed. OH-LIF is used to track the reaction-zone position and flame normal direction in 3D space, while SPIV measures the convection of the identified flame contours. Based on the vectorial difference of the 3D convection and absolute propagation of the reaction-zone, the 3D displacement speed (s T) is calculated. An instantaneous flame realization shows a large dynamic range of local s T and local flow transport, while also revealing the importance to resolve these quantities in 3D. Several flame-flow configurations are shown along the flame surface and each uniquely defined the local flame transport along the individual flame realization. A detailed uncertainty and sensitivity analysis is performed, confirming the validity of the s T distribution resolved for the methodology and operating conditions. A discussion on the different mechanisms leading to the large distribution of s T for the given operations is included and testifies to the complex nature of the in-cylinder flame development at this early stage. The limitations of the presented methodology are discussed particularly in the need for improved spatial resolution and additional volumetric information. The merits and limitations of the presented work provides an improved understanding of what is further needed to better resolve local 3D flame transport in engines for both experimental and numerical methodologies.